[Closed] Calling the electricianists of STW

Sounds like everything worked fine till the armoured was installed?

If so then could be that there is an issue with the termination of the armoured cable, the wiring arrangement in the garage or that the earthing is picking something up from that end. Id start investigating there. Not sure whats around your garage, if its close to another installation

Could be worth installing a single way consumer unit that is fed before the main RCD in the house and install an RCD at the garage

We've checked that the Armoured is terminated properly at both ends. Even belled through the cable to check for short circuit or anything. Wouldn't expect us to be able to switch on the breaker in the house if there was a short anyway. But we checked all the same.

Until we try and switch anything on it sits there showing 240v out onto the circuits, but turn the lights on or plug something in and off goes the RCD in the house.

Check you haven't wired the neutrals in the new/old consumer correctly. I remember having the same issue years ago and it was due to one wire being wired into the neutral bus bar on the wrong side of the RCD. Can't remember off the top of my head exactly which one but it was obvious when I cast a critical eye over it. I only discovered the solution by phoning a mate who was a sparky and he instantly knew the answer as it seems to be a rite of passage, ie. everyone does it wrong at least once.

Just reading that is it because we have two RCD in the equation?

Maybe we should take our feed from the other side of the RCD in the house as the garage has its own RCD anyway?

What happens if the main switch in the garage and the MCB's in the garage are on on but nothing plugged into the sockets and no lights are switched on?

The two RCD's shouldnt cause the other one to trip. Its not ideal to have two RCD's in series unless one has a time delay on it, otherwise an issue in the garage will trip the house. Inconvenient and potentially expensive, freezer, central heating not able to work

@turin breakers and RCD in the garage turned on but nothing plugged in and lights not on and it sits there quite happily. We have tested and there is 240v output from the breakers.

@welshfarmer don't think it's possible on this consumer unit. Live and neg feed into top of RCD. Preinstalled cable from N output of RCD to N buzzbar. Copper bar from L side of RCD to input for breakers.

Just been and checked that no neutrals have strayed into the adjacent earth bar.

Check you haven’t wired the neutrals in the new/old consumer correctly.

+1

Sounds like you've got a split load CU in the house and you've taken the line (live) from the RCD protected side of the house CU and returned the neutral to the non-RCD side of the house CU - every time you draw a load the house RCD senses an imbalance and trips off.

Best to take both line (live) and neutral from the non-RCD part of the CU. Otherwise make sure that the neutral from the shed is also returned to the RCD protected neutral busbar.

Edit to add (as I've just seen your last reply) it could be a neutral-earth fault in the shed wirin, but your qualified sparky should have tested for that before connecting it all up.

Its hard to tell remotely but things that spring to mind

COULD be a faulty RCD at the garage - only causes an issue under load, but if it trips immediately this is unlikely. Can the RCD at the garage be swapped for a main switch? If that fixes it and you want RCD protection then you could install RCBO's in the garage

If it was my house id have the supply to the garage fed from a point before the house RCD.

Has the BIL tested the installation? not meaning to sound liek a dick but often people wire and switch on and dont do any testing before or after installation.

Edit - what Tillydog says could be spot on, if you have dual RCD's in the house?

EDIT 2 - in turn completely disconnect the 3 wires from each mcb at the garage and try to energise, that should help focus where the issue is

Have you checked all the wiring to the sockets?
Are they wired on a ring or radial? If on a ring you could try dropping each socket off the ring in turn and seeing if that's causing an issue.

@dirkpitt74. The sockets are on a radial. Just one single and a pair of doubles.

He's checked / tested the socket and lighting cabling and we also know the lighting worked when the cable from the switch had a plug on the end connected to an extension lead.

Have sent the BIL some of these replies to see if he has any lightbulb moments.

For me now I'm off to freeze my dangly bits off for a couple of hours on the bike.

My garage is fed from the house before the house CU. If a fault in the garage it doesn't affect the house.

Starting with that would also isolate or eradicate your problem.

My practical but non sparky brain would disconnect at the house end, then put a temporary extension lead to the garage CU fed from a house socket. If it fails on load then that points to a fault in the garage. If not then it's the garage feed.

Just shows how even a pro sparky dealing with something outside of their normal remit can miss something.

Sparky here.

Easy to get tied in knots looking for these type of faults, actually its normally straightforward to sort providing you approach logically.

The difficult bit is gently approaching your BiL with the following advice*

1. Disconnect the supply
2. Grab a copy of Guidance Note 3 and follow the tests in the correct order, dead tests first

Sounds like a bit of an arsey answer, but there is a very good reason to do the above (and understand what your doing and why)

if the rcd is not tripping on energization , but only when "under load" , £5 says the swa cable is connected to the wrong neutral bar in the house C.U. , or a similar wiring fault at the garage

we've all done it whilst tired or rushing near the end of  a tough day  🙂

Isolate each bit of the circuit in sequence. Rewire with a dummy circuit as you have the sea so you can easily move things around to test.

I am out of touch with latest reg but there was a requirement for discrimination between rcd's if in series. Easiest way was to have a 100ma supply and 30ma closer to the load.

Qualified sparky here own a contracting firm that specialises in inspection and testing....what you’ve got is a neutral fault.

Couple things to try, turn new CU off and have sparky do a loop test on the armoured cable, this’ll prove the swa can take a load. Make sure loop tester is on RCD setting so it doesn’t trip the house. After you’ve proven this double checking no cores have been crossed and same colours been used at both ends you can then connect in one circuit at a time. Tbh had the new install been fully tested first this wouldn’t have happened but you can rewind and do that now 👍

You can randomly check possible/probable causes (I am betting neutral fault)

Or you could test/diagnose the fault.

@tillydog and @brownsauce win the prize (qudos)

Was just the neutral in the wrong non RCD bar in the CU.

Took 1 minute to check and correct. I'm blaming the fact that we'd frozen our bits off pulling the armoured through in sub zero conditions that our brains no longer worked.

Cheers! STW for the win yet again.

Ahem, I think I win the prize too! 🙂

@welshfarmer haha, ok I'll give you that now I've been back and read the post again. 👍