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Guest123
Well here is the table to tell you.
Discuss Can we use the armour of an SWA as the CPC??? in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net
Why is it that recently people seem to find using the SWA armour as bad practice or unacceptable. Seems to be serveral posts each week asking if its ok to do.
If running a cable outside, then IMO it is bad practice to use steel armouring as CPC. I have seen numerous times what happens to the armour when the sheath of the cable is damaged, and water starts to ingress. The amouring rots away.
However if you believe that there is no chance of the cable being damaged, or of water ingressing then go for it.
Lenny that is brilliant. I've been looking for something like this for ages, where did you get it.
Check out www.earthingnuts.co.uk
Lenny that is brilliant. I've been looking for something like this for ages, where did you get it.
In reply to Amp David, I think people who don't really know how to make glans off are the ones against it. Yes it's good practice to run a seperate earth but it's not always practical.
cheers, Ron
I think it's poor practice not to use the armour as the cpc when it is adequate to be used as such.
i've been trying to clear this up(for myself)
there is no reason not to parallel the armour and separate cpc is there?-for SP and 3P SWA on PME
thanks
The separate cpc must be sized as if it alone were to take the earth fault current, it is not permissible to add the CSA's of the two conductors together
yes-i know,but otherwise there is no reason why they can't be paralleled is there? on pme
If you are exporting PME earthing out to an outbuilding that HAS extraneous metalwork (=<22000ohms between metalwork and main earth terminal) and you are intending to use the armouring only as an earth conductor then for a:
TNCS system you will need 8 x the required equivalent in copper e.g 10.00 copper required = 80.00mm armouring.
TNS system you will need 4 x the required equivalent in copper.
If after installation it is found to require external CPC it should be a minimum of 25% csa of phase conductor.
"ECA guide to the wiring regs."
Hello everyone just been reading this thread and i find it very interesting......
I must admit i´m a little surprised that only one person has mentioned using the adiabitc equation for calculating the size of a cpc... It doesnt take long and i have found i have never needed to run a seperate cpc when making calculations for distribution cables. As a general rule though, if the cable is to be run outside or where other external influences are present then i always run a copper earth (not a seperate single core cable, an extra internal core) due to corrosion.
I undertook the 2391-20 design course where a lot of cable calculations were made and i always used the adiabatic, as by using the table at the start of this thread you will generally find that you run in an earth that frankly is oversized. If you want to price a job competitively (im talking larger commercial, industrial jobs) then using the adiabatic is alot more accurate, if were talking about large SWA cables from say 95mm upwards you will find a seperate earth costs a fair bit... 50mm BS6491x say 150m.... NOT CHEAP! a simple calc.. oh its not required so why bother....?
If anyone wants a bit more clarity on this like exactly how the calculation is made (can show examples) then let me know as i would be more than happy to help....!
cheers Dave
Show me the calcs Dave!
Seriously though lately i've been trying to gen up on using the adiabatic more lately as like you say the cost can differ massively on some jobs
Cheers
I'm supprised that no one has mentioned that running a separate CPC contravenes BS7671.
Specifically Regulation 521.5.2.
I'm supprised that no one has mentioned that running a separate CPC contravenes BS7671.
Specifically Regulation 521.5.2.
It doesn't just refer specifically to single core armoured cable.Where does that reg state that you can't run a separate cpc.
It's referring specifically to single core armoured cable in an ac circuit.
This Regulation is aimed at mitigating the effects that are caused by unwanted magnetic fields (eddy currents).I know IQ, as I said it's not clear. I just think that in this instance the IEE are not meaning the armoure as an enclosure as stated. Which is why they say single armoured cable & ferromagnetic enclosures. Otherwise they would not say single core armoured, as it would apply to all armoured.
(if that makes sense)
Reply to Can we use the armour of an SWA as the CPC??? in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net
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