30mA RCD as main switch

[leep82]

Done a little bit of searching and found that a situation such as the title of this thread would be against current regs, heres my situation. Been to look at a few jobs on a bungalow. The customer wants lights on there garage, ( which already has a supply present), an outside socket, and an extra lighting point in there living room. Currently the installation has no RCD protection whatsoever. Supply is TNCS and feeds a DB with only 5 circuits ( sockets, cooker, lighting, garage and burglar alarm ). Could it be argued that i have improved the state of the installation and note it as a deviation if i fitted a 30mA RCD as the main switch. Its just that cost is a big issue for the customer and i already have in my possesion the RCD so this would be much cheaper than going down the 3 separate RCBO's route for the individual circuits i would be working on.

 

[Darkwood]

TT systems have main switch RCD's although the set-up differs a bit it shows that front end RCD protection is not against regulation, in the event of an existing board having a 30mA DP front end rcd then this would satisfy any new circuit that requires it.

 

[NickD]

The customer wants lights on there garage, ( which already has a supply present), an outside socket, and an extra lighting point in there living room..

Subject to no cables getting buried <50mm deep, the only bit on there that screams "requires RCD protection" is the socket. Obviously it is for you to make the definitive assessment on that. External sockets with integral RCD are readily available and not that expensive (although avoid the double ones which are actually only rated to 13A total, unless feeding from a 13A fused FCU...in which case you may as well feed from an RCD FCU and use a standard outdoor socket, which is the obvious alternative). None of that will add to the overall job cost that significantly. And if they were that strapped for cash they wouldn't be getting the work done, it's all discretionary spending what you're listing.

 

[davesparks]

It's not just about the moment that the RCD trips, you've got to think a bit further ahead!

Let's say a N-E fault occurs on the 1st floor lights and the RCD main switch trips, the homeowner try's to reset it and it won't hold. They actually listened when you explained what to do after you had fitted it and go and unplug everything and switch off all MCBs, and they still can't get it to hold on.

They phone you up to get you out to fix it, it's Friday afternoon and you are already in the pub and a couple of pints have gone down lovely, you explain that you can't get there until Monday.

Faced with the whole house off until Monday and the freezer starting to thaw they start phoning round to get another electrician, you've lost a client and maybe dented your reputation when all their friends hear about the trip you installed knocking the whole house out and them having to get someone else to fix it.

Or the same fault takes out just the upstairs lighting circuit as you have installed RCBOs, it's inconvenient but they have bedside lamps and can survive until Monday.

 

[NickD]

PS Unless the living room or the garage contains a bath or a shower ;-)

 

[HappyHippyDad]

Completely agree with Dave above.

Plus Reg 314.2 does make it clear that each circuit should not be affected by the failure of other circuits and 'due account' should be taken of the consequences of the operation of any single protective device.

 

[Brightspark2]

Just a note, the deviations box is to write down any parts that deviate from BS7671 BUT offer the same degree of safety/protection etc as BS7671

 

[Darkwood]

It's not just about the moment that the RCD trips, you've got to think a bit further ahead!

Let's say a N-E fault occurs on the 1st floor lights and the RCD main switch trips, the homeowner try's to reset it and it won't hold. They actually listened when you explained what to do after you had fitted it and go and unplug everything and switch off all MCBs, and they still can't get it to hold on.

They phone you up to get you out to fix it, it's Friday afternoon and you are already in the pub and a couple of pints have gone down lovely, you explain that you can't get there until Monday.

Faced with the whole house off until Monday and the freezer starting to thaw they start phoning round to get another electrician, you've lost a client and maybe dented your reputation when all their friends hear about the trip you installed knocking the whole house out and them having to get someone else to fix it.

Or the same fault takes out just the upstairs lighting circuit as you have installed RCBOs, it's inconvenient but they have bedside lamps and can survive until Monday.

Your a preacher of doom lol... the clause of design to avoid inconvenience and nuisance shouldn't be over applied to domestic unless requested or circumstances require extra precautions (disabled, medical machines frail etc) and if said case above ever happened Im sure they would ring another available spark not like he's the only one out there.

 

[leep82]

Completely agree with Dave above.

Plus Reg 314.2 does make it clear that each circuit should not be affected by the failure of other circuits and 'due account' should be taken of the consequences of the operation of any single protective device.

so where does this leave a split load board that develops the same N-E fault? Any circuits protected by that RCD are still affected?

 

[NickD]

so where does this leave a split load board that develops the same N-E fault? Any circuits protected by that RCD are still affected?

Then you've still got half a house worth of power for light, heating, plugging the freezer into, watching Cats Do The Funniest Things Down Under 3.

 

[leep82]

so where does this leave a split load board that develops the same N-E fault? Any circuits protected by that RCD are still affected?

Then you've still got half a house worth of power for light, heating, plugging the freezer into.

yes of course but it completely contradicts the regulation that somebody has just stated.

 

[Darkwood]

Completely agree with Dave above.

Plus Reg 314.2 does make it clear that each circuit should not be affected by the failure of other circuits and 'due account' should be taken of the consequences of the operation of any single protective device.

You are misinterpreting this reg' if it was the case as suggested then RCD over multiple circuits wouldn't be allowed even in domestic and as this is clearly not the case then you just have to ensure that losing that half a board is not going to be anything more than a minor disruption at most.

A house owner having to get a sparks out in the rare worse case scenario where they cant reset is a minor disruption and inconvenience as its a rare occurance, where as telecom exchange losing its main servers and cutting of half a city is a major disruption whether rare or not ... you forget the regs cover domestic, commercial and industrial and looking at this regulation in the bigger picture will give better guidance on when to apply it.

When you get a sparks who solely works domestic then its easy to forget the regs cover a wider field and can lead to mis-interpreting and over applying of some regs... take it from a spark that installed under the 15th 16th and 17th edition ... although don't bother domestic now and can easily design a domestic to 3 levels of application of that regulation from minimal , moderate to higher risk of 'small' inconvenience and all comply but down to customers preference and pockets.

 

[davesparks]

Your a preacher of doom lol... the clause of design to avoid inconvenience and nuisance shouldn't be over applied to domestic unless requested or circumstances require extra precautions (disabled, medical machines frail etc) and if said case above ever happened Im sure they would ring another available spark not like he's the only one out there.

I wouldn't say I'm a preacher of doom, but I do attend a fair number of domestic callouts and can honestly say the clients are always far less happy when they've lost the whole house or half of the house than when it's just one circuit out!

 

[Badged01]

I wouldn't say I'm a preacher of doom, but I do attend a fair number of domestic callouts and can honestly say the clients are always far less happy when they've lost the whole house or half of the house than when it's just one circuit out!

Very true but I think in answer to the OP's original question which I read as the client not wanting to pay for a fancy split board, all RCBO sexy number, then a single RCD upfront can be interpreted as meeting the regs?

Let the buyer beware .........

 

[Octopus]

What constantly amazes me is the push to allow fixed appliances WITHOUT DP isolation and SP isolation for garden circuits on shared rcd.s

Madness.

 

[Octopus]

And what about the bonding?