recorded cpc size

[pepparz]

on a schedule of circuit details for a installation certificate, under the circuit conductors cpc size in mm², what should be recorded when a SWA cable has been used but one of the inner conductors is used as the cpc (say single phase circuit supplied by 2.5mm² 3 core, 1 x phase, 1 x neutral, 1 x earth). should the cpc be recorded as the armouring or the 2.5mm² designated cpc conductor?
I personally think it should be the 2.5mm² designated conductor and not the armouring, which is the earth by default.

 

[telectrix]

agree with that, as the armour is not always used as cpc, although it must be earthed.

 

[Badged01]

On a two core you would declare the armour as the CPC size. If using a 3rd core and the armour both as your CPC, would you not aggregate the two sizes?

If you are just earthing the armour at one end then just the core size would be the CPC

 

[pepparz]

On a two core you would declare the armour as the CPC size. If using a 3rd core and the armour both as your CPC, would you not aggregate the two sizes?

If you are just earthing the armour at one end then just the core size would be the CPC

but when would you design and install a circuit which needed both the armoring and a inner core to be the cpc. surely the cable should comply with just the inner core been the cpc?

 

[telectrix]

but when would you design and install a circuit which needed both the armoring and a inner core to be the cpc. surely the cable should comply with just the inner core been the cpc?

it must comply if the cpc core is the same size as the line conductor. the point is that on your sotr, there's just room in the box to enter the core size e.g.2.5. where in hell are you going to fit "22mm steel armour having an equivalent copper size of 3mm"?

 

[pepparz]

it must comply if the cpc core is the same size as the line conductor. the point is that on your sotr, there's just room in the box to enter the core size e.g.2.5. where in hell are you going to fit "22mm steel armour having an equivalent copper size of 3mm"?

ive got the schedules of about 20 DB's and the cpc size has been entered as "ARM"

 

[Badged01]

I normally just put it in the remarks column. "Armour XXmm & Core XXmm"

 

[Badged01]

ive got the schedules of about 20 DB's and the cpc size has been entered as "ARM"

They should be entering a figure! As above, I enter the total in the CPC column and annotate in the remarks how Ive calculated it.

 

[Richard Burns]

ive got the schedules of about 20 DB's and the cpc size has been entered as "ARM"

I would say that would be OK for a two core cable without a core used as the cpc, if there is a core as the cpc then that is the size of the cpc, though I suppose you could say 2.5+armour, but this would not be totally according to the regs as you cannot use a combined mix of materials and sizes to meet the cpc requirements.

 

[Badged01]

...... you could say 2.5+armour, but this would not be totally according to the regs as you cannot use a combined mix of materials and sizes to meet the cpc requirements.

I always believed the regs did allow this, certainly the mix of cable & sheath (armour) to meet the CPC is my interpretation of 543.2. And by default Ive always assumed that this (copper & steel) allows different materials/sizes to be used unless there is another reg I've overlooked?

 

[Engineer54]

In this instance if 3 core SWA cable is used, you only record the 3rd core not the swa. If 2 core then you record the CSA of the swa and in the notes state in compliance with Table *** (can't remember the number of the top of my head)

What you DON'T DO, is ever try and combine any copper CPC and swa. Only the highest complying CPC conductor is recorded.... Also remember, that SWA armouring is unlikely to comply if any main bonding is also involved....

 

[telectrix]

In this instance if 3 core SWA cable is used, you only record the 3rd core not the swa. If 2 core then you record the CSA of the swa and in the notes state in compliance with Table *** (can't remember the number of the top of my head)

What you DON'T DO, is ever try and combine any copper CPC and swa. Only the highest complying CPC conductor is recorded.... Also remember, that SWA armouring is unlikely to comply if any main bonding is also involved....

that's what i remember from distant past. think it was in latin, then.

 

[pepparz]

that's what i remember from distant past. think it was in latin, then.

is that from the GS7671 (Greek standards7671)?

 

[telectrix]

it's from the gospel according to eng54.first published in chinese and translated into the latin by tony ( aka pope tony 1st).

 

[pepparz]

i always knew eng thought of himself as a deity!!!lol"""

 

[pepparz]

look eng, see that, above me pic, it says respected.
read it and weep lol!!!

 

[telectrix]

so was harold shipman

 

[pepparz]

By whom? not by any grannies I bet!

 

[Engineer54]

look eng, see that, above me pic, it says respected.
read it and weep lol!!!

Me weep, Nah.

Just means you have 400 posts to your name. It has nothing to do with the content of those 400 posts...lol!!

 

[pepparz]

hook, line, sinker and copy of angling times. lol!!

 

[Engineer54]

hook, line, sinker and copy of angling times. lol!!

