RCBO for old Square D distribution board

soms · Nov 17, 2018

Hi,
A relative has moved into a flat with a mid-80's Square D QO1 12F distribution board, which has MCBs on all outgoing ways.

There are proposals to update the kitchen with a desire for some additional socket outlets. To meet the requirements of Part P and by extension, BS 7671, RCD protection will be required and the simplest way to implement this would be to find a way of providing it for the entire ring final circuit supplying the socket outlets.

My thinking is to install a 32 A RCBO in place of the original MCB, if I can get something electrically compatible with the DB.
I removed an existing MCB (though a later addition itself) to see what fits in this board, and it is the 'clip' type bus bar connection.

I have seen some 'clip' type Square D and Schneider Electric RCBOs for sale on eBay, but just wanted an opinion as to whether there is anything else I should be aware of in terms of product compability before committing to buy something?

The installation has a TN earthing system (the supply to the DB coming from a separate meter room), I haven't measured the Zs on the circuit but of course should bear this in mind as in some cases B type breakers are not easy to get whereas C types are.

Pics attached.
Thanks.

[ElectriciansForums.net] RCBO for old Square D distribution board

Toneyz · Nov 17, 2018

Schneider do protective devices that fit in old boards we had a 3 phase old D.B. with MCB's same as those that had to be de-rated to 20A. On Monday give their technical department a call give them all the info of existing inc protective devices. Not sure of the cost as non-stocked items at wholesalers like this usually aren't heavily discounted.

Judd · Nov 17, 2018

I think i have one of these in my garage if your interested, are they KQ?

westward10 · Nov 17, 2018

The protective devices at that board are BS3871 type 4 code No. QOH-X. These have never been recognised by any version of the wiring regulations but this does not mean they are not suitable to provide suitable circuit protection however, type 4 devices are not considered suitable for the protection of general socket outlets and in modern terms for any circuit in a domestic premises. Schneider who took over Square D have to their credit produced compatible devices and for a type B 32A rcbo you require part no. QO132B1ORCBO30F.

Gavin John Hyde · Nov 17, 2018

westward10 said:
The protective devices at that board are BS3871 type 4 code No. QOH-X. These have never been recognised by any version of the wiring regulations but this does not mean they are not suitable to provide suitable circuit protection however, type 4 devices are not considered suitable for the protection of general socket outlets and in modern terms for any circuit in a domestic premises. Schneider who took over Square D have to their credit produced compatible devices and for a type B 32A rcbo you require part no. QO132B1ORCBO30F.

I am liking schneider more and more of late, the stuff they make via the many brands in the stable are pretty well made, not too pricey and the tech team are on the ball. Schneider are now my go to instead of Hager.

Rpa07 · Nov 17, 2018

That’s a proper main switch on that board mind, kerlunk - power on!

suffolkspark · Nov 17, 2018

Always find this site below usefull for random and obscure rcbos

QOvs (formerly QOE) RCBO's > RCBOs > Square D > Electrical Supplies > Zetmet Ltd - https://www.electricaldiscountedsupplies.com/section.php/210/2/qovs__formerly_qoe__rcbos

ChrisElectrical88 · Nov 18, 2018

suffolkspark said:
Always find this site below usefull for random and obscure rcbos

QOvs (formerly QOE) RCBO's > RCBOs > Square D > Electrical Supplies > Zetmet Ltd - https://www.electricaldiscountedsupplies.com/section.php/210/2/qovs__formerly_qoe__rcbos

They are fantastic prices for them, there was a point we were paying up to £100 plus VAT for them from Edmunsons. Alot of schools have these boards in and we used to always find a few they didnt meet disconnection times. Schneider still make the RCBOs to fit.

telectrix · Nov 18, 2018

fit a stand alone RCD alongside the DB. feed from existing MCB and N, with 6.0mm, then on to RFC. ( divert the RFC legs from MCB to RCD.).

soms · Nov 18, 2018

anthonybragg said:
Schneider do protective devices that fit in old boards we had a 3 phase old D.B. with MCB's same as those that had to be de-rated to 20A. On Monday give their technical department a call give them all the info of existing inc protective devices. Not sure of the cost as non-stocked items at wholesalers like this usually aren't heavily discounted.

Thanks for the advice, it is nice to know you can actually make contact with a manufacturer and get sense from them if required.

westward10 said:
The protective devices at that board are BS3871 type 4 code No. QOH-X. These have never been recognised by any version of the wiring regulations but this does not mean they are not suitable to provide suitable circuit protection however, type 4 devices are not considered suitable for the protection of general socket outlets and in modern terms for any circuit in a domestic premises. Schneider who took over Square D have to their credit produced compatible devices and for a type B 32A rcbo you require part no. QO132B1ORCBO30F.

@westward10 thank you for this information, that is very useful to know.
Thanks for quoting the correct part number, I have had a quick look online and they seem expensive to purchase, which is understandable.

telectrix said:
fit a stand alone RCD alongside the DB. feed from existing MCB and N, with 6.0mm, then on to RFC. ( divert the RFC legs from MCB to RCD.).

@telectrix that is a good idea which had not occurred to me, it would be a cheaper way to get around it and there is plenty of room below the board to do it.

Given what @westward10 said, do you think I should be concerned about the existing MCB with respect to meeting the disconnection times, which is for fault protection (using ADS) if I recall? I am away from home so do not have my books to hand to check on what can be considered to be provided by the RCD, which otherwise is offering additional protection. I am now a third year apprentice so the details of BS 7671 are not fully committed to memory yet. To be made a little more complicated to commit with the upcoming switch to the 18th Edition.

Thank you for all the useful input

westward10 · Nov 18, 2018

Maximum Zs values for Type 4 devices have never been quoted in the Regulations so you have to refer to manufacturers figures. Type 4 devices unlike other circuit breakers used 0.4 and 5 sec disconnection times, so 0.4 for socket outlets and 5 sec for fixed equipment.

Toneyz · Nov 18, 2018

It may get to a point that if any further additions/work is carried out and requires RCD/RCBO protection a new consumer unit would be cheaper in the long run if the prices are too high eg a BG 5 +5 split £73 inc VAT.