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

[Tonkatoy27]

Well mate you have a 3 phase supply so you put the 2 heaters on a phase each so there is 8/9 amps there you have a couple of smallish 3 phase lathes/ drilling machines so what would you say 9/12 amps spread over your 3 phases that make 3/4 per phase so your worse case will be 15amps per phase.

The cabins are coming pre installed, I'm going to check with the supplier today but you can bet there is only one ring main. If 5 kids are all using heat guns at the time then thats 30 amps pulled through one phase staraight away. :0(
I'll get hold of the tech department and ask them for a list of machines that will be used at the same time to try and get an accurate Ib as unless I'm missing something, I'm still struggling to get my Voltdrop acceptable using 10 or even 16mm over 150m
Thanks for the help.e

The rest of the load will go on the other phase lights, smallish hand tools etc, former so you may have a load of 15/17 amps per phase.

You could get away with 10mm especially if your being generous and the run is less that the 150 you think it is.

The cabins are coming pre installed so I'll bet they only have 1 ring main. If 5 kids are using heat guns then that 30amps through one phase straight away. I'll call the cabin company today and find out.
I'll also get hold of technology and ask what will be used at the same time as if I calculate with 10 or even 16mm over 150m with 32a Ib I'm still struggling to get an acceptable vd. (unless I'm missing something)
Again, thanks for your help

 

[Tonkatoy27]

And the prat of the week award goes to......me. I was indeed missing something.

I was presuming my 3% vd for lighting was 3% of 230v as it was single phase equipment. With a bit of digging I am now wiser. I'm allowed 12v drop not 6.9v

'hangs head in shame'

 

[netblindpaul]

Tonkatoy,Don't forget that Technology classrooms must comply the CoP BS4163.This require further control considerations for the machinery.

 

[Skittles]

Well here is the table to tell you.

That chart is incorrect or at best misleading, for example it appears to state that the swa of a 1.5mm 2core swa cable is equivalent to a copper Cu conductor of 6.85mm ?

 

[johnboy6083]

That chart is incorrect or at best misleading, for example it appears to state that the swa of a 1.5mm 2core swa cable is equivalent to a copper Cu conductor of 6.85mm ?

Bear in mind that the table refers to the heating capacity of the material, and not it's current carrying capacity.So in other words will the material be able to take the fault current for 5 secs without rising to a temperature that would cause adverse effects to the cable.

 

[Skittles]

I'm sorry johnboy but I don't get it, it states a copper equivalent Cu, if this isn't meant to be the size of a copper conductor having the same conductance as the swa, then whats the point .
From that chart how would I determine if the swa armour was equivalent or better than a 10mm copper conductor , for the sake of complying with TNCS minimum main bond size ?

 

[stef]

If you take a 10 mm swa two core and take the swa off the cable and bundle it together you'll find that it will make up more than 10 mm so it would be OK to use as cpc. However, as a good code of practice use a separate copper conductor half the size ( in this case 6mm ) additional to the swa as cpc.

 

[Skittles]

If you take a 2 core SWA pvc cable the swa is equivalent to a 4.7mm copper conducter
a 2 core SWA XLPE cable the swa is equivalent to a 3mm copper conducter

Now either we are discussing different matters , or that Chart is seriously flawed ?

 

[Engineer54]

If you take a 10 mm swa two core and take the swa off the cable and bundle it together you'll find that it will make up more than 10 mm so it would be OK to use as cpc. However, as a good code of practice use a separate copper conductor half the size ( in this case 6mm ) additional to the swa as cpc.

Where do you get the idea that running a separate CPC for a more than adequately protected SWA cable is a ''good code of practice'' ?? If you think about it a little more, you may find that it could be just the opposite!!!

 

[Engineer54]

If you take a 2 core SWA pvc cable the swa is equivalent to a 4.7mm copper conducter
a 2 core SWA XLPE cable the swa is equivalent to a 3mm copper conducter

Now either we are discussing different matters , or that Chart is seriously flawed ?

Are you talking about the chart at the beginning of this thread, or the cart i posted (post 155) Which is a far better table to follow...

Anyway we are talking about using the SWA as the CPC, ...NOT using it as a bonding conductor...

 

[stef]

Brass gland and swa in moist atmosphere means contact corrosion ( for some reason it builds up) A crimp lug provides a more secure contact than a brass gland used on a Glasgow isolator. Less mistakes can be made. So, yes, I still think it is a good practise to do so.

 

[Engineer54]

Brass gland and swa in moist atmosphere means contact corrosion ( for some reason it builds up)

In this instance it would be even better practice to replace the shroud with an adhesive lined heat shrink tube!!!

 

[Chr!s]

I'm sorry johnboy but I don't get it, it states a copper equivalent Cu, if this isn't meant to be the size of a copper conductor having the same conductance as the swa, then whats the point .
From that chart how would I determine if the swa armour was equivalent or better than a 10mm copper conductor , for the sake of complying with TNCS minimum main bond size ?

Times by 8

 

[Engineer54]

I'm sorry johnboy but I don't get it, it states a copper equivalent Cu, if this isn't meant to be the size of a copper conductor having the same conductance as the swa, then whats the point .
From that chart how would I determine if the swa armour was equivalent or better than a 10mm copper conductor , for the sake of complying with TNCS minimum main bond size ?

Both the tables posted in this thread are relating to the armour CSA complying with suitability as a CPC. As i stated previously, the tables do not, and are not intended to be used to size for main bonding purposes. If you require your SWA cable to carry a bonding requirement,t then you'll need to use one of the cores (if 10mm or over) or run a separate bonding cable of the correct size, with the SWA....

In essence, don't confuse CPC's with Bonding, ...they are completely different animals, with completely different compliance requirements...

 

[Guest123]

From that chart how would I determine if the swa armour was equivalent or better than a 10mm copper conductor , for the sake of complying with TNCS minimum main bond size ?

You need to be careful when considering using the armour as a bonding conductor on a TN-C-S network due to the possibility of overheating of the live conductors under the (very rare admittedly) diverted neutral current situation arising from an open circuited neutral conductor on the supply system.