Current capacity in rings

[DT]

I picked up on a post from last year which indicates that:

"2.5 T+CPC cable can carry about 24 amps. In a ring, that effectively doubles it to 48 amps - it is protected by a 30Amp fuse/MCB, therefore safe"

but I can't find anything confirming this on the TLC site, so...
1. is this correct?
2. does this means the cable (not its protective MCB) could cope with an 11kW load ((48*240)(grouping / temp factors not yet included)
3. Assuming the above to be true, coud I safely use a 40A MCB?

All of the above is for planning purposes only, as I have a professional electrician lined up to do the work, but need to avoid going through the unit next door if at all possible

 

[dingbat]

I picked up on a post from last year which indicates that:

"2.5 T+CPC cable can carry about 24 amps. In a ring, that effectively doubles it to 48 amps - it is protected by a 30Amp fuse/MCB, therefore safe"

but I can't find anything confirming this on the TLC site, so...
1. is this correct?

Current-carrying capacity depends on several factors. In domestic situations it generally varies between 18 and 27 amps.

2. does this means the cable (not its protective MCB) could cope with an 11kW load ((48*240)(grouping / temp factors not yet included)

No. First, you have to use 230V, not 240, but in any case, a load of that size should be on its own radial circuit.

3. Assuming the above to be true, could I safely use a 40A MCB?

No again. Ring circuits are used where the actual use of the circuit cannot be predicted accurately. They are designed for most appliances to be plugged in and the plug/socket arrangements are designed for a maximum 13A load (And that's even for a twin socket). The ring gives two main benefits: One is the increase in (total) load that may be connected at one time. The other is that sharing the current across two conductors helps to prevent overloading any one section of cable. (In a radial socket circuit the cable nearest the origin will always carry the greatest load)

And, about that 40A breaker - if the ring is broken in any single place you don't lose any sockets, but you do now have two 2.5 sq mm radials with inadequate overcurrent protection.

All of the above is for planning purposes only, as I have a professional electrician lined up to do the work, but need to avoid going through the unit next door if at all possible

Ask the spark. This doesn't sound like a domestic situation. Anyway, if that's a single high load device it should be on its own circuit. If that's what you reckon you'll be putting in total on a socket ring you will probably need two rings, or thicker cable.

 

[DT]

Thanks Dingbat.

I was trying to avoid it, but it sounds like we'll have to go through the unit next door with swa after all, rather than through the existing channeling in the joists.

PS, it's a hair salon, so quite a bit of fluctuation on the circuit use, but you've answered my biggest query.

DT

 

[dingbat]

From what you've added I would think the most appropriate arangement would be a sub-main from the supply origin to a consumer unit in the actual salon, from where you can add as many circuits as you need. That way, the local isolation and circuit protection is in the most convenient place and you have the flexibility for future work without ever having to disturb the intermediate unit again.

 

[DT]

that was my original idea ( it stops the wife having to go outside to re-set the trips in the dark ), but the tennants next door asked if it could be avoided. unfortunaltely, as the landlord said no to an external routing......

 

[dw3101]

cellar? under the floor instead?