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Re: computing electrical loads

To: shop-talk@Autox.Team.Net
Subject: Re: computing electrical loads
From: "John T. Blair" <>
Date: Mon, 15 Nov 2004 17:42:30 -0500
At 04:50 PM 11/15/2004 -0500, Mark Andy wrote:

>Anyone know of a chart or whatnot that lists common amperage loads for 
>things like:
>100W lightbulb
>3/4 hp garage door opener
>small 110V hot tub heater/pump
>Etc. etc. etc.?

>Just trying to see if I'm going a little insane on the number of circuits 
>on this "rewire the garage" project...


Just the easy way, read the lables.  Then do a little math:

Power = Voltage * Current
Watts =  volts  *  amps

So for your 100W light bulb assuming it's on a 110 circuit

   P = E * I   -->  using some algebra  I = P / E  or  I = 100W / 110V
   or  approximately  1amp per 100 W bulb.

For HorsePower  1hp = 750W  approximately
  so 3/4 hp = 3/4 * 750 = 562.5 watts   ignoring start up surge current
  now converting 562 watts assuming it on a 110V circuit
  I = P / E  or  562 / 110  or roughly  5 amps

Got no idea on the hot tub unless there's a lable on it stating the watts
it uses.

Again, this ignores start up currents which can go a lot higher.  The secret
is to wire the garage so that you don't put a load on every outlet all the
time.  For instance you won't run a bench grinder at the same time you're
running the table saw.  This is how the wire a house and have 20 circuits.
If you were to turn on everything on a given circuit, you'd trip the circuit

Hope this helps


John T. Blair  WA4OHZ     email:
Va. Beach, Va             (eBay id: zebra48-1)
Phone:  (757) 495-8229

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