Maximum Zs

[DanBrown]

H i Guys!
Ive already asked for a maximum zs for a bs 88 20 amp fuse!,
but any idea about a bs 88 fuse rated at 63 amps.
I can only see one table and that suggests 5 seconds disconnection.

It comes off a bussbar to a fused isolator and the to a ventilation heater. Am i right in saying 5 seconds is too high, or because it comes from the bussbar to a fused isolator it is classed as a distribution circuit.
Thanks anyway

 

[BillR3]

Dan,

If you look at BS7671-2008 you will see from regulation 411.3.2.3 that a 5 second disconnection time is allowed.

The maximum Zs for the 63 amp BS 88-2.2 is 0.82 ohms as per table 41.4

You probably worked this out already but here it is anyway.

BR3