Armoured cabling questions

[Risteard]

He's presumably seen the question, so maybe he'll now answer it.

Apologies. I am working in a school (to BS 7671 rather than ET 101 on this occasion!) between 3p.m. and 3a.m. so have only just seen your post. I'm not sure why you feel multiple cables need to be run. For two-way switching the twin brown for the strappers is all that needs to be run between switches, with a single brown to the first switch for the permanent phase and a single brown to the last switch for the switched phase.

This was the way it was always done when I was an Apprentice, and the 3-core & Earth method was known as the "conversion method" as it could be used to convert a one-way switching arrangement to two-way switching. Obviously under ETCI Wiring Rules this arrangement would not be permitted.

I work on both sides of the border so have familiarity with both IEE/IET Wiring Regulations and ETCI National Wiring Rules.

Regarding single-phase circuits fed from a three-phase dis board under ETCI Rules, as pointed out, the respective phase colour may be used (and in my experience generally is), however despite what many seem to believe this is permitted as opposed to required. (Many contractors believe that it is mandatory, but it isn't.)

 

[JohnW2]

Insulated and sheathed PVC/PVC single brown, single blue, brown and earth and blue and earth are all available.

Interesting. Do I therefore take it that all of those are in widespread use in Ireland?

They are indeed, including in the north where BS 7671 prevails. No-one in the north would ever consider using brown & blue T&E and oversleeving it - twin brown is always used, as was twin red before.

Even over here, twin brown & E (previously twin red) is readily available, and is used a reasonable amount for switch drops etc. However, my question was about the various other types of cable you mention above. Whilst I don't doubt that they are available in the UK, if one looks hard enough, I certainly would not say that they were 'readily available', and (although my experience is limited) I have personally rarely, if ever, seen any of them used.

Kind Regards, John

 

[JohnW2]

I'm not sure why you feel multiple cables need to be run. For two-way switching the twin brown for the strappers is all that needs to be run between switches, with a single brown to the first switch for the permanent phase and a single brown to the last switch for the switched phase. This was the way it was always done when I was an Apprentice, and the 3-core & Earth method was known as the "conversion method" as it could be used to convert a one-way switching arrangement to two-way switching.

Yes, that's the method I, many others, were brought up with and certainly when it first came into use, the 'modern' method was also called the 'conversion method' over here. However, even with that old method, it was (IME) quite common to use to 3C+E, the third core being used to provide a neutral feed to the light at 'the far end' - or, alternatively, if the power feed comes 'from the other end', the third core can be used for 'permanent L'). As I've said, if one doesn't do that, but provides a neutral (or permanent L) feed by some other route (in a separate cable), one thereby creates a big 'current loop' that can radiate 50Hz and, which, for example, can induce hum in audio equipment. If one uses T+E for the strappers, then there clearly is need for some 'second cable' to the lamp, to provide its neutral.

Obviously under ETCI Wiring Rules this arrangement would not be permitted.

As I recently wrote to BAS, as far as I can see, the ETCI rules probably would allow 3C+E to be used for the 'conversion method' (in which all three conductors are Ls), since it appears to be acceptable to over-sleeve black and grey with brown (although not with blue). Is that not the case?

Kind Regards, John

 

[ban-all-sheds]

I'm not sure why you feel multiple cables need to be run. For two-way switching the twin brown for the strappers is all that needs to be run between switches, with a single brown to the first switch for the permanent phase and a single brown to the last switch for the switched phase.

And that single brown from the last switch is going to end up at the place where the single to the first originates, so for convenience it will almost certainly follow the same route as the strappers. So it might as well be in the same cable.

A twin & earth + a DI single (with or without a cpc) uses more raw materials.

I believe that the use of a 2-core strapper and singles as you describe can generate EMI.

Obviously under ETCI Wiring Rules this arrangement would not be permitted.

Is the ETCI "FAQ" wrong or incomplete?

3C+E does not contain a blue core, and when used as a strapper in 2-way switching only ever carries a phase, so does not contravene

• Brown, black or grey cores shall be used only as line/ phase conductors, and shall not be converted e.g. by sleeving for use either as protective conductors or as neutral conductors.

And if the black and grey cores are oversleeved with brown, it complies with

• Where more than one conductor in a multi-core cable is fed from the same phase, both shall be identified by the relevant phase colour, using sleeving as needed.

 

[scousespark]

Why are pages 2 onwards in Electrics UK? The fact that Eire has different regs is irrelevant to a question posted by a guy in Scotland.

 

[Risteard]

However, my question was about the various other types of cable you mention above. Whilst I don't doubt that they are available in the UK, if one looks hard enough, I certainly would not say that they were 'readily available', and (although my experience is limited) I have personally rarely, if ever, seen any of them used.

PVC/PVC single brown, brown & earth and single blue are used a lot here in houses. Blue and earth also exists.

 

[Risteard]

As I recently wrote to BAS, as far as I can see, the ETCI rules probably would allow 3C+E to be used for the 'conversion method' (in which all three conductors are Ls), since it appears to be acceptable to over-sleeve black and grey with brown (although not with blue). Is that not the case?

I don't believe that that is the intention of 514.3.6 taken in conjunction with Table 51A, so I would say no.

 

[Risteard]

And that single brown from the last switch is going to end up at the place where the single to the first originates, so for convenience it will almost certainly follow the same route as the strappers. So it might as well be in the same cable.

