# calculate electrical draw

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Is there  a tool for calculating the total electrical draw on a server room
based on typical equipment usage.
Our electrician asked us what we needed?   I dont want to go short.

thanks

CR

## Re: calculate electrical draw

wrote:

What's "typical equipment usage"?  It'll depend on # of
servers, what they are exactly, what else is in the room

You might not even want everything on one circuit because if
there were a problem with one systemcausing a short, you
wouldn't want the power to everything shutting off.  A main
breaker for the room might be reasonable but still a further
breaker panel for individual circuits in that room is a good
idea - depending on scale of things.

Probably not a tool that will have all the variables you
need, because there are so many different possible system
and PSU configurations possible, let alone all the
non-server electrical items that may or may not be in a
server room like monitors or A/C and ventilation, heaters,
etc... but you can still do it by hand.

For each system, estimate the amount of current it uses,
divided by 0.7 (70%) (assuming PSU is about that efficient),
then divided by about 0.75 if PSU is passive PFC or by 0.9
if active PFC type.  Divide that total by the PSU input
voltage to arrive at current per system, then add up all the
individual currents per system to arrive at a total current
capability of the wiring over what the expected load is.

For example a server using 200W with an APFC PSU running on

200 / (0.7 * 0.9 * 110) = 2.9 amps

If you had 4 identical systems then (4 * 2.9) / 50% = 23A,
but of course you need the current consumption of all other
equipment as well.  Some things like a 60W light bulb are
easy to know, other things like and air conditioning unit
are not as easy as they have peak startup current, but a
large A/C unit or heater, anything with a medium or larger
moter, etc., ought to be on a separate circuit anyway and
the electrician should be able to figure out it's load on
his own since an A/C unit is a pretty common fixture.

## Re: calculate electrical draw

necessary tool - an ammeter.  If you're starting from scratch, owner's
manuals and spec sheets will give you a pretty good idea.  Your
electrician can measure some of the 'typical' equipment and multiply
from there.  HVAC company can tell you what their needs are; electrician
will know what the lighting requires.

UseNet wrote:

## Re: calculate electrical draw

something like this from maplin. A plug that displays how many watts
and other things are being used

http://www.maplin.co.uk/Module.aspx?ModuleNo=38343&doy=search

I think they are called
plug in electricity meter  <-- note, US-meter,  UK-metre.

I have used it to check that my 120W fanless power supply  is not
being overloaded.. And to measure how many watts were being used by
regular sized hard disk drives, and to see for myself the lesse watts
produced by lower power versions  - 2.5" HDDs and mini ide optical
drives.

If everything goes into one plug then just one.   Like if everything
goes into a multi adaptor plug which goes into one. Then one plug in
electricity metre is fine. Otherwise you may want a few and add up the
Watts.

Power is measured in watts.  The plug shows the watts.
P=IV,  power =current * voltage.    I think E=PT energy=power *
times , so power is joules per second.  An alternative unit for energy
is calories. So you can work out if your wife at work - your computer
- eats more than your wife.