UK changing or swapping a MCB

[mmichael stath]

Hi, I have a garden studio that is fed from the main consumer unit in the house. It is wired into a B6 MCB on a radial circuit which is fine but occasionally, if I use something that draws too much power the MCB trips. I use power tools which work fine as I only use one at a time obviously, but I have recently acquired a new Hoover which just trips the MCB when it is switched on.

There is a spare B20 MCB in the CU and I have tried to move the live from the B6 to the B20 but this just trips straight away. Would this indicate that this B20 is faulty (it's a reasonably old Steeple CU)?
I'm wondering if I would be able to just replace the B6 with a higher rating MCB?

I have attached a photo. In short I have tried moving the wiring from B6 (A) to B20 (B) with no luck. Can I just replace the B6 (A) with a higher rating MCB?

Thanks in advance.

 

[Avo Mk8]

If you've moved an (L) from one side of the consumer unit to the other, you need to move the corresponding neutral for that circuit to the other neutral bar in the CU! That why the RCD is tripping!
Make sure the cable you want to move is compatible with 20A protection.

 

[littlespark]

stop stop stop!

the 6A is there to protect the CABLE just as much as the load on the end of it.
There is no point uprating the circuit breaker to allow 20A through if the cable is only rated to something like 16


The reason it is tripping after moving it over, is because the neutral of the circuit will still be connected to the right hand side neutral bar.... protected by the right hand side rcd.
The 20A is on the left hand side rcd.

 

[mmichael stath]

Thank's for the reply.

Ah, right, I see that now. I'd assumed (which is a stupid thing to do, I know) that the neutrals were all connected to the same place?! I've attached another photo. The red line indicates the path of the current cable set up.

All of the cabling was in when I bought the house a couple of years ago. There is a small CU in the studio with two MCB's - one B6 for the lights and a B32 for the sockets and it is approx 10m from the house. The cable looks like 4mill.

Will prob contact an electrician.

 

[littlespark]

Will prob contact an electrician.

best advice anyone can give you.


I don't mean to come across as all high and mighty, and a little preachy.... but please... put the cover back on before there's an accident...


Interesting to see those RCD's are not polarity sensitive... Normally, the L and N are marked on the same side

 

[mmichael stath]

best advice anyone can give you.


I don't mean to come across as all high and mighty, and a little preachy.... but please... put the cover back on before there's an accident...


Interesting to see those RCD's are not polarity sensitive... Normally, the L and N are marked on the same side

No you are absolutely right. Just thought I'd take a gander first.

Don't know how old this is, 10 years maybe. The house was rented before we bought it and the landlord did his own work, apparently. I've had to fix a lot of his handiwork.
Thanks littlespark.

 

[brianmoooore]

It's very unusual to feed a sub main from a 6A MCB. Electrian needed to determine why this has been done.

 

[richy3333]

I don't mean to come across as all high and mighty, and a little preachy

High and mighty with your username

 

[Yellowhammer]

It looks a lot to me like that used to be fed from the B20, there will be a safety related reason it's moved. As others have said get someone qualified in to test and inspect the circuit. At a guess something might have been found on an EICR, like a high Zs that necessitated the move to the B6 that was perhaps already in the board as a spare, and would keep the light on in the studio. Given there's a B32 and B6 upstream, it all sounds very DIY.

This is all total guess work online and it absolutely needs a physical inspection from someone suitably qualified. I just like to speculate. It's also nice when people come back and inform what was the issue, I'm often left reading threads with no conclusion..

 

[MDJ]

Just to throw an egg at the OP, if you change the OCPD on a circuit then an EICR is needed as well for insurance reasons as well as regs to BS 7671, popcorn ready, let me have it

 

[davesparks]

Just to throw an egg at the OP, if you change the OCPD on a circuit then an EICR is needed as well for insurance reasons as well as regs to BS 7671, popcorn ready, let me have it

An EICR isn't required, some form of certification would be though.

 

[MDJ]

An EICR isn't required, some form of certification would be though.

interesting Dave, I thought, and obviously wrongly (I will check the book) that if you change the OCPD by increasing it then the characteristics of the supply has changed an a EICR needed rather than a minor works. changing a 6 amp circuit to 20 amp cannot be minor works, I will look into that and find hopefully the reg number, if I am wrong, fair play, apologies, but I think not

 

[davesparks]

interesting Dave, I thought, and obviously wrongly (I will check the book) that if you change the OCPD by increasing it then the characteristics of the supply has changed an a EICR needed rather than a minor works. changing a 6 amp circuit to 20 amp cannot be minor works, I will look into that and find hopefully the reg number, if I am wrong, fair play, apologies, but I think not

An EIC would be the most appropriate of the model forms in bs7671, a lot of certification software packages now have single circuit versions of this model form which would also be suitable.

An EICR is never used to certify work carried out, an EICR is a report on the condition of an existing installation.

 

[MDJ]

An EIC would be the most appropriate of the model forms in bs7671, a lot of certification software packages now have single circuit versions of this model form which would also be suitable.

An EICR is never used to certify work carried out, an EICR is a report on the condition of an existing installation.

I meant EIC, No idea why I put EICR down, thanks for the clarification