One day, if you're at all lucky.... You may actually Grow Up!! lol!!

 

[Hawkmoon]

If you have circuits run in metal trunking (with cpcs) you don't include the trunking when determining/recording the cpc size...

SWA sheath is no different if you are using a core as cpc

 

[Badged01]

If you have circuits run in metal trunking (with cpcs) you don't include the trunking when determining/recording the cpc size...

And the reg that tells you not to?

Not saying you have to include it in the CPC size above the cable conductor CPC size but there is nothing stopping you using it ...... reg 543.2.1

 

[Engineer54]

If you have circuits run in metal trunking (with cpcs) you don't include the trunking when determining/recording the cpc size...

SWA sheath is no different if you are using a core as cpc

Why would anyone be bloody daft enough to include a CPC in earthed trunking containment system?? lol!!

 

[Badged01]

Why would anyone be bloody daft enough to include a CPC in earthed trunking

Strangely enough I have come across a few cases in the past where the 'electrican' was taught on his course that as good practise you should run a seperate CPC to the conduit/trunking ...... new type "apprentice" electrician not a short course!

 

[Hawkmoon]

Why would anyone be bloody daft enough to include a CPC in earthed trunking
?? lol!!

I agree but if you're carrying out EICRs then you will come across it - there have been instances in the past (80s ish) where it has been required for installations in military establishments (if I remember correctly).

 

[pepparz]

Why would anyone be bloody daft enough to include a CPC in earthed trunking containment system?? lol!!

Is that right eng, u should include a cpc if only for good working practice. What happens if the trunking continuity fails! We'll all be buggered if we scrimp on safety. Lol!!!

 

[Hawkmoon]

Is that right eng, u should include a cpc if only for good working practice. What happens if the trunking continuity fails! We'll all be buggered if we scrimp on safety. Lol!!!

But you could say the same about cpc cables...

The benefit to using trunking as cpc is the very favourable R2 values you achieve, to add cable cpcs is just a waste of time, money and the world's resources - don't you care about the environment??

 

[pepparz]

Haven't got time to answer that, got to go to market to buy a pig.

 

[Engineer54]

And the reg that tells you not to?

Not saying you have to include it in the CPC size above the cable conductor CPC size but there is nothing stopping you using it ...... reg 543.2.1

If you are still arguing that you can combine a copper CPC and a steel CPC to make up the required minimum CSA you are WRONG!! Which ever one you do choose, it must be capable of taking the full fault current on it's own, not as a combined entity. A fault will always choose the easiest route to earth, so it will be the copper conductor (with superior conductivity) that will take the hit in a combined copper/steel arrangement!!

 

[Engineer54]

Is that right eng, u should include a cpc if only for good working practice. What happens if the trunking continuity fails! We'll all be buggered if we scrimp on safety. Lol!!!

What would you know about ''Good Working Practice''?? lol!!

 

[Engineer54]

But you could say the same about cpc cables...

The benefit to using trunking as cpc is the very favourable R2 values you achieve, to add cable cpcs is just a waste of time, money and the world's resources - don't you care about the environment??

Also, all you will achieve, is filling up the containment systems with pointless CPC's, that can't come close to matching that of the containment system they are enclosed in!!

 

[pepparz]

Ive been to conduit and trunking jobs with no cpc that suffered with poor zs, if there had been a cpc this wouldn't have happened. So you do it your way eng and I'll do it mine, ok.

 

[pepparz]

Please stop loling ur messages it doesn't make the offensive ones less offending. Saying "what would you know" is childish.

 

[Hawkmoon]

Also, all you will achieve, is filling up the containment systems with pointless CPC's, that can't come close to matching that of the containment system they are enclosed in!!

Looking at the part of my post you highlighted, then your reply, I am guessing you perhaps 'speed read' it lol

 

[Badged01]

If you are still arguing that you can combine a copper CPC and a steel CPC to make up the required minimum CSA you are WRONG!! Which ever one you do choose, it must be capable of taking the full fault current on it's own, not as a combined entity. A fault will always choose the easiest route to earth, so it will be the copper conductor (with superior conductivity) that will take the hit in a combined copper/steel arrangement!!

Have to disagree with you there.

A fault current will split itself between the two with a ratio depending on resistance of the conductors. It will not all just flow down the one conductor. The steel has an equivalent copper x-sectional area (less than copper because its resistance to current flow is higher) so provided the two together meet the minimum x-sectional area required for the fault you satisfy the requirement.

That is my understanding of why reg 543 permits the mixed use of conductors.

 

[pepparz]

What would you know about ''Good Working Practice''?? lol!!

Nice edit.

