Just trying to calculate maximum lengths of cable for standard circuits (Just CPD)
OSG tells us...
A1 Ring - 100m2 A3 Radial 50m2
Now I don't find m2 a useful number, as it doesn't tell us the conductor length. Its not necessarily the run of the cable.
So I thought I would use volt drop to find the maximum length so
VD = Mv/A/m /1000
So need the design current. Not sure what this is on circuits which have fluctuating loads
Maximum loads assumed per circuit (OSG)
Lighting - 6A Load 5A
Ring final - 32A - Load 26A
Radial - 20A - Load - 16A
So Ib could be this assumed maximum load? and not the rating of the protective device?
I get that, with the RF circuit Assuming 2.5mm flat cable has a CCC of 27A protected by a 32A MCB.
But Radial? why not 20 A
If I calculate at 20A for a 2.5mm radial protected by a 20A MCB
and transpose the formula.
So maximum volt drop 11.5v
11.5 / 18x20 x 1000 =31.9 m
and 16A
11.5 / 18 x 16 x 1000 = 39.9m
So which value do we use for radial and ring final Ib ?
and the maximum length of a radial circuit is at most 39.9 meters or 31.9 m
Which is not that long is it really if you consider the circuit starting in CU down stairs, and then upstairs and around a couple of rooms. 31 m can soon be used up?
So as we move away from rings. If you consider a 'standard' three bed house, and wanted to wire in radials. I understand this is difficult to say, just very basic minimum design basics. (And before correction factor are used)
I would think you would need a radial for downstairs sockets (Living room - dining room) (Mainly low demand TV, lamps, media...) two radials for upstairs longer length (More use of power (Hair dryers, tongs etc...) (Kitchen sockets on 4mm) Appliances on own radials.
Would you consider one 20A radial adequate for the two downstairs rooms. I can't really see what large loads would be plugged in, unless the central heating failed and you needed to use electrics heating for a short while.
Appreciate your thoughts
Thanks
OSG tells us...
A1 Ring - 100m2 A3 Radial 50m2
Now I don't find m2 a useful number, as it doesn't tell us the conductor length. Its not necessarily the run of the cable.
So I thought I would use volt drop to find the maximum length so
VD = Mv/A/m /1000
So need the design current. Not sure what this is on circuits which have fluctuating loads
Maximum loads assumed per circuit (OSG)
Lighting - 6A Load 5A
Ring final - 32A - Load 26A
Radial - 20A - Load - 16A
So Ib could be this assumed maximum load? and not the rating of the protective device?
I get that, with the RF circuit Assuming 2.5mm flat cable has a CCC of 27A protected by a 32A MCB.
But Radial? why not 20 A
If I calculate at 20A for a 2.5mm radial protected by a 20A MCB
and transpose the formula.
So maximum volt drop 11.5v
11.5 / 18x20 x 1000 =31.9 m
and 16A
11.5 / 18 x 16 x 1000 = 39.9m
So which value do we use for radial and ring final Ib ?
and the maximum length of a radial circuit is at most 39.9 meters or 31.9 m
Which is not that long is it really if you consider the circuit starting in CU down stairs, and then upstairs and around a couple of rooms. 31 m can soon be used up?
So as we move away from rings. If you consider a 'standard' three bed house, and wanted to wire in radials. I understand this is difficult to say, just very basic minimum design basics. (And before correction factor are used)
I would think you would need a radial for downstairs sockets (Living room - dining room) (Mainly low demand TV, lamps, media...) two radials for upstairs longer length (More use of power (Hair dryers, tongs etc...) (Kitchen sockets on 4mm) Appliances on own radials.
Would you consider one 20A radial adequate for the two downstairs rooms. I can't really see what large loads would be plugged in, unless the central heating failed and you needed to use electrics heating for a short while.
Appreciate your thoughts
Thanks