Generator load during "normal use"

BobRip · Dec 5, 2011

A couple of years ago during a power outage I was curious as to how much current was being put out by the generator. No big loads such as the well or hot water heater were running and most of my lighting is florescent. So, one leg was 4 amps and one was 1 amp. This kinda surprised me in that is was so low. Has anyone else measured their loads?

hr3 · Dec 5, 2011

I test every one I install and have never seen over 25a per leg.. Yours is about normal..

BobRip · Dec 5, 2011

I made some cables to use with my clamp on amp meter for the 120 and 240 volt generators

Craig Clayton · Dec 5, 2011

For you to have different currents on different legs you must of had 2 cords plugged into the generator ( or 120/240 plug or gentran type of panel ).
Here are some very simple electrical figures
At 120 Volts AC and drawing 10 Amps = 1200 Watts that is about what a household kitchen toaster draws.
At 120 Volts AC and drawing 4 amps = 480 Watts that is about what a Tube TV and several 60 W bulbs draw.
At 120 Volts AC and drawing 1 amp = 120 watt light bulb
At 120 Volts AC and drawing 0.5 amp = 60 Watt light bulb

To figure anything else out Volts X Amps = Watts ( rearrange the figures to cal the unknown).
On a single extension cord at 120 Volts AC if 1 amp goes out the black wire to the light bulb and makes it light and 1 amp returns back the white wire. There should be no current on the green. ( this happens at a very high speed ).
A typical home generator at 3000 watts continous and 4000 watts inrush, means it can operate (2) 1200 watt toasters at the same time per circuit ie. (2)15 amp breakers
The 4000 watts would be a heavy starting motor ie. heavy air compressors at 240 Volts but the load must drop below 3000 running or the generator will be overloaded.
This heavy starting does need a cooling period when running say once every 15 minutes.

I kept the above figures easy and I did not start splitting the decimals.

Craig Clayton

BobRip · Dec 5, 2011

Craig, thanks for your analysis. I thought my loads would be higher. What bothers me is that we have to size generators to start the motor loads because of the huge starting currents of these motors. Then most of the time a much smaller generator would do. I think it would be interesting for people to post what they see for actual loads to help others size generators.

grsthegreat · Dec 5, 2011

Yup... its the motor starting loads that are the killers to these generators. Even alot of the really large gen sets i set up on community well systems require a soft start (frequency drive) to gently ramp up the motor.. otherwise the generator trips off.

I have a 4,500 +/- SF house on a 10K generator. All major appliances are gas. My generator panel has twin guages showing loads on each leg. There never more than 25% of peak. And im running all lights, 1/2 of kitchen, freezer, built in refrigerator, furnace (110 fan), twin water heaters (again just exhause 110 v fans and circ pump), tv, bedrooms, bathrooms and garage and garage door openers. Oh...and christmas lights (to piss off the neighbors).

I prob could get along fine with a 5kw system. The a/c is a heat pump, so thats out no mater which system i use, but im in N. Idaho so no issue. Heat has a gas emergency backup.

Larry Caldwell · Dec 5, 2011

The UPS on my computer reports 148 watts to run my large LCD monitor and an i7 cpu with a high end graphic card.

My high def front projector TV, satellite dish and THX certified sound system with separately powered subwoofer draws about 500 watts during normal viewing, though if I ran the projector bulb at full power it would draw 500 watts all by itself and the sound system can use 2500 watts at full power. I'm not filling an auditorium, just my living room.

My little 1000 watt camping generator provides plenty of power 90% of the time, and it will run 4.5 hours on a gallon of gas at 50% load. I only crank up the "big" generator when I want to run the water heater and well pump.