Time delay RCCB

[JohnW2]

May be the main switch has a time delay will let you have all the details tomorrow not sure how to include a picture.

Things would be a bit more reasonable if it were time-daelayed.

The main switch has never tripped. Halogeng bulbs have tripped the lighting circuit mcb's . A faulty toaster and a kettle both tripped the RCCB on the power CU . It also tripped when I stripped. Wall and got a socket wet. The pond RCBO trips every time you cough but that is when the rain got into the external boxes when I left them open and a pump that had a fault on it. But as I say never the main switch.

That's all as expected. However, I thought your explanation for the lack of RCD protection of the lighting circuit was that when halogens die, they would trip it - which, as I said, is very unlikely.

If as at seems 1 main switch is bad practice can I ask why and what it should be like.

As I think BAS suggested, the simplest 'quick fix' (albeit not the ideal) would be to get rid of the up-front single RCD and have it replaced just by a 'junction box' (probably 'Henley blocks') which directly fed the three CUs in the house - and have all circuits protected by a RCD in each of those three CUs (i.e. I think that would mean just putting one into the lighting CU - the other two already have, or will have, RCDs). That still wouldn't represent the ideal split of circuits between RCDs (e.g. the entire house's lighting would be on the same RCD), but it would certainly be better than having everything on one RCD.

Kind Regards, John

 

[deadshort]

Thanks DS

To fit RCBO,s instead of mcb,s is an enormous cost especially for the Square D ones I have to be honest that seems so over the top as to be ridiculous even to me as an amature. Why on earth would you want an RCBO for a few lights in a lounge ceiling.

Regards
Andy

All circuits on a TT system must be RCD protected, that is why your electrican fitted an RCD as a mains switch. That would have been the cost effective solution at the time.

Kind regards,

DS

 

[Andypease1]

Sorry what is a TT system

 

[deadshort]

Thanks for that. Yes we do run on an earth rod (Very rural)

Why would you also need an rccb in the out house as well. Surely protection is provided by the rccb unit in the small cu at the house. The cu in the out house is really just a distribution box using mcb,s

Sorry if sound a bit thick

That's what you apparently have ?

 

[Andypease1]

Thanks DS all clear now

 

[JohnW2]

To fit RCBO,s instead of mcb,s is an enormous cost especially for the Square D ones I have to be honest that seems so over the top as to be ridiculous even to me as an amature. Why on earth would you want an RCBO for a few lights in a lounge ceiling.

All circuits on a TT system must be RCD protected, that is why your electrican fitted an RCD as a mains switch. That would have been the cost effective solution at the time.

True, and that is the same reason (cost-effectiveness) I suggested the compromise of putting an RCD in the lighting CU. If it could be split into a dual-RCD one (or moving at least one or two lighting circuits over to the other CU), even better. Individual RCBOs is obviously the ideal solution in terms of separation between circuits, but certainly not cheap, given that the OP appears to have a lot of circuits.

Kind Regards, John

 

[Andypease1]

Thanks John

It has clicked now

A. Will check my main switch tommorow

B Was confused halogens blow the circuit at my flat where everything is on an rcd.

C. As DS says on a TT earth rod set up all circuits should be rcd protected so that us why I have the main switch.

D Down side of no seperate Rcd for lighting is that if we get a lighting circuit fault we lose everything. We are used to that with the power cuts so no worries. Have emergency lighting over the boards.

E. Answer. Already have a 4 way block in Situ put an rcd in the lighting circuit and bypass the main switch. Or if the main switch turns out to be a time delay the just put an rcb in the lighting cu

Bloody predictive text drives me mad I texted my neighbour and told him I used his Wife. He shot her, then I texted him to say it was a predictive text error and that I had used his Wi fi. Whoops

 

[ban-all-sheds]

Why have RCBO's in the posh outhouse .

The nature of the outbuilding wasn't made clear before, so I assumed shed/summerhouse/workshop or similar. Typically those have only 2 or 3 circuits, so 2 or 3 RCBOs vs 1 RCB + 2 or 3 MCBs is not £££, and often you really don't want the lights to go out when a socket circuit trips, so an RCD + MCBs is not ideal.

No extraneous metal or water or gas pipes. I do have RCBO's for the shower and the pond for obvious reasons.

For equally obvious reasons - your TT supply - everything needs RCD protection.

The outhouse cu is protected with a 63amp 30ma RCCB

If you are using a hand-held power tool at night and the circuit trips you will be plunged into darkness. That might not be enjoyable. For the sake of the price of a couple of curries, ditch the up-front RCD and use RCBOs.

This was a real quality installation done to an extremely high standard and also looked at by my building inspector

Sorry - I disagree.

It was done to a very low standard. It may well have been installed to an extremely high standard but it was definitely not designed that way.

 

[JohnW2]

B Was confused halogens blow the circuit at my flat where everything is on an rcd.

fair enough, but I strongly suspect it was an MCB tripping, not the RCD.

C. As DS says on a TT earth rod set up all circuits should be rcd protected so that us why I have the main switch.

Indeed, but, as I've said, if you added RCD (or RCBOs, per his suggestion) protection to the lighting CU, all circuits would then be RCD protected and you therefore would not need that up-front RCD protecting everything

D Down side of no seperate Rcd for lighting is that if we get a lighting circuit fault we lose everything.

Exactly. As I hinted in my recent response to DS, if you did add an RCD to the present lighting CU, you might want to consider having some circuits swapped between your two 'main CUs' - so, for example, not all lighting circuits were on the same RCD.

E. Answer. Already have a 4 way block in Situ put an rcd in the lighting circuit and bypass the main switch. Or if the main switch turns out to be a time delay the just put an rcb in the lighting cu

Yep, that's essentially what I was suggesting. Not the ideal, but certainly an improvement, and a lot cheaper than lots of RCBOs.

Kind Regards, John

 

[ban-all-sheds]

That's fair enough, but the problem we've all identified (in some cases more gently than BAS) is that, unless that single upstream RCD is time-delayed, a fault anywhere, even on a circuit protected by another RCD, is at serious risk of taking out the entire installation in your large house

And if it is time delayed it is not providing regulation compliant protection for the circuits from the CU with only a switch incomer.

I can but presume that BAS was thinking of having RCBOs (or an RCD+MCBs) in the outhouse instead of in the CU in the house supplying it.

I wouldn't have an "instead of" to worry about, as I would not recommend coming from the house CU in the first place. A switchfuse on the meter tails would be my choice, and in this case as it's TT you'd also need RCD protection at source for the cable , and this should be chosen to provide discrimination between it and the device(s) in the outbuilding.

 

[Andypease1]

Thanks BAS

I do have emergency lighting over my work bench which was installed because of power cuts.

 

[ban-all-sheds]

That would have been the cost effective solution at the time.

Where you see "cost effective" I see "shameful penny-pinching".

In the context of "new circuits for a very large extension" how much would it have cost to have sorted it out properly?

 

[ban-all-sheds]

Later in about 2009 we put in new circuits for a very large extension both installations were fully tested and certified.

I'm going to disagree again - with that scale of additional work I do not believe that your electrician should have certified the installation as compliant with BS 7671:2008 with a single up-front RCD. He should not have left it like that - it's disappointing to say the least.

 

[Andypease1]

Just one question before bed.

Is it dangerous or unsafe or just bad practice

 

[ban-all-sheds]

It's certainly bad practice.

It might be dangerous to lose all electricity in a house because of a single fault, which is why your design is now pretty universally regarded as non-compliant with the Wiring Regulations.

It's not dangerous in the sense of you being at risk of an electric shock or a fire etc, so you may go to bed and sleep soundly.