Electric Reference

 Please note that this is a dead test and the circuit must be isolated when testing

 Top be carried out on radial circuits to ensure the CPC of the circuit is undamaged and connected throughout the circuit

 The highest reading should be obtained from the furthest part of the circuit. If the highest reading appears not to be at the end of the circuit, then further investigation should proceed (It maybe because of how the circuit was installed, although one end may appear to be closer to the CU than other points, it may still be the end of the circuit)

1. Safely isolate supply
2. Cross connect the Line and CPC at one end of the circuit, preferably at the consumer unit
3. At each point of the circuit, a test should been made between Line and CPC
4. The highest reading will determine the R1 + R2 value of the circuit

note: when the Line and CPC conductors are the same size, the total resistance can be simply divided by 2 to find the resistance of just the CPC

In most cases Twin & Earth is used and the size of the CPC is smaller than the Live conductors, therefore this equation should be used to determine the size of the CPC.

eg. Total resistance r1 + r2 = 0.35 ohms

r2= 0.35 x (2.5/(2.5+1.5))