3 Phase current usage

I need to estimate my factory current requirement as a result of moving to a new premises. The electricity bill states 30000kWhr/month and there is no instrumentation on the main switchboard apart from usage.

Can I estimate current requirements for the new factory like so


then I=P/V so I=187500/415=452 amp

so 150 amp/phase on average

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** What on earth use is it to know the AVERAGE current consumption ??

For all practical purposes (ie incoming service and breaker amp ratings ) you need to know the MAXIMUM current draw that occurs at any time and lasts for even a few seconds.

Better get yourself an AC clamp meter and do some testing with everything going at once.

.... Phil

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Phil Allison

"Phil Allison" wrote in news: snipped-for-privacy@mid.individual.net:


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Geoff C

If you are using the line to line voltage (415) you need to divide by sqrt(3) not 3 to get the phase current. You also need to take into account power factor, so the current will be much higher than 150A/phase.

You will actually need to do a proper maximum demand calculation, as described in AS3000. This will take all your loads and their diversity into account. Your energy supplier will probably require this information for the connection anyway.


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And if you have any significant electric drives with direct-on-line starting, remember that the starting current can be up to 6 times full load current. If you don't consider transients you could well end up with a system that trips out regularly.

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you can't do that without knowing the power factor.

yeah, but the electric company probably wants to know peak, and that that will determine the fuse they fit,

the best move is probably to go to the warehouse and grab one of their cheap clamp ammeters and measure the current yourself

or call your electrician and get him/her to do it,

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Reply to
Jasen Betts

"Jasen Betts"

** Thank GOD the sheep shagging Calvary has finally arrived !!

Better late than never......

... Phil

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Phil Allison

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