Breaking capacity of 3871 fuse lower than pfc?

Gerry Savage · Oct 26, 2016

i have just done a test on a property and the pfc at origin of installation was 0.712ka. The 3871 mobs have a 6000a breaking capacity. I am a bit confused as I have read something about it always being higher anyway (16ka) for a fuse or main switch 100a or less. Any info here would be much appreciated as I don't want to say this needs to be changed if it doesn't as customer will unlikely get it done anyway and what code would it be if it is a fault. Cheers

hightower · Oct 26, 2016

Wouldn't a fully qualified spark know a 0.7kA reading is less than the 6kA maximum and that is all tickety boo?

Silly Sausage · Oct 26, 2016

@hightower You need to get 'Trainee' removed from your forum picture

Richard Burns · Oct 26, 2016

You have maximum potential current (PFC) of 712A, the circuit breaker can handle a maximum current of 6000A, therefore the circuit breaker will never have to handle a current above its maximum rating and is therefore safe.
Even if the fault current were above 6000A then annex Zb of BS EN 61439 states for the UK that domestic consumer units must be type tested to withstand, as an assembly, a fault current up to 16,000A if the consumer unit is protected at origin by a 100A or less service fuse.

hightower · Oct 26, 2016

Archy Styrigg said:
@hightower You need to get 'Trainee' removed from your forum picture

Once I'm fully qualified mate. Got years to go yet

westward10 · Oct 26, 2016

hightower said:
Once I'm fully qualified mate. Got years to go yet

Your on the wrong course many complete in five weeks now.

hightower · Oct 26, 2016

westward10 said:
Your on the wrong course many complete in five weeks now.

Ah, in that case I'm 8x qualified. Where do I get my JIB card?!

Midwest · Oct 27, 2016

Don't be too embarrassed OP, even if your maths is flawed, you quest for knowledge is not. Hope you haven't been put off.

I usually get my noughts in a tiswas with Ω, kΩ & mΩ. Mind I also get confused when I get 4 numbers on euromillions, and somehow only get £29