been mapping out the circuits in our old house.

I have a random wire ending in a 30amp junction box in a built in cupboard. I am pretty certain this was part of the partial update the previous owner was part way through.

I have a simple ac voltage tester. this flashes suggesting it’s live. turning off the consumer unit means no flashing. but no individual trip seems to isolate it. flip all of them and it’s dead.

Is there something simple I’m missing here? Want to work out what circuit it is on….

One of the trips isn’t a trip but the master?

Can’t you just open the consumer unit and SEE which it’s screwed into ? 30A will probably not be on a shared RCD anyway ???

Do you have electric showers ??? (Or was the previous owner planning )

We have some interesting wiring where you have to trip two breakers to isolate either of the circuits. Sparky was doing some work for us recently and said whilst it’s wrong it’s actually quite common and is a pain in the ass to trace, usually a slightly dodgy upgrade, but he said at least one of the neighbours is the same and so possibly all the houses were done wrong. He believes that provided you know to trip both (I have a sticker on my Consumer unit) that it is not unsafe per se.

it’s in a built in bedroom cupboard so can’t trace back without carpets and floorboards up. reckon it might be 2 trips. trip all light circuits still live. trip all socket circuits still live. trip all of them it’s dead.

want to know if it is a lighting circuit which would be useful to fit a switch and light in the cupboard or whether it is a mains ring (or the start of one for a rewire)

some very odd wiring. found sockets in the same room on different rings. “upstairs circuits” also cover the garage….old seperate annex consumer unit also covers the master bed in the main houde etc…

90 years of modifications I suppose

Cupboard. 30 amps. Could it be for an old water heater? Although a plan to convert to ensuite is feasible.

maybe an ensuite but would be surprised as it’s the smaller of the bedrooms and the other side of the house from the utilities.

it is the room above the hall / consumer unit so I’m half thinking it was possibly the start of the rewire of the sockets

can’t ask the last owner as they passed away.

A flashing voltage checker will trigger from induced voltages. Stick a meter on it.

maybe an ensuite but would be surprised as it’s the smaller of the bedrooms and the other side of the house from the utilities.

it is the room above the hall / consumer unit so I’m half thinking it was possibly the start of the rewire of the sockets

can’t ask the last owner as they passed away.

dunno what happened there…

you will have to help me out, can borrow a volt meter. what am I looking for?

by induced do you mean it’s not ‘live’ but because it’s close to other wires it is picking up some of that wires voltage?

You can get a cheap voltmeter from Maplin etc. for <£10 … (obviously not the most sophisticated but would work as a one off)

Our house is similar with90 years of upgrades … but bugger all in removing unused/redundant

When I moved the consumer unit I pulled out kg of unused old cables .. and there are still some I have no idea where they go if anywhere ….

Lick the end of it. If you wake up at the other end of the room, it’s still live.

IANAelectrician.

Years ago I was helping a mate with a bit of renovation. Floorboards up. We turned the power off pulled the fuses and double checked. Imagine our surprise when he flew across the room in an upstairs bedroom. Turns out the double socket was wired into next door.

Free electricity!

It could be a subpanel? If not maybe two circuits are cross connected.

If thats the case then two breakers would have to be off together to kill it. As someone mentioned above.

Shut off the breaker one at a time and test, don’t turn them back on after you turn them off. Keep turning off breakers till it goes dead. Mark that breaker and leave it off. Next turn on the previously turned off breakers one at a time until its live again. Mark that breaker and you have found the two.

Turns out the double socket was wired into next door.

On a similar note bloke I knew took the manky bit of hardboard in the back of a built in bedroom cupboard out only to find out it was also the manky bit of hardboard in the back of his next door neighbours built in bedroom cupboard.

One solution would be to change the 30A junction box to a fused spur.
You could then down rate the circuit to 3A or 5A, which would then be adequate for wiring in a lighting circuit?
Obviously isolate before doing the work.

One possibility is that an enthusiastic amateur knew he needed 30A for a heater, knew he didn’t have enough capacity on the ring main but thought that if he shared it between circuits that would be fine. Alternatively, in extending a ring main, managed to connect two circuits.

In either case, there is evidence that the entire house might be bodged. If it was my house I wouldn’t be happy until I’d got it all sorted out properly.

Quotes to sort the whole house are a long way north of £5k hence why I’m trying to work out and plan what I can do myself and what I get the sparky in for and hopefully be able.to be clear in what I ask for and reduce cost where possible.

So is it a 30a supply / cable…..or just a cable going into a junction box that has 30a stamped on it?
What size cable is it?

Sounds likely a spur from one of the ring mains, but could be giving odd results due to some bodging / crossing of circuits…

A good electrician with a few meters should be able to test the integrity of each circuit in a couple of hours. Add another hour for figuring out where the mis-wiring is located.

I think Poly is on the right track. My mothers new house had a similar bodge for the old immersion heater with the wiring loop being on two fuses

I believe it is probably a spur – grey flex, looks mains ring sized, single cable going into the junction box with 30A stamped on it. I haven’t opened up the box yet as I’m not confident I am isolating it properly

Think I’ll have to get the boards up to try and trace it