Type of Lighting Bulbs (Shapes and Sizes) Part-4

What is difference between R,BR,MR and PAR bulbs

(1) Difference between an R and BR Bulb

• There is confusion between selecting R and BR type of Bulbs.
• There is minor difference between R and BR type Bulb.
• Both types of Bulbs have a reflector flood, and that is what the R stands for in the code.
• The R is an old design for reflectors that are not as energy efficient as a BR reflector.
• The BR was designed to replace the older R.
• For same Light output and size in length and width, BR Bulb use less watts (due to the reflector in a BR is more directed) hence BR Bulb produce less heat and more efficient.
• Both of these lamp types are interchangeable.
• BR is an upgraded version of R 

(2) Difference between PAR and BR / MR Bulb:

• The main difference between PAR and MR is according to its Size, variety, and heat transformation.
• The primary difference between these bulbs is according to Beam Angle, internal construction and as per Reflector.
• Different Type of Beam Angles.
• BR (for bulged reflector) bulbs are lamps with “wide flood” beam angles, which means that they provide more than a 45 degree angle when lighting an area.
• PAR (Parabolic Aluminized Reflector) bulbs are available in these angles:
• Narrow spot (5 to 15 degrees)
• Spot, (16 to 22 degrees)
• Narrow flood,( 23 to 32 degrees)
• Flood, (33 to 45 degrees(
• Wide flood beam, over 45 degrees.

• Different Type of Reflector and Application of Bulb.
• The BR bulbs have a frosted/patterned coating of reflector (for broad beam angle ) allows to less concentrated light and provides better coverage thus eliminating shadows in the intended area hence BR Bulb produces less shadow than PAR bulbs.
• BR Bulbs are commonly used indoors in household ceilings like in kitchens, family rooms, and stair lighting with high ceilings with recessed type.
• The reflective surface of PAR does not allow light to spread much further than the angle of the beam spread hence PAR lamps deliver strong, narrow to wide, directional light , which is little harsher where the light starts and where it ends.
• A PAR bulb is used in indoor/outdoor security lighting, theatre, performance sets, and spot-lighting signs and restaurant lighting applications as well.
• Different Type of Construction and Heat dissipation.
• BR bulbs are a common reflector lamp with a bulged reflector. They are incandescent, LED bulbs. The sides of the outer part of the blown glass bulb are coated with a reflecting material that directs light. The light transmission pattern can be clear, frosted, or even patterned.
• PAR bulbs are incandescent, tungsten-halogen, metal halide, LED Bulbs. They have a hard glass cover which is hermetically (airtight) sealed to the reflecting surface. Inside there is a lenses that controls beam spread and cannot be altered in position in relation to the filament. There are flood bulbs and spot bulbs. Flood bulbs diffuse or scatter light, while spots focus all light in one direction.
• MR type bulbs have dichotic glass reflectors while PAR bulbs have aluminized glass reflectors which direct the heat generated by the bulb to the front of the bulb. Due of this, PAR bulbs are not suitable for ceiling installations of 8 feet or lower.
• PAR bulbs also produce more directional yet duller lighting and have a standard, medium screw-in type of base and work in medium sized E26 sockets.
• MR on the other hand, generates heat to the rear of the bulb and produces a lot more light for the wattage because of the multi-faceted reflector (MR).

Lighting Bulb according to HID Technology:

(1) E (Elliptical) Type HID Bulbs (Code: E)

• E means HID Type light bulb that has a shape of “Elliptical”.
• E Type Halogen light bulbs can be used to replace incandescent light bulbs. High intensity discharge light bulbs.
• Nomenclature:
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• E20 bulb: 20/8 = 2-1/2″ diameter
• Lighting direction: illuminates its light in one direction.
• Bulb Technology: incandescent, CFL, High Intension Discharge Lamps, Metal Halide Lamp, Sodium Discharge, Mercury Vapor Lamp and LED.

(2) ED (Elliptical Dimple) Type HID Bulbs (Code: ED)

• ED means “Elliptical Dimple”.
• ED light bulbs have an elliptical shape to house the arc tube of a high intensity discharge light bulb.
• They are not as efficient as their alternatives, but their use may be dictated by color rendering requirements. The lamps require only ballast for additional control.
• Inside surfaces coated with europium-activated phosphor which converts the UV elements in ’warm’ light to produce a cool white light. They are an acceptable alternative to fluorescent lighting
  Nomenclature: ED17.
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• EDR20 bulb: 20/8 = 2-1/2″ diameter
• Lighting direction: illuminates its light in one direction.
• Bulb Technology: High Intension Discharge Lamps, Metal Halide Lamp, Sodium Discharge, Mercury Vapor Lamp and LED.
• Applications:

• ED light bulbs are used in sports arenas, high bay industrial lighting, parking lots and garages and car dealerships.
• These lamps are used in some industrial, warehousing applications as a floodlight and other suitable light fittings with appropriate ballast gear.
• FEATURES & BENEFITS
• Metal Halide HID light bulb produces high light output
• Ideal for various commercial and industrial applications where color rendering is important
• RECOMMENDED USES
• Retail areas
• Area lighting
• Accent lighting
• Sports lighting
• Security lighting
• Parking garages

(3) ER (Elliptical Reflector) Type HID Bulbs (Code: ER)

• ER means “Elliptical Reflector”.
• In ER bulb, the elliptical reflector increases the overall lumen output by redirecting side light of Bulb (Which is normally lost) to the redirect it to the forward Side of Bulb.
• Elliptical (ellipsoidal) reflector light bulbs are uniquely designed to project light further than other reflector bulbs. They are a great option for use in deep recessed can lights as they lose less light in baffles than standard BR or R type bulbs. 
• ER halogen light bulbs can be used to replace incandescent light bulbs. High intensity discharge light bulbs.
• An incandescent lamp with a built-in elliptically-shaped reflecting surface. This shape produces a focal point directly in front of the lamp which reduces the light absorption in some types of luminaires. It is particularly effective at increasing the efficacy of baffled down lights.
• Nomenclature: ER28, ER37.
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• ER20 bulb: 20/8 = 2-1/2″ diameter
• ER30 bulb: 30/8 = 3-3/4″ diameter
• ER36 bulb: 36/8 = 4-1/2″ diameter
• Lighting direction: illuminates its light in one direction.
• Bulb Technology: incandescent, CFL, High Intension Discharge Lamps, Metal Halide Lamp, Sodium Discharge, Mercury Vapor Lamp and LED.

• Applications:
• The most common size is ER30. These light bulbs are used for down lighting in recessed cans for residential, hotel, and office applications.