 

[Engineer54]

Ive been to conduit and trunking jobs with no cpc that suffered with poor zs, if there had been a cpc this wouldn't have happened. So you do it your way eng and I'll do it mine, ok.

You would also swear that black was white if it suited your purpose!! ...lol!!

Oh i most certainly will, and actually am. There is not a single ''SEPARATE CPC'' in any of our metal containment systems throughout this project (which is around 85% overall, metal containment systems), and our Zs values will be far superior than anything you install with your superfluous CPC's...

 

[Engineer54]

Looking at the part of my post you highlighted, then your reply, I am guessing you perhaps 'speed read' it lol

I was agreeing with you Hawkmoon, i just added the containment fill factor

 

[Engineer54]

Have to disagree with you there.

A fault current will split itself between the two with a ratio depending on resistance of the conductors. It will not all just flow down the one conductor. The steel has an equivalent copper x-sectional area (less than copper because its resistance to current flow is higher) so provided the two together meet the minimum x-sectional area required for the fault you satisfy the requirement.

That is my understanding of why reg 543 permits the mixed use of conductors.

Think about your electrical training, and you'll see that it doesn't and can't work like that!!

 

[telectrix]

so, just to play devil, isf as you say, eng., that the containment acting as cpc is superior to a copper cable, then by that you mean that the containment has a lower R2 value. therefore the containment will carry a larger proportion of the fault current than the copper cable.

 

[gazj82]

I will add to this the words of my old mentor, "If you need to put a CPC in steel conduit, then you can't do steel conduit properly!"

 

[Engineer54]

Please stop loling ur messages it doesn't make the offensive ones less offending. Saying "what would you know" is childish.

I speak as i find i'm afraid!!

What can i say, you just keep making me laugh with your childish antics!! lol!!

 

[pepparz]

In the past I have had to rewire factory lighting because the continity of conduit has failed and there's been no cpc so had to rewire in swa 2 week job on a cherry picker.if there had been a internal cpc this wouldn't have happened.

 

[pepparz]

I will add to this the words of my old mentor, "If you need to put a CPC in steel conduit, then you can't do steel conduit properly!"

I agree to a point but go back in 25 years and check zs!

 

[MDJ]

I have also been in factories where the trunking is so old and also hanging off the wall to consider using it as a CPC would have been ridiculous. That said a new metal containment system I agree should not need seperate CPCs.

 

[Engineer54]

so, just to play devil, isf as you say, eng., that the containment acting as cpc is superior to a copper cable, then by that you mean that the containment has a lower R2 value. therefore the containment will carry a larger proportion of the fault current than the copper cable.

Correct, if the metal containment meets the CSA requirement in it's own right and not as a combined figure with a copper conductor, then the metal containment will be the main CPC and therefore carry the larger proportion (if not virtually all) of the fault current

We are talking separate CPC's, so you will only be measuring ONE CPC per circuit, average is what between 1 mm to 2.5 mm for most final circuits, whereas even the smallest containment is many times that figure and even allowing for the 8X conductivity difference, will still outperform that of a single separate CPC...

Jesus, i'm getting really tired now, so i hope i'm still making sense, and not drifting off course...lol!!

 

[telectrix]

In the past I have had to rewire factory lighting because the continity of conduit has failed and there's been no cpc so had to rewire in swa 2 week job on a cherry picker.if there had been a internal cpc this wouldn't have happened.

your other options would have been:

1. fish a cpc through the conduit.

2. repair the conduit as cpc.

 

[Engineer54]

I agree to a point but go back in 25 years and check zs!

I have also been in factories where the trunking is so old and also hanging off the wall to consider using it as a CPC would have been ridiculous. That said a new metal containment system I agree should not need seperate CPCs.

Some of the companies factories where i did my training were nigh on 40 years old, as was the metal electrical containment systems. Hand on heart, in all the time i was with that company i never came across any containment trunking or conduit etc, that failed either Zs or high current continuity testing (old Clare conduit tester)!! And believe me, all building installations were tested on a regular ongoing rota, as were factory machinery and equipment...

Never been a more true statement than that Gaz made above....

"If you need to put a CPC in steel conduit, then you can't do steel conduit properly!"

 

[MDJ]

Some of the companies factories where i did my training were nigh on 40 years old, as was the metal electrical containment systems. Hand on heart, in all the time i was with that company i never came across any containment trunking or conduit etc, that failed either Zs or high current continuity testing (old Clare conduit tester)!! And believe me, all building installations were tested on a regular ongoing rota, as were factory machinery and equipment...

Never been a more true statement than that Gaz made above....

"If you need to put a CPC in steel conduit, then you can't do steel conduit properly!"

Yes I agree of course, we are told to install cpcs in steel conduit by engineers who work for the council mind, and although there is no need we do as we are told unfortunately.