Shaun Potter asks a question about concerns over a main protective earth split at the surge protection device before the main earthing terminal (MET) in the distribution board. His question has been answered by the NICEIC (Theme – Distribution Equipment including Cable Management):
Question: Please can you tell me whether the following arrangement found on a periodic inspection (Electrical Installation Condition Report) is compliant?
An industrial unit has a metal distribution board supplied with SWA cable. The main protective earth from the banjo goes to a surge protection unit within an extension box on the distribution board first - one leg into one connection on the surge protection device (SPD), then using the second common connection on the SPD, it continues up to the MET within the board.
From my early days, I was always taught that earth conductors were always one complete length; the same as bonding groups of water pipe, when we were never allowed to cut the earth conductor, but loop it through the bonding straps. The reason was that if one came away, you wouldn't loose all the earthing.
Therefore, should the main earth conductor be one complete length from banjo to MET?
Answer: This situation warrants a Code 2. The supplies' earthing arrangement should be connected to the MET and then an earthing arrangement should connect straight to the distribution board.
If the SPD fails, then the earthing arrangement could become impaired and then automatic disconnection of supply (ADS) may not be achieved on the electrical installation.
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