Lost neutral, or something else?

[GeoffTitch]

I have been working on a small outbuilding we have next to the house. It was a slightly enforced job, after the storm back in January took the roof off, and my wife said "while we are at it, why don't we..."

It was constructed of two small rooms, a shower room and a pump room, each with its own light. While we were doing the roof we took the opportunity to extend it slightly, moving the end walls by just over a metre and inserting a third small room in the middle.

Needless to say, this involved moving the electrics and spuring off another light, and this is where my problem begins. I have taken out all the old wiring from the first junction after the mains input and replaced it with new wiring, as I needed to extend the cables and rather than add short extensions it made sense to put in new cable from the input to the lights.

But now when I turn on the lights it appears that they are in series; any one light is fine, but turn on two and they are using half voltage each, or at least half as bright each).

I have checked and rechecked the connections. All neutrals are tight. If I unplug any one the others still work so I am sure they are not in series. I have tested everything from the point of input to the final rose. My input feed connects directly to the next light feed, switches feed off the live and the bulb returns to neutral.

Arrgh.

Also, after about 30 minutes the whole light circuit goes off. The main fuse is fine, the 15 amp circuit is still functional, but the 5 amp lighting just doesn't work. If I re-cycle the mains switch then it all works again ok.

Anybody got any ideas what I am doing wrong?

 

[AndyPRK]

I think we would need more info on the method you have used to wire.

I assume u have 3 switches now.

And what lamp types u have.

Is there a fuse box in there.

 

[AndyPRK]

Sounds like a poor connection at the supply maybe ?

 

[GeoffTitch]

I think we would need more info on the method you have used to wire.

I assume u have 3 switches now.

And what lamp types u have.

Is there a fuse box in there.

Ok, setup was originally wired back in the late 1970s, so runs off an old fuse box rather than an RCD, but the fuses are all sound and working.

Mains cable runs underground to a junction box. I haven't touched any of that. At the junction box is the one cable containing 4 incoming wires, which appear to split into 3 live and 1 common neutral return. From there we have:

1 live and common neutral return is 30 amp which runs the pump, and works fine.

1 live and common neutral return is 15 amp and runs a socket, which works fine.

1 live and neutral return is 5 amp and goes to the first lighting junction box. I haven't changed anything up to this point.

In the junction box I have mains in connecting directly to mains out, which goes to the next junction box, live to live, neutral to neutral, earth to earth. Within that I have live to switch, switch to light, light to neutral return. Only t I have done here is replace the outgoing cable (originally went to light 2) with a new longer cable to the next junction box.

Same in junction box 2 for the middle light.

It then goes to the third light, which is connected in the ceiling rose; neutral to end, live to loop. From loop live to switch, switch to live on light, light returns to neutral.

So yes, 3 switches and all lamps are standard 60w bulbs.

All lights work independently (until the power turns off) but I have this weird problem if I turn 2 of them on.

 

[securespark]

What happens if you turn 3 on?

I'm thinking it could be a burnt-out neutral on the supply?

 

[bernardgreen]

Also, after about 30 minutes the whole light circuit goes off. The main fuse is fine, the 15 amp circuit is still functional, but the 5 amp lighting just doesn't work. If I re-cycle the mains switch then it all works again ok.

What do you mean by "" I re-cycle the mains switch "" ? Is it an MCB ?

The lamps being in series with each other will create the dim effect. Shorting one lamp at a time will make that lamp go out and the other come on full brightness. Have the switches been incorrectly wired in parallel with the lamps ? Does the switch for lamp 1 appear to control lamp 2 ?

The strange thing is that when you turn both lamps "OFF" ( both switches ON thus shorting out both lamps ) there will be a short across the supply and the MCB should trip immediately and not 30 minutes later. Unless there is another item in series, a heater or something, that is limiting the current to about 50% above the rating of the MCB which would then take several minutes to trip. Or maybe the impedance of the cabling is so high that the fault current from the short circuit is limited by the resistance of the cable. That would means seriously undersized cable had been used or there were very long cables involved.,

 

[333rocky333]

if the lamps were in series, surely with only 1 switch on at least two lamps would come on dim and with removal of one of them lamps when dim will turn off the other dim lamp and unlikely to trip an mcb

sounds more like something breaking down under load, though the difference between 60watts and 120 watts is not really excessive, or a possibility is a partialy damp or damaged cable on the load side of the switch

Are you also saying you are using 3 circuits on 3 seperate mcbs using just 1 common neutral

 

[GeoffTitch]

1.5mm cable throughout.

