Maximum cable length

[Disk]

Many thanks to all for very helpful advice, looks like I'll be lifting floorboards some time soon

 

[paulh53]

I would be grateful for some help re the following: Where the floor area served by a domestic power ring main falls within the 100sqm max, does the recommended max 60m cable length refer to the total cable ring length from and back to Fuse board or half of the overall length because of the effect of the ring?

I am having a similar problem on a house I'm rewiring
Ground floor ring circuit supplying 9 twin sockets,
Total floor area = 43m2
Total ring circuit length = 80m
All ground floors are concrete,

Would it be practicle/allowable to run a length of 4mm2 earth cable from the middle socket on the ring, Back to the main earth terminal in the consumer unit to reduce the earth loop impedance, And supply a "Clean Earth" at the socket for a computer etc
Basically it will be splitting the ring circuit earth into two earth rings

 

[il78]

I would say No.....is the Zs high? and would the CPC's be split (basically two rings?)

 

[paulh53]

I would say No.....is the Zs high? and would the CPC's be split (basically two rings?)

Zs = 0.8
(R1+R2) = 0.75
MCB = 32a Type B

CPCs will not be split,
The 4mm2 additional earth cable will simply provide a more direct path for fault currents, Rather than it having to flow around an 80m CPC,

 

[il78]

Is the circuit protected by an RCD?