Correct Consumer Unit For TT Supply

edzblue · 6 May 2011

RF Lighting said:
It wont keep you just as safe and it directly contravenes regulation 314.1

If you take you head out of your arse for one second and actually read what I have written, you'll realise how stupid you are making your self look.

A single RCD at the head of the board is dangerous and does not comply with BS7671. It never has.

You then go on to tell me everything that I've already written earlier in the thread.

What's with the attitude anyway?

I fail to see how one RCD is any less safe than 2? and what does dividing installations in to circuits have to do with this anyway? The installation would no doubt be divided in to circuits. It's how many RCD's are required to protect those circuits we are on about. Answer = How many circuits do you have? 6 circuits = 6 RCBO's (other than if for exceptions under 411.3.3 or unless requirements of 522.6.5 / 6 are met

2 RCD's don't make it anymore safe and doesn't comply with regs (the same as 1 RCD doesn't)

Read the reg below it the one you have quoted. The only way of complying with regs is to fit RCBO's to each circuit.

I'm not saying it is right to only fit one RCD, but it is no more/less dangerous than fitting 2 RCD's.

Pre 2008 we only ever fitted one RCD and this complied with the 7671 (so don't say it NEVER has)

Thank u and please don't call mention my arse

ban-all-sheds · 6 May 2011

RF Lighting said:
... you'll realise how stupid you are making your self look.

I think you are crediting him with far more intelligence and self awareness than he actually has.

314-01-01 Every installation shall be divided into circuits as necessary to:

a) avoid danger and reduce to the least possible degree or amount inconvenience in the event of a fault....

edzblue said:
Pre 2008 we only ever fitted one RCD and this complied with the 7671 (so don't say it NEVER has)

See what I mean?

edzblue · 6 May 2011

I never said complied, but that is the fact. 1 RCD was fitted at the head of the board on all TT installations and one RCD was fitted in split load boards on all others (pre 2008) Don't remember the NIC ever picking me up on it for being wrong.

I suppose I should've gone to Wickes and found you buying your 5 metres of 2.5, what with all the mains board you've obviously fitted.

As for Noah building the Arc. He's not real and it never existed. Two of every animal, makes about as much sense as you.

Don't reply to me again until you can tell me how 2 RCD's satisfies reg 314.2
and I won't respond to you!

ban-all-sheds · 7 May 2011

edzblue said:
I never said complied,

edzblue said:
Pre 2008 we only ever fitted one RCD and this complied with the 7671

Don't reply to me again until you can tell me how 2 RCD's satisfies reg 314.2

I haven't got the time for such an onerous task as trying to explain things to you.

and I won't respond to you!

Could you stop responding to everybody please.

bernardgreen · 7 May 2011

In 1981 when we started building our house the electricity meter installer refused to install the meter for our temporary supply as it had " two RCDs" and therefore did not comply.

I pointed out to his boss that one fed the caravan, our temporary home, and the other fed the "builders" supply and that in the event of an accident that tripped the bulder's supply we would still need lights in the caravan to find the phone and do first aid. The boss agreed that made sense and sent the meter installer back to install the meter.

comms · 7 May 2011

How many circuits are on the NON rcd side of the current board?

If only a couple just drop in rcbo's

Adam_151 · 8 May 2011

comms said:
How many circuits are on the NON rcd side of the current board?

If only a couple just drop in rcbo's

Single pole rcbos on TT don't sit right with me, but i'd need to sit down with the regs to check the position, I certainly dont think I'd be happy doing it whatever the BS says tbh.

Don't think anyone makes double pole ones anymore? and anyway they were normally dual module so unlikely to fit

JohnW2 · 8 May 2011

Adam_151 said:
Single pole rcbos on TT don't sit right with me, but i'd need to sit down with the regs to check the position, I certainly dont think I'd be happy doing it whatever the BS says tbh.

