Down rating an MCB on a socket circuit

[Flanders]

When carrying out an EICR in a commercial office I have found 2.5mm radial socket circuits on 32 amp MCB with NO RCD protection
Now one way to rectify this deviation is to fit a 20amp RCBO.

My question is

Is it permissible just to fit a 20 amp MCB so omitting the RCD protection ?
I have always gone down the line of fitting RCBOs because I feel I am altering the circuit ,but wondering if I am going over the Top and an MCB would be suitable.

 

[Deleted member 72666]

Re: Down ratting an MCB on a socket circuit

A good question, I personally would be happy just swapping out the mcb for a 20 amp one.

 

[Octopus]

Re: Down ratting an MCB on a socket circuit

So how does down reading the mcb make omitting the RCD ok?

 

[Pete999]

Re: Down ratting an MCB on a socket circuit

How many sockets, and what are they being used for?

 

[Flanders]

Re: Down ratting an MCB on a socket circuit

How many sockets, and what are they being used for?

I think I see were your coming from Pete and this as one of the reasons for the post
I find this on various sites but there could be a lot of computers on the circuit so pushing the earth leakage close to the 30ma and so I change the 32 amp mcb 20 amp 30 mA RCBO and now I have course the customer a problem with nuisance tripping !!

 

[Deleted member 72666]

Re: Down ratting an MCB on a socket circuit

I would class this job as a repair as the wrong size ocpd was fitted previously and I'm also assuming rcd protection wasn't a requirement originally. As I said it was a good question and after deliberation I would be happy to swap out the mcb.

 

[Deleted member 72666]

Re: Down ratting an MCB on a socket circuit

Flanders: I've just thought you may require rcd protection anyway......because of all the rats!

 

[Pete999]

Re: Down ratting an MCB on a socket circuit

I think I see were your coming from Pete and this as one of the reasons for the post
I find this on various sites but there could be a lot of computers on the circuit so pushing the earth leakage close to the 30ma and so I change the 32 amp mcb 20 amp 30 mA RCBO and now I have course the customer a problem with nuisance tripping !!

If you envisage a large Earth Leakage then ideally you should be changing the circuit configuration for the ones described in BS 7671, sorry not sure which reg that is, maybe doing away with the RCD and get the responsible person to issue a suitable risk assessment for those sockets.

 

[Flanders]

Re: Down ratting an MCB on a socket circuit

If you envisage a large Earth Leakage then ideally you should be changing the circuit configuration for the ones described in BS 7671, sorry not sure which reg that is, maybe doing away with the RCD and get the responsible person to issue a suitable risk assessment for those sockets.

Yes this is the trouble you can open a whole can of worms just because someone fitted the wrong size MCB in the first place and what starts as an over ratted MCB turn into a rewire. I don't think I could get away with a risk assessment in these types of environments

 

[Pete999]

Re: Down ratting an MCB on a socket circuit

Yes this is the trouble you can open a whole can of worms just because someone fitted the wrong size MCB in the first place and what starts as an over ratted MCB turn into a rewire. I don't think I could get away with a risk assessment in these types of environments

What does the customer say? show him the regulation regarding this type of installation, if he is unreceptive, walk on by, after all it's your neck on the line, my experience of no electrical managers is one of dismay, as lng as it works they don't care, not what you want to hear I know, sadly I feel it's your only option, but I'm remote so don't know the full SP.

 

[Flanders]

Re: Down ratting an MCB on a socket circuit

I would class this job as a repair as the wrong size ocpd was fitted previously and I'm also assuming rcd protection wasn't a requirement originally. As I said it was a good question and after deliberation I would be happy to swap out the mcb.

Thanks for you input Stan and in the passed I would of agreed but its that question that, is it a repair or am I altering the circuit , if there was no RCD protection on the sockets this would have to be mentioned on the minor works , So I would be saying I have altered the circuit but failed to fit RCD protection for sockets outlets , and then god forbid some one gets killed from directly using that circuit and I was the last person working on it I think it would be me in the court room ( may be going over the top a bit but always thinking worst case)

 

[Flanders]

Re: Down ratting an MCB on a socket circuit

What does the customer say? show him the regulation regarding this type of installation, if he is unreceptive, walk on by, after all it's your neck on the line, my experience of no electrical managers is one of dismay, as lng as it works they don't care, not what you want to hear I know, sadly I feel it's your only option, but I'm remote so don't know the full SP.

Yes I agree Customers always want the cheapest option It just trying to explain it to them that they require an RCD/RCBO
The cost of a RCBO pushes the quote up , Yes I stand by my guns and say that what Is required, I was just confirming that I am not pricing myself out of Jobs by fitting an RCBOs rather than an MCBs in these cases.

 

[Baker1988]

Re: Down ratting an MCB on a socket circuit

I know this is going a different way but have you checked that both the radials are not actually one ring circuit and someone who hasn't known what they are doing has put them on separate mcbs. i have had this before, Maby check if there is a end to end on the conductors.

------------------------------EDIT-----------------------------------

Never mind just read it again and you didnt say 2 radials haha ignore my comment.