Type of Lighting Bulbs (Shapes and Sizes) Part-3

Lighting Bulbs According to Reflector:

(1) R (Reflector) Type Bulb (Code: R)

• “R” stands for Reflector.
• This light bulb contains a mirrored coating on the back of the light bulb that maximizes the direction of the light which emitted by Bulb.
• Traditionally, inside of R type Bulb was covered with a reflector material coating that used to gather light and cast it away from the bulb. Nowadays, R type bulbs have an evenly frosted coating that works to diffuse light and prevents glare.
• Unlike the PAR bulb, the entire envelope of R type bulb, excluding the base is constructed by using blown glass and the exterior part of the bulb is very smooth. The few components of this bulb which includes a brass base, a thin glass and filament make it lightweight.
• Reflective Coating of Bulb In Reflector (R) or Bulged Reflector (BR) bulbs directs light forward side , while Flood types (FL) bulb spread light and Spot types (SP) concentrate the light.
• Reflector (R) bulbs put approximately double the amount of light (Lumen) on the front central area as General Standard “A” Shape Bulb for same wattage
• Nomenclature:
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• R20 bulb: 20/8 = 2-1/2″ diameter
• Lighting direction: one direction.
• Bulb Technology: incandescent , LED,  tungsten-halogen, CFL

• Application:
• The R type bulb is usually not waterproof but can be used in a fixture protected from the weather as long as it is not sealed.
• Reflector light bulbs are used mainly in recessed Lights for hotels, restaurants, retail and residential lighting.
• R bulbs are ideal for display lights as well as for providing soft ambient and directional light. The right place to use R bulbs is in hallways, in a kitchen, living room, media rooms or pool area.
• R Type floods provide a wider beam angle with a soft edge and are perfect for recessed down lights, track lighting, display lighting and various outdoor fixtures.

(2) BR (Bulged Reflector) Type Bulb (Code: BR)

• BR stands for “Bulged Reflector”.
• The ‘bulge’ allows the light to be distributed in a manner which is very pleasing to our eye.
• R shapes have largely been replaced by the more efficient “bulged reflector” BR shape. 
• BR lamps are a new and improved version of the R Type reflector lamp. The primary difference is the “bulge” in the shape of lamp. This shape focuses more light into the beam of light to direct it out of the recessed fixture.
• In traditional, the inside surface of BR bulb is covered in reflector material that is used to gather and cast a wide beam of light away from the bulb.
• It is considered a wide-angle floodlight often exceeding 100-degree beam angles.
• However in LED BR bulbs do not require the reflector material coating.
• These bulbs can have a frosted, clear, or patterned dome-shaped lens that diffuses light and provides a gradual fade into no illuminated areas.
• BR bulbs also produce less shadow compared to PAR bulbs. They have a bit longer than PAR bulbs and tend to protrude from light housings but are used in similar applications, such as track lights, recessed lights, display lights, or can lights.
• As per the comparison to the R20 and BR20, the glass part of BR20 is more curved.
• One disadvantage of the BR lamp is that it’s a little longer than the PAR and MR, which means it tends to sit lower in the recessed fixture and perhaps, protrude from the bottom of the recessed light fixture.
• The light transmission pattern can be clear, frosted, or even patterned.

• Nomenclature: BR20, BR40.
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• BR20 bulb: 20/8 = 2-1/2″ diameter
• Lighting direction: one direction.
• Bulb Technology: incandescent , LED,  tungsten-halogen, CFL
• Application:
• The BR bulbs kind of balloon out of Light fixtures. Often they are bulging down just below the ceiling from recessed fixtures.

(3) MR (Mirror / Multi Reflector) Type Bulb (Code: MR)

• MR stands for “Multi-faceted Reflector”.
• MR Bulb use mirror as a technique for reflecting the maximum light out in the front of a lamp, It help gather light from the filament to create a very concentrated light beam (narrower light beam).
• It is normally used for small lamps. It is the narrowest of the bulb types (2 inches in diameter or less) mostly used as a spotlight.
• MR Lamps provide various beam spread (narrow flood, flood and spotlight).
• LED MR doesn’t require tiny mirrored squares to put the light where we want it to be.

• Nomenclature: MR11, MR16.
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• MR11 bulb: 11/8 = 1-3/8″ diameter
• Lighting direction: one direction.
• Bulb Technology: incandescent , LED
• Applications:
• It is used for accent and spot lighting in various retail, residential, commercial applications, track lighting and all kinds of display case lighting.
• These bulbs are available in a variety of colors and can be used for many applications, including track lighting, recessed lighting, desk lights, and display case lighting.
• Many MR bulbs operate on low-voltage wiring systems, which makes them great for outdoor and landscape applications such as driveway lights, path lights, gazebo lights, paver lights that have weatherproof housings.
• A light bulb, often a halogen style, that plugs into the socket with two prongs, it’s often used in kitchen settings.

 (4) PAR (Parabolic Aluminized Reflector) Type Bulb (Code: PAR)

• PAR means “Parabolic Aluminized Reflector”.
• PAR Bulb uses an aluminized reflector in a parabola shape for directing the light.
• Bulb is covered with a hard glass lens to control the light beam, which is available in a variety of beam spreads from narrow spot to wide flood. This hard glass covering also helps to withstand harsh environmental conditions.
• Parabola shape Reflector (U-shaped) collect and reflect the light out the front of the bulb, produces a tighter and more controlled beam of light than standard reflector bulbs.
• PAR bulbs are commonly used in stage and theatrical lighting, as well as in the home for accent and art lighting. Many halogen spot and flood lights use a parabolic (however this technique is generally not required in LED lamps).
• It is best used for a focused, narrow beam of light.
• Most PARs do not exceed a beam angle of 45 degrees in most cases. 
• If brightness is priority in a recessed light, than we need to select a PAR lamp in the appropriate size.
• These bulbs have a shorter body than BR bulbs and usually install flush with ceilings or fixtures, which reduces glare.
• PAR’s look a more modern, and often have a clear lens
• Unlike R Type bulbs, PAR bulbs feature an aluminum reflector with a special pattern of impressions that amplifies and concentrates light in a single area.
• The bulb envelope is made of two pieces, the glass face and the shiny aluminum wall of the envelope. The texture of the bulb will be either rough or textured and the bulb will be heavier than an R Type bulb due to thicker glass construction.
• Both LED PAR bulbs and CFL PAR bulbs are easy to find, though they are not always weatherproof like traditional halogen so be sure to check their IP listing before installing them outdoors.  
• This PAR shape is very similar to the R shape and in some cases the PAR and R is interchangeable as per shapes but PAR LED bulbshave a shorter body than R type bulbs.