Not necessarily. Who said that the runs to the luminaire and the switches would be running together? I've never felt the need to use a 3-Core & Earth cable instead of strappers and single brown.

• Brown, black or grey cores shall be used only as line/ phase conductors, and shall not be converted e.g. by sleeving for use either as protective conductors or as neutral conductors.

Table 51A stipulates that brown is L1, black is L2 and grey is L3. I certainly don't think RECI, ECSSA or the ESB would take such a liberal view on reidentifying phases as other phases.

 

[JohnW2]

As I recently wrote to BAS, as far as I can see, the ETCI rules probably would allow 3C+E to be used for the 'conversion method' (in which all three conductors are Ls), since it appears to be acceptable to over-sleeve black and grey with brown (although not with blue). Is that not the case?

I don't believe that that is the intention of 514.3.6 taken in conjunction with Table 51A, so I would say no.

What "514.3.6" are you talking about - there is no such regulation in BS7671? Are you talking about an Irish regulation?

As often discussed, BS7671 appears to say that any insulated conductor (other than a G/Y single) can be over-sleeved with any colour (usually brown or blue) to 'identify' it.

Kind Regards, John

 

[JohnW2]

I've never felt the need to use a 3-Core & Earth cable instead of strappers and single brown.

As BAS and myself have said, apart from potential inconvenience of having two cables, use of single browns (or single blues) may raise issues of EMI - is that not a concern to you? ... and what about the timer fans - do you run two cables (a T+E and a separate single brown) to them?

Kind Regards, John

 

[ban-all-sheds]

Not necessarily. Who said that the runs to the luminaire and the switches would be running together?

They don't have to - I said for convenience it will almost certainly follow the same route as the strappers.

1-way switch: Permanent live comes from the luminaire (or very near it), goes to the switch, and switched live returns to the luminaire (or very near it), usually in the same T/E.

2-way, ditto permanent live to the first switch (in a chase in the wall), then your T/E strapper (in a chase in the wall), and then the switched live from that has to return to the luminaire (or very near it), in a chase in the wall.

Argue over whether my "almost certainly" should have been "quite probably" or "fairly likely" if you want, but it does seem to me that you might very well want that switched live to go in the other chase(s).

I've never felt the need to use a 3-Core & Earth cable instead of strappers and single brown.

What do you do in NI, where you have the choice of either method?

Table 51A stipulates that brown is L1, black is L2 and grey is L3. I certainly don't think RECI, ECSSA or the ESB would take such a liberal view on reidentifying phases as other phases.

So what does

"Where more than one conductor in a multi-core cable is fed from the same phase, both shall be identified by the relevant phase colour, using sleeving as needed"

mean, or imply? When is it relevant?

If you had 3C+E when all the cores were brown, you wouldn't need to oversleeve. So why have that requirement ("shall be identified...") if there's never a situation where you've got a cable with black and grey cores which you want to use for the same phase as the brown?

And if you cannot oversleeve black or grey with brown, that also means you cannot oversleeve brown with black or grey, which makes a mockery of "Where single-core cables are used to supply single-phase circuits fed from a three-phase distribution board, the respective line/phase conductor colour may be extended to the single-phase circuits fed from that phase".

And it must also mean that black+blue and grey+blue twin and earth cables are readily available to use on single phase circuits in 3-phase environments.

 

[ban-all-sheds]

and what about the timer fans - do you run two cables (a T+E and a separate single brown) to them?

That's not Risteard's choice - the regulations would prevent him using 3C+E even if he wanted to, unless he could find one with a blue core.

As unnecessary as that regulation seems to us, we can't hold him responsible, but it does seem to me as if the use of 3C+E to carry nothing but lives is allowed.

 

[Risteard]

What "514.3.6" are you talking about - there is no such regulation in BS7671? Are you talking about an Irish regulation?

As the discussion is about ET101 I was referring to that document and not BS7671.

 

[Risteard]

what about the timer fans - do you run two cables (a T+E and a separate single brown) to them?

In the south, yes. In the north, no.

 

[Risteard]

What do you do in NI, where you have the choice of either method?

In the north I (and most others) would use twin brown for strappers and a single brown for the switched phase (and permanent phase if not already available at the switch).

However, for timer fans and for interlinked smoke detectors I would use a 3C & E for convenience (but only in the north).

"Where more than one conductor in a multi-core cable is fed from the same phase, both shall be identified by the relevant phase colour, using sleeving as needed"

It actually states "using supplementary colour marking" as opposed to "using sleeving", but obviously that does not alter the meaning. I can see how you might interpret that your way, but I will point out that no-one ever uses 3-core for two-way switching like that so I certainly wouldn't advise trying it.

makes a mockery of "Where single-core cables are used to supply single-phase circuits fed from a three-phase distribution board, the respective line/phase conductor colour may be extended to the single-phase circuits fed from that phase".

I don't follow. If using singles in containment as you would (should) be there is no issue in using the respective phase colour for the single phase circuits. This is always the way I've done it on southern jobs.

And it must also mean that black+blue and grey+blue twin and earth cables are readily available to use on single phase circuits in 3-phase environments.

Again, no. Because who in their right mind would consider using T&E in such environments, assuming that these are not domestic installations?