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Topic Title: Three-Phase, Running L1 & L2 in the same containment
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Created On: 15 January 2013 08:36 AM
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 15 January 2013 08:36 AM
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Sanft

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Joined: 22 August 2011

Hello- Just a really quick question- I can't seem to find any reference to this- but how dire is it when you come across say- Dado Trunking with the potential of 400 volts between conductors? I.e. L2 and L3 being run within the same containment-

I've seen this on a few EICR's noted down as a C1- and I beg to differ with it, I just can't seem to justify it- I can imagine possibly a C2 as it is potential- but certainly not a C1?

Thanks in advance for getting back to me


Sanfttt
 15 January 2013 08:55 AM
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Parsley

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What reg would you refer to?

Regards
 15 January 2013 09:32 AM
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AJJewsbury

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but how dire is it when you come across say- Dado Trunking with the potential of 400 volts between conductors? I.e. L2 and L3 being run within the same containment-

That's exactly how it should be done for 3-phase (or 2-phase) circuits - the regs prohibit different conductors from the same circuit being run in different containment (521.8.1).
- Andy.
 15 January 2013 09:38 AM
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Sanft

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Thank you Andy-

Does this apply to where the circuits are all of single-phase nature, running alongside each other? So they are supposed to be at 230v, but in the event of a fault, could possibly become 400v? If it is a three-phase circuit, of course the conductors should be run together- is it the same either way?
 15 January 2013 09:42 AM
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Parsley

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As per my previous post what reg would you refer to on a EICR for the code 2 recommendation you suggested might be applicable?

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 15 January 2013 09:57 AM
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Sanft

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Not sure on the Reg, hence me saying that I'm uncertain of how to justify this- however in terms of placement on the EICR itself- I would probably link this to either of the following:-

First Choice-
6.12 Cable installation methods/practices appropriate to
the type and nature of installation and external influences

Possible Other- (but is vague in regards to the potential of 400v)
6.22 General condition of wiring systems
 15 January 2013 10:28 AM
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Parsley

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As far as I'm concerned this is normal practice and no code would be required.

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 15 January 2013 10:32 AM
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MrP

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Nothing wrong with the installation practice
And it beggars the question ?


MrPGood luck buddy we all have to start somewhere
 15 January 2013 10:54 AM
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AJJewsbury

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Does this apply to where the circuits are all of single-phase nature, running alongside each other? So they are supposed to be at 230v, but in the event of a fault, could possibly become 400v? If it is a three-phase circuit, of course the conductors should be run together- is it the same either way?

Basically, yes. The insulation would need to be suitable for 400V between live conductors, but you get that using standard cables anyway.

There is a good question lurking behind this - that is the problem of faults between different circuits. The regs don't actually address that problem, just admit (in the first line of 434) that it's a limitation of the regs (it's not the only one either). If they did we'd have all kinds of challenges making sure that a lighting c.p.c. cope with a short from a shower or submain L. That might seem odd where you have unsheathed singles from several circuits in the same conduit or trunking, but I guess experience shows it's not a significant problem.

- Andy.
 15 January 2013 11:18 AM
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Sanft

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Cheers guys-

It's just I look over all certificates that pass through here, I wanted to mention that this code would have to be removed or reduced from a C1 to a C2-C3, but had no evidence to go on, this has helped me with my judgements-

Great Help Guys,

Many Thanks to all of you-

Andrew
 15 January 2013 11:38 AM
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OMS

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There is a good question lurking behind this - that is the problem of faults between different circuits. The regs don't actually address that problem, just admit (in the first line of 434) that it's a limitation of the regs (it's not the only one either). If they did we'd have all kinds of challenges making sure that a lighting c.p.c. cope with a short from a shower or submain L. That might seem odd where you have unsheathed singles from several circuits in the same conduit or trunking, but I guess experience shows it's not a significant problem.


It would also raise the issue of short circuits between phases with or without a further fault to earth, Andy

As you say, experience suggests to us that it's not a major problem - although I did once have an unrevealed problem where a 16mm2 sub main circuit in singles had a fault to an outgoing lighting circuit from that DB - effectively leaving the lighting circuit live regardless of the MCB and subject to all sorts of dangerous aspects on the neutral if the DB main switch was opened (being all pole).

Contractor had hauled in the new circuit under the illusion he was operating a masted schooner - the 1.5mm2 single had "burned" a friction path through the sub main and also had a chunk out of the insulation - I suspect it had been there for some time before routine fixed wire testing picked it up.

It happens I guess, but not often - and on the occasions I've calculated for it, most cases aren't a problem (in terms of thermal withstand at least - things might get a bit toasty, but usually the CPD will go)

Regards

OMS

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Failure is always an option
 15 January 2013 12:14 PM
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John Peckham

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Is that not one of the best kept secrets of BS7671 that it does not address possible faults between individual circuits? I feel sure someone will correct me if I am wrong?

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John Peckham

http://www.astutetechnicalservices.co.uk/
 15 January 2013 01:30 PM
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AJJewsbury

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Is that not one of the best kept secrets of BS7671 that it does not address possible faults between individual circuits?

Opps, I didn't realise it was meant to be secret!

Better not mention faults of non-negligible impedance, why we have the same disconnection times inside and outside the equipotential zone, or mixed disconnection times then?
- Andy.
 15 January 2013 01:45 PM
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OMS

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Originally posted by: John Peckham

Is that not one of the best kept secrets of BS7671 that it does not address possible faults between individual circuits? I feel sure someone will correct me if I am wrong?


Happy to oblige you John -

Chapter 43 may only be focused on faults between conductors of the same circuit - that doesn't relieve the objectives of Chapter 13

regards

OMS

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Failure is always an option
 15 January 2013 01:54 PM
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weirdbeard

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Originally posted by: John Peckham

Is that not one of the best kept secrets of BS7671 that it does not address possible faults between individual circuits? I feel sure someone will correct me if I am wrong?


Hi John, just thinking aloud, but in the OPs situation of singles in trunking, surely in an installation that has been properly selected and erected and certified as such, it could only be abuse or negligence that could cause a fault between insulated conductors- and the regs can't be expected to allow for random combinations of circumstances?
 15 January 2013 02:09 PM
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AJJewsbury

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Hi John, just thinking aloud, but in the OPs situation of singles in trunking, surely in an installation that has been properly selected and erected and certified as such, it could only be abuse or negligence that could cause a fault between insulated conductors- and the regs can't be expected to allow for random combinations of circumstances?

If we could assume that everything was perfect and would stay so indefinitely , then life would be much easier - we wouldn't have all these complications about earthing or double insulation, or RCDs for additional protection. Unfortunately, the real world isn't like that. Fortunately a lot of imperfections are reasonably foreseeable and so can be guarded against.
- Andy.
 15 January 2013 02:25 PM
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OMS

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Originally posted by: weirdbeard

Originally posted by: John Peckham

Is that not one of the best kept secrets of BS7671 that it does not address possible faults between individual circuits? I feel sure someone will correct me if I am wrong?


Hi John, just thinking aloud, but in the OPs situation of singles in trunking, surely in an installation that has been properly selected and erected and certified as such, it could only be abuse or negligence that could cause a fault between insulated conductors- and the regs can't be expected to allow for random combinations of circumstances?


the regs (effectively) assume at least one fault has occured and describes what's required to deal with a second fault condition.

Faults between conductors of different circuits is easily predicted

regards

OMS

-------------------------
Failure is always an option
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