• Nomenclature: PAR36, PAR20.
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• PAR20 bulb: 20/8 = 2-1/2″ diameter
• PAR30 bulb: 30/8 = 3-3/4″ diameter
• Lighting direction: PAR illuminates its light in one direction having various Beam Angles.
• 12° to 20° = Spot
• 25° to 30° = Narrow Flood
• 35° to 40° = Flood
• >45° = Wide Flood
• Bulb Technology: incandescent, tungsten-halogen, metal halite and LED.
• Applications:
• PAR Type floods provide a tighter beam angle with a hard edge and act more like a spot light and used both indoor and outdoor applications.
• PAR LEDs are perfect for track lighting, recessed lighting and Down Lighting and flood lights.
• Unlike R or BR bulbs that offer general area lighting, PAR shaped bulbs have more sharply focused light to help highlight specific areas or objects like in indoors to emphasize one area of a room over the rest of the room, or to highlight a piece of art, furniture or retail items in commercial .
• These bulbs come in a variety of “beam angles” or “beam spreads” to meet these highlighting needs; the smaller the beam angle, the smaller an area the light will cover.
• Ceiling Light Fixtures, Flood Light, soft light fixtures, garage security light, kitchen can light.
• These bulbs run on low-voltage and suitable for outdoor fixtures as either spotlights (narrower beam angle) or floodlights (wider beam angle) and other outdoor applications like landscape lighting applications such as architectural lights, driveway lights, path lights, gazebo lights, and paver lights, clothing store, museum and gallery applications..
• They’re commonly found in outdoor emergency light, spot light, or floodlight fixtures but can also be used indoors for track lights, recessed lights, display lights, or can lights.

Type of Lighting Bulbs (Shapes and Sizes) Part-2

(6) S (Straight Side) Type Bulb (Code: S)

• “S” means Straight Side.
• Nomenclature:
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• S20 bulb: 20/8 = 2-1/2″ diameter
• Lighting direction: Uni direction.
• Bulb Technology: incandescent , LED,  tungsten-halogen, CFL

• Application:
• S type miniature light bulbs are found in many applications including: indicator, auto stop and turn signal lights, scientific and medical instruments, microscopes and aircraft.

(7) T (Tubular) Type Bulb (Code: T)

• T means “Tubular”.
• It is known as “T” type because it has a shape of cylindrical Tube.
• (T )Tubular type light bulb is available in wide bulb technology like Incandescent, Linear fluorescent, HID and LED.
• T light bulbs have very different applications according to its shape.
• Incandescent T6 light bulbs are used in exit and stairway signs and picture lights.
• Linear fluorescent T12, T10, T8, and T5 light bulbs come in a variety of lengths, ranging from 2 to 8 feet. These light bulbs are used for general lighting in offices, retail outlets, hospitals, and parking garages.
• High intensity discharge light bulbs also come in T shapes, including T9 and T15. These light bulbs are used in sports arenas, billboard signage, and industrial applications.
• Tube Type bulbs are available in different shape like
• Linear Tube Light Shape:
• T12, T8 and T5 are naming convention for tube lights where “12” is the thickest and “5” is the slimmest tube light. 
• U-Bend :
• U-Bend Tube light bulbs T8 is created by bending a 4-foot length T light bulb into a U shape in order to reduce the maximum overall length of the light bulb. This is desirable in some locations that have limited space. By bending a 4-foot light bulb into a U configuration that is comparable to a 2 foot light bulb in length, the end user will receive double the light output in the smaller space. This light bulb is used in offices, hospitals, and retail applications.
• Spiral Shape:
• The spiral light bulb is the shape of a compact fluorescent light bulb. A smaller diameter fluorescent T light bulb, such as T4, T3, T2, or T1, is twisted into a spiral or coil configuration in order to provide the most amount of light output in the least amount of space.
• Spiral light bulbs are typically used to replace incandescent light bulbs and can be used virtually anywhere, including residential, commercial, retail, hospitality, and restaurant applications.
• Nomenclature: T4, T8.
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• T8 bulb: 8/8 = 1″ diameter
• Lighting direction: illuminates its light in Omni direction.
• Bulb Technology: Incandescent, CFL, High Intension Discharge Lamps, Metal Halide Lamp, Sodium Discharge, Mercury Vapor Lamp and LED.

• Applications:
• Depending on their size, these bulbs can be used in applications ranging from chandeliers, wall sconces, and pendant lights to basement and garage light fixtures.
• Exhibition hall, showing and advertising board
• Industry plant, workshop, warehouse
• Sports lighting, stadium, gymnasium and car parking area
• Flood lighting for tunnel, port, viaduct, Public Square and construction site etc.

(8) Double Ended Type Bulb (Code: T3)

• It is “T” Type cylindrical Tube Blub having a both end connection.
• Double ended Bulb (T3) is installed in horizontal position.
• These light bulbs are a cost-effective alternative to standard light bulbs and a completely dimmable in multiple lighting applications
• Nomenclature:
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• T3 bulb: 3/8 = 0.3″ diameter
• Lighting direction: illuminates in Omni direction.
• Bulb Technology: Incandescent, Metal Halide, halogen, LED.

 

• Application:
• Mostly used in commercial lighting, ambient lighting and flood lighting.
• It can be horizontally installed. With a compact size it provides a uniform lighting for a large area.

 (9) PS (Pear shape) Type Bulbs (Code: PS)

• PS means “Pear shape”.
• Pear shape light bulbs are similar to A Type light bulbs, except they have a larger diameter, which causes the bulb to look like a pear.
• Nomenclature: PS30,PS40.
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• PS15 bulb: 15/8 = 1-7/8″ diameter
• Lighting direction: illuminates its light in Omni direction.
• Bulb Technology: incandescent, LED, CFL.

• Application:
• Office buildings and retail stores, Radio towers, cellular towers, bridge power lines, and high tension wires.

(10) S (Sign) Type Bulbs (Code: S)

• S means “Sign light”.
• Sign light bulbs also known as the “original light bulb” of the incandescent.
• Sign Bulbs also used in low-wattage lights.
• Sign Bulbs come in clear, frosted and colored options.
• Sign Bulbs available in transparent amber, blue, green, pink, red and yellow.
• Nomenclature: S30, S40.
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• S15 bulb: 15/8 = 1-7/8″ diameter
• Lighting direction: illuminates its light in Omni direction.
• Bulb Technology: incandescent, LED, CFL.

• Application:
• Ideal for multiple residential and commercial uses with incandescent lamps features excellent light output and good optic control along with dimming capabilities.
• Sign light bulbs are found in outdoor signs used by casinos, hotels, restaurants, and theatres.
• Sign lamps can be as simple as a way to promote your business by eye-catching company Signage installations.

Type of Lighting Bulbs (Shapes and Sizes) Part-1

Introduction:

• There are various Shapes of bulbs available in market. Some lamp shape is widely used on other hand some lamp shape is used in special requirements.
• If we properly understand bulb codes, it’s easy to select appropriate bulb for a light fixture.
• Bulbs shapes are mostly classified according to direction of lights, lighting glare and Bulb size.
• Every light bulb has identifying characteristics that are represented by a letter or series of letters and a number, these are known as light bulb codes.

