regs clarification

[jim23]

would appreciate if somebody would clarify this for me please. use this as an example;- page 226 regs, where it says 16mm cable rated at 77 amps for ''1 three or four core cable, 3 phase a.c''

is this 77 amps for the whole cable or 77 amps per phase, i.e 241 amps total that the cable can take( presuming balanced load).

cheers.

 

[Adam_151]

Each conductor can carry 77 Amps ... to quote figures any other way would be nonsensical

 

[jim23]

ok cheers for that.

 

[jim23]

so a 3 phase appliance taking 150 amps could be wired using swa 4 core 16mm? thats 50 amps per phase and you could protect each phase with a 63 amp bs88?

 

[RF Lighting]

Yep.

(assuming there are no derating factors etc)

 

[Spark123]

so a 3 phase appliance taking 150 amps could be wired using swa 4 core 16mm? thats 50 amps per phase and you could protect each phase with a 63 amp bs88?

And if it were ballanced eg a motor a 3core would surfice

 

[Lectrician]

so a 3 phase appliance taking 150 amps could be wired using swa 4 core 16mm? thats 50 amps per phase and you could protect each phase with a 63 amp bs88?

And if it were ballanced eg a motor a 3core would surfice

But you would still use a 4 core, as you never know what might go there next

 

[Spark123]

Only on distribution, if it were from a MCC to a motor then there is really no need. I have also known on some distribution systems there to be 415-240v or 415-110v transformers on the end of a long 3phase 3core supply to power ancillaries as the only reasonable explination I can think of it is cheaper than buying a 4core.

 

[Pensdown]

so a 3 phase appliance taking 150 amps could be wired using swa 4 core 16mm? thats 50 amps per phase and you could protect each phase with a 63 amp bs88?

If it's a 3 phase only appliance then the quoted current is normally per phase. You would normally only divide by 3 if the total load is quoted in kW's. If it's quoted in kVA then you use root 3, power factor etc. (I bet someone knows the asci code for root 3 )

 

[Lectrician]

I have also known on some distribution systems there to be 415-240v or 415-110v transformers on the end of a long 3phase 3core supply to power ancillaries as the only reasonable explination I can think of it is cheaper than buying a 4core.

Or that some fool originally installed a long run of 3 core, and they then needed a neutral

 

[Spark123]

Nope, the only thing running on 240v is a few sodium lights, 110v for control and the 3phase runs a few whopping great big motors.