20A BS1362 Fuses!

[ericmark]

I remember having a problem in that the RCBO I had was rated at 4.7kA and the prospective was above that figure, so I started looking up let through figures and tried to work out what I needed. Anyway to start with I fitted a 100A fuse to feed the 16A type B RCBO with the idea of looking up how to calculate the let through figures. However once the 100A fuse was fitted the resistance of the fuse was enough to drop the PSSC.

The point being the fuse would never likely rupture, however it was still required, and it is really the same with a fuse in a plug, however although in theory the MCB should trip first, with a C16 feeding a welding set it was common for the 13A fuse to rupture where following the the chart that should not really happen.

 

[JohnW2]

I remember having a problem in that the RCBO I had was rated at 4.7kA and the prospective was above that figure....

As I often say, I'm amazed by some of these high PFCs I read about, at least as far as domestic installations are concerned. I would think that one could only get a PFC of 4.7kA or greater if there was a substation in one's garden! Even if the final circuit had a zero impedance, 16mm² supply cable could only be a maximum of about 18 metres long to get such a PFC.

Kind Regards, John.