Types of Lamps in a Lighting system

• There are following types of lamps which are available in different shapes.
• Incandescent lamps
• Fluorescent tube
• Compact fluorescent lamps (CFL)
• Halogen lamps
• Light Emitting Diode (LED)
• Neon lamps
• High intensity discharge lamps

1. Metal Halide.
2. High-Pressure Sodium
3. Low-Pressure Sodium
4. Mercury Vapor

Nomenclature of Bulb:

• The Bulb Code is indicating as a Letter-Number-Letterformat, the last letter is optional.
• The First Letter in a bulb code indicates either shape or special features such as reflector type.
• The Second Letter (Number) in a bulb code indicates size of Bulb in millimeters or eighths of an inch .It will tell us whether the bulb will fit in fixture or not.
• The Third Letter is optional which indicate Bulb length.
• Example: BR30S
• First Letter: BR=” Bulged Reflector”
• Second Letter = diameter of Light Bulb =30/8 inches, or 3 and 3/4 inches.
• We can say that PAR30, R30 and BR30 all have same size bulb.
• Knowing the diameter and sizes of these light bulbs is important because in some unique cases the R and PAR are interchangeable as LED bulb replacements.
• If in Code there is “S” or an “L” indication in last, that stands for either short neck or long neck.

Shapes of Lighting Bulbs:

• There are following Shapes of Lamps, Some are very common in everyday uses while some are use in special requirements.
• According to Shape:

1. A (Arbitrary) Type Bulb (Code: A)
2. B (Blunt Tip) Type Bulb (Code : C )
3. C (Candle / Flame Tip ) Type Bulb (Code : C , CA)
4. F (Flame Tip ) Type Bulb (Code : F)
5. G (Globe) Type Bulb (Code: G)
6. S (Straight Side) Type Bulb (Code: S)
7. T (Tubes) Type Bulb: (Code : T,T3)
8. Double Ended Type Bulb (Code:T3)
9. Pear Shape Type Bulb (Code: PS)
10. Sign Type Bulb (Code : S)
11. H (Chimney ) Type Bulb (Code: H)

• According to Reflector:

1. R (Reflector) Type Bulb (Code : R)
2. BR (Bulged Reflector) Type Bulb (Code : BR)
3. MR (Mirror Reflector) Type Bulb (Code : MR)
4. PAR (Parabolic Aluminized Reflector) Type Bulb (Code : PAR)

• According to HID:

1. E (Elliptical) Type Bulb (Code : E)
2. ED (Elliptical Dimple) Type Bulb (Code : ED)
3. ER (Elliptical Reflector) Type Bulb (Code : ER)
4. BT (Blown or Bulbous Tube) Type Bulb (Code : ET)

• According to Application:

1. Flood Light (Code: E)
2. Panel Light (Code: Panel Light)
3. Strip Light
4. Down Light (Code: GU)
5. Recess Down Light (Code: Down light)
6. Spot Light
7. Corn Type Bulb
8. Flat Tube
9. High Bay
10. RGB Light
11. Street Light

Lighting Bulb according to Shape:

(1) A (Arbitrary) Type Bulb (Code: A):

• A Means “Arbitrary”. It shape looks like ordinary Light Bulb.
• It is also known as “Classic Globe Type” or “Standard shape Type” Bulb.
• Thislamp is the most commonly used as household lamp.
• It is normally used in fixtures where the bulb is visible.
• It is not known that why it known as A Type. It doesn’t look like an A Shape until we turn it down.
• We can assume that this is the first type of light bulb introduce in market hence it called “A” Type.
• Nomenclature: A35, A20.
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• A15 bulb: 15/8 = 1-7/8″ diameter
• Lighting direction: Omni direction.
• Bulb Technology: incandescent, LED, CFL.

• Application:
• Standard / arbitrary (A) bulbs are normally widely used in Household lighting.
• These bulbs work well for a variety of applications, such as ceiling lights, lamps, vanity lights, kitchen lights, closet lights, porch light fixtures, Room lighting, Reading lamps, Ceiling Light, Wall Light and Hallways Light. It also used in some chandeliers.

(2) B (Blunt Tip) Type Bulb (Code: B):

• “B” means Blunt-tip.
• This is a slimmer version of the Type A Bulb.
• The bulb is generally in narrow and bullet shape.
• B bulbs are very similar to C-type bulbs but they have a bulged base that tapers to a pointed tip hence look like a torpedo or bullet shape.
• It is available in Clear or Frosted(opal)
• Nomenclature:
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• B10 bulb: 10/8 = 1-1/4″ diameter
• Lighting direction: Omni direction.
• Bulb Technology: incandescent, LED, Tungsten-halogen, CFL.

• Application:
• This is most often used for decorative purposes and chandeliers, wall sconces, pendant lights.
• It is also used in low wattage applications as a home lighting applications and night lights.

(3) C (Candle / Flame Tip) Type Bulb (Code: C, CA):

• “C” means Conical or Candle and “CA” means Conical Angular.
• CA bulbs are shaped like a cone but have a bent tip.
• The shape of this Bulb is look like as a candle flame and referred to as candle bulbs.
• Candelabra Light Bulbs are similar as B Shaped bulbs but bulb’s tip is bent giving the slight look of a flicking flame.
• It is available in Clear or Frosted(opal)
• Nomenclature:
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• C7 bulb: 7/8 = 7/8″ diameter
• Lighting direction: Omni direction.
• Bulb Technology: incandescent , LED,  Tungsten-halogen , CFL

• Application:
• These bulbs are common in chandeliers and decorative light strands, holiday light strands, pendant lights, and night lights.
• We choose a blunt shape in more contemporary chandeliers if the bulb were seen.
• It also use in low voltage application and as s night lights.

(4) F (Flame Tip) Type Bulb (Code: F):

• “F” means “Flame” .
• F light bulbs are similar in size and shape to C Type light bulbs.
• However the glass of the bulb is blown or etched in such a way that causes the light to look as though it is flickering like a flame.
• This bulb comes with a white finish, but to achieve candle-like appearance, a clear finish is preferred.
• If the bulb is colored, a transparent color allows the filament to be visible.
• It is available in clear or frosted(opal)
• Nomenclature:
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• F10 bulb: 10/8 = 1-1/4″ diameter.
• Lighting direction: Omni direction.
• Bulb Technology: incandescent , LED,  Tungsten-halogen , CFL

• Application:
• F light bulbs are used in decorative applications such as chandeliers, bathrooms, and restaurants and commercial applications..

