Suitability of circuit accessories.

David Prosser · Mar 20, 2020

IEC standard 60947-3 (same BSEN number) which covers switch disconnectors or isolators will tell you that they must be designed to withstand fault currents flowing through them until the protective device operates.

From what you have discribed there is no problem with the way the circuit has been installed.

Leezo · Mar 20, 2020

Julie. said:
Your thought, that the isolator is undersized @ 20A, is based on the fact that the protection is 32A

This is EXACTLY the same as saying the protection @32A is oversized as the isolator is only 20A

The regs only need to cover one point of view as the other is automatically covered!

Not really, the circuit supplies 2 split units each drawing around 12A so it has been designed as a 32A cct for that reason. I see what you're getting at but this has been designed as a 32A cct & is wired in 4mm singles. The isolators that have been fitted are there because of the availability of the correct parts in the location I'm in.

Julie. · Mar 20, 2020

Leezo said:
Not really, the circuit supplies 2 split units each drawing around 12A so it has been designed as a 32A cct for that reason. I see what you're getting at but this has been designed as a 32A cct & is wired in 4mm singles. The isolators that have been fitted are there because of the availability of the correct parts in the location I'm in.

OK, but your view is that the isolators are undersized @20A, based on the protection device of 32A. This is exactly the same as the protection device is oversized @ 32A compared to the 20A isolators as far as the regs are concerned; 432.3 details why this situation is permissible.

As long as it's a fixed load and it has fault protection, it is compliant

If these same isolators supplied multiple outlets, then it's not a fixed load and your point would be valid as someone could just plug in more loads resulting in overloaded isolators.

Strima · Mar 20, 2020

The what about 20AX switches on a ring final circuit with a 32 amp protective device? Millions of homes in the UK have this set up with no adverse effects.