I think I know the answer, but here goes.....
Commercial property (hotel). Public entertainment PIR picked up sockets in the public area (ring) served by a 3871/32A type 2 - no RCD protection (among other things). So this afternoon, I had a nice shiny new RCBo to stuff in instead. Then it all went Pete Tong..............
The ring is in singles; fed from an old square "D" 36 way TPN, which is barred out to single phase. Access to the board is hindered by a chiller unit for the bar soft drinks being on the floor in front of the board.
Supply is TN-C-S. Naturally, I cannot isolate the board. Found the neutrals by clamping cables in turn, and disconnecting the live. When the load disappeared - got neutrals . O Happy day
The circuit schedule says the ring is fed via contactor. No contactor in the room, so maybe they did away with it (25 yr old install - sched could be out of date???).
Grab the neutrals and phases, and chuck `em in the RCBo (end-to-end of ring is what i`d expect ). BUT I`m reading 39 ohms from the neutral of the ring to the neutral bar of the board.
This is either - a borrowed neutral at the undiscovered contactor, or a N-E fault on the ring.
Sooooooooo. I convince everyone I HAVE to isolate all these circuits ( bar, reception and lounge lighting & sockets), strip ALL the neutrals out of the neutral bar (except my shiny new RCBo), THEN switch on........
(trip).
So......All that has told me is that, if there is a hidden contactor, the neutral returns to a different board (there`re only 85 other boards it could be), or an N-E fault (which is my expectation).
RCBo out - MCB back in. All neutrals back in, and put power back on ( LOTS of complaints starting by this time........Whadda they WANT me to do? Poo a miracle and widdle champagne?)
If we accept that we cannot find the CPC`s for the ring without a shutdown (won`t be signed off) ; can anyone think of another way to determine the problem, or would you just recommend RCD sockets instead?
Thanks.
KME
Commercial property (hotel). Public entertainment PIR picked up sockets in the public area (ring) served by a 3871/32A type 2 - no RCD protection (among other things). So this afternoon, I had a nice shiny new RCBo to stuff in instead. Then it all went Pete Tong..............
The ring is in singles; fed from an old square "D" 36 way TPN, which is barred out to single phase. Access to the board is hindered by a chiller unit for the bar soft drinks being on the floor in front of the board.
Supply is TN-C-S. Naturally, I cannot isolate the board. Found the neutrals by clamping cables in turn, and disconnecting the live. When the load disappeared - got neutrals . O Happy day
The circuit schedule says the ring is fed via contactor. No contactor in the room, so maybe they did away with it (25 yr old install - sched could be out of date???).
Grab the neutrals and phases, and chuck `em in the RCBo (end-to-end of ring is what i`d expect ). BUT I`m reading 39 ohms from the neutral of the ring to the neutral bar of the board.
This is either - a borrowed neutral at the undiscovered contactor, or a N-E fault on the ring.
Sooooooooo. I convince everyone I HAVE to isolate all these circuits ( bar, reception and lounge lighting & sockets), strip ALL the neutrals out of the neutral bar (except my shiny new RCBo), THEN switch on........
(trip).
So......All that has told me is that, if there is a hidden contactor, the neutral returns to a different board (there`re only 85 other boards it could be), or an N-E fault (which is my expectation).
RCBo out - MCB back in. All neutrals back in, and put power back on ( LOTS of complaints starting by this time........Whadda they WANT me to do? Poo a miracle and widdle champagne?)
If we accept that we cannot find the CPC`s for the ring without a shutdown (won`t be signed off) ; can anyone think of another way to determine the problem, or would you just recommend RCD sockets instead?
Thanks.
KME