New house wiring woes

[Snacker]

I've recently moved into a 1978 3 bed detached house and it seems to have a few strange electrical issues. I won't list them all here but there's one in particular that I need to get sorted and that's the bathroom light because trying to bath a toddler by lamplight is a royal pain in the @ss, as is shaving!

The other day my gf plugged the iron into one of the kitchen sockets and as soon as she switched it on, it immediately tripped the MCB in the consumer unit. Bizarrely though, it'd tripped the one for the upstairs lights. I flicked it back on and all seemed ok until I tried the bathroom light, which no longer worked. I hoped that maybe it'd just somehow blown the bulb but there's not actually any electricity going to the switch itself.

My question is, where should I start in trying to figure out what the problem is? Should I trace the wiring from the switch and try to find out what it's connected to, or would it make more sense to start at the consumer unit? I studied electrical and electronic engineering at uni years ago but only ever went on to work in electronics since then, so I've never done any fault-finding on this sort of scale.

 

[flyingsparks]

Its probability worth getting a registered electrician to carry out an EICR (test) on the house as it sounds like some bod going has gone on in the past. Sounds like that socket is on the lighting circuit - not good.

 

[Snacker]

Its probability worth getting a registered electrician to carry out an EICR (test) on the house as it sounds like some bod going has gone on in the past. Sounds like that socket is on the lighting circuit - not good.

Given the numerous other issues we've found you're probably right. Any ideas how much an EICR is likely to cost? If it helps it's a two storey, three bed detached house with 11 rooms.

 

[AndyPRK]

the socket that the iron was plugged into. Does it look new/different to the others? When you turn the light circuit off, does the socket no longer work? Probably best not to use it for large loads!

As for the lights, an inspection into the other lights near the bathroom is probably the place to start.
Look for loose wires or blackness.

 

[Snacker]

the socket that the iron was plugged into. Does it look new/different to the others? When you turn the light circuit off, does the socket no longer work? Probably best not to use it for large loads!

As for the lights, an inspection into the other lights near the bathroom is probably the place to start.
Look for loose wires or blackness.

The socket doesn't look any different to the others, but I've just been speaking to my gf and she says that since then, the kettle and the hoover have both tripped out the upstairs lights as well, and both of them were plugged into different sockets (the kettle was another socket in the kitchen and the hoover was one in the downstairs hallway).
I'm pretty sure that the kitchen was replaced within the past few years and that definitely involved some electrical work because they had an electric oven installed. The consumer unit is also fairly new because the bloke who sold me the house was actually using it as a selling point and I've got some very reassuring-looking (but based on recent events, worthless) electrician's sign-off certificates, forms etc!

 

[diyer56]

When the MCB trips do the upstairs lights stop working? I know it sounds strange but the reason I ask is that when I moved into my house we couldn't work out how the electric shower was connected to the CU. It turned out that as the CU was full the 'electrician' had replaced the old 6A MCB previously used for the upstairs lights with a 40A version and connected the shower to that (still labelled UP LIGHTS). The upstairs light circuit had been combined with the downstairs lights in the other 6A MCB (labelled DOWN LIGHTS)

I have since re-labelled the CU accordingly.

It may be worth checking that something similar didn't happen when the work was carried out in your kitchen. I know this wouldn't explain the failure with the bathroom light but it may help further diagnose the tripping issue.

 

[Snacker]

Yeah they do, as that's the first thing that alerted us to there being anything wrong. I was upstairs and it suddenly went pitch black, then 30 seconds or so later I hear my gf shout up first saying that the iron won't work and then shortly afterwards asking why I'm sat in the dark

Now that you describe your situation it's given me an idea as to how I can at least work out what's wired up to what. When I get home tonight I'll switch off the MCBs one by one and make a note of exactly which lights and/or sockets are affected by each one.

 

[diyer56]

why I'm sat in the dark

And the MCB trip was your best explanation

 

[ericmark]

MCB sizes are a good indicator as to what they should do.
B6 Normally lights very little else uses this size.
B16 Often immersion heater where it's been removed often used for radial socket circuits instead. Also often oven.
B20 Radial socket circuits.
B32 Ring sockets, Cooker, hob.
B40 and above shower, sometimes cooker.
With RCBO's there can be other issues where the neutrals have been swapped. The same applies to twin RCD where neutral are shared or swapped.
One of the common faults is two way lighting I would try a different switch combination every two way switch has four options two will switch lights on and two off they them all.

It may seem odd but with neutral earth faults switching on a load on an unrelated circuit can cause a trip. The more load the bigger difference between earth volts and neutral volts so more likely earth - neutral fault will cause a trip.

 

[Snacker]

why I'm sat in the dark

And the MCB trip was your best explanation

It's not one I can use very often

 

[bernardgreen]

It may seem odd but with neutral earth faults switching on a load on an unrelated circuit can cause a trip. The more load the bigger difference between earth volts and neutral volts so more likely earth - neutral fault will cause a trip.

Neutral_Earth_trip

• bernardgreen
• 16 Jan 2011
• 48

 

[Snacker]

That's a good little diagram. I was struggling to get my head around how that could happen but that illustrates it well.

 

[aesmith]

Is it definitely an MCB that trips, not an RCD? It would be quite normal for an RCD to be arranged to cover downstairs sockets and upstairs lights, with another one doing the opposite.

 

[Snacker]

Is it definitely an MCB that trips, not an RCD? It would be quite normal for an RCD to be arranged to cover downstairs sockets and upstairs lights, with another one doing the opposite.

I've been asking myself the same question since seeing the above diagram because there are definitely two RCDs in the consumer unit along with 5 MCBs, arranged as downstairs lights, downstairs sockets, cooker, RCD and upstairs lights, upstairs sockets, RCD).

At the time I just quickly flipped whichever switch was down on the consumer unit, which is difficult to see as it's mounted high up on a wall and is also currently behind a stack of boxes waiting to be unpacked, so I didn't take enough notice. I'll do some testing tonight though. I was going to do some last night and then the bl00dy boiler packed up

Hopefully things don't go wrong in threes...

 

[Snacker]

I managed to do some testing last night and made a couple of breakthroughs. Firstly, it was indeed an RCD being tripped by the iron (and kettle, and hoover) rather than an MCB. That got me thinking about the bathroom light and the fact that it has a fan powered off it (which I probably should've mentioned earlier). At the back of what was once the airing cupboard I found an isolator switch and a power breaker, and resetting the power breaker restored power to the bathroom light.

I also discovered that one of the problem sockets is definitely connected to a lighting circuit rather than a sockets one, so have had a sparkie out this morning to do an EICR as suggested by flyingsparks. He said that there are a couple of dodgy DIY socket conversions (singles to doubles, one of these being the one connected to the lights) and has fixed a few other minor issues but apart from that everything is fine, so I can breathe a sigh of relief that it's nothing serious/expensive.

Thanks a lot for all your help, which enabled me to fix some stuff on my own and narrow the rest of it down enough to save the electrician a load of time.