Derating a BS3871 following an EICR C2

[CalHD29]

Hi, I’m interested to hear other views on BS3871 MCBs being changed following a C2 non compliance on an EICR for over rated protective device. Eg. A 2.5mm radial circuit protected by a 32A device and then swapping the BS3871 for another BS 3871 but a 20A device.

 

[westward10]

What make/type is the board?

 

[Bsharp]

Ref method A 20 amps
Ref method C 27 amps
So yes I’d agree to downgrade the 32A. What to depends on the Ref method.

 

[James]

What is the cable supplying?
It may be ok as it is.

 

[Bsharp]

What is the cable supplying?
It may be ok as it is.

I suppose if it was supplying a fixed rate piece of equipment (I.e. less than 27 amps with correct install
methods and seating factors applied) you could say it’s “ok”

 

[mainline]

I suppose if it was supplying a fixed rate piece of equipment (I.e. less than 27 amps with correct install
methods and seating factors applied) you could say it’s “ok”

More information is required really such as length, installation method and what it's supplying.

 

[pc1966]

If it is a fixed load of 20A-ish or less it might be fine, subject to end of circuit Zs being able to meed ADS time.

Otherwise (e.g. socket outlets so unknown load profile) it ought to be down rated to 20A or 25A depending on the method(s) along the length of the cable.

 

[CalHD29]

So starting from the top.
I’m looking for general thoughts rather than a particular installation. But to keep it simple I’ll use an example I’ve come across. MEM 32A Type C feeding a radial socket outlets, singles in trunking and conduit with flush floor box. Located in a public area of a shopping center for pop up traders to use. A direct and approved MCB is not available in a 60898 or RCBO to 61009. Old stock 3871 are available from national wholesaler, but would you agree that fitting this then changes the design of the circuit ? My question is if available would you or would you not fit ?

 

[davesparks]

If the problem can be solved by fitting a 20A old stock MCB then yes I would do that.

 

[davesparks]

What is the cable supplying?
It may be ok as it is.

It isn't OK as it is otherwise it wouldn't have been coded C2 on an EICR.