Earth Size etc?

[i=p/u]

Doesnt show 5c.. My mistake. Confusing you.

 

[i=p/u]

But if that was results for 5c and wasnt using armour as cpc, could i use as bonding conductor and would i use 10mm fly lead on tn-c-s from bolt/gland

 

[ste77]

No probs. I dont see why not, ive never seen it stated anywhere that an armour cant be used as a main bonding conductor providing the connections are sound and id probably label it so when its periodic is due its not flagged up. As ive said in a previous post its not the way id do it but i have seen it done that way before.

 

[ste77]

Depends where your main earth terminal is, if its within say an mccb panel id use whatever size link the bonding conductor was that was required, plus you'd have the metallic frame of the db.

 

[i=p/u]

So could it be used as earthing conductor and binding conductor again 16mm earth and 10mm bonding = 26mm where armour is 31.9mm

 

[i=p/u]

Yeah but normally they normally 2.5 or 4mm from frame to earth bar

depends where your main earth terminal is, if its within say an mccb panel id use whatever size link the bonding conductor was that was required, plus you'd have the metallic frame of the db.

 

[ste77]

So could it be used as earthing conductor and binding conductor again 16mm earth and 10mm bonding = 26mm where armour is 31.9mm

I dont see why not. is it just to keep costs down?

 

[i=p/u]

Curiosity , lol exciting ain't i

 

[Engineer54]

Hi Guys
Thanks for all your interest. First, cost is a factor on this job (isn't it always!) Client thought he could just have a 1ph supply and a domestic CU. lol. Requirements have changed today (again)!
Yep, you're right! You've clarified my muddled thinking! Best is a 3ph board, 4 core SWA using the armour as earth. I can just about balance demand across all phases. Max 35 amps/ph so may even drop to 6sqmm ( with 40 Amp fuses in the switchfuse) after checking volt drop calc. Whether 10sqmm or 6sqmm I think I'm correct in saying that the Cu equivalent csa of the armour on both sizes is 13.5 sqmm and 11.5 sqmm respectively so no seperate earth required.
Re bonding - none required at the mo. - no extraneous services/steel (water only in plastic).
I assume that if bonding is required, I have to take a seperate 10sqmm conductor all the way back to main earth terminal in the meter cupboard?

Cheers
Pete

As this is a PME installation, it's the bonding side of things that complicate things when extraneous services etc are involved!! As there aren't any in this case, continue as if this is a TN-S supply!! The armour of the SWA cable is more than suitable for the CPC and probably the earthing arrangement at the DB, but as always this should be confirmed by calculation/measurement etc!!


One thing to point out on this thread, Bonding requirements need to be related back to copper equivalents when talking about using any other type of metal conductor. They can't be mixed either, so you can't use the SWA and a smaller copper conductor to comply with minimum mm CSA.... Either the copper conductor needs to be of sufficient CSA to carry the full fault current, or the armouring needs to be of a sufficient CSA copper equivalent...

 

[ste77]

As this is a PME installation, it's the bonding side of things that complicate things when extraneous services etc are involved!! As there aren't any in this case, continue as if this is a TN-S supply!! The armour of the SWA cable is more than suitable for the CPC and probably the earthing arrangement at the DB, but as always this should be confirmed by calculation/measurement etc!!


One thing to point out on this thread, Bonding requirements need to be related back to copper equivalents when talking about using any other type of metal conductor. They can't be mixed either, so you can't use the SWA and a smaller copper conductor to comply with minimum mm CSA.... Either the copper conductor needs to be of sufficient CSA to carry the full fault current, or the armouring needs to be of a sufficient CSA copper equivalent...

Whereabouts does it state that? just for my future reference, never been able to put my finger on it. Cheers

 

[Guitarist]

Whereabouts does it state that? just for my future reference, never been able to put my finger on it. Cheers

Look in GN8 at 9.3.4

 

[Engineer54]

Resistivity factors should be telling you this, without needing it to be laid out in black and white!! Steel has a far higher resistance value than that of copper, so mixing CSA's of the two metals is a complete NO, NO!! That's not to say that you don't earth the SWA, just don't use it as a make-up for bonding purposes, it'll be acting purely as a CPC!!