Load calc for 3 phase supply??????

[mickytuff]

Hi all, i need the calculation applied to work out the current per phase for a 3 phase circuit.
Found a 9.1 kwatt heater on a 25A triple pole mcb (60898), so on single phase load divide by volts = amps, but this is not the case for 3 phase, any help much appreciated?????
Oh i found the heater on a hospital periodic, the cable used was a 4 core 2.5mm armoured...............

 

[ipf]

Power = root3 x V x I x cos phi. To be worked out..........

 

[johnboy6083]

Ib= Kw
1.732x400x pf

 

[plugsandsparks]

23A, will make the cable a little warm

 

[Guest123]

Out of interest, why was this flagged on an EICR???

 

[Amp David]

Interesting:Mr-T:

 

[Knobhead]

23A, will make the cable a little warm

Don't know where you got that from. I get 13.1A

 

[ackbarthestar]

I recon if you clamped a line you'd probably have about 12.5A....

Curious to know why this has been mentioned in a periodic ? damaged cable/breaker?

 

[plugsandsparks]

Don't know where you got that from. I get 13.1A

oops - not paying attention, glad you were...lol

 

[telectrix]

and on a heater, pf will be unity.

 

[Knobhead]

Just in fun (not a dig at you P&S) I worked out the PF that would be required to get 23A for 9.1KW @ 400V. It comes out at a staggering 0.375 lagging.

I’ve only ever seen figures like that on huge induction furnaces (they had massive capacitor banks linked to them). The cables had that much current flowing through them they had to have water pumped through to keep them cool.

As I said I did it for fun as I like playing around with maths.

 

[plugsandsparks]

Hey stop it now Tony, if you stick in 230V and use PF1 you get 23, my excuse was i was multi-tasking and just did it in my head but with wrong V .
:dunce2:

 

[Knobhead]

Have sent you a PM

 

[plugsandsparks]

replied - cheers

 

[mickytuff]

i was testing this circuit as part of a periodic on the hospital, saw the cable size feeding this heater rated at 9.1 Kwatt and looked a bit on the slim side copper size wise, but couldnt think of the calculation required, thanks for your help as alaways its good to discuss )))))