Electrics/consumer unit problems

[Lofty Bob]

The other day I put a junction box in my lighting circuit. The circuit was off (it was tripped but the circuit breaker was in place), but when I went to turn it on the power wouldn't come back on.

Trouble shooting wasn't obvious: power was going into the circuit breaker, it appeared to be crossing the circuit breaker, but it wasn't reaching the first junction box on the circuit. A multimeter showed a current going across the circuit breaker, and swapping the circuit breaker for another working circuit breaker (from another lighting circuit) didn't solve anything either.

I called an electrician who perform some wizardry at the consumer unit. He said there were black marks behind the circuit breaker at the consumer unit (not sure where) and suggested I'd shorted the circuit when I cut the wire, but wouldn't show me what he did to fix it.

I've now had another mishap and shorted the oven circuit. The circuit breaker tripped, but power wouldn't return to the circuit when I switched it back on (no sign of life from the oven; no power detected by a non-contact voltage detector on the cable where it meets the oven).

This appears to be exactly the same as the problem with the lighting circuit: power is going to the circuit breaker and appears to be going across the circuit breaker, but not reaching the appliance.

In addition, the lighting circuit also doesn't work as a result of the oven circuit blowing even though it didn't trip when the oven circuit tripped. Again, the circuit breaker looks fine and swapping it for a good circuit breaker (from another lighting circuit) doesn't solve the problem.

Does anyone know what's going on or how to solve it? Don't worry, I won't work on electrics again once this is sorted!

 

[PrenticeBoyofDerry]

Okay can you upload a picture of your consumer unit?
If your are having tripping issues and the MCB (breaker) is still in the on position and you have lost power to some circuits but not completely lost power to all circuits. This would indicate that an RCD has more than likely tripped, RCDs can trip even if you have isolated the circuit you are working on.
Testing for current at the breaker is not what you would ideally be looking for, as it is voltage that is best measured and a non-contact stick/pen would be best substituted for a two pole/probe voltage indicator.

 

[Lofty Bob]

Here's a picture of the consumer unit. I did try to test with a non-contact voltage detector but it beeps as soon as it's near the consumer unit - it can't distinguish between different breakers. That's why I tested it at the back of the oven instead, but didn't find any voltage there.

I was using a cheap LAP detector from Screwfix. Would a more expensive one be better? If so, can you recommend one?

 

[PrenticeBoyofDerry]

No non-contact can be handy but unreliable when multi- circuits are local to testing or where insulation of conductors is high. You are always better testing using an a two pole voltage indicator, a simple multi-meter will have this facility and then testing for voltage between line and neutral, line and earth and neutral and earth. As this will help identify the issue.
But the safest method is to test on the circuit while it is isolated, using continuity tests and a simple multi-meter will perform these.

Right to your issue:
Well there is no evidence of RCD protection, unless you have remote isolator somewhere else before the fuse board?
And you are saying even though the breakers are in the on position you have no power on the circuits, we first need to confirm that the breakers have not fried or become faulty, so you do need test at the output point of the breaker, if you isolate all other breakers you can test using the non-contact for voltage at each individual circuit at the board. But ideally we could do with the two pole version.

 

[Lectrician]

All those breakers are in the off position?

 

[PrenticeBoyofDerry]

All those breakers are in the off position?

They are indeed! So to the OP have they been isolated intentionally or have you not been able to reset them? It is the larger button near the top of the breaker that needs to be pushed inwards for it to become live.

 

[Lofty Bob]

Well there is no evidence of RCD protection, unless you have remote isolator somewhere else before the fuse board?
And you are saying even though the breakers are in the on position you have no power on the circuits, we first need to confirm that the breakers have not fried or become faulty, so you do need test at the output point of the breaker, if you isolate all other breakers you can test using the non-contact for voltage at each individual circuit at the board. But ideally we could do with the two pole version.

There is RCD protection, it's out of shot just below the consumer unit. I've switchrd it off and on but no difference.

I think the lighting breakers are okay because swapping between the good downstairs circuit and the faulty upstairs circuit doesn't help. I can't do the same for the oven. I also used a neon screwdriver to show there was power getting across the breakers when in position, and a multimeter to confirm continuity in the breakers. I'll do the testing you suggest once the others and left the house and I can isolate circuits.

 

[Lofty Bob]

All those breakers are in the off position?

Sorry, that picture was mid-troubleshooting when everything was intentionally turned off. All breakers are now in the on position except the oven - I've removed the breaker to be sure the circuit's safe as the oven isn't fully assembled. We have power everywhere except the oven circuit and the upstairs lighting circuit.

 

[PrenticeBoyofDerry]

Don't use a neon screwdriver, they are unreliable and potentially dangerous!
If you have continuity and voltage across a closed breaker, then you are now looking for a loss of continuity upstream of the breaker, either down to damaged or loose conductor, this could be line or neutral (that is why you require two pole testing) or possibly faulty contractors on an isolator or an upstream fuse.

It would be worth checking that the line cable in the breaker is making good contact and the neutrals in the neutral busbar, also check earths are making good contact. As it seems some work has gone on at the board they may have become disconnected or loose.

 

[bernardgreen]

I'll do the testing you suggest once the others and left the house and I can isolate circuits.

With your methods of "testing" I would advise you NOT to work on electrics when alone in the house. Having someone able to call for help may be a life saver.

 

[Lofty Bob]

With your methods of "testing" I would advise you NOT to work on electrics when alone in the house. Having someone able to call for help may be a life saver.

Is that specifically about the neon screwdriver or anything else? Or more a comment on general naivety? I appreciate the feedback but it would be more helpful if you were more specific. Clearly I want to operate safely and any guidance is well received.

 

[bernardgreen]

Using a two pole tester ( for example a multi-meter that you know how to use ) will be safer than using a neon screw driver. A neon screw driver can remain dark when touching a live wire and light up when touching an earth. Obviously these are incorrect indications and extremely dangerous to anyone who trusts them. This happens because a neon screw driver lights up when the potential difference between the person holding it and the wire it is touching is more than 70 volts. If the person holding it is close to a live wire, such as the wires in the wall going to a switch then the person's potential could be as high as 230 volts. Hence the neon will not light when touching a Live wire but will light when touching an earth. The 230 v potential on the person is via a very small capacitive coupling between the wire and person. This can pass enough energy to falsely light the neon when it touches earth but not enough to cause any noticable "tingle" when the person touches an earth with a finger.