Introduction…
Initial Verification: Dead testing must be completed after your inspection and always before any live testing takes place. This is to ensure that all safety systems such as the main earthing, main bonding and all circuit protective conductors are in place and that there is no risk of any short circuits or earth faults occurring once the installation is energised (switched on).
It’s all about proving satisfactory levels of safety before moving on to the next series of tests and any faults detected must be rectified and the circuit retested before continuing
The sequence of dead testing is as follows…
- #1: Continuity of main earth, bonding conductors and circuit protective conductors
- #2: Continuity of ring final circuit conductors
- #3: Insulation resistance
- #4: Polarity
Dead Testing…
#1: Continuity of main earth, bonding conductors and circuit protective conductors (radial circuits)
The object of the test is to ensure that the main earth, any bonding conductors and all circuit protective conductors (CPCs) are correctly connected, and are electrically sound with an electrical resistance which is low enough to permit the overcurrent protective device to operate within its maximum disconnection time should an earth fault occur (see Chapter 41 BS7671).
Every protective conductor must be separately tested from the consumer’s main protective earthing terminal to verify that it is electrically sound and correctly connected, including the protective equipotential and supplementary bonding conductors.
One of the methods used is to use a long ‘flying lead’ measuring from the consumer’s main protective earthing terminal to the far end of each earth conductor or CPC.
The resistance of the long test lead is subtracted from these readings to give the resistance value of the earth conductor or CPC. A satisfactory test result for the bonding conductors will be in the order of 0.05Ω and the result of each individual CPC can be recorded on the schedule of test results as R2.
Another, easier and more often used method of testing the continuity of each radial circuit’s CPC is to use the circuit’s line conductor instead of the ‘flying lead’. This is done by connecting the radial circuit’s line conductor to the CPC at the consumer unit and then taking a measurement with your continuity tester at the furthest point on the circuit between line and earth.
Each individual measurement is recorded and because this is the combined resistance value of the line and earth conductor it is recorded on the schedule of test results as R1+R2
NOTE: There is no need to record both the R1 and the R1+R2 value on the schedule of test results as they both prove that the CPC is continuous and 99.9% of the time just the line to earth method is used during an initial verification.
Next: Continuity of Ring Final Conductors (Socket Ring Circuits)