M
mojorebel
This was an interesting problem and solution
I recently wired an community hall - the supply was a TPNE – one phase was being used for E7 heating. One phase was unused. And the third was to supply the lighting and power. I fitted a split board 12 way CU and ran two A2 radials for the sockets. The hall was fitted with around 30 wall mounted fluorescent lighting fittings via an 8 gang switchplate. I very wisely fitted a “lighting control” connection box (where all lighting cables terminated before going to the relevant switches and fittings) All circuits tested ok. But the RCD would trip occasionally when a light switch operated . The RCD would not always trip with the same switch . It could be any of the 8 – retested circuit – all ok, changed RCD – problem persisted . I took the lighting circuit off RCD protection (split board) . But the problem persisted. Fitted a separate CU for lights only with no RCD protection . Problem not solved. The RCD would still trip when light switches used (not every time , but now and again) I decided to put the lighting CU on its own phase – so utilised the unused phase. The problem still persisted. I eventually realised what the problem was ( Back emf on the neutral caused by inductive discharge lighting) . I solved the problem by fitted double pole light switches and switching both line and neutral conductors. First time in 40 yrs that I have come across this problem
I recently wired an community hall - the supply was a TPNE – one phase was being used for E7 heating. One phase was unused. And the third was to supply the lighting and power. I fitted a split board 12 way CU and ran two A2 radials for the sockets. The hall was fitted with around 30 wall mounted fluorescent lighting fittings via an 8 gang switchplate. I very wisely fitted a “lighting control” connection box (where all lighting cables terminated before going to the relevant switches and fittings) All circuits tested ok. But the RCD would trip occasionally when a light switch operated . The RCD would not always trip with the same switch . It could be any of the 8 – retested circuit – all ok, changed RCD – problem persisted . I took the lighting circuit off RCD protection (split board) . But the problem persisted. Fitted a separate CU for lights only with no RCD protection . Problem not solved. The RCD would still trip when light switches used (not every time , but now and again) I decided to put the lighting CU on its own phase – so utilised the unused phase. The problem still persisted. I eventually realised what the problem was ( Back emf on the neutral caused by inductive discharge lighting) . I solved the problem by fitted double pole light switches and switching both line and neutral conductors. First time in 40 yrs that I have come across this problem
