Forced RCD Upgrade in CU

[musashi79uk]

I've had a quote from an electrician to install an electricity supply to a garden room. The current CU was installed in 2020 when another electrician did a full rewire.
The first thing this electrician said when he saw the CU was, "Installed in 2020 and already outdated," and then proceeded to tell me how he will need to change the RCDs at a cost of £50 each to run the new supply to the garden room. I've attached a copy of one of the RCDs (they're both the same). Would the RCDs need changing to run 6mm armoured cable to the new garden room RCD protected CU?

 

[EFLImpudence]

You don't want or need an RCD 'protecting' the armoured cable to the garden room.

Armoured cable is used so you don't have to have an RCD at the house end so find an electrician who knows what he is doing.

 

[musashi79uk]

So I don't need to have the RCDs changed in the house CU?

 

[EFLImpudence]

So I don't need to have the RCDs changed in the house CU?

Not for running a supply to the garden room.

That supply should not be run from the house RCDs.

 

[musashi79uk]

Not for running a supply to the garden room.

That supply should not be run from the house RCDs.

He said he was going to connect the armoured cable to the spare B40 MCB but would need to change the BG RCD in the photo from a type AC to a type A one to bring it up to the current regs due to it being non-compliant.

 

[flameport]

If they are connecting to that consumer unit, then the RCD will need to be changed - but then you would not have any RCD in the garden room.
That also means any fault in the garden room disconnects half of your house. A poor design.

If you are having an RCD in the garden room, the supply to it should NOT have any RCD.
However that may not be possible with the consumer unit you have got.

The fact that is has a 'spare' 40A MCB is unrelated, the protective device(s) should be selected according to the new circuit that's being installed, not just because it happened to be there already.

 

[SUNRAY]

He said he was going to connect the armoured cable to the spare B40 MCB but would need to change the BG RCD in the photo from a type AC to a type A one to bring it up to the current regs due to it being non-compliant.

The thing that strikes me is seeing a time delayed RCD.
Ideally the SWA cable has a non RCD feed and a CU in the outbuilding containing its own local RCD

 

[AndyPRK]

Yeah, looking at the RCD itself, I’m not sure if it really is timedelayed?

Yeah the first electrician used the cheapest materials available.
If you want to keep costs down, try getting him back

 

[SUNRAY]

If they are connecting to that consumer unit, then the RCD will need to be changed - but then you would not have any RCD in the garden room.
That also means any fault in the garden room disconnects half of your house. A poor design.

If you are having an RCD in the garden room, the supply to it should NOT have any RCD.
However that may not be possible with the consumer unit you have got.

Anything is possible, BG boards are supplied in a whole variety of combinations, converting between those variations does not invalidate thier compliancy.

The fact that is has a 'spare' 40A MCB is unrelated, the protective device(s) should be selected according to the new circuit that's being installed, not just because it happened to be there already.

That's not strictly true.
A circuit is a circuit as long as it's designed correctly. It may very well have been a 32A MCB if designed from scratch but providing the whole circuit is safe and sound as far as the new CU for 40A, even if it only contains a 6A MCB for lights, then no harm in using an existing spare 40A OCPD

 

[flameport]

a time delayed RCD.

It's the Intertek logo, previously SEMKO

The S Mark

www.intertek.se

Time delayed is S inside a square.

 

[SUNRAY]

Yeah, looking at the RCD itself, I’m not sure if it really is timedelayed?

I beg my pardon with the switch up I hadn't noticed the short code number and didn't look close enough at the symbols

Yeah the first electrician used the cheapest materials available.
If you want to keep costs down, try getting him back

There is nothing wrong with the BG range per se, admittedly not the nicest products but there are loads in service and all seem to pass any required electrical tests.

 

[musashi79uk]

The plan for the circuit was as follows:
In the garden room there will be a three-way garage CU with 32A, 16A and 6A MCBs.
A PC, monitor, TV, printer and a kettle will use the 32A MCB.
A 2kW panel heater will use the 16A MCB.
Lighting circuit with 7 internal and 3 external downlights on the 6A MCB.

If the house CU has a 63A RCD (as it does) and the garden room non-RCD CU electrics tripped it, half of the house electrics if connected to the 63A RCD circuit would trip. If that happened, wouldn't I just turn off the MCB supplying the garden room in the house CU and be OK (without the garden electrics being live of course)?

 

[SUNRAY]

The plan for the circuit was as follows:
In the garden room there will be a three-way garage CU with 32A, 16A and 6A MCBs.
A PC, monitor, TV, printer and a kettle will use the 32A MCB.
A 2kW panel heater will use the 16A MCB.
Lighting circuit with 7 internal and 3 external downlights on the 6A MCB.

The circuit design looks ok in principle.

Although:

If the house CU has a 63A RCD (as it does) and the garden room non-RCD CU electrics tripped it, half of the house electrics if connected to the 63A RCD circuit would trip.

Is not an ideal situation.

If that happened, wouldn't I just turn off the MCB supplying the garden room in the house CU and be OK (without the garden electrics being live of course)?

The basic answer is maybe.

The longer answer is it depends what the fault is.

 

[flameport]

The plan for the circuit was as follows:

All of that stuff could be installed, but it's massive overkill what is effectively a few socket outlets and a light.

dwouldn't I just turn off the MCB supplying the garden room in the house CU and be OK

Only if the problem was between L&E.
Anything between N&E will still be there and tripping is likely to still occur.
The same applies to any other circuit in your house.

 

[musashi79uk]

As for the previous electrician using the cheapest materials; yeah, he was an absolute clown. Mentioned the excessive damage he caused during the work and he said he'd claim on his insurance once we were paid. Paid him for the work and then asked him to make the insurance claim, to which he said the excess would be more than we'd get so wouldn't claim. Then because we complained, he refused to supply the certificate for the installation unless we paid him an additional £720 (which included a discount of £500 we got that he could revoke at any time). All T&Cs were on a website that was not on any paperwork he supplied. The website on his paperwork threw an error up but I thought it was just down at the time I looked.