Circuit Question

[IQ Electrical]

As long as the CPD is selected to suit the smallest CSA then there is no reason why CSA cannot be reduced as a circuit progresses.

A common example is factory lighting, running say a 6mm leg from the DB to the first point to combat volt drop, perhaps reducing to 4mm or 2.5mm eventually. In this case, the current carrying capacity of the lowest CSA would be taken into account.

 

[nickblake]

ive done a ring in 4 mm because of the length of the cable runs the calculated Zs was going to be higher than permitted

 

[Paul.M]

As long as the CPD is selected to suit the smallest CSA then there is no reason why CSA cannot be reduced as a circuit progresses.

Could not have said it better. There is no reason why any circuit could not be in different sizes along its length and long as the smallest csa can carry the load, eg 25mm to a 16mm to a 1.5mm to a 50w gu10. This is what happens from a sub station to your house. The question is about protection of the circuit. Select the correct rated fuse for the smallest csa and your ok. Closest I can find in the brb is 133.2.2 page 19 but even that doesn't give us a defined answer. Good point about putting too much stress on terminals. Sounds like this is domestic, in your case I would change it all to 2.5 (ring) or all to 6mm radial to stop any confusion for the next sparky.

 

[ldworks]

ok heres the deal, the upstaires ring comes from the board to 1st floor(all in 2.5mm cable) does upstaires ring and part of the leg comes down to the conservetory and does 4 double sockets there which is comprised of 2.5mm cable then the next leg to next socket is 6mm and then next leg from that socket is 2.5mm and random cable used within conservatory. Me personally as an electrician have never come across this way to wire so im advising the client to have all 6mm replace with 2.5mm in the conservatory then back to board. the ring is on a 32A Rcd. ive been advised maybe to put the conservatory on its own ring then at least everything ive done will be up to spec and at least be right cable etc. Such a strange problem just not sure which way to go for the best of the clients house.

 

[olly w]

If all the readings are ok (r1,r2, insulation resistance, polarity, earth fault loop impedance) then I would leave it as it is and note it on the certificate.

You didn't say what you were doing to the installation?