On Apr 13, 8:43*pm, John Williamson
wrote:
newshound wrote:

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Cheers
Adam- Hide quoted text -

- Show quoted text -

If each phase was taking 100Amps there would be no neutral current at
all.
A neutral current only appears when the phase currents are unbalanced..

Not if the OP is only using 230V appliances.

Please pay attention to what is written.

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Adam

I really hesitate to differ, but are you saying that, if each 230 V
appliance was taking 100A, there would be 300A in the neutral?

I calculate it that if you have all three phases drawing 100A, the
neutral would be carrying only stray currents, but if only one phase was
loaded, the neutral current would be equal to the load current. With two
running, it's something on the order of 1/ (square root of 2) multiplied
by the combined load current, so in this case about 141A maximum with
full load on two phases. With three phases running in balance, it's
close to zero. It's a vector sum, and the worst case is with two phases
running at full load, and the other one drawing zero load. For other
combinations, it depends on the loads on each phase.

I think you'll find that with resistive loads (which would seem to be
what we'd have with fryers - most of the power into heating elements)
the vector sum for two phases drawing 100 Amps each will still be 100A
- which is why when you add the third phase it just cancels that out
to give no current in the supply neutral.
What Adam may have been thinking of is that in some circumstances the
power factors on the three phases could be diffferent when supplying
single phase loads, and that could certainly result in more than 100A
neutral current if the difference was extreme enough. A piece of three
phase kit would normally be expected to have similar power factor on
all three phases, so the neutral currents would balance.

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Mike