32A ring - Electricians Forum | Electrical Forum | An electrical forum for electricians in the UK

Pat Tester · 13-03-2008

Can someone confirm longest legth for a ring main using 4mm singles P,N & E that can be run without exceeding max voltage drop or Ze ?

I have a length in mind, but don't wish to appear a twat, so will await some answers and then nod my head in agreement

Thanks in advance

Grae79 · 13-03-2008

i've got about 105m for max voltage drop of 9.2V; using 32A for Ib and clipped direct.

take it you mean Zs not Ze?

Pat Tester · 13-03-2008

Yes Zs, I must try harder, another self inflicted wound coming up as punishment

Grae79 · 13-03-2008

for 105m i get 1.36Ω for Zs...which is OVER the max. of 1.2Ω (1.15Ω for 17th). using a TN-C-S supply and a 32A type B 60898.

therefore the length of the circuit would need to be reduced to bring it into compliance with the max Zs. (would do the math but have had one of those days

)

Max circuit length to comply with both voltage drop and Zs is: 88.6m (83.4m for 17th)

MacSparky · 13-03-2008

Quote:

Originally Posted by Grae79

i've got about 105m for max voltage drop of 9.2V; using 32A for Ib and clipped direct.

Would you mind explaining your method for this Grae! only i am doing this at college at the moment and got a completely different figure.....

Grae79 · 13-03-2008

what'd u get? 26.1m? 52.3m? none of the above?

MacSparky · 13-03-2008

16.1 m based on table 6D2 osg methods 3&4 .....pat tester mentioned the 4mm in singles!

Grae79 · 13-03-2008

hope that helps.

13-03-2008

Quote:

Originally Posted by Grae79

for 105m i get 1.36Ω for Zs...which is under the max. of 1.5Ω. using a TN-C-S supply and a 32A type B 60898.

yep 1.36 for Zs. Tabulated value of 1.5 (1.44 in 17th edition)

so max value that you be allowed to read on the circuit is 1.12 ohms, and so the 1.36 would not comply. thats why we dont design to the maximum!

MacSparky · 14-03-2008

Thanks Grae.... very helpfull cheers