 (5) G (Globe) Type Bulb (Code: G)

• G means “Globe”.
• Globe (G) bulbs have a full, round shape and are available in various sizes
• It is available in candelabra or medium base.
• Nomenclature: G15, G20.
• Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
• G15 bulb: 15/8 = 1-7/8″ diameter.
• Lighting direction: Omni direction.
• Bulb Technology: incandescent , LED,  tungsten-halogen

• Application:
• Globe light bulbs are used in decorative applications in theatres, restaurants, and hotels
• Globe light bulbs are used in a variety of applications where a decorative ball shaped light source is required such as ceiling fans, accent fixtures, kitchen lights, bathroom and makeup vanities, chandeliers, ornamental fixtures and table lamp, wall and floor lamps.

Methods of Earth Resistance Testing (Part-3)

(3) Two Point (Dead Earth) Method.

• This method is used where the driving of ground spike is neither practical nor possible
• To perform this test we have access to a good known ground such as an all metal water pipe. The water pipe should be extensive enough and be metallic throughout without any insulating couplings or flanges.
• This method is not as accurate as three-point methods (62% method), as it is particularly affected by the distance between the tested electrode and the dead ground or water pipe

Required  Equipment:

• Earth Tester (4 Terminal or 3 Terminal)
• 2 No’s of Insulated Wires
• Hammer

Connections:

• In This method, the resistance of two electrodes in a series is measured by connecting the P1 and C1 terminals to the ground electrode under test; P2 and C2 connect to a separate all-metallic grounding point like a water pipe or building steel.
• The earth electrode under test must be far enough away from the secondary grounding point to be outside its sphere of influence.

Testing Procedure:

• Press START and read out the resistance value. This is the actual value of earthing resistance of the ground electrode under test.
• Record the reading on the Field Sheet at the appropriate location. If the reading is not stable or displays an error indication, double check the connections.
• Two terminals testing of earth resistance is appropriate for most general purpose testing in normally conductive soil.
• Two terminal measurements include less test lead and contact resistance in the measurement and the result will be a reading slightly higher than the true earth resistance.
• When measured results are higher than desired or if measurement directives require multi terminal techniques, switch to the 3 or 4 terminal techniques as needed.

Advantage:

• It does Not Require Disconnecting Equipment
• This is the simplest way to obtain a ground resistance reading.
• It is most effective for quickly testing the connections and conductors between connection points.
• Required Less Test Lead.
• Required small area for Measurement.

Disadvantage:

• This is not as accurate as the three-point method and should only be used as a last resort.
• Non-metallic (high resistance) return Resistance areas should not overlap.

  (4) Clamp-on test method

• For the clamp-on method to be effective there must be a complete grounding circuit in place. The tester measures the complete resistance path (loop) that the signal is taking. All elements of the loop are measured in series.
• The Induced Frequency testing or commonly called the “Clamp-On” test is one of the newest test methods for measuring the resistance-to-ground of a grounding system or electrode.
• This is Convenient, Quick ,easy and safe Method
• It does Not Require Disconnecting Equipment

Required equipment:

• Clamp-on Ground Resistance Meter.
• 2 No’s of Insulated Wires

Connections setup:

Testing Procedure:

• Press START and read out the resistance value. This is the actual value of earthing resistance of the ground electrode under test.
• The clamp-on methodology is based on Ohm’s Law (R=V/I).
• The source coil inside the clamp of the earth tester inducing the voltage. This voltage is inductively applied to a complete circuit .The resulting current flow in the earthing circuit due to the induced voltage is measured by the current coil installed in the same clamp of the earth tester.
• The resistance of the circuit can then be calculated by taking the ratio of the induced voltage and the circulated current in the earthing circuit.
• It has to be ensured that the earthing system under test is included in the current circulation loop. The clamp-on earth tester measures the resistance of the path traversed by the induced current.
• All elements of the loop are measured in series. This method assumes that only the resistance of the earthing system under test contributes significantly.
• A low return path is required for readings. A high resistance return path will yield high readings.

Advantage

• There is no need to turn off the equipment power or disconnect the earth rod.
• Not disconnecting the connections between the earthed body and the metal work of the electrical Earthing Point.
• Not dangerous to human life because no any DC current injected in Probe.

Disadvantages:

• If the frequency of AC current injected into the earth by the tester is the same as that of disturbance current in the earth then accuracy of the readings are seriously affected.
• The mutual inductance between the voltage and current loops of the clamp tester may affect accuracy of the readings.
• The clamp-on method is only effective in situations with multiple earthing electrodes are in parallel and a closed circuit is available for the current circulation.
• It cannot be used on isolated grounds, as there is no return path.
• Measurement of low earth resistance (0.5Ω) is difficult with this method.
• This method id effective only in situations with multiple grounds in parallel.
• This method cannot be used on isolated grounds, not applicable for installation checks or commissioning new sites.
• This method cannot be used if an alternate lower resistance return exists not involving the soil, such as with cellular towers or substations.

 (5) Star Delta Method

•  If the testing area is so limited that an required spacing cannot be found then it may be necessary to use the Star-Delta Method. Named for the configuration of the test probes and lines of measurement (a graphic of it resembles the familiar symbols for “delta” and “star” windings).
• This method saves space by employing a tight configuration of three probes around the test ground

Required equipment:

• Earth Tester (4 Terminal or 3 Terminal)
• 2 No’s of Insulated Wires
• Hammer

Connections:

• The ground electrode under test (E) is connect to C1 Terminal of Tester.
• Three Potential and current probes (P2, P3 and P4) are placed equidistant from “E” with a 120º angle between them. Separation of potential and current circuits is abandoned, and a series of two-point measurements made between all pairs of probes, and probes to the ground under test.

Testing Procedure:

• Press START and read out the resistance value. This is the actual value of earthing resistance of the ground electrode under test.

Application:

• Ground systems located in congested urban areas or rocky area where probe positioning is difficult
• where required probe positioning is difficult

Advantage:

• Knowledge of electrical center not necessary

Disadvantage:

• number of calculations required
• Long distances to test probes is still required;

(6) Slope Method

•  If soil is non homogeneous Soil Slope Method is useful for earth resistance measurement.

Required equipment:

• Earth Tester (4 Terminal or 3 Terminal)
• 4 No’s of Insulated Wires
• Hammer
• Measuring Tap

Connections:

• First, isolate the grounding electrode under measurement by disconnecting it from the rest of the system.
• The earth electrode under measurement (E) is connected to C1 Terminal of Earth Tester.
• E is either one of many paralleled rods forming the complex earth system.
• Insert the current probe C2 at a distance (D) from E (distance D is normally 2 to 3 times the maximum dimension of the system).
• Insert potential probes P1,P2 and P3 at distances equal to 20% of D, 40% of D and 60% D.

