RCD-protected circuit that is not on a separate breaker

[RookieTony]

Hello DIYNot forum members!

I need to find a suitable and accessable place to add a switched 3A-fused spur for a boiler. I have two accessible rings to add it to:

1) Upstairs lights - not suitable, as it lives on a 6A RCD (B6)
2) A mysterious 63A RCD Protected Circuits breaker that gives power to a Vent-Axia unit in the loft (right above the boiler switch -perfect!).

The vent unit unit and the two sockets in the loft continue to function when all other RCDs are OFF and only the "RCD PROTECTED CIRCUITS" one is ON.

Question 1: Is there any professional reason for the two sockets in the loft (and cable that carries current to them) not to be protected against overloading (sitting on a 63A RCD)? Is that normal? I can see that vent unit is on a fused spur, so at least that is current-limited.

Question 2: I would like to add another fused spur to come out of the same point as the Vent-Axia one, using an approppriate cable, protected by a 3A fuse. Would it a problem? If you require more information - please do ask.

Thank you in advance!

 

[chivers67]

I'm not entirely sure what you mean in Q1. circuits 6,7,8 & 9 are FED from the RCD by the looks of it. Doesn't the MCB circuit 6 B32A power that double socket and vent-axia?

Q2 - can't see a problem could sit right next to the other one if that was moved a couple of inches to the left

 

[RookieTony]

I'm not entirely sure what you mean in Q1. circuits 6,7,8 & 9 are FED from the RCD by the looks of it. Doesn't the MCB circuit 6 B32A power that double socket and vent-axia?

That's the thing - all RCDs OFF (Apart from the large one called "RCD Protected Circuits") and the sockets upstairs are still working! What would explain it? Are they wired-in directly without a separate breaker?

Q2 - can't see a problem could sit right next to the other one if that was moved a couple of inches to the left

Excellent, thank you!

 

[chivers67]

Those are MCBs not RCDs. If all those MCBS FED from the 63A RCD are off it must be being Fed from an MCB something to the left of the RCD shown - can you try those? Can you post a photo with all the MCBS in the board as looking at the photo it looks like you have a dual RCD board?

N.B. Might need a photo with the cover off to see what exactly that RCD is feeding, I'm not asking you to do that unless you would be comfortable?

 

[RookieTony]

Those are MCBs not RCDs. If all those MCBS FED from the 63A RCD are off it must be being Fed from an MCB something to the left of the RCD shown - can you try those? Can you post a photo with all the MCBS in the board as looking at the photo it looks like you have a dual RCD board?

Will provide this tomorrow, thank you!

N.B. Might need a photo with the cover off to see what exactly that RCD is feeding, I'm not asking you to do that unless you would be comfortable?

Sadly, not comfortable, apologies!

 

[EFLImpudence]

That's the thing - all RCDs OFF (Apart from the large one called "RCD Protected Circuits")

What it means is that all the circuits with a green label - i.e. ALL of them that we can see - are protected by the RCDs (the large ones).

 

[EFLImpudence]

Sadly, not comfortable, apologies!

Very wise.

 

[ericmark]

When I moved in here I wanted to work on a socket so turned off main isolator which did nothing as there was a fuse box hidden in the ceiling.

Only way is to test.

 

[RookieTony]

What it means is that all the circuits with a green label - i.e. ALL of them that we can see - are protected by the RCDs (the large ones).

Understood! So that label is not labelling the "MK Sentry 63A RCD" right above it, but rather describes all the other circuits.

I don't suppose there is some sort of a convention for newbuilds that would explain what is the role of these 63A RCDs?

For illustration purposes, here is the full unit:

I can confirm that the sockets in the loft are working when only one (the second 63A RCD) is UP and ALL other switches (apart from the MAIN SWITCH) are down.

I just reasoned that, like @ericmark said, unless there is a hidden fuse installed prior to the sockets - the cable length is unprotected and I would call it a tad insecure (given it's not documented and we weren't told not to install computer servers or aircon units in the loft, for example)

 

[flameport]

I don't suppose there is some sort of a convention for newbuilds that would explain what is the role of these 63A RCDs?

The RCD disconnects if the current in the L&N conductors is not equal, as in current is flowing somewhere it shouldn't.
The 80A RCD covers circuits 1,2,3,4,5.
The 63A RCD covers circuits 6,7,8,9.

The individual circuit breakers marked B40, B32 and so on disconnect if too much current flows in that circuit. Every circuit must have one of these.
If anything is still working with all of the circuit breakers off, then something is seriously wrong.

 

[RookieTony]

Thank you for explaining!

If anything is still working with all of the circuit breakers off, then something is seriously wrong.

Is it worth getting an expert in then? I guess so!

 

[ericmark]

Try the simple test first

turn off isolator and all should be dead, assuming that is OK then turn on isolator and turn off the RCD's in turn, and again all should be fed through one or the other, then move to MCB's and label what they supply.

My house has 14 RCBO's and two Isolators like shown, and two MCB,s but also two independent AC isolators, and two DC isolators and even with all them off 4 sockets and a FCU are still live, I need to press a button on my battery to switch them off, and although I know what is required to switch it off, I am not happy as I feel it should be written on the inverter or battery how to switch off.

However I have a compliance certificate to say it all complies, I feel I should be able to lock it off, however the whole idea of an uninterruptible power supply (UPS) is it will stay live when we loose the grid supply. They are coming on Tuesday and I will be asking for an isolator I can lock off.

But what I am saying there is an exception to every rule, you have not said you have solar panels or batteries so I would think the one isolator will turn off all.

The UPS sockets and FCU have a label on them to say EPS, don't know why EPS rather than UPS but they are clearly marked.

In the main size of MCB gives one a good idea what it is likely to feed, so B40 likely shower, the B32's are ring finals, the B6's are marked lights, server, smoke alarm, door bell etc, so only one not marked is the B20, I would guess on an immersion heater.

 

[chivers67]

Thank you for explaining!


Is it worth getting an expert in then? I guess so!

Hi Tony,

I think so,

As per Flameport's comments - If every MCB is switched off and both RCDS off and the only way of powering down that socket and Vent-Axia Fused Spur is by the Main switch then it sounds like a secondary cable is feeding that circuit and does require investigating.

 

[RookieTony]

turn off isolator and all should be dead

All is dead.

then turn on isolator and turn off the RCD's in turn

All is dead.

Then I turn ON the second RCD and the loft sockets come up (all MCBs are still OFF). Is that normal?

 

[flameport]

Is that normal?

No.

Either one of the MCBs has failed closed internally, or someone has wired that circuit directly to the RCD.
Investigations and repairs are required.