Overcurrent protection on PV

[BruceB]

The branch in the sub-main to the PV distribution board is part of the sub-main so protected by the sub-main circuit breaker. You would need to ensure the branch in the sub-main to the PV distribution board was a suitable size for the existing breaker to provide fault protection. If too small or too long then it would need its own mcb.

 

[paulsamuel1984]

BruceB,

What would you consider to be too long a length fro the branch to warrant its own breaker? The cable size agaisnt the existing breaker is acceptable.

And last one for everyone: I know you cannot piggy-back onto a final circuit breaker, but what about a sub-main breaker (i know it not good practice). Presumably the DTI guide still applies and it cannot be done.

PS

 

[BruceB]

By too long, I mean that the Zs at the far end is too high to cause the mcb to trip within the TN time or TT time for a distribution circuit. In which case you would need to add an rcd. But if you are anywhere near those limits you have probably gone way over the 1% voltage drop limit which will cause other problems.

I see no problem piggybacking onto a sub-main breaker provided:
- the sub-main breaker (and rcd if there is one) provide adequate fault protection for the piggybacked bit; and
- there is a separate breaker downstream to define/protect the pv final circuit.

It is not standard and without double checking, the DTI guide might not like it, but it would not be against 7671 in my opinion.

Regards
Bruce