 Testing Procedure:

• Press START and read out the resistance value. This is the actual value of earthing resistance of the ground electrode under test.

Methods of Earth Resistance Testing (Part-2)

Can we use an Megger or Multimeter for earth resistivity Testing

• We cannot use Megger or Mulitimeter for Earth resistivity Testing.

Insulation Tester (Megger):

• Insulation testers are designed to measure at the opposite end of the resistance by inserting high DC Voltage.
• Insulation testers use high test voltages in the kilovolt range. The area between electrode and ground is charged with high DC Voltage and we do not want grounds that measure in megohms.
• Ground testers use Low Voltage for testing for operator safety, to low voltages.

Multimeter:

• However, a Multimeter or continuity test can use very low Voltage between an installed electrode and a reference ground, which is assumed to have negligible.
• Low voltage DC can produce a resistance reading between ground and an earth electrode but it is not an accurate measurement.
• Multimeter measurement may not be reliable, since reading can be influenced by soil transients, the electrical noise that is generated by utility ground currents trying to get back to the transformer, as well as other sources.

Can Earth resistance reduce by pouring Water around Test Earth Probe

• By pouring water is near test probe reduce contact resistance of between probe and ground at some extent.
• If there is sufficient contact between probe and ground then pouring water near test probe is never decrease earth resistance of the system.
• Earth resistance is the resistance of the ground electrode that is being measured, not that of the test probe. The Test probe is a tool to use measurement of earth resistance.
• If the test setup has adequate spacing, the probes will be far enough away outside of the electrical field of the test ground so that watering them has no influence on the test result.

 Test Methods for Measuring Earth Resistance

There are six basic test methods to measure earth resistance

1. Four Point Method (Wenner Method)
2. Three-terminal Method (Fall-of-potential Method / 68.1 % Method))
3. Two-point Method (Dead Earth Method)
4. Clamp-on test method
5. Slope Method
6. Star-Delta Method

 

 (1) Four Point Method (Wenner Method):

• This method is the most commonly used for measuring soil resistivity,

Required Equipments:

• Earth Tester (4 Terminal)
• 4 No’s of Electrodes (Spike)
• 4 No’s of Insulated Wires
• Hammer
• Measuring Tap

Connections:

• First, isolate the grounding electrode under measurement by disconnecting it from the rest of the system.
• Earth tester set has four terminals, two current terminals marked C1 and C2 and two potential terminals marked P1 and P2.
• P1 = Green lead, C1 = Black lead, P2 = Yellow lead, C2 = Red lead
• In this method, four small-sized electrodes are driven into the soil at the same depth and equal distance from one another in a straight line.
• The distance between earth electrodes should be at least 20 times greater than the electrode depth in ground.
• Example, if the depth of each earth electrode is 1 foot then the distance between electrodes is greater than 20 feet.
• The earth electrode under measurement is connected to C1 Terminal of Earth Tester.
• Drive another potential Earth terminal (P1) at depth of 6 to 12 inches from some distance at C1 Earth Electrode and connect to P1 Terminal of Earth Tester by insulted wire.
• Drive another potential Earth terminal (P2) at depth of 6 to 12 inches from some distance at P1 Earth Electrode and connect to P2 Terminal of Earth Tester by insulted wire.
• Drive another Current Electrode (C2) at depth of 6 to 12 inches from some distance at P2 Earth Electrode and connect to C2 Terminal of Earth Tester by insulted wire.
• Connect the ground tester as shown in the picture.

Testing Procedure:

• Press START and read out the resistance value. This is the actual value of the ground Resistance of the electrode under test.
• Record the reading on the Field Sheet at the appropriate location. If the reading is not stable or displays an error indication, double check the connections. For some meters, the RANGE and TEST CURRENT settings may be changed until a combination that provides a stable reading without error indications is reached.
• The Earthing Tester has basically Constant Current generator which injects current into the earth between the two current terminals C1 (E) and C2 (H).
• The potential probes P1 & P2 detect the voltage ΔV (a function of the resistance) due to the current injected in the earth by the current terminals C1 & C2.
• The test set measures both the current and the voltage and internally calculates and then displays the resistance. R=V/I
• If this ground electrode is in parallel or series with other ground rods, the resistance value is the total value of all resistances.
• Ground resistance measurements are often corrupted by the existence of ground currents and their harmonics. To prevent this it is advisable to use Automatic Frequency Control (AFC) System. This automatically selects the testing frequency with the least amount of noise enabling you to get a clear reading.
• Repeat above steps by increasing spacing between each electrode at equal distance and measure earth resistance value.
• Average the all readings
• An effective way of decreasing the electrode resistance to ground is by pouring water around it. The addition of moisture is insignificant for the reading; it will only achieve a better electrical connection and will not influence the overall results. Also a longer probe or multiple probes (within a short distance) may help.

Application:

• It is advisable for Medium or Large electrode System.
• It is use for Multiple Depth Testing

Advantage:

• This is most accurate Method.
• It is Quick, easy method.
• Extremely reliable conforms to IEEE 81;

Disadvantage:

• There need to turn off the equipment power or disconnect the earth electrode.
• One major drawback to this method is that it requires a large distance for measurement.
• This distance can range up to 2,000 feet or more for ground systems covering a large area or of very low resistance.
• Time consuming and labor intensive

 

2) Three Point (Fall-of-potential) Method.

• The Fall-of-Potential method or Three-Terminal method  is the most common way to measure earth electrode system resistance, but it requires special procedures when used to measure large electrode systems
• There are three basic fall-of-potential test method.
• Full fall-of-Potential: A number of tests are made at different spaces of Potential Probe “P” and the resistance curve is plotted.
• Simplified Fall-of-Potential: Three measurements are made at defined distance of Potential Probe ”P” and mathematical calculations are used to determine the resistance.
• 8% Rule: A single measurement is made with Potential Probe “P” at a distance 61.8% (62%) of the distance between the electrode under test and “C”.

Required Equipment:

• Earth Tester (4 Terminal or 3 Terminal)
• 4 No’s of Electrodes (Spike)
• 4 No’s of Insulated Wires
• Hammer
• Measuring Tap

Connections:

• First, isolate the grounding electrode under measurement by disconnecting it from the rest of the system.
• For Small System:
• For 4 Terminal Earth Tester Short Current Terminal (C1) and Potential Terminal (P1) together with a short jumper on the earth tester and connect it to earthing electrode under test.
• For 3 Terminal Earth Tester Connect current terminal (C1) to the earth electrode under measurement.
• Drive another Current Electrode (C2) into the earth 100 to 200 feet at depth of 6 to 12 inches from the center of the electrode and connect to C2 Terminal of earth tester.
• Drive another potential terminal (P2) at depth of 6 to 12 inches into the earth midway between the Current Electrode (C1) and Current Electrode (C2) and connect to Earth Tester on P2
• For Large System
• Place the current electrode (C2) 400 to 600 feet from the measuring Earth Current Electrode (C1)
• Place the potential electrode (P1)8% of the distance from the Earth Current Electrode (C1)
• Measure the resistance
• Move the current electrode (C2) farther 50 to 100 Feet away from its present position.
• Place the potential electrode (P2) 61.8% of the distance from the Earth Current Electrode (C1).
• Spike length in the earth should not be more than 1/20th distance between two spikes.

