Todays PITA job / rantlet / question

[kme]

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 No contactor in the room, so maybe they did away with it (25 yr old install - sched could be out of date???).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

 

[M107]

I'd go for SRCD's in the intrim, but put in a written statement requesting a shutdown to find the fault as without it the circuit will not be signed off.

 

[ProDave]

I'd go with a whole load of RCD sockets, and leave the rest of the can of worms alone.

How many sockets are there?

 

[ianmacd]

RCD sockets and suggest an off season complete i&t and upgrade.

---------- Post Auto-Merged at 14:26 ---------- Previous post was made at 14:24 ----------

See what goes off when you switch off the mcb and what doesn't when you isolate the N's. Could be a fun one to watch from a distance. Not suggesiting you really do this though.

 

[Fracticus]

Assuming the following 1- No CPC at board 2- Old system wired in singles through trunking conduit etc. 3- Back boxes are metal 4- all equipment unplugged

If getting 39 ohms i would agree N-E fault as you would get 0 ohms if there is a netral in your ring connected to another board, would suggest removing and checking for crushed cables behind sockets.

sorry for all the assumptions

 

[Evans Electric]

Martyn , I may be way off here ,but if something is still plugged in and you meggered between L and N bar it could be the Res. of whatever s plugged in .

It sounds more like this hidden contactor or a proper fault TBH. For commercial situations can you desist from fitting the RCD until fault is found. Not your fault if they are too busy to investigate properly.

 

[Andy™]

id go with RCD sockets with a note of fault still there and needs shutdown to fault find/repair

 

[Sidewinder]

First Q, why would the ring be fed from a contactor?

If it is there must be an on off switch surely?

Could you temporarily stick in an up front rcd this would tell you if the shared N is on another board?

I suppose this is one situation where by you can't stop things from being plugged in!

Says he typing on a laptop plugged into a socket in the bar of a hotel!

 

[kme]

Thanks for all input guys - resolution as follows:

Snakehips - ALL the S/O ccts in public areas are fed from contactors. The idea is that, if they`re having a disco or live band, and the fire alarms go off; the rings are shut down at the same time; i.e. contactor fed via 24V relay from fire alarm outputs. They also have a noise pollution system, which will isolate certain circuits if the noise level is above H&S recommended maximums

Fracticus: Assumptions fairly sound - there ARE CPCs at the DB - 49 of them to be precise. Which 2 belong to MY ring? Gawd only knows. The earth bar only has 15 holes, so they`re not in the same order (naturally).

The hotel chain simply wouldn`t sign off on a shutdown - they`d ignore it first. SRCDs would have worked; but it`d have been messy, as many of the sockets are singles flush mounted - the conduits protrude into the boxes approx 12mm, so getting the boxes OUT to replace `em with DSOs would have been a `mare.

The issue was a (brass) platescrew, which had snagged and ripped the neutral conductor behind a SSO- said conductor was leaning against side of back box...........Repaired, refitted and RCBo`d within 2 hrs.

Thanks again for the input guys Guinness

KME

 

[Ali]

I hope the hotel appreciated your great work. It sounds like you saved them a lot of agro and a big shut down. I'm sure they are still whining about how long it took, but I think you need a big pat on the back. Do you have a nice warm satisfied glow of a job well done?

 

[ianmacd]

many of the sockets are singles flush mounted - the conduits protrude into the boxes approx 12mm, so getting the boxes OUT to replace `em with DSOs would have been a `mare.

Glad to hear its fixed but maybe one of these could have been used as they only add 16mm to the projection of the face plate

 

[Andy™]

Glad to hear its fixed but maybe one of these could have been used as they only add 16mm to the projection of the face plate

but will an RCD socket fit into it though?

 

[ianmacd]

If the RCD socket fits a 25mm box they should fit this (depending on cable entry points). Another option would be:

 

[kme]

Thanks Ian - you`ve been scoobed mate

I couldn`t have used the conversion box - they`re all stainless or brass sockets

Ali: The hotel doesn`t know (or care) what I did or how I did it. They just need a Public Entertainments Licence; and the LA picked up on some of the obs. I made last year. They ignored a load of others, but they`ll prob. get done next year........

But yes, I DO have a really good attitude tonight; I`d originally estimated 2 days, and, although yesterday was a problem, I caught up today All I have to do now is get the paperwork in by the 26th to get paid mid March, rather than mid-April

KME