Garage consumer unit trip

[TheAverageJoe]

Trying to add Garage consumer unit and having an issue I was hoping for direction on. Previously garage feed was from house consumer unit via garage RCBO to socket in the garage with no problems. Was looking to get some lights & extra socket so purchased garage consumer unit kit so can have light and socket circuits and tidy the whole thing up.
So have connected exiting armoured cable and new garage consumer unit, so the new run which consists of below:

From house to garage
-------------------------------
House CU via Garage RCBO = 20A-30mA
Armored Cable 2.5mm 3 Core
Garage CU via RCD 40A-30mA
Garage CU via MCB 32A
Garage 2.5 Twin & Core to single socket

Problem
---------
1: Socket tester powers ok & shows as "correct" with expected voltage readout.
2: Socket tester RCD test button trips the garage RCD.
3: However, if I plug any load in it trips the "House garage RCBO only."

So looking for any advice on what could cause this? Nothing changed on the house side, and everything worked when was just armoured cable to the socket so am hoping its a relatively straight forward solution.
Was actually wondering if the trip was being caused by the lower-rated house garage RCBO which is 20A? Was looking to swap it out anyway to match both sides but could this also possibly be the root cause of the tripping?

Have provided some pics FYI and thanks in advance for any advice given...

 

[ericmark]

One would not, except for marinas and caravan sites, feed a 30 mA RCD/RCBO from another 30 mA RCD/RCBO with SWA cable feeding garage normally in the house only a MCB is used.

However I would expect you have a neutral earth fault, while no current is drawn the neutral will be same voltage as earth, so there is no current flow between the two, when you put a load on the circuit the neutral voltage raises slightly so now current will flow.

So step one is turn off the garage RCD and test between neutral and earth it should be more than 1 MΩ and you should use an insulation tester which uses 500 volt to test, or 250 volt if you think the 500 volt may cause damage, but 9 volt of a multimeter may not be enough.

If fault not in garage then need to test house, likely you will need to remove the neutral wire to test, as the majority of RCBO do not switch the neutral. Again using a 500 volt tester.

If you find the fault with a multimeter then OK, but if multimeter shows no fault then there may still be a fault.

 

[TheAverageJoe]

Thanks for the swift reply and guidance on tester I will look at swapping out the house RCBO for MCB as suggested. Regarding the problem I have traced it to exactly what you mentioned, I found a junction box I didn't know existed in loft that joined armoured cable to 2.5 twin and earth for consumer and sure enough it was the earth & neutral cables swapped. I have now corrected, and I have no more nuisance trips and can finally see the light in the garage.

 

[EFLImpudence]

Thanks for the swift reply and guidance on tester I will look at swapping out the house RCBO for MCB as suggested.

You should not do that if the cable from the CU is installed using a method that requires RCD protection, i.e. buried in the wall <50mm deep.

Regarding the problem I have traced it to exactly what you mentioned, I found a junction box I didn't know existed in loft that joined armoured cable to 2.5 twin and earth for consumer and sure enough it was the earth & neutral cables swapped.

Does that translate as - you connected them the wrong way round in your garage CU?

 

[AndyPRK]

it's that common problem of new colours again!

ppl see a black and think it's neutral !
where as the grey is neutral I believe

 

[winston1]

it's that common problem of new colours again!

ppl see a black and think it's neutral !
where as the grey is neutral I believe

That may be preferred but I don't believe it is a requirement. What is required is sleeving the wires at both ends to the statuary colours.

 

[AndyPRK]

op did sleeve the wire in the earth bar, only it wasn't the CPC !

 

[JohnW2]

Does that translate as - you connected them the wrong way round in your garage CU?

Sounds like it, but if the OP didn't know that the JB in the loft (which had the N/E reversal) existed, I presume that the error was not of his doing.

Kind Regards, John

 

[EFLImpudence]

Obviously he didn't know about it (he said so) but the T&E had to change to SWA somewhere.

The junction box did not have an N/E reversal.

His error was connecting the garage incorrectly.

 

[JohnW2]

The junction box did not have an N/E reversal. ... His error was connecting the garage incorrectly.

Oh, maybe - but I took ....

... I found a junction box I didn't know existed in loft that joined armoured cable to 2.5 twin and earth for consumer and sure enough it was the earth & neutral cables swapped....

... to mean that the N/E reversal was in/at the JB (hence, by implication, not of the OP's doing).

Hopefully the OP will clarify.

Kind Regards, John

 

[EFLImpudence]

Oh, maybe - but I took ....
... to mean that the N/E reversal was in/at the JB (hence, by implication, not of the OP's doing).
Hopefully the OP will clarify.

It was only an N/E reversal in the JB because he connected the garage CU N & E (Grey & Black) the wrong way round.

He seemed to grasp the concept as soon as I wrote it.

 

[JohnW2]

It was only an N/E reversal in the JB because he connected the garage CU N & E (Grey & Black) the wrong way round. He seemed to grasp the concept as soon as I wrote it.

I'm a bit confused - he doesn't seem to have been back since "you wrote it" - it was Andy who made the comment about black and grey ... or have I missed something?

Kind Regards, John

 

[AndyPRK]

Remember this garage install used to work. He was adding a cu to add more lights or something.

So when he wired in the swa to cu
He must have thought how on earth do these silly colours work? Googled it or guessed.

 

[JohnW2]

Remember this garage install used to work. He was adding a cu to add more lights or something. ... So when he wired in the swa to cu ... He must have thought how on earth do these silly colours work? Googled it or guessed.

Yes. that makes total sense, although I'm still confused by ...

... I found a junction box I didn't know existed in loft that joined armoured cable to 2.5 twin and earth for consumer and sure enough it was the earth & neutral cables swapped. I have now corrected ....

Ah. A thought has just occurred to me, which would make more sense of the above quote ... if, as you say is likely, he misunderstood what the colours were being used for, maybe he did think that the connections were reversed at the JB, and therefore changed them (at the JB) (thereby aligning them with the way the conductors were being used at the garage CU) - and hence 'cured' the problem, without changing anything at the garage CU?

An important question would seem to be that of what (if anything) the SWA armour was (and now is, if things at the JB have been changed) is connected to at the JB (it doesn't seem to be connected to anything at the garage CU).

Kind Regards, John

 

[EFLImpudence]

I'm a bit confused - he doesn't seem to have been back since "you wrote it" - it was Andy who made the comment about black and grey ... or have I missed something?

You certainly have missed something:

12.29 OP wrote he had found reversed N/E at junction box.
12.45 I wrote that that was actually because he had connected them the wrong way round - Edit - at garage.
12.56 OP 'liked' my post. I take this to mean he understood.