The incoming SEB mains supply feeds the main MCB for the house (RCD), and also a small separate MCB (plug in fuses) for this outbuilding (labelled dual supply). By recycling the main power I mean turning the MCB off and on for the outbuilding at the main switch on the MCB. The 5 amp fuse is not getting blown.

Th MCB for this has 3 separate fuses, 30, 15 and 5 amp. One thick cable, with 4 wires, runs from that to the outbuilding. In the outbuilding is a small metal junction box. The neutrals from each circuit in the outbuilding all connect together here, so the is one common neutral going back to the MCB. The other 3 wires are the supply feed to each circuit. This has worked fine since about 1978 and I haven't touched or changed it, although I am contemplating changing the fuse box for a RCD.

Surely if the main neutral was burnt, nothing would work?

I can happily run a drill on the 15 amp circuit, and the 30 amp pump runs fine. it's only the light circuit that is effected, whether or not anything else is functioning. If I turn on all 3 lights they are all on, but very very dim, as if it was wired in series, but if I take one bulb out the others still work normally.

The switches for each lamp control only that lamp. The switches work as expected for each lamp, ie switch one only controls lamp one, etc.

I'm sure it's a neutral problem somewhere, but I'll be buggered if I can work out where!

 

[AndyPRK]

By MCB I think you mean fuse box.

When the lamps are dim try operating the drill if its plastic.
What happens ?

 

[GeoffTitch]

By MCB I mean fuse box.

I can run drill without affecting lamps. Not sure what you mean by "If it's plastic"

 

[AndyPRK]

Sounds like a poor connection in the first lighting junction box you have been in.

 

[GeoffTitch]

Just taken out all wires, cleaned and reconnected. All connections seem tight. ... same problem.

 

[GeoffTitch]

See if this helps any...

Main board

• GeoffTitch
• 13 Jul 2014
• 1

Main incoming supply on right. Main RCD for house across top. Fuse box for outbuilding bottom left

Main supply in garage. Mains incoming on right, marked dual supply. Main RCD for house along top. Outbuilding fuse box bottom left. (Third feed running off to right goes to solar panels).

There are four fuses. One 30 amp goes to a separate circuit for a shower. The other three (5A, 15A, 30A) all go to this metal junction box:

Junction box

• GeoffTitch
• 13 Jul 2014
• 1

Not changed. 4 incoming wires (red, blue, yellow, black). Red, blue and yellow go to each...

There are 4 incoming wires, red, blue, yellow and black, feeding in from bottom. Each colour is (presumably) connected to a different fuse and becomes the live for each circuit within the outbuilding at this point. All returning neutrals connect together here, connecting to the black wire and (presumably) returning to a common neutral in the fuse box.

As a thought, there is no earth here, ie although I have earth connected throughout the earth wires coming in at this point dont connect to anything - could that be a problem?

I haven't touched this, other than to open the box to see what is happening inside, unless pulling the yellow wire out has disturbed the neutrals here?

From there it goes to the first lighting junction box:

First lighting junction

• GeoffTitch
• 13 Jul 2014
• 1

White 1.5mm on left is incoming supply. Grey is ongoing to next light. Right hand cable is...

Incoming supply is on the left. Outgoing supply to next light is the grey wire at the top (so I have a thru live and thru neutral, yes?)

Switch is right cable, connected to live and loop, light is bottom cable, connected to loop and neutral.

 

[AndyPRK]

I think you could do with an electrician to make sure things are safe ( earthed)

The thing at the top isn't an rcd.

Lacking earth sleeveing in outbuilding and possibly not earthed.

 

[Adam_151]

I can't actually see any earth running into that lower wylex board at all... Any chance of a wider shot that shows the electricity board meter and cable head to?

As to the fault, I'm thinking along the lines of a high impedance earth connection either through a deliberate earth electrode or by a path thats occurred through some other means (water pipe, etc). Lack of RCD protection (evident from the pictures) and the lights using the high impedance earth as a return instead of the neutral.

But to be honest it looks a bit of a mess; the 4 core SWA (the steel armouring is supposed to be the earth in answer to another point you raise) with three circuits and one neutral is certainly not permitted for a start. You really need to get an electrician there before the ceilings go back to sort the mess out properly as you more than likely have lack of an effective earth to parts of the installation