Can we use the armour of an SWA as the CPC???

[Jeffmo65]

As a respected member i will bow to your superior knowledge , as it happens our qualifying supervisor at the time then held the nic mans words to be good and all installs from then were done with compliance with his argument . i was not trying to say that this was wrong or wright , but just passing comment on my personal experience . As it happens i very rarely install a seperate CPC until as you say we get to the larger cables in which my AMTECH program works it all out quite nicely for me .

 

[Deleted member 26818]

Up untill this amendment, it was in actual fact a non-compliance to run a separate CPC with SWA.
They had to amend 521.5.2 (now 521.5.1), to allow it.

 

[Jeffmo65]

My appreciation for the quote of regs , however for at least the last 5 years on most of the large coporate installs i have been attached to the majority of SWA have had external seperate CPC's ran with them , so i assume not many people either do not read or understand the regs with or without new ammendments . not complaining just commenting

 

[Engineer54]

My appreciation for the quote of regs , however for at least the last 5 years on most of the large coporate installs i have been attached to the majority of SWA have had external seperate CPC's ran with them , so i assume not many people either do not read or understand the regs with or without new ammendments . not complaining just commenting

Don't doubt it, as it was the only way to provide a CPC for a SWA when the wire armouring couldn't comply as the CPC!! lol!!

But it just shows you how the NICEIC likes to make-up it's own regulations, and often getting things totally wrong in the process!! lol!!

 

[pactrol]

Hi Hawk81

yes I come across that quite a lot myself & whats the betting that they have used Bw glands instead of weatherproof cw type

 

[ojchurch]

A guy I worked with last year reckoned he'd read an article about some studies done on the actual routes taken by the fault current for SWA distribution cables with & without additional cpcs. I never managed to get them off him before he left the job. He thought it said that very little current travelled through a separate cpc irrespective of this or the SWA csa. He thought it would alter the regs in the near future. Unfortunately I didn't get the publication either. Anybody hear of this? Cheers.

 

[pactrol]

Hi ojchurch

yes thats right it was a study done by the ERA where it was shown that the fault current is shared fairly equal between the swa & seperate cpc therfore negating the need for the seperate cpc to be fully rated for the fault current the same report also shows that the swa is suitable as the cpc in nearly all cases
I will see if I can find it but try googling ERA cable study.

 

[ojchurch]

Cheers for that, just tried a couple of combinations in google and got nothing.

Was on a job briefly recently where they had what seemed to be under sized additional/external cpcs with SWA cables. Didn't manage to get hold of enough info to do the calcs myself at the time before I left. I think one example was 25mm2 4c feeding a final DB, they added a 2.5mm2 cpc. The only comment I made without all of the info was that it needed to be 4mm2 minimum without mechanical protection. I always used to be under the impression that an additional cpc needed to be sized to take the full fault current. I'm thinking maybe this study has filtered down to the design companies. Although how they get round non compliance with the regs I don't know?

 

[Silly Sausage]

Hi ojchurch

yes thats right it was a study done by the ERA where it was shown that the fault current is shared fairly equal between the swa & seperate cpc therfore negating the need for the seperate cpc to be fully rated for the fault current the same report also shows that the swa is suitable as the cpc in nearly all cases
I will see if I can find it but try googling ERA cable study.

Is this it...?
http://www.wiley.com/legacy/wileychi/eca_wiringregulations/supp/Appendix_16.pdf

 

[ojchurch]

Looks good, I'll have a read later cheers.

(What exciting lives we lead!)

 

[pactrol]

Is this it...?
http://www.wiley.com/legacy/wileychi...ppendix_16.pdf

Yes thats the boy

Pity that The writers of BS7671 havent read it

 

[theroadblock]

haha this old chestnut! many a time ive been preached to by other electricians that you are to run a seperate earth alongside your swa and not just use the armouring, hell it states in the regs that the armouring on swa is adequate means of earthing! from what i have read so far in various places the idea of running a seperate earth came from the older types of SWA cable now not in production, where over a certain size of csa the armouring was not adequate means of earthing, but nowadays i believe that this has been resolved ( evidently from the 17th's section on earthing ).

 

[Des 56]

http://www.electriciansforums.net/e...ulations/23288-can-we-use-armour-swa-cpc.html

 

[Silly Sausage]

http://www.electriciansforums.net/e...ulations/23288-can-we-use-armour-swa-cpc.html

I suspect he already knows that. T & E54 might have a new brother here

 

[adiewadie247]

Surely running a separate CPC on the outside runs into all the same (and probably worse) problems that arise when using the armour. Given that the cost differential between 4-core/3-core/2-core is small (compared to the total cost of the job) why not just use an extra core for the CPC? As the CPC is so important it needs to benefit from the protection that the PVC/armour provides...