What size your CPC

[Chr!s]

but it will be when it is in conduit? thats the whole point, did you read the Post I quoted chris?

Errm no sorry, sound like i need to lol

 

[Pete999]

Look if you are installing a RFC in conduit using 2.5mm singles the logic will be to use a 2.5mm single as the cpc, lighting circuit using 1.5mm singles or 1.00 mm singles then use the same size cpc when closing the circuit in conduit or trunking.

 

[MDJ]

I agree pete I wouldn't consider using anything less than a 2.5mm2 for the CPC myself, My point was just in regard to the post that 2.5mm2 is the smallest cpc you can use if the cpc is not integral to the cable (ie for example a twin and earth) I don't agree with that thats why I mentioned it, just hoping for some clarity regarding that comment from the owner of that post

 

[Pete999]

I agree pete I wouldn't consider using anything less than a 2.5mm2 for the CPC myself, My point was just in regard to the post that 2.5mm2 is the smallest cpc you can use if the cpc is not integral to the cable (ie for example a twin and earth) I don't agree with that thats why I mentioned it, just hoping for some clarity regarding that comment from the owner of that post

Not sure I agree with that either mate, from the poster is saying that 2.5mm is the smallest cable used if not an integral cpc ie Twin with cpc as you say,begs the question, why the Hell do the cable manufactures make 1.5mm and 1.00 green and yellow cables? I s the OP getting confused the the size problem when the g/y is being used a supplementary bonding 2.5mm if protected and 4.0mm if unprotected? just a thought,

 

[spark 68]

I wasn't saying categorically either was necessarily correct, I originally posted off the top of my head, because where I have worked in the past 2.5mm CPC minimum was always used for singles, and the habit stuck with me, just my opinion. I even gave part v) as a possible exception in that post.

If you look at reg 543.1.1 it says it may be calculated in accordance with 543.1.3 or selected according to 543.1.4, it then goes into exceptions for:

iii) not part of an integral cable
iv) is not formed by conduit, ducting, or trunking (ie. metallic)
v) is not contained in an enclosure formed by a wiring system

Shall not be less than 2.5mm copper equivalent if mechanical protection is provided.

This part v) leaves a bit of an open question, ie. enclosure formed by a wiring system, would plastic conduit form part of a wiring system ? (metal could), or is it just an enclosure ?, or is it providing only mechanical protection ?, or all three ?

Earthed metallic containment could provide both electrical and mechanical protection (even when not used as a CPC) , plastic only mechanical.

The next part of the same reg states that the minimum size of CPC with mechanical protection is 2.5mm

So it is either a contradiction or it's not, either the minimum size is 2.5mm with mechanical protection, or we are allowed to use a smaller size in plastic conduit/enclosures (mechanically protected).

Hence my comment "typical bloody regs", if it was clear then we would not even be discussing it

 

[jibjob]

Thanks guys for all your comments & insights. I agree the regs do seem to muddy the waters somewhat on this. However, I have calculated using the adiabatic that a 1.5mm cpc will be suitable for my needs.

 

[Risteard]

would plastic conduit form part of a wiring system ?

Of course it would. Why would you think that it doesn't?

 

[spark 68]

Of course it would. Why would you think that it doesn't?

Look at the precise wording of that part of the reg,

v) is not contained in an enclosure formed by a wiring system

it doesn't mention containment once only enclosure (I accept the containment may be considered an enclosure).

I was talking about specifically about plastic conduit/trunking, is plastic a wiring system ?

Besides it was partly a rhetorical question seen as how singles wiring needs to be in some form of containment anyway.

And I already gave part v) as a possible exception to the rule.

How about some input on the next part of the same reg ? which states that the CPC Shall not be less than 2.5mm copper equivalent if mechanical protection is provided. ?



Does this mean that the CPC shall be a minimum of 2.5mm in plastic containment which only provides mechanical protection ? notice it does not say mechanical and electrical protection as the case would be with an earthed metallic containment system, which would in that instance form an actual part of the wiring system.

Where do the regs for protective conductors state minimum 2.5mm when mechanically protected but should not apply to a CPC ?, and the fact that particular reg is for protective conductors in general, it does not differentiate between CPCs or SB or any other type of protective conductor.

Would you agree that the reg is badly worded ?, or that I am categorically wrong ?

It is entirely possible I may be misinterpreting that reg, but only on the side of caution, 2.5mm CPC is the smallest size I keep anyway, plus wherever possible I would try to keep the CPC the same size as the live conductors in singles for the smaller cable sizes subject to a minimum 2.5mm for the CPC.

 

[Knobhead]

"typical bloody regs", if it was clear then we would not even be discussing it

Nuff said!

 

[HandySparks]

How about some input on the next part of the same reg ? which states that the CPC Shall not be less than 2.5mm copper equivalent if mechanical protection is provided. ?Does this mean that the CPC shall be a minimum of 2.5mm in plastic containment which only provides mechanical protection ? notice it does not say mechanical and electrical protection as the case would be with an earthed metallic containment system, which would in that instance form an actual part of the wiring system.

The line starting: "the cross sectional area shall be not less than 2.5mm² copper equivalent...." isn't "the next part of the reg", it's the end of the paragraph starting "If the protective conductor:...", and should be read as part of that paragraph, which includes (iii), (iv) and (v), hence the meaning I drew from it in post 15.

If it was a separate clause, it would start with a capital letter.

 

[spark 68]

The line starting: "the cross sectional area shall be not less than 2.5mm² copper equivalent...." isn't "the next part of the reg", it's the end of the paragraph starting "If the protective conductor:...", and should be read as part of that paragraph, which includes (iii), (iv) and (v), hence the meaning I drew from it in post 15.

If it was a separate clause, it would start with a capital letter.

OK fair enough HS, I am not sure it makes it any clearer though, why insert that part at all if it did not apply to the above exceptions ?, as I said it does not draw any distinction between a CPC and other types of protective conductors such as SB, earthing conductors or any other type of protective conductor, so surely if we apply that reg to other types of protective conductor why should it not apply to a CPC ?

I will have a look later through GNs, 1, 5, and 8 to see if it clarifies anything (not holding my breath lol), in the meantime I will just agree to disagree lol, besides it is no big deal to me as I am over and above anyway.

 

[Silly Sausage]

I agree with Handy, taking account the defn. of 'wiring system', 543.1.1, etc., etc.,
A 1.5 CPC with 2.5 single L&N in PVC conduit is perfectly acceptable, assuming 543.1.3 is satisfied.

Remember, the Regs are in 'Tech Speak', not conversational English.
A lot of the time I need to repeat what I read in my head numerous times to get a clear understanding!