Testing Procedure:

• Press START and read out the resistance value. This is the actual value of the ground electrode under test.
• Move the potential electrode 10 feet farther away from the electrode and make a second Measurement.
• Move the potential probe 10 feet closer to the electrode and make a third measurement.
• If the three measurements agree with each other within a few percent of their average, then the average of the three measurements may be used as the electrode resistance.
• If the three measurements disagree by more than a few percent from their average, then additional measurement procedures are required.
• The electrode center location seldom is known. In this case, at least three sets of measurements are made, each with the current probe a different distance from the electrode, preferably in different directions.
• When space is not available and it prevent measurements in different directions, suitable measurements can be made by moving the current probe in a line away from or closer to the electrode.
• For example, the measurement may be made with the current probe located 200, 300 and 400 feet along a line from the electrode.
• Each set of measurements involves placing the current probe and then moving the potential probe in 10 feet increments toward or away from the electrode.
• The starting point is not critical but should be 20 to 30 feet from the electrode connection point, in which case the potential probe is moved in 10 feet increments toward the current probe, or 20 to 30 feet from the current probe, in which case the potential probe is moved in 10 feet increments back toward the electrode.
• The spacing between successive potential probe locations is not particularly critical, and does not have to be 10 feet, as long as the measurements are taken at equal intervals along a line between the electrode connection and the current probe.
• Larger spacing means quicker measurements with fewer data points. smaller spacing means more data points with slower measurements.
• Once all measurements have been made, the data is plotted with the distance from the electrode on the horizontal scale and the measured resistance on the vertical scale.

Importance of Position of Current Electrode (C2):

• Fall-of-Potential measurements are based on the distance of the current and potential probes from the center of the electrode under test.
• For highest degree of accuracy, it is necessary that the probe is placed outside the sphere of influence of the ground electrode under test and the auxiliary earth.
• If we Place Current Electrode (C2) too near to Earth Electrode (C1) then the sphere of influence, the effective areas of resistance will overlap and invalidate measurements taken.
• For the accurate results and to ensure that the ground stakes are outside the spheres of influence.
• Reposition the inner Potation Electrode (P1) 1meter in either direction and take a fresh measurement. If there is a significant change in the reading (30 %), we need to increase the distance between the ground rod under test, the inner stake (probe) and the outer stake (auxiliary ground) until the measured values remain fairly constant when repositioning the inner stake (probe).
• The best distance for the current probe is at least 10 to 20 times the largest dimension of the electrode.
• Because measurement results are often distorted by underground pieces of metal, underground aquifers, etc so re measurements are done by changing axis of earth spike by 90 degrees, by changing the depth and distance several times, these results can be a suitable ground resistance system.
• The table is a guide for appropriately setting the probe (inner stake) and auxiliary ground (outer stake).

Distance of  Probe
Depth of the ground electrode	Distance to the inner stake	Distance to the outer stake
2 m	15 m	25 m
3 m	20 m	30 m
6 m	25 m	40 m
10 m	30 m	50 m

Application:

• It is advisable for High Electrical Load.
• It is suitable for small and medium electrodes system (1 or 2 rods/plates). .
• It is useful for homogeneous Soil

Advantage:

• The three-point method is the most reliable test method;
• This test is the most suitable test for large grounding systems.
• Three-terminal is the quicker and simpler, with one less lead to string Spacing For Current Probe

Disadvantage:

• Individual ground electrodes must be disconnected from the system to be measured.
• It is extremely time consuming and labor intensive.
• There are situations where disconnection is not possible.
• Knowledge of location of center probe is necessary
• Time consuming and labor intensive Ineffective if the electrical center is unknown.
• If less measurements are being made then less accurate than full Fall of Potential

 

61.8% Rule:

• It is proven that the actual electrode resistance is measured when the potential probe is located 61.8% of the distance between the center of the electrode and the current probe. For example, if the current probe is located 400 feet from the electrode center, then the resistance can be measured with the potential probe located 61.8% x 400 = 247 feet from the electrode center.
• The 61.8% measurement point assumes the current and potential probes are located in a straight line and the soil is homogeneous (same type of soil surrounding the electrode area and to a depth equal to 10 times the largest electrode dimension).
• The 61.8% measurement point still provides suitable accuracy for most measurements.

• Suppose, the distance of Current Spike from Earth Electrode D = 60 ft, Then, distance of Potential Spike would be 62 % of D = 0.62D i.e.  0.62 x 60 ft = 37 ft.

Application:

• It is suitable for small and medium electrodes system.
• It is useful for homogeneous Soil

Advantage:

• Simplest to carry out.
• Required minimum calculation;
• Fewest number of test probe moves.

Disadvantage:

• Soil must be homogeneous.
• Less accurate
• Susceptible for non-homogeneous soil

Methods of Earth Resistance Testing (Part-1)

Introduction:

• The measurement of ground / Earth resistance for an earth electrode is very important for not only for human safety but also for preventing damages of equipment, industrial plants and to reduce system downtime.
• It also provides protection against natural phenomenon such as lightning stock by providing path to the lightning current to the ground.
• Ground resistance is the measurement of the resistance between conducting connection and earth Soil.
• Earth Resistance should be Low as possible to provide low resistance path to leakage current to the earth.
• Ground resistance depends on grounding electrode selection, soil resistivity, soil contact, and other factors

 Difference between Ground Resistance and Ground Resistivity

•  Ground / Earth Resistance:
• Ground Resistance is the resistance (Which oppose of current flow) of an installed earthing electrode system.
• It is the resistance between a buried electrode and the surrounding soil.
• It is measured in
• Ground Resistance is measured with a four-point, three-point or clamp on tester.
• Ground / Earth Resistivity:
• Ground resistivity is a measurement of how much the soil resists the flow of electricity.
• Ground resistivity is the electrical properties of the soil for conducting current.
• It indicates how good the soil /Earth conducts electric currents. For the lower the resistivity, the lower the earth electrode resistance at that location.
• Ground resistivity is theoretical resistance of a cylinder of earth Piece having a cross-section area of 1 Sq. meter.
• Ground resistivity (ρ)is measured in Ohm centimeters.
• Ground resistivity has nothing to deal with any installed electrical structure, but is a pure measurement of the electrical conductivity of the soil itself.
• Ground resistivity is measured with a four-point tester.
• Ground resistivity varies significantly according to the region, season and the type of soil because it depends on the level of humidity and the temperature (frost or drought increase it).

