Yeah, that'll do it. So if his boiler develops a fault, he cant use any sockets or heat the place in any way until a spark has been.
dual rcd?
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OK, so you don't mind hunderds of pounds worth of your freezer food defrosting when the fault on the immersion also cuts the power off to the freezer socket?
Ahh Steve, beat me to it with similar thoughts...
Its a bit acedemic for a 4-way board. by the time you've messed around with an RCD and a RCBO the cost would be about the same as an RCBO per circuit. Much much better too!
Ahh Steve, beat me to it with similar thoughts...
Its a bit acedemic for a 4-way board. by the time you've messed around with an RCD and a RCBO the cost would be about the same as an RCBO per circuit. Much much better too!
At the end of the day it's what you think is right and how far you think you should be reducing the risk to persons using that installation to a reasonably practicable level. The reg is just to make sure you consider this risk and that you put reasonable steps in place to mitigate it.
So you have to ask yourself what is the total risk of: it being dark outside AND you're on a landing AND there's an earth fault. Remember the latter is pretty rare.
How you percieve the risk will depend on your profession and experience. In an ideal world, nothing leaks current so you can say 1 RCD is enough, however we all know that's not true.
The Electrician
The electrician knows that things can leak current, such as washing machines and computers. He also knows that if he connects each circuit onto a separate RCBO then he's done everything reasonably practicable to reduce the risk of the RCBO tripping and him having to come back to fix it. He doesn't like doing that - it wastes his time, he has to try to explain to the customer that really it's not his fault, and ultimately he may have to spend a long time 'fixing' it.
The DIYer
The DIYer has only himself to blame, and therefore may consider that two (or possibly even one) RCD is enough. He won't have anyone knocking at his door for a refund, and he knows he can feel his way back to the consumer unit well enough to turn it all back on again.
BTW what TTC's talking about has happened countless times on TT installs with a single 100mA RCD
So you have to ask yourself what is the total risk of: it being dark outside AND you're on a landing AND there's an earth fault. Remember the latter is pretty rare.
How you percieve the risk will depend on your profession and experience. In an ideal world, nothing leaks current so you can say 1 RCD is enough, however we all know that's not true.
The Electrician
The electrician knows that things can leak current, such as washing machines and computers. He also knows that if he connects each circuit onto a separate RCBO then he's done everything reasonably practicable to reduce the risk of the RCBO tripping and him having to come back to fix it. He doesn't like doing that - it wastes his time, he has to try to explain to the customer that really it's not his fault, and ultimately he may have to spend a long time 'fixing' it.
The DIYer
The DIYer has only himself to blame, and therefore may consider that two (or possibly even one) RCD is enough. He won't have anyone knocking at his door for a refund, and he knows he can feel his way back to the consumer unit well enough to turn it all back on again.
BTW what TTC's talking about has happened countless times on TT installs with a single 100mA RCD
The DIYer also has a legal obligation to make reasonable provisions to protect persons operating, maintaining or altering the installations from fire or injury.
Not just him, but anybody else who lives in the house in the future.
Not just him, but anybody else who lives in the house in the future.
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Indeed it may well have, but it is unavoidable on a TT system.
And it has been agreed on here that a TT system under the 17th edition CAN be protected solely by the two 30mA RCDs in a "17th edition board" - no overall RCD is required as long as all circuits are covered by one of the two RCDs, and there is a main isolator.
Thus it becomes no different to a TN install in most cases.
You've been able to do that for years - nothing changed in the 17th which made it allowable where it hadn't been before.
But twin RCD boards werent as widespread until now. Its just one of the quirks of the 17th edition that means it makes it easier to protect TT systems.
There was no motivation to split loads across two RCDs before, and installation of single 30mA RCD incomer boards was common to save costs. Now the loads have to be split, as its in the regs.
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Although I quoted the regs the real point is how it will work out in practice.
Back in early 1990's I fitted two 30ma RCD's feeding whole house. When fitted all worked A1. As time has gone on we have had more and more problems with RCD's tripping out until the children left one by one taking their PC's with them and now not a rare as back in 1990's but back to acceptable limits.
There was a time when I had decided to rip out the twin system and fit RCBO's because it was tripping too often but never got around to it and now not so much a problem.
I have emergency lights at top of stairs and in garage the latter to light consumer unit.
From experience in my house I would not recommend anyone using just two RCD's and I would always advocate multi RCBO's and would never consider fitting a single unit.
15ma (Amount 30ma RCD is guaranteed not to trip at) is not much spread out over whole house. Using 4 RBCO's would give you 60ma and be much more likely to hold in and give trouble free life.
However my son has two single 30ma RCD's in series and has no problems at all. He has all 12vdc lighting and even heating is all 12vdc driving pumps etc. So the supply powers about 6 sockets and the 30A step battery charger. [Lives on a narrow boat] So clearly there are times when one could fit a single RCD. But how many houses have 12vdc lighting through out the house. Gas oil and solid fuel heating which is also all 12vdc. And a back-up engine they can start to give 140A at 12V charging to keep it all running without the mains power? Plus 400AH of battery back-up? And of course solid fuel cooking and a 3KVA inverter to boot.
So although one could have a situation where multi-RCD's are not required in practice it is very unlikely.
Forget regulations it's just not a viable set-up.
Back in early 1990's I fitted two 30ma RCD's feeding whole house. When fitted all worked A1. As time has gone on we have had more and more problems with RCD's tripping out until the children left one by one taking their PC's with them and now not a rare as back in 1990's but back to acceptable limits.
There was a time when I had decided to rip out the twin system and fit RCBO's because it was tripping too often but never got around to it and now not so much a problem.
