Is this RCD/MCB consumer unit suitable? And wiring Help please.

[Grim Reaper]

There is a requirement in the 18th edition electrical regs where each incoming supply shall be directly connected to its associated RCD. Having a double pole MCB before the RCD functionality of the RCBOs doesn’t comply.

My consumer unit has a double pole switch before all the RCBO's? Its a 100A red switch one like most consumer units have?

 

[t0mb0]

There is a requirement in the 18th edition electrical regs where each incoming supply shall be directly connected to its associated RCD. Having a double pole MCB before the RCD functionality of the RCBOs doesn’t comply.

The 18th edition (BS 7671:2018) launch - revisited

Geoff Cronshaw takes another close look at the launch of this years 18th Edition of the IET Wiring Regulations.

electrical.theiet.org

That seems pretty clear then, to comply with those regs an RCD followed by MCB(s) is sufficient. If you want to comply with the regs and reduce your reliance on the campsite protection then you can swap out the RCD for an RCBO which gives you additional protection against failure mode (1) in my post above at 11:01, but obviously doesn't mitigate against failure mode (2) for which you are always going to be reliant on the campsite/provider for.

 

[MarkW-T6]

My consumer unit has a double pole switch before all the RCBO's? Its a 100A red switch one like most consumer units have?

Yes, it will have. As you say, it’s a “switch”. It’s not an mcb. The switch which has been shown in the post with the RCD is also DP.

 

[Stay Frosty]

So is my suggestion of a double pole MCB rated at say 20A for the main incoming switch (don't need an RCD because that will be covered by the RCBO's alongside it, 20A to avoid nuisance tripping over campsite breaker) and a few RCBO's with switched neutrals for each output to sockets a good option? Single busbar along the bottom, earth from campsite connection socket to van chassis and common earth rail in the consumer unit, earths to sockets connect here too, neutrals from DP 20A MCB and RCBO's to common neutral rail in consumer unit, Live to top of DP 20A MCB and busbar from bottom to RCBO live inputs at bottom. Then live and neutrals to sockets to tops of RCBO's.

In at @HubertK consumer unit the mcbs are just that, double pole overcurrent devices so no earth leakage detection so the layout in his photo is correct.
Again if the 25A RCD shown was rated at 16A and an RCBO instead then overcurrent protection would protect the cable supplying the van from the EHU as long as that cable was of a modest length eg 15M and that the phase conductors we're flexible copper of 2.5mm2.
Realistically if we're going to start quoting the 18th edition, latest revision, we should be in the campervan mobile home section and probably treating the van as a TT installation and taking our loop tester and stakes with us.
I should hasten to add I'm a retired electrician these days and thankfully so, I got out in 2020 just after getting the first 18th amendment test out of the way and don't miss having to have a C&G in Regs, one in 415V testing, Pasma, IPAF and ECS cards just to earn less than £30k a year at the time... easiest decision ever... this thread does show the brain teasing aspect of the job though which was actually quite fun in a perverse way.

 

[EAN]

That seems pretty clear then, to comply with those regs an RCD followed by MCB(s) is sufficient. If you want to comply with the regs and reduce your reliance on the campsite protection then you can swap out the RCD for an RCBO which gives you additional protection against failure mode (1) in my post above at 11:01, but obviously doesn't mitigate against failure mode (2) for which you are always going to be reliant on the campsite/provider for.

Using an RCBO instead of an RCD as the first device can be used to limit the total current you can draw from your consumer unit across your MCBs if you want but it doesn’t give you any more protection above and beyond that given from the campsite feed with regard to protecting the incoming cable from overcurrent as that is the job of the upstream protection device to do that. It can stop nuisance tripping of the campsite feed if you size things accordingly and have a habit of plugging in too much at the same time.
But to theoretically generate the fault condition for your failure mode (1) you’d need to have MCB’s that total in excess of about 25A (current carrying capacity of 2.5mm2 cable) (quite possible), load them up accordingly to draw more than the cable rating and the campsite would have to install something like a non compliant and overrated 32A breaker and over sized cabling to allow that current to be drawn, without you noticing the breaker rating being above 16A when you go to connect up. Is that realistic?

 

[t0mb0]

Using an RCBO instead of an RCD as the first device can be used to limit the total current you can draw from your consumer unit across your MCBs if you want but it doesn’t give you any more protection above and beyond that given from the campsite feed with regard to protecting the incoming cable from overcurrent as that is the job of the upstream protection device to do that. It can stop nuisance tripping of the campsite feed if you size things accordingly and have a habit of plugging in too much at the same time.
But to theoretically generate the fault condition for your failure mode (1) you’d need to have MCB’s that total in excess of about 25A (current carrying capacity of 2.5mm2 cable) (quite possible), load them up accordingly to draw more than the cable rating and the campsite would have to install something like a non compliant and overrated 32A breaker and over sized cabling to allow that current to be drawn, without you noticing the breaker rating being above 16A when you go to connect up. Is that realistic?

I agree, it's not likely. But if you want the additional reassurance when you're hooking up in some campsite where you don't entirely trust the supply side to do things properly, maybe in a country where the regulations and standard of electrics are very different, then it might be worthwhile to consider as an option.

Obviously it becomes more relevant the higher the sum of the individual circuits MCBs is and what kind of loads you're expecting to use.

The other thing to note is that the ¬25A maximum current rating of that 2.5mm cable is only where the cable is essentially clipped direct in free air. Once you've put it in conduit and especially if there's any amount of insulation around it then you can end up de-rated down to 20A or so and your margin for error has decreased somewhat.

So no, I wouldn't consider it always necessary but you might consider it worthwhile risk mitigation if your anticipated usage involves potentially high load and you don't always have a high level of trust in the standards of the supply.