Long swa run to campsite 2c or 3c???......,

[bigspark17]

have a job to price up, its a camping site temp supply with caterers & mobile shower blocks in remote field on a mountain.

60A supply required
180M (ish) SWA required
Tncs supply in farm house

Question is should i run 3c or 2c. As i will be TT the temp install at the campsite.
Is this table correct below stating that copper equivalant of 35mm 2c swa is 29.2mm? If so this will help with disconection times & price of cable.. any help apprechiated

 

[telectrix]

the steel armour will be OK as a cpc. it's only acting for the SWA. do your adiabatic. is VD OK?

 

[westward10]

Why the third core if you are tea teaing it it serves no purpose.

 

[cprfenom]

Will need to check VD over that length too. As its a TT running a third core for earth is pointless and not allowed if I recall for anything over 6mm?

 

[cprfenom]

People beat me to it lol

 

[bigspark17]

the steel armour will be OK as a cpc. it's only acting for the SWA. do your adiabatic. is VD OK?

Why the third core if you are tea teaing it it serves no purpose.

Meeting disconnection times of the bs88 63A fuse that going to be in the farm house..

it does seem pointless running a very expensive 3rd core thats not even going to be used.. can any1 confirm that the copper equivelant of 2c 35mm is 29.2 & 2c 50mm is 32.8?

VD for the 35mm is getting me just over 150M & 50mm would be need over that up to 200M

 

[westward10]

Copper equivalent in terms of conductivity the armour is less than 10.0.

 

[bigspark17]

Copper equivalent in terms of conductivity the armour is less than 10.0.

I would agree,, but where did you get this info?

 

[westward10]

I would agree,, but where did you get this info?

In my head but it is in GN8 which I don't have to hand to be exact.

 

[dmxtothemax]

Boy wouldn't want your cable bill for that job !

 

[Richard Burns]

it does seem pointless running a very expensive 3rd core that's not even going to be used.. can anyone confirm that the copper equivalent of 2c 35mm is 29.2 & 2c 50mm is 32.8?

Copper equivalent for cpc purposes is 51/115 (k values) x actual steel csa of 70°C SWA, which is 60mm² for 35mm² and 68mm² for 50mm², so 26.6mm² and 30.2mm² respectively.
Values in appendix A and B of GN8.
I think, it is not going to matter the cable armour can be used as a cpc at those sizes.
No need for a third core on the cable.

 

[bigspark17]

Copper equivalent for cpc purposes is 51/115 (k values) x actual steel csa of 70°C SWA, which is 60mm² for 35mm² and 68mm² for 50mm², so 26.6mm² and 30.2mm² respectively.
Values in appendix A and B of GN8.
I think, it is not going to matter the cable armour can be used as a cpc at those sizes.
No need for a third core on the cable.

Thanks for your response. They are the equivalent figures i found from swa data charts. That means i can now work out my zs to check aggainst my disconnection times.

Boy wouldn't want your cable bill for that job !

No neither will the customer haha

 

[Simlec]

Have you got a site ze reading? as this could be the difference between 70mm and 95mm as I dont think you will get disconnection times for 50mm

 

[bigspark17]

0.35 tncs bang on.. disconnection time for 35mm around 150M.. 200M for 50mm

 

[Simlec]

humm 0.35 is poor & high! I get 70mm by the skin of my teeth on cablecalc but 95mm on other software so I would be looking at 95mm. I would also be looking at trying to get that ze down.
You did say BS88 63a with 60a load and 180m

 

[bigspark17]

humm 0.35 is poor & high! I get 70mm by the skin of my teeth on cablecalc but 95mm on other software so I would be looking at 95mm. I would also be looking at trying to get that ze down.
You did say BS88 63a with 60a load and 180m

How would you get the ze down? Its on top of a mountain. Appreachiate your input..

 

[mattg4321]

Going to be fun running that cable in!

 

[shaun1]

Out of interest, do you need to take in to account the Zdb(?) value at the remote DB, via the TT earth, to confirm this also meets disconection times for the protective device at the supply end. As a live to earth fault in the switchgear would return via the TT earth? Or have I misunderstood somewhere.

 

[bigspark17]

Out of interest, do you need to take in to account the Zdb(?) value at the remote DB, via the TT earth, to confirm this also meets disconection times for the protective device at the supply end. As a live to earth fault in the switchgear would return via the TT earth? Or have I misunderstood somewhere.

Yes the supply to the isolator will need to meet disc time of fuse at supply end even though the cpc will be isolated before entering the time delayed main rcd switch.,
If the zs is slightly high i could always rcd the sub at source but not good practice..