Will the mini (or larger) RCBO fir in the this starbreaker board?

HappyHippyDad said:

1. Will the mini Starbreaker RCBO's fit in this board?

Click to expand...

99% sure yes, they are just about 2 cm shorter in height than the original ones.

HappyHippyDad said:

Would not the blinding of the Type AC RCD (due to DC earth leakage) be equally possible with or without the Type A RCBO in place?

Click to expand...

Yes. But by fitting the Type A you are adding something that will protect anything downstream of it if there is DC leakage on that circuit.
Basically that way around is ok for co-ordination. You have to go from "vague" at origin to "more specialised" as you head down the tree.
You can't do it the other way around. e.g. If you had a Type A main switch, you shouldn't use a type AC downstream.

A diagram I pinched from Napit:

timhoward said:

99% sure yes, they are just about 2 cm shorter in height than the original ones.

Yes. But by fitting the Type A you are adding something that will protect anything downstream of it if there is DC leakage on that circuit.
Basically that way around is ok for co-ordination. You have to go from "vague" at origin to "more specialised" as you head down the tree.
You can't do it the other way around. e.g. If you had a Type A main switch, you shouldn't use a type AC downstream.

A diagram I pinched from Napit:
View attachment 116141

Click to expand...

I've seen that diagram Tim and never really questioned it, as it is correct. However, after questioning it, I thought 'why'?
I like your choice of words 'vague' and 'specialised' to help explain. However, that still just sounds sensible rather than actually explaining what additional problem will occur (or danger), by fitting a type A downstream from a type AC.

Example
Case 1: You have a a type AC RCD protecting the whole consumer unit. The RCD is at risk of blinding due to DC earth leakage from potential electronics on all circuits.
Case 2: You use one of the spare MCB's in the above CU to feed an EVCP which has a type A RCD fitted in it. The type AC RCD is still at equal risk of blinding by all the original circuits, it is no worse or better.

I'm thinking that there simply isn't any greater danger by fitting a type A downstream from a type AC, it is simple a poor design. It also wouldn't meet the regulations, again this doesn't mean it's dangerous, but it does mean we are not meeting the regulations which I guess is enough of an argument to fit it as in your picture.

Of course I could just change the main switch for a 30mA type A RCD and pretend the other consumer unit is actually part of that one and it is just one big dual RCD board!

They've spent £9000 on lights but don't want to upgrade the CU's

Agreed. I wasn’t actually intending to suggest there is any issue with what you suggest, it would work and all devices would work to the best of their abilities.
I was basically trying to say that it’s only a problem if the rcds were reversed as the level of protection decreases as you head further from the origin, and it needs to increase.
I think I didn’t put it very well!