Running 3 phase 780s on single phase power (was RE: hams on classiccmp)
roger.holmes at microspot.co.uk
Mon Jan 19 13:17:07 CST 2009
>> Ian King (IanK at vulcan.com) wrote:
>> We *are* running the machine off three separate 110V single-phase
>> apparently you missed that part.
> People need to understand the danger in this - in any multiphase
> system, the neutral current is the DIFFERENCE of the current in the
> individual phases. If the load is perfectly balanced, then the
> current will be zero.
> But, if you run the same load from three separate single phase
> and (worst case) the three circuits are all the same phase, then the
> current will be the SUM of all three phase currents. That's 3 times
> what it
> would be otherwise and runs a serious danger of melting the neutral
> starting a fire.
I agree with all but the last bit, because if he's running it from
three separate supplies, surely he will have three neutral conductors,
so no problem.
(Who has a 440v three phase computer drawing 13kVA which has three
phase bridge rectifiers to generate fairly ripple free DC)
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