Any arguments against RCBOs?

[aesmith]

Hi,

Just a hypothetical question, more of a homeowner than DIY subject. I'm kind of sorry that when our house was rewired in 2011 we didn't go for RCBOs instead of a dual RCD board, not only is the split of which circuits are on which side not ideal, but it would have saved the width of two RCDs. However at the time the estimator really didn't seem to recommend them and really only stressed the extra cost.

By contrast the electrician who put the supply to our outbuildings was very much in favour.

So that got me wondering, are there any down sides other than cost? For example any disadvantage to the fact that RCBOs only disconnect the Live, and still leave the Neutral in circuit? I suppose the natural evolution would be RCBO switching both L and N, but I'm pretty sure the ones in the outbuilding (Hager) are single pole.

I'm interested in understanding, although realistically the choice isn't likely to come up again for a while.

Tony S

 

[Marvo]

Electrically I don't see any downside to RCBO's, only upsides. Cost has been an issue but as with all items they've come down in price as volumes being used have gone up so they're a serious contender nowadays. Some RCBO's are somewhat on the large side and can be a tight squeeze into an existiing CU but more compact versions are readily available now as well. The only issue I might see is that if a CU is custom built with RCBO's it won't be considered 'type tested' so it won't be able to claim the fairy-tail KA rating that a type tested unit does. Maybe one of the UK guys will elaborate on the importance of this (or lack of importance).

 

[Octopus]

Most customers get put off RCBO's because of the costs

 

[Marvo]

After a quick Google I see they're available at £11.99 for a 2-pole and under a tenner for a s/pole which wouldn't strike me as being prohibitive pricing but I don't know the UK market.

 

[Deleted member 9648]

After a quick Google I see they're available at £11.99 for a 2-pole and under a tenner for a s/pole which wouldn't strike me as being prohibitive pricing but I don't know the UK market.

Noooo!!.....Don't tell the punters that!

 

[Marvo]

Lol, I think the punters know about Google already

 

[Octopus]

After a quick Google I see they're available at £11.99 for a 2-pole and under a tenner for a s/pole which wouldn't strike me as being prohibitive pricing but I don't know the UK market.

best you edit that price matey.

they weren't that price in 2011

 

[Marvo]

I just googled ''RCBO+UK+price'' and that's what came up in the first two pages of results. You may get slightly different results as I'm in a different country and the results returned by google are locally formulated but they looked genuine.

 

[Leesparkykent]

I just googled ''RCBO+UK+price'' and that's what came up in the first two pages of results. You may get slightly different results as I'm in a different country and the results returned by google are locally formulated but they looked genuine.

You can get RCBO's for about £12 but most of the well known reputable brands are well in to the £20's per RCBO.

 

[Marvo]

So for decent RCBO's in an average domestic CU how much more would it cost a customer if you factor in the saving of the 2x RCD?

 

[Leesparkykent]

For example a 10way hager board with 100A main switch is about £25 and hager RCBO's are about £25 each. So if you had 8 circuits leaving a couple of spare ways that's £225 where as you could pick up a hager 10 way dual RCD board for £50 and 8 MCB's for about £3 each making it about £75.

 

[aesmith]

Thanks for the comments. I suspect the original estimator just didn't think I'd go for the more expensive solution, so didn't do more that mention it in passing. We have 11 circuits in the house, so it sounds like it might have added £300 (Hager board). Knowing what I know now I would have gone for that. On the other hand in four years the only trips have been two resulting from a faulty dishwasher. So maybe the advantage is more theoretical than real.

So on the technical side I was trying to think whether leaving the N still connected on the fault circuit could ever be an issue, but I don't see anyone saying that.

Tony S

 

[aesmith]

By the way, is it required, or good practice to use breakers from the same make as the consumer unit (ie Hager, which is what the local electricians all seem to prefer)?

 

[Octopus]

By the way, is it required, or good practice to use breakers from the same make as the consumer unit (ie Hager, which is what the local electricians all seem to prefer)?

Good practice is use the breakers that match the box! Manufacturers will suggest mixing and matching is "bad"!

 

[telectrix]

Good practice is use the breakers that match the box! Manufacturers will suggest mixing and matching is "bad"!

bad for technical reasons, or bad for their profits?

 

[Richard Burns]

bad for technical reasons, or bad for their profits?

Hmm.. yes, one does wonder on the level of risk they claim.

Thanks for the comments. I suspect the original estimator just didn't think I'd go for the more expensive solution, so didn't do more that mention it in passing. We have 11 circuits in the house, so it sounds like it might have added £300 (Hager board). Knowing what I know now I would have gone for that. On the other hand in four years the only trips have been two resulting from a faulty dishwasher. So maybe the advantage is more theoretical than real.

So on the technical side I was trying to think whether leaving the N still connected on the fault circuit could ever be an issue, but I don't see anyone saying that.

Tony S

If the RCBO disconnects because of a neutral earth fault then obviously that fault has not been cleared and remains in place (albeit the power is disconnected from the fault). This is clearly not a good situation but in practice this will not be an issue with your setup. The problems will occur if you have discriminating protective devices in series. e.g. 100mA time delay RCD as main switch and 30mA RCBO for the circuit
On a fault the first protective device operates, as it should, however as it has not cleared the fault the next protective device upstream also operates and can cause unrelated circuits to power down and cause nuisance.

 

[aesmith]

Cheers. There's no upfront RCD on the feed to the outbuildings, it's a switch and fuse in the house, then SWA all the way to the board. The installing electrician said there was no need for RCD protection on armoured cable. That surprised me a bit because in our last house but one the electrician put an RCD in the house and fed the outbuildings from that (however that was a crap job in other respects). We're TNS by the way, and the outbuilding earths are via a third core on the SWA.

Regarding different make RCBOs, I suppose that's a moot point. If they'd offered an all RCBO solution for say £300 extra, I'm hardly going to suggest they use £9.99 parts off Ebay instead of they're preferred parts. I can just imagine the response.