I have emergency lights at top of stairs and in garage the latter to light consumer unit.
From experience in my house I would not recommend anyone using just two RCD's and I would always advocate multi RCBO's and would never consider fitting a single unit.
15ma (Amount 30ma RCD is guaranteed not to trip at) is not much spread out over whole house. Using 4 RBCO's would give you 60ma and be much more likely to hold in and give trouble free life.
However my son has two single 30ma RCD's in series and has no problems at all. He has all 12vdc lighting and even heating is all 12vdc driving pumps etc. So the supply powers about 6 sockets and the 30A step battery charger. [Lives on a narrow boat] So clearly there are times when one could fit a single RCD. But how many houses have 12vdc lighting through out the house. Gas oil and solid fuel heating which is also all 12vdc. And a back-up engine they can start to give 140A at 12V charging to keep it all running without the mains power? Plus 400AH of battery back-up? And of course solid fuel cooking and a 3KVA inverter to boot.
So although one could have a situation where multi-RCD's are not required in practice it is very unlikely.
Forget regulations it's just not a viable set-up.
Hello?
Anyone there?
Read 314-01-01.
The only thing which has changed is that it's spelt out more explicitly for the benefit of electricians who design and install without thinking.
Which, sadly, as the never ending discussions about "17th edition boards" and "16th edition boards" shows, is almost all of them.
Why did it need a specific mention in 314.1(iii) to get people to think about it?
I'll tell you why - it's because 99.99% of electricians are incapable of thinking for themselves - it's just installation by numbers, doing what has always been done, with not a spark of originality or intellect brought to bear.
It's shameful.
IMO both the old 16th edition split load boards and the new 17th dual RCD boards are barely skirting the edge of what is acceptable.
If I was doing a house to live in myself I'd at least look into how much it would cost to do it properly using RCD protection only where nessacery and as close to the point of use as possible.
If I was doing a house to live in myself I'd at least look into how much it would cost to do it properly using RCD protection only where nessacery and as close to the point of use as possible.
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I think some people really need to take a brief forage in to the real world. A world where money isn't infinite, where common sense prevails, where 1-1,000,000,000 shots don't happen every day, and where people actually live and life goes on. Books are good, but life is something different. Books may give one the ability to feel smug on internet forums, and yes, they may be the standards (non-statutory, some may need to be reminded, lest they through around shouts of 'illegal' and what-not), but reality is somewhat different.
Yes, a dual-RCD board does NOT meet BS7671:2008 in most cases.
BUT
A dual-RCD board will be installed by most 'sparks' in most domestic situations.
Because it offers adequate protection and at least some discrimination
RCBOs all-round are the way to go, but that way will not be gone due to cost and cost alone.
It is so unlikely that anyone would lose a freezer worth of food or break their neck due to an RCD DOING IT'S JOB that this kind of posturing is nothing else than pathetic internet talk.
Anyway, I'm installing all RCBOs in my house because I think it's best. However, I don't think the Lord would send me to hell if I used a daul-RCD CU....
Yes, a dual-RCD board does NOT meet BS7671:2008 in most cases.
BUT
A dual-RCD board will be installed by most 'sparks' in most domestic situations.
Because it offers adequate protection and at least some discrimination
RCBOs all-round are the way to go, but that way will not be gone due to cost and cost alone.
It is so unlikely that anyone would lose a freezer worth of food or break their neck due to an RCD DOING IT'S JOB that this kind of posturing is nothing else than pathetic internet talk.
Anyway, I'm installing all RCBOs in my house because I think it's best. However, I don't think the Lord would send me to hell if I used a daul-RCD CU....
Only as far as reasonably practicable though (as per your quote). Safety is always no. 1 priority but cost is always a close second. RCBOs can almost double the cost of a CU installation.
If he was being prudent he should, but in practise this is irrelevant. He has considered his own appliances, loadings etc and has accounted for the foreseable loads he may be adding. No-one should really try to second guess what the future homeowners might be moving in with them.ban-all-sheds said:
Whilst this may not be in the spirit of 314.2, I doubt anyone has ever put it down on a PIR.
Just to add to the arguement
i think RCD protection for domestic lighting circuits is mad, as quoted earlier and by others old person alone in the dark is a bad situation..
At the end of the day domestic wiring should be inspected and tested 5 yearly to reduce the of fire etc and our insurance companies give us a discount!
and
emergency lights are cheap, we should all fit them in our homes, i havent got one in this house yet but its on my to do list!
i think RCD protection for domestic lighting circuits is mad, as quoted earlier and by others old person alone in the dark is a bad situation..
At the end of the day domestic wiring should be inspected and tested 5 yearly to reduce the of fire etc and our insurance companies give us a discount!
and
emergency lights are cheap, we should all fit them in our homes, i havent got one in this house yet but its on my to do list!
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I agree Mike, the 17th goes too far with RCD requirements.
RCDs on all sockets? Great! RCDs for anything in a bathroom? Very sensible! RCDs for any non-protected cable buried less than 50mm, thus meaning pretty much all circuits including lighting? A bridge too far.
I've heard rumours that the RCD protection for cables was a last minute addition to the 17th, anyone else heard this and know why?
RCDs on all sockets? Great! RCDs for anything in a bathroom? Very sensible! RCDs for any non-protected cable buried less than 50mm, thus meaning pretty much all circuits including lighting? A bridge too far.
I've heard rumours that the RCD protection for cables was a last minute addition to the 17th, anyone else heard this and know why?
If you dont like it, run the lighting cables in metal conduit and SWA or MICC. Its the simple answer to a robust lighting circuit.
More than one way to skin a rabbit.
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