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Topic Title: Light ccts - Two MCB's
Topic Summary: Borrowed neutral?
Created On: 16 January 2013 07:49 AM
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 16 January 2013 07:49 AM
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SherlockOhms

Posts: 325
Joined: 05 April 2011

Chaps,

Looking at a fault yesterday.
Two lighting ccts, upstairs and down.

In order to isolatate either cct it is necessary to switch off both MCB's.

With one or the other switched off, operating the stairs lighting causes dimmed/flickering of the lights.

I assume this is a borrowed neutral scenario?

Any other thoughts or input much appreciated.

Given that the place has just been decorated, is an acceptable fix to simply put both lighting ccts on one MCB?

S.
 16 January 2013 07:53 AM
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daveparry1

Posts: 6239
Joined: 04 July 2007

That's what i'd do under the circumstances Sherlock, they obviously don't want their new decorating bu**ered up! I do this on c/unit changes quite often when I find shared neutrals,

Dave.
 16 January 2013 10:14 AM
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Ricicle

Posts: 843
Joined: 23 October 2006

If it requires both mcbs to isolate both circuits then it is more than just a borrowed neutral. It sounds more like the lines are linked together somewhere with some other mis-wiring of some sort ? (hall/landing switching might be the first port of call)

-------------------------
Empty barrels make the most noise.
 16 January 2013 10:30 AM
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AJJewsbury

Posts: 11553
Joined: 13 August 2003

With one or the other switched off, operating the stairs lighting causes dimmed/flickering of the lights.

I agree with Ricicle - there's more going on there than just a borrowed N. I'm presuming they're not DP MCBs and the Ns are still supposedly connected during this flickering? I might guess a loose connection in L somewhere that someone's attempted to by-pass but taken the feed from the wrong circuit.
- Andy.
 16 January 2013 11:09 AM
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Avatar for OMS.
OMS

Posts: 19747
Joined: 23 March 2004

Lights dimming also suggests that a bit of series connection is going on somewhere - certainly not just a borrowed neutral issue as highlighted by Andy and Ricicle

regards

OMS

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Failure is always an option
 16 January 2013 10:41 PM
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antric2

Posts: 1068
Joined: 20 October 2006

It does seem more than borrowed neutral.

Referring to hall\landing lighting circuit,.either the decorator has taken pendant off\or disturbed and refitted the an unflagged neutral coloured switched live in the neutral of the pendant or he has trapped cables at the switches.
When they are dim knock the switches and see if anything happens.
regards
Antric
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