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Guest Alphonsox

Open neutral

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Guest Alphonsox

I have been wiring up the last few lights in the house. The en-suite has a switched light connection for an above mirror light. Unfortunately although the live is switched, present and correct (according to my voltage detector pen) it seems that the neutral is AWOL. Any ideas how I go about fixing this without knocking holes in the expensive tile work ?

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Well if it is wired according to regs, then all junctions will be accesible, so follow it back to the previous junction where it was looped from and test there.

 

If that's not the issue and you think you have a severed cable, then there is no option but find and repair the break, or replace the whole leg of cable.

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Dodgy cable from the start or have you damaged it?

 

I assume everything is NOT in conduit?

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Can you reroute to the fitting say from the other side of the wall if not tiled?

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Not taking the pi$$ but did you do dead testing or just hope for the best? I've had duff T&E off a new roll.

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1 hour ago, Alphonsox said:

I have been wiring up the last few lights in the house. The en-suite has a switched light connection for an above mirror light. Unfortunately although the live is switched, present and correct (according to my voltage detector pen) it seems that the neutral is AWOL. Any ideas how I go about fixing this without knocking holes in the expensive tile work ?

Where does the neutral come from or don't you know ? Does th switch have the neutral there, connected together so it goes to the fitting ?

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46 minutes ago, Onoff said:

Not taking the pi$$ but did you do dead testing or just hope for the best? I've had duff T&E off a new roll.

Don't tell me that it is standard practice to ring every core through and check for cross connections.

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18 hours ago, MikeSharp01 said:

Don't tell me that it is standard practice to ring every core through and check for cross connections.

 

Erm...yes! Lack of dead testing is why this sort of thing can happen. Not being condescending either.

 

Anyone seriously interested get a copy of the IET's Guidance Note 3. Never ceases to amaze me the amount of proper electricians who don't bother. I said to one on site "You not going to test that?" to which he replied "You can chuck a Martindale at it if you want!" 

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41 minutes ago, MikeSharp01 said:

Don't tell me that it is standard practice to ring every core through and check for cross connections.

If you know where all the cables start and end, then it's not really ever practiced in real life, ( but every time we second fix and everything switches on nicely first time, we do breathe a sigh of relief ). ;)

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3 minutes ago, Nickfromwales said:

If you know where all the cables start and end, then it's not really ever practiced in real life, ( but every time we second fix and everything switches on nicely first time, we do breathe a sigh of relief ). ;)

 

And that's why I'll never make any real money! 

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20 minutes ago, Onoff said:

 

And that's why I'll never make any real money! 

When working on the Royal Fleet Auxiliary contracts we tested until it hurt, but that was 17 years ago and I was on £54k basic so didn't care :D

 

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Guest Alphonsox

Thanks for all the input - To answer some of the questions above.

- It was wired by our sparky who isn't currently around. I have no idea what testing he performed (if any).

- I have tried checking back to the previous junction but cant see a connection for this fitting.

- The other side of the wall is a double socket so there may be some possibility of picking up a feed from there.

- The switch is switched live only

 

The other bit of info I have just received is that there was a last minute change to the wiring around this point - from two fixtures either side of the mirror to one immediately above. My guess is that the fault was introduced during this change.

 

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Guest Alphonsox

Got it ! I used the signal trace function of my network tester connected between earth and the dodgy neutral. This let me trace the wire back along the ceiling to a point above a non-obvious ceiling rose where the missing neutral had been taped-up for some reason.

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FWIW, I discovered a lifted neutral a couple of weeks ago, completely by accident.  We fitted a couple of fused switched connector units in the bedrooms, in case we ever wanted to add some small wall heaters.  It's clear that we don't, and I had a need for a switched FCU, and happened to have a spare unswitched FCU.  So, I decided to just swap them over.  When I removed the switched FCU faceplate the neutral fell out..........

 

This was on the upstairs ring final, and I know that it had tested out OK when installed, I can only assume that the wire wasn't clamped properly and came out as I removed the plate.  Needless to say the next few hours were spent taking off faceplates and making sure all the the screws and wires were tight on every single fitting (they were - this must have been a one-off).

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15 hours ago, Onoff said:

Anyone seriously interested get a copy of the IET's Guidance Note 3. Never ceases to amaze me the amount of proper electricians who don't bother. I said to one on site "You not going to test that?" to which he replied "You can chuck a Martindale at it if you want!" 

I can see why we did this when pulling through cables in petrochemical plants in the 80s / 90s and I guess it does have value in self building (or general building) but where do you stop? You could ring the drum through before you pull it through the building, ring it again once it is in place and before cover up. The essential difference between industrial and domestic practice is that, generally - not always, the cables are accessible on trays etc which makes doing the checks in domestic environments more important where cover up is everything. Ho Hum...

 

 

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The real issue here is the archaic practice in the UK of using ring finals.  It's a hang over from the high cost of cable back in the 1950's, I believe, but there is absolutely no excuse to continue wiring new houses like this in the day and age.  I was sorely tempted to wire the house as I have my workshop, all radials, with an all RCBO CU, but didn't as space was too tight where the CU was going to go (bad planning on my part).  At least with an all radial scheme you have an indication when a line or neutral gets disconnected somewhere - the circuit stops working.  When the same happens with a ring final the circuit carries on working, but with the cable potentially overloaded, as the protection device will have too high a rating (outlet ring finals in 2.5mm² T&E will typically have 32 A protection, radial finals in the same cable will have 20 A protection).

Edited by JSHarris
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4 hours ago, Alphonsox said:

Got it ! I used the signal trace function of my network tester connected between earth and the dodgy neutral. This let me trace the wire back along the ceiling to a point above a non-obvious ceiling rose where the missing neutral had been taped-up for some reason.

Result ?

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