RCBO for old Square D distribution board

[soms]

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.

 

[soms]

I cant see how **** arsing around putting an rcd inline below the board is gonna work out cheaper than the £65.28 that a correct new rcbo is?

That is probably true. They won't grudge spending the money, I told them something should be done before any alterations are made.

I will just buy one.

Thank you all for helping me bat some ideas around and pointing me to a suitable retrofit item.

 

[soms]

I replaced the circuit breaker with the new RCBO last night.
I tested the circuit Riso, Zs, and the RCD trip times.

Riso live conductors to earth was under 1 Mohm so needs some further investigation, but not at 8.30 in the evening.
Zs 0.77 ohms.

The RCD trip times are not meeting the requirements for additional protection.

I repeated the test three times using a Fluke MFT, the meter was set for the correct characteristics - type AC, 30 mA.

x1 - 49.4 ms and 76.5 ms - less than 300 ms so acceptable.
x5 - 41.6 ms (180 deg.) and greater than 50 ms (0 deg.) - neither are acceptable readings for providing additional protection as over 40 ms.

A quick Internet search did not reveal what the operating times should be for the BS EN 61009-1 product standard (if any different to those quoted to meet the requirements in BS 7671).

I am considering contacting the supplier to ask about a replacement RCBO as I am not entirely happy with it, but I first I wanted to try and find out whether the product is working as it should or not, hence the question about the product standard requirements versus BS 7671.

 

[westward10]

Did you test it with the outgoing circuit disconnected.

 

[soms]

Did you test it with the outgoing circuit disconnected.

No, I didn't, I tested it at a socket outlet with the circuit connected.

I can see where you are going with this, would you repeat the tests at the RCBO terminals without the circuit connected?

 

[westward10]

Yes, it should trip within the prescribed times for an EN61009 device.

 

[soms]

Yes, it should trip within the prescribed times for an EN61009 device.

@westward10 thank you for the advice. I will give that a try.

 

[soms]

Just to let you know I have performed the tests again with the circuit disconnected and achieved considerably better disconnection times.
I was surprised what a difference it makes.

Having checked my own notes I appreciate that it was my error in forgetting to disconnect all loads the first time, which they always should be.
I see GN3 advises it can be dangerous to perform RCD tests with load connected as potentially dangerous voltages could appear on exposed conductive parts as well as extraneous conductive parts.
Perhaps this is why I have heard the argument between people about testing being carried out at the RCD or anywhere in the installation.
If testing an RCCB in a consumer unit for example, this could be done at the board with all outgoing circuit breakers open and thus all load disconnected, which cannot be so easily ensured if testing at a point on a live final circuit.

Thanks for the advice, this was a useful experience for me which I can bear in mind for carrying out testing in similar circumstances at work in the future.