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Discuss RCD Protection for submains in the Electrical Forum area at ElectriciansForums.net

TJC1

Regular EF Member
Evening all

We have been asked to do some redial work picked up by a testing company i a hostel. It has been picked up that is no RCD protection in the rooms

There are 5 submain circuits that feed the 20 consumer units, 4 consumers units per submain (B32) Each room have a consumer unit which has two double sockets off a 16a radial and a lighting.

They asked my advice on whether to change the submain MCB to RCBOs or whether to change the consumer units for main switch and RCBOs

They supply cables to each consumer unit are above a plasterboard ceiling but cant be sure of the installation method, does the submain need to be RCD protected? As i dont want to put RCBOs on each circuit and also on the submain also

Thanks
 

essex

Forum Mentor
If the installation method of the sub-main requires RCD protection then how will fitting RCBOs on the final circuits protect the sub-mains?
 
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TJC1

Regular EF Member
If the installation method of the sub-main requires RCD protection then how will fitting RCBOs on the final circuits protect the sub-mains?
That's my question, do the submains need to be RCD protected? Seems ridiculous that i need to install an RCD on the submain when it protects 4 consumer unit. It would be much better to be able to install separate RCBOs on the consumer unit and leave the submain.

Does above plasterboard ceiling count as buried? Or require an RCD
 

spinlondon

Forum Mentor
Whilst cables above ceilings and below floors require additional protection where they pass through joists or battens. RCD protection is not an acceptable method.
 

FLICK

Electrician's Arms
What type of cable are the subs and what edition of the regs was the original work done to?
 

spinlondon

Forum Mentor
Seems to me, that you have been asked to supply RCD protection for the rooms.
I’m assuming that’s for socket-outlets and circuits of locations containing baths or showers?
You can either install an up front RCD for each room, or swap MCBs for RCBOs.
How you do that is up to you.
 

essex

Forum Mentor
I have just re-read the op.

The EICR that was done has highlighted a lack of RCD protection on final circuits on all CUs.

The client is trying to cut costs by asking if fitting ‘up front’ RCDs on the sub-mains instead of the CUs therfore installing five RCBOs rather than 40.

This is not an option due to selectivity so I would say no to that.
 

spinlondon

Forum Mentor
Im not sure on the depth and the cable is T&E
If the cables are just laid on plasterboard, there’s no requirement for a minimum depth.
The drill through the plasterboard, the drill will push the cable away.
Where cables run through joists or battens, the drill can’t push the cable away, so additional protection is required.
1.Depth between cable and the surface of the floor or ceiling has to be greater than 50mm.
2.Earthed sheath, conduit or trunking.
3.Steel plate between the ceiling/floor and the joist/batten.
Unlike for cables concealed in walls, RCD protection is not an option.
 

FLICK

Electrician's Arms
My take on this is that if it was installed to the 16th edition or before then the sockets don’t require the additional protection unless they could be reasonably expected to be used for outdoor equipment.
 

spinlondon

Forum Mentor
My take on this is that if it was installed to the 16th edition or before then the sockets don’t require the additional protection unless they could be reasonably expected to be used for outdoor equipment.
Yes, that’s correct.
Only started needing RCD protection when the 17th came in, as they would be used by unsupervised ordinary persons.
 

FLICK

Electrician's Arms
The thing is we don’t know when it was installed. We also don’t know if the guy who issued the report is aware of the changes between the 16th and 17th. My point is that I’d like to know these facts before banging in RCD’s.
 

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