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About consumer earthing
About consumer earthing
The conductor that connects the exposed metallic parts of the consumer's electrical installation is called protective earth.
Consumer earthing a commonly applied on to residential houses, shops, buildings, and factories.
Mandatory as protection
Mandatory as protection
When there is a fault in electrical system it is very important to protect any person from electrocution. According to Electricity Regulations, it is required to install earthing systems or methods of grounding on electrical supply system.
Component of earthing
Component of earthing
earth chamber (or earth pit) - This is where the wiring discharge the any fault or leakage current to the ground.
main earthing conductor (commonly known as electrode copper rod)
earth lead wire (or earth protective conductor)
earth clamp (or terminal)
earth coupler or jointer (for extending the rod longer length)
earth compound (for earth contact between the soil and copper rod)
Earthing requirement
Earthing requirement
the main earth conductor shall be following the standard CPC sizing. (Table 54G Wiring Regulation IEE)
earth lead wire minimal shall be at least 4mm.sq connected between the earth clamp and DB earth terminal. Standard color for this is green with a single yellow line.
the depth of the main earth conductor shall be at least 3 meter or earth resistances value of below one(1) ohm ( <1Ω) .
CPC or circuit protective conductor is where all electrical apparatus or appliances shall be connected with earth terminal.
Earthing methods
Earthing methods
There are various methods for earthing.
single rod
multiple rod earthing
copper mesh
copper plate
Method 1: Single rod
Method 1: Single rod
Refer to figure on the right, this method is commonly installed on to houses, shops and buildings.
The main earth conductor size shall be same sized as phase conductor.
Example if the phase conductor is 16mm.sq then the earth rod shall be 16.0mm. diameter at length of at least 3 meter.
For Reference
Method 2: multiple earth chamber
Method 2: multiple earth chamber
Refer to figure on the right, this method is commonly installed on to buildings or factories system.
This due to poor earth resistance and this method allows additional earth chamber to bring down the total earth resistance value to one ohm or lower.
For Reference
Method 3: Wire mesh
Method 3: Wire mesh
Refer to figure on the right, this method is suited for power substation.
The value of this mesh configuration must be below one(1) ohm. The voltage applies on substation can be greater than 500 volts in certain areas or site.
For Reference
Method 4: Copper plate
Method 4: Copper plate
Refer to figure on the right, this method is suited for high voltage pylon tower (HT overhead lines).
The depth of this copper plate installation must be at least 15 meter or greater depending on soil at site.
For Reference
Earth resistance
Earth resistance
Earth value of earth conductor connected with the ground or earth must be achieved as low resistance possible. This is a purpose to allow any fault current (leakage current) from electrical loads can allow these current to quickly flow to the ground. The ground acts as absorbing any current from faulty electrical equipment by preventing any person from electrocution.
Earth resistance value can be tested with a test set known as earth resistance test (or ground testset).
Formula earth resistance
Formula earth resistance
Re = (Z + Z1 + Z2) ÷ 3
where
Z - point 1 measured value
Z1 - point 2 measured value
Z2 - point 3 measured value
In order to achieve lowest resistance value, the depth of the main earth conductor shall be at least 3 meter.
Example earth resistance calculation
Example earth resistance calculation
Given the 1st point Z measured 1.1Ω , z1 is 0.5Ω and z2 reads 0.8Ω. Calculate the total earth resistance ?
Solution: Re = (Z + Z1 + Z2 ) ÷ 3
Re = ( 1.1Ω + 0.5Ω + 0.8Ω ) ÷ 3 = 0.8Ω GOOD earth value
What if earth resistance is greater than 1Ω ?
What if earth resistance is greater than 1Ω ?
Certain places where the ground is dry and hard or sometimes may have rocks on the ground. When such conditions happen you may not able to achieve a good earth resistance value. Therefore you may need to reposition the earth chamber or find another soft ground spot.
Solution:
add earth compound
change the location of the testing test spikes point (z,z1,z2) to another direction or angle.
find softer ground such as near by drainage or wet ground.
if the ground has some rocks underneath then put soft soil into the earth rod hole this may help soften and allow better contact.
Sizing of Protective Conductor
Sizing of Protective Conductor
According IEE Wiring Regulation on Table 54G Sizing of conductor
Phase conductor size (mm²) Protective conductor (mm²) Example
RYBN is <16 1:1 or same When RYBN is 10mm² then E shall be 10mm²
RYBN is 16 ~35 Fixed at 16mm² When RYBN is 30mm² then E shall be fixed 16mm²
RYBN is >35 Shall be 1/2 of phase conductor When RYBN is 75mm² then E shall be 35mm²
More information about earth resistance test can be found on this topic page.
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