I think we've been through this before, but I've forgotten (and can't find) the answer ... can you remind me what is the perceived risk resulting from having a single-pole protective device with TT? On the face of it, the only scenarios I can think of where there could be an issue are almost vanishingly improbable.

Kind Regards, John

Spark123 · 8 May 2011

The only one that strikes me is a problem resulting from an open circuit neutral on the supply side.

JohnW2 · 8 May 2011

Spark123 said:
The only one that strikes me is a problem resulting from an open circuit neutral on the supply side.

If there were an open circuit neutral on the supply side, the protective device (RCD or RCBO) would surely not operate (whether SP or DP), and nor would anything on the circuit function (hence user would be aware of a problem), since there would be no return path for any current to flow down - unless there were simultaneously a L-E path (fault or human being) for current to flow through - which is one of the 'vanishingly improbable' scenarios/coincidences I had thought about.

Kind Regards, John.

comms · 9 May 2011

Doesnt a TT required to have DP for isolation purposes, but can be single pole for disconnection of line under fault conditions?
The main switch would suffice for isolation & single pole rcbo for the fault condition....

If you were so inclined a 100mA td in place of the main switch + single pole rcbo's?

JohnW2 · 9 May 2011

comms said:
Doesnt a TT required to have DP for isolation purposes, but can be single pole for disconnection of line under fault conditions? The main switch would suffice for isolation & single pole rcbo for the fault condition....

That is certainly what I thought, but I have (often) been known to be wrong! As I implied before, it does seem to make sense, since (as far as I can make out) it would require a ('vanishingly improbable') coincidental simultaneous supply-side fault at the very time a fault/incident caused the disconnection device to operate for there to be any risk with having only single pole disconnection device.

Isolation is obviously a different matter. With a TN system, provided that adequate main protective bonding is in place, the neutral should not be able to present any hazard, even under extreme supply-side fault conditions, so DP isolation is probably not necessary. With a TT system, however, there is the possibility that a supply-side fault could result in a dangerous potential difference existing between neutral and everything earthed (to the TT electrode) within the premises - hence DP isolation makes very good sense - at least at the origin of the installation.

comms said:
If you were so inclined a 100mA td in place of the main switch + single pole rcbo's?

Indeed. That would be an up-to-date version of the 'old' arrangement of a 100mA Type S RCD at the origin with a 'split load' CU (i.e. some circuits not protected by RCDs/RCBOs).

Kind Regards, John.

edzblue · 9 May 2011

Don't reply to me again until you can tell me how 2 RCD's satisfies reg 314.2

I haven't got the time for such an onerous task as trying to explain things to you.

Ban all sheds. I apologise for my tone and would be most grateful if you would undertake the onerous task of explaining this the above to me?

Thank you

bernardgreen · 9 May 2011

What is the problem ?

Double pole isolation reduces to near zero the risk of the installation creating any hazard. That applies to both TT and PME installations.

Though for PME the neutral derived "earth" could present a hazard if the neutral has been bounced up above 50 volts by a network fault or severe phase unbalance. ( it does happen )

JohnW2 · 9 May 2011

bernardgreen said:
Double pole isolation reduces to near zero the risk of the installation creating any hazard. That applies to both TT and PME installations.

Indeed.

bernardgreen said:
Though for PME the neutral derived "earth" could present a hazard if the neutral has been bounced up above 50 volts by a network fault or severe phase unbalance. ( it does happen )

Yes, but as I said in my last post, provided that adequate primary bonding is in place, that should not present any hazard, since everything 'earthed' in the premises should be at that elevated potential (hence no potential differences) - which I presume is the reason that SP isolation is allowed. The potential (sorry for pun!) hazard with TT in the presence of a high potential 'neutral' due to a supply-side fault is clear - hence the need for DP isolation. However, no-one can disagree with your view that DP isolation always affords that extra degree of 'comfort', no matter what earthing arrangements one has!

Kind Regards, John

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Correct Consumer Unit For TT Supply

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