>
> This looks like a microprocessor job then. I think that you have to 
> monitor both
> current and voltage on all three phases to work around the 'generator' 
> effect
> pointed out by someone else.

I have to monitor voltage on all phases, yes. But the current, my testys 
have indicated, can be monitored on just one phase. Any abnormality on any 
of the 3 phases is bound to result in the current deviating from the 
'normal'.


Plus (remote ?) sensing of some kind for water
> flow. This could be expensive. Also speaking of 'not too fast', the inrush
> current of the motor will be huge and probably read off scale for your 
> metering
> arrangement. It would probably be indistinguishable from a short circuit. 
> Also
> depending on whether the pump starts primed or not there could be a second
> current peak later when the pump gets primed after starting.

The water sensing part is already working satisfactorily in my earkier 
design, no issues there. And the inrush current is another reason I'm using 
a PIC instead of discrete circuitry; I can start sensing the current a few 
seconds after the motor has stabilised. Also, the pump has a valve that self 
primes the pump; just in case this valve malfunctions, the water sensor will 
detect it, and also the fact that the pump, if runnung dry, would draw a 
different amount of current than otherwise.

Regards,

Anand
 

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