# 3 Phase current usage

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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

30000/(20*8)18%7.5kW

then I=P/V so I18%7500/41545%2 amp

so 150 amp/phase on average

Re: 3 Phase current usage

"Warren"

** 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

Re: 3 Phase current usage

OK.

Re: 3 Phase current usage

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.

David

Re: 3 Phase current usage

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.

Re: 3 Phase current usage

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,

Re: 3 Phase current usage

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

Better late than never......

...   Phil