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Electricity - Brandon Brubaker


This will be where I will post electrical questions &/or problems with some answers and solutions.

Calculating “Amperage Draw”

Formula: Watts / Volts = Amps

Add up the total wattage on circuit under question. For example, said circuit has 9, 300watt incandescent light bulbs. That is a total of 2,700 watts being used. For standard calculations we’ll use the normal residential voltage of 120volts.

Now we can calculate our amperage. 2,700 / 120 = 22.5 At 22.5 amps we now know that we would overload a 20amp breaker.

Correction to breaker overload problem:

We will replace some of the incandescent bulbs with CFL’s (compact fluorescent lamps).
Lowes carries a 65-Watt Twist CFL that is a 300watt equivalent for around $16-$18.

Let’s update our formula now with the 9, 65watt CFL’s. (9 * 65 = 585watts)
585 / 120 = 4.88amps. Wow, that’s a serious drop in amp draw! Keep in mind, with electricity, you only pay for the amps being used not the voltage or service size.

Theoretically, with CFL’s we could now install 29, yes 29, lights on that one 20amp circuit. (29 * 65 = 1,885watts) 1,885 / 120 = 15.7 amps. That’s a total amp draw just under the maximum allowed (per NEC) at 80% the breaker capacity.

Disclaimer: I am a certified journeyman electrician but that does not legalize that what I say on this page is law. I will try to be as accurate as I can with my info. If you have major electrical questions and/or problems “CALL AN ELECTRICIAN”. You may also consult the “electricians bible”, the National Electric Code, aka NEC, for the specific lettering if the law. Don’t attempt to try any of these on your own without qualified supervision. I can not be held responsible for injury, damage to or loss of property as a result of your actions based on my information here. Thanks for visiting my website and reading this, Brandon Brubaker

PS. website with lighting calculation = Watt calculation table