Purpose of Measurement of Earth Resistivity:

• Earth resistivity measurements have a Main three purpose.
• Earth resistivity data is used to use survey for Surface of Land to identifying locations, depth to bedrock and other geological phe­nomena.
• Earth resistivity data is used for protective anticorrosion treatment of underground pipelines, because Earth resistivity is direct related on the degree of corro­sion of underground pipelines. Lower in resistivity increase in corrosion of Underground Pipes.
• Earth resistivity directly affects the design of an Earthing system. When we design an Earthing system, it is advisable to locate the area of lowest soil resistivity to achieve the most economical grounding installation. If the lower the soil resistivity value, the lower the grounding electrode resistance.

Earth Resistivity depends on:

• There are various that affect the ground resistance of a ground system

(1)  Diameter of Ground Rod:

• Increasing the diameter of the ground electrode has very little effect in lowering the resistance.
• Doubling diameter of ground rod reduces resistance only 10%.
• Using larger diameter ground rods is mainly a strength issue. In rocky conditions, a larger diameter ground rod might be advantageous.

(2) Depth of Ground Rod:

• As per NEC code minimum ground electrode length of 2.5 meters (8.0 feet) to be in contact with the soil.
• Doubling depth of Rod theoretically reduces resistance 40%.
• Earthing Spike (electrodes) deeper is a very effective way to lower Earthing resistance.
• Actual reduction of resistance depends on soil resistivity encountered in multi-layered soils.
• The resistance decreases rapidly as the length of the electrode increases and less rapidly as the diameter increases.

(3) Spacing of Ground Rod:

• Earth resistance decrease when distance between adjustments earthing Rod is twice the length of the rod in Ground (in good soil).

Probe Spacing
Probe distance (m)	Soil resistance, Re (Ω)	Soil resistivity, ρρ (Ω m)
0.3	14.75	27.79
0.6	7.93	29.88
0.9	6.37	36.00
1.2	4.36	32.86
1.5	4.31	40.60

(4) No of Ground Rods:

• Using multiple ground electrodes provides another way to lower ground resistance.
• More than one electrode is driven into the ground and connected in parallel to lower the resistance.
• The spacing of additional rods must be at least equal to the depth of the driven rod.
• Two well-spaced rods driven into the earth provide parallel paths and act as two resistances in parallel. However the rule for two resistances in parallel does not apply exactly so the resultant resistance is not one-half the individual rod resistances.
• The reduction in Earth resistance for equal resistance rods is
• 40 % for 2 rods
• 60 % for 3 rods
• 66 % for 4 rods

(5) Material & Surface Condition of Ground Rod:

• Grounding electrodes are usually made of a very conductive metal (stainless steel, copper or copper clad) with adequate cross sections so that the overall resistance is negligible.
• The resistance between the electrode and the surrounding earth is eligible if the electrode is not free of paint, grease, or other coating, and not firmly packed with earth.
• If the electrode is free from paint or grease, and the earth is packed firmly, contact resistance is negligible.
• Rust on an iron electrode has little or no effect .But if an iron pipe has rusted through, the part below the break is not effective as a part of the earth electrode

(6) Moisture

• Low-resistivity soils are highly influenced by the presence of moisture.
• The amount of moisture and salt content of soil affects its resistivity.
• Actually, pure water has an infinitely high resistivity. Naturally occurring salts in the earth, dissolved in water, lower the resistivity. Only a small amount of salt can reduce earth resistivity quite a bit.

(7) Temperature

• Increase in temperature will decrease resistivity
• Increase in temperature markedly decreases the resistivity of water.
• When water in the soil freezes, the resistivity jumps appreciably; ice has a high resistivity. The resistivity continues to increase a temperatures go below freezing.

(8) Soil type

• Some soils such as sandy soils have high resistivity that conventional ground.
• Frozen and very dry soils are good insulators and have high resistivity.
• In low resistivity soils, the corrosion rate is often greater than in high resistivity soils
• The resistivity is much lower below the subsoil water level than above it. In frozen soil, as in a surface layer in winter, it is particularly high.

(9) Choosing Proper Instrument:

• Use a dedicated ground tester for measuring earth resistance.
• Do not use a generalized ohmmeter, multi meter or Megger for that.

Soil Resistivity (approximate ohm-meters)
Soil Description	Minimum	Median	Maximum
Topsoil, loam	1	26	50
Inorganic clays of high plasticity	10	33	55
Fills – ashes, cinders, brine wastes	6	38	70
Gravelly clays, sandy clays, silty clays, lean clays	25	43	60
Slates, shale	10	55	100
Silty or clayey fine sands with slight plasticity	30	55	80
Clayey sands, poorly graded sand-clay mixtures	50	125	200
Fine sandy or silty clays, lean clays	80	190	300
Decomposed gneisses	50	275	500
Silty sands, poorly graded sand-silt mixtures	100	300	500
Clayey gravel, poorly graded gravel, sand-clay mixture	200	300	400
Well graded gravel, gravel-sand mixtures	600	800	1000
Granites, basalts, etc.	–	1000	–
Sandstone	20	1010	2000
Poorly graded gravel, gravel-sand mixtures	1000	1750	2500
Gravel, sand, stones, little clay or loam	590	2585	4580
Surface limestone	100	5050	10000

  

Soil Resistivity Ranges
1000 Ohm cm	Wet organic soil
10000 Ohm cm	Moist soil
100000  Ohm cm	Dry soil
1000000 Ohm cm	Bed rock
590 to 7000 Ohm cm	Ashes, cinders, brine, waste
340 to 1630 Ohm cm	Clay, Shale, Loam
59000 to 458000 Ohm cm	Gravel , Sand , Stone with little Clay
300 to 500 Ohm meter	Concrete
900 to 1100 Ohm meter	Granite
20 to 2000 Ohm meter	Sand Stone
100 – 15,000 Ohm cm	Standard Design OK
15,000- 25,000 Ohm cm	Standard Design Maybe
25,000 – 50,000 Ohm cm	Special – Contact the carrier, owner or engineering firm
50,000 + Ohm cm	Very Special – Perhaps not practical

 

Ground Resistance Values
Industrial plant:	5 Ω
Chemical plant:	3 Ω
Computer System	3 Ω
Lighting Protection	1 Ω
Generating station:	1 Ω
Large HV sub-station, Generating Station (IEEE Std 142 clause 4.1.2)	1 Ω
Small Distribution sub-station (IEEE Std 142 clause 4.1.2)	5 Ω
Telecommunication facilities	<5Ω
Water pipe ground should	<3Ω