# How many watts equal 1 amp?

Asked Oct 1, 2008, 05:10 PM — 14 Answers
I am trying to figure how many watts a 20 amp circuit can carry.

 Xrayman Posts: 1,176, Reputation: 1007 Ultra Member #2 Oct 1, 2008, 05:37 PM

use P = I^2 x R

You need to know what load resistance you intend to load the circuit with.

then go (20x20) x (load resistance in ohms) = power in Watts

cheers
 ceilingfanrepair Posts: 5,738, Reputation: 616 Uber Member #3 Oct 1, 2008, 06:52 PM

2400 watts. Derated 1920 watts, I forget the rules for derating.
 Dave Ermeling Posts: 173, Reputation: 10 Junior Member #4 Oct 1, 2008, 07:00 PM
Assuming your talking about a 120 volt circuit, a 20 amp circuit is potentially capable of 2400 watts. That's forty light bulbs with 60 watt output. It all depends on how much resistance your putting in the circuit though.
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 Stratmando Posts: 10,772, Reputation: 2580 Uber Member #5 Oct 1, 2008, 08:12 PM

Also, Volts X Amps equals Watts.
1 Amp at 12 volts is 12 watts
1 Amp at 120 volts is 120 watts
A 1200 watt hair dryer draws 10 amps
(1200/120=10)watts divided by volts equals amps
 Dave Ermeling Posts: 173, Reputation: 10 Junior Member #6 Oct 2, 2008, 04:20 PM

Yes, E x I = P
P / E = I
P / I = E

It's all there in the Ohms law chart. All you need is 2 of the factors P, I, E, R and you can just plug it into the chart.
 iceqube Posts: 1, Reputation: 10 Junior Member #7 Mar 16, 2011, 05:10 PM
Usually a circuit breaker is rated for 80% for continuous loading. Therefore at 120 volt circuit
120 X 20 X 0.8=1920 watts. For 240 volt circuit of 240X20X0.8=3840 watts. All calculations for a single pole breakers
 stanfortyman Posts: 5,199, Reputation: 1401 Electrical & Lighting Expert #8 Mar 16, 2011, 06:40 PM

Quote:
 Originally Posted by iceqube Usually a circuit breaker is rated for 80% for continuous loading. Therefore at 120 volt circuit 120 X 20 X 0.8=1920 watts. For 240 volt circuit of 240X20X0.8=3840 watts. All calculations for a single pole breakers
First off, you are aware that this thread is well over two years old.

Second, how can you say "All calculations for a single pole breakers"? And how are you getting a 240v circuit from a single pole breaker? The amount of poles is irrelevant.

Lastly, there is very little in a residential setting that is a continuous load, excepting of course things that are required to be considered a continuous load, such as an electric water heater.
 dearman Posts: 1, Reputation: 10 Junior Member #9 Jan 12, 2012, 01:10 AM
1 amp is equal to 120 watts,
 stanfortyman Posts: 5,199, Reputation: 1401 Electrical & Lighting Expert #10 Jan 12, 2012, 04:29 AM

Quote:
 Originally Posted by dearman 1 amp is equal to 120 watts,
First off, you are aware that this thread is almost a year old?

Second, what you wrote is meaningless without all the parameters.
Your statement is not accurate unless you include the voltage.

1 amp is equal to 120 watts @ 120v
Or
1 amp is equal to 240 watts @ 240v
Or
1 amp is equal to 12 watts @ 12v

Get it?

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