Zs of Lighting spured from ring

[Wattsy]

Hi, i did a cu change today where the garage has been converted into a room and the lighting has been taken from the ring via FCU.

My question is, do you use the Zs upto the the FCU for the MCB for that circuit as norm, then relate the Zs past the FCU to the fuse in the FCU as thats what protecting that part of the circuit.

Hope this make sense. I know what i mean. Lol

 

[PC Electrics]

Yes

 

[green-hornet]

We have had this discussion before about the limits of testing up to and including a fused spur.

The way I see it is like this, the circuit past the FCU is protected from overcurrent by the rating of the fuse and as such should be tested separately, almost as if it was from a distribution board.

However any RCD on the parent circuit would effect the circuit past the fuse, so its always what are you going to do if kind of senario.

 

[Wattsy]

Thanks guys. How would this be recorded on the EIC as although its kind of treated as a different circuit its also the same circuit?

 

[Wattsy]

Been thinking some more about this this morning and i came to the conclusion that as long as the measured Zs past the FCU is still within the reqirements ie 1.16ohms then fault protection will still be provided by the 32A MCB and Overcurrent by the fuse in the FCU.

All seems so much clearer the next day:coffee

 

[ianmacd]

As long as the feed to the FCU is under 1.16ohm then thats ok. Past that it can be whatever is needed depending on the fuse in the FCU.

What fault protection will an MCB provide that a fuse in a FCU will not?

List it either on a seperate circuit sheet or on the same circuit sheet but with a gap to note the destinction on the EIC.