Is all RCBOs a good idea?

[Dippy]

I've read a few posts on the possible changes in BS7671:2008 and people's reactions to it. If I understand it correctly, the new standard recommends increased use of RCD protection?

In my case the house I bought last year has no RCD protection, so I had planned to change the CU to a split load type and put all the final rings on the RCD side. However it seems that for the new standard, with the way my house is wired*, it would be best if all my circuits had RCD protection.

Clearly having an RCD trip take out all circuits is not a good idea, and simply using RCDs on both side of the split CU just changes that to half the circuits. So it seems to me that the ideal solution is to not use a split CU after all, but to use a large one and fill it with MCBOs.

So, apart from the extra cost, is this a good idea?


*Although the concealed cables all run vertically or horizontally from points, they are only protected by plastic conduit and relatively near the surface of the wall. Irrespective of the "rules", to me this seems a good reason to have RCD protection.

 

[kai]

If you can afford the cost of the RCBO's, then go ahead...

 

[Dippy]

Thanks.

I noticed that commonly available MCBOs are designed to fit standard CUs so they have 'trailing' neutal and earth wires. Does anyone know of a manufacturer who makes CUs which are specifically designed for MCBOs so that these 'trailing' wires are not needed?

 

[GaryMo]

If you can afford the cost of the RCBO's, then go ahead...

Totally agree. Not cheap at £25-£30 each though

 

[GaryMo]

Thanks.

I noticed that commonly available MCBOs are designed to fit standard CUs so they have 'trailing' neutal and earth wires. Does anyone know of a manufacturer who makes CUs which are specifically designed for MCBOs so that these 'trailing' wires are not needed?

Those are still RCBO's.
Some have trailing neutral wires, some don't. The only difference is whether you terminate the circuit neutral into the RCBO or the neutral bar within the consumer unit.

 

[Dippy]

Sorry, what I meant was is there a type of RCBO which does not have the trailing wires because it will fit a specially-designed CU which has three bus-bars instead of just one?

 

[GaryMo]

Sorry, what I meant was is there a type of RCBO which does not have the trailing wires because it will fit a specially-designed CU which has three bus-bars instead of just one?

I don't think so. RCBO's without the trailing neutral wire have termination points for both phase and neutral whereas the type with the trailing neutral only has a termination for the phase conductor.
All RCBO's I've come across have the trailing white functional earth lead which needs to be terminated to the earth bar within the consumer unit.

 

[Lectrician]

RCBO's will come down in price smartish.

The only niggle I have with RCBO's is that you do not know if they have tripped due to overcurrent or an earth fault. Some do indicate this, but the majority do not.

I would also like to see switched neutral versions, although this is not to much of an issue.

Testing will be a little harder - you will have to disconnect all cables from the RCBO to meggar them, and of course more RCD tests to do.

 

[GaryMo]

The only niggle I have with RCBO's is that you do not know if they have tripped due to overcurrent or an earth fault. Some do indicate this, but the majority do not.

Which manufacturer(s)? I'm curious as this sounds like a great idea.

 

[kai]

That is one downside of using RCBO's - they are not yet megger-resistant, so the hassle of remembering to disconnect to RCBO's before meggering, to avoid an expensive damage bill, unlike a normal RCD, which is normally megger-resistant.