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!!