Are MCBs and RCDOs interchangeable?

[Adam_151]

RCBOs without a "functional earth" would have to be non electronic (*) as they could not trip if the Neutral supply was disconnected.

The Memshield 3 / eaton compact rcbos (as pictured) do not trip with the neutral disconnected.

 

[JohnW2]

RCBOs without a "functional earth" would have to be non electronic (*) as they could not trip if the Neutral supply was disconnected.

The Memshield 3 / eaton compact rcbos (as pictured) do not trip with the neutral disconnected.

Do you know whether they are 'electronic'? They do not appear to have 'functional earths'.

However, how are you testing them? If with the test button, I imagine that, depending on how it is wired, that might not 'work' in the absence of a neutral.

Kind Regards, John

 

[Adam_151]

There are no functional earths. I do not know whether they are electronic inside as I have not opened one

With the neutral disconnected they will not trip with test button, high current loop test, n-e insulation fault present, borrowed neutral to another circuit present, or even back feed from another circuit present on the output!

 

[JohnW2]

There are no functional earths. I do not know whether they are electronic inside as I have not opened one

Fair enough. From what you go on to say, it sounds as if they may well be 'electronic', but with no functional earth connection.

With the neutral disconnected they will not trip with test button, high current loop test, n-e insulation fault present, borrowed neutral to another circuit present, or even back feed from another circuit present on the output!

That sounds fairly comprehensive! With no neutral, there will obviously be no current through the N side of the RCBO, so that any current (>IΔn) through the L side ought to result in a trip - and at least some of scenarios you mention would achieve that.

Kind Regards, John

 

[kai]

The mechanical RCD's i.e. Wylex ones, have an advantage of not having to be removed before a megger test takes place, unlike the delicate electronic ones.

 

[JohnW2]

The mechanical RCD's i.e. Wylex ones, have an advantage of not having to be removed before a megger test takes place, unlike the delicate electronic ones.

Are you sure about that? I'm all but certain that Wylex ones I've dissected in recent times have (just like other makes) been 'electronic'.

Kind Regards, John

 

[Adam_151]

And if you take care how you apply the test, electronic ones can be left in place for IR with only a small amount of disconnecting of conductors necessary

 

[JohnW2]

And if you take care how you apply the test, electronic ones can be left in place for IR with only a small amount of disconnecting of conductors necessary

Indeed so. In fact, given the uncertainties about which (whether all or otherwise) are 'electronic', it would seem sensible to treat them all as if they were.

Kind Regards, John