What size your CPC

jibjob · Feb 28, 2014

Hi Guys,

I have been asked to install a some lighting & sockets in a lean too come garage come workshop type of thing. I was going to do it in PVC conduit & make a proper job of it rather than surface clip T&E all over the place. I haven't done much in the way of circuit installation using this method, I'm planning to do lights in 1.5mm singles & sockets in 2.5mm. I was thinking of doing the socket radial CPC in 1.5mm, any of you guys do this or would you stick to same size CPC as L&N? Thought as it's a small install, 5 sockets max on 16a MCB it would be a cost effective use of 100m drum of 1.5mm G&Y.

Baker1988 · Feb 28, 2014

Me personally I would stick to the same size as l and n if using singles but I'm sure it would still be OK if you use 1.5 CPC as that's what they use in twin and CPC cable

trev · Feb 28, 2014

Your cable selection calculations will tell you whether this is a viable method

Plonker 3 · Feb 28, 2014

Depends what your cable calcs say it should be?

- - - Updated - - -

Damn Trev and his fast fingers

spark 68 · Feb 28, 2014

The smallest size of a CPC if not an integral part of a cable is 2.5mm, I will look the reg up in a while.

edit: reg number 543.1.1, but there may be an exception see part (V) of that reg, there is a bit of a contradiction as below that it states that it shall be no less than 2.5mm if mechanically protected.

Typical bloody regs, lol

Badged01 · Feb 28, 2014

and a 3rd consideration, table B7 of the OSG!

telectrix · Feb 28, 2014

or use galv. conduit and no need for a cpc cable.

trev · Feb 28, 2014

spark 68 said:
The smallest size of a CPC if not an integral part of a cable is 2.5mm, I will look the reg up in a while.

Sigh. You mean you haven't memorised them?

spark 68 · Feb 28, 2014

lol see above Trev, I only know of that reg due to the 4mm requirement of adding seperate CPCs where not mechanically protected.

spark 68 said:
The smallest size of a CPC if not an integral part of a cable is 2.5mm, I will look the reg up in a while.

edit: reg number 543.1.1, but there may be an exception see part (V) of that reg, there is a bit of a contradiction as below that it states that it shall be no less than 2.5mm if mechanically protected.

Typical bloody regs, lol

Badged01 · Feb 28, 2014

spark 68 said:
reg number 534.1.1, but there may be an exception see part (V) of that reg,

Which regs you quoting?

spark 68 · Feb 28, 2014

Badged01 said:
Which regs you quoting?

oops my bad, lol, should be 543.1.1

Bloody IE 11 keeps missing characters out when I am typing, and I have to edit, I put the number edit in the wrong place, I will re-edit the earlier posts to correct

Badged01 · Feb 28, 2014

Quoting regs will pull the chicks but even they sometimes check you're not bullsh*tting them :smile5:

HandySparks · Feb 28, 2014

spark 68 said:
The smallest size of a CPC if not an integral part of a cable is 2.5mm, I will look the reg up in a while.

edit: reg number 543.1.1, but there may be an exception see part (V) of that reg, there is a bit of a contradiction as below that it states that it shall be no less than 2.5mm if mechanically protected.

Typical bloody regs, lol

Surely 543.1.1 (v) allows the use of 1.5mm² cpc in PVC conduit (which is the case for the OP)?

Certainly for a lighting circuit.

spark 68 · Feb 28, 2014

HandySparks said:
Surely 543.1.1 (v) allows the use of 1.5mm² cpc in PVC conduit (which is the case for the OP)?

Keep reading a bit further down lol

It contradicts itself

HandySparks · Feb 28, 2014

spark 68 said:
Keep reading a bit further down lol

It contradicts itself

Does it? If so, I can't see it.
Surely, you need to read the paragraph as a whole:

If the protective conductor:

(iii) is not an integral part of the cable, or

(iv) is not formed by conduit, ducting or trunking, or

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

the cross-sectional area shall be not less than 2.5mm² copper equivalent if protection against mechanical damage is provided, and 4mm² copper equivalent if mechanical protection is not provided...

ie, if the cpc is in a cable, or in conduit or formed from metallic containment, the 2.5mm² minimum doesn't apply.

spark 68 · Feb 28, 2014

I would say the opposite applies,

That 2.5mm is the minimum size, however on larger CSA live cables then a smaller csa CPC may be used to a minimum of 2.5mm subject to adiabatic etc. subject to the other conditions of that reg.

Besides the smallest size I stock is 2.5mm (smiley)

Agree about metallic containment btw.

Edit: that is what I meant about "typical bloody regs", it is either minimum 2.5mm with mechanical protection or it is contradictory by allowing a smaller size in containment (which is mechanical protection),lol

Clive P · Mar 1, 2014

Hi,
Wired a small workshop a while ago for a friend, did all the rings and lighting in 2.5 singles; one size no messing about with different sizes or running out of this or that.

Regards.

MDJ · Mar 1, 2014

spark 68 said:
The smallest size of a CPC if not an integral part of a cable is 2.5mm, I will look the reg up in a while.

edit: reg number 543.1.1, but there may be an exception see part (V) of that reg, there is a bit of a contradiction as below that it states that it shall be no less than 2.5mm if mechanically protected.

Typical bloody regs, lol

Why do they make 1.5mm2 Green and yellow then?

Chr!s · Mar 1, 2014

MDJ said:
Why do they make 1.5mm2 Green and yellow then?

Because it will be enclosed within a wiring system.

Chris

MDJ · Mar 1, 2014

Chr!s said:
Because it will be enclosed within a wiring system.

Chris

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

Chr!s · Mar 1, 2014

MDJ said:
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 · Mar 1, 2014

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 · Mar 1, 2014

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 · Mar 1, 2014

MDJ said:
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 · Mar 1, 2014

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 · Mar 2, 2014

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 · Mar 2, 2014

spark 68 said:
would plastic conduit form part of a wiring system ?

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

spark 68 · Mar 2, 2014

Risteard said:
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 · Mar 3, 2014

spark 68 said:
"typical bloody regs", if it was clear then we would not even be discussing it

Nuff said!

HandySparks · Mar 3, 2014

spark 68 said:
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 · Mar 3, 2014

HandySparks said:
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 · Mar 3, 2014

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!