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hajeser · Sep 7, 2007, 10:37 PM

How Many Watts Can A 20 A Circuit Safely Carry?

tkrussell · Sep 8, 2007, 06:08 AM

Ohms Law is Power equals Volts times Amps. Insert the voltage you have multiply by 20 amps, and you have the result.

If in the USA, if the load runs 3 hours or more,it shall be considered as continuous and be derated to 80% of the rating of the circuit.

Stratmando · Sep 8, 2007, 10:01 AM

120 volts X 20 Amps = 2400 Watts... X .8(80%)= 1920 Watts
240 volts X 20 Amps = 4800 Watts... X .8(80%)= 3840 Watts

tkrussell · Sep 8, 2007, 12:19 PM

Strat, I think it would be good to see posters do a little thinking and work on their own.

Stratmando · Sep 9, 2007, 06:35 AM

I Love to learn, love to teach. I don't want to answer questions for testers. But if someone is curious, I like to make it clear. The basics need to be understood.

Beandip · Jan 2, 2008, 11:56 AM

Easy way to remember the formula W = VA --
"West VirginA"

KISS · Jan 2, 2008, 12:22 PM

VA and Watts are a little different.

W = V * A for DC and Resistive AC loads
W = V * A * Cos (Theta) for reactive sinusoidal loads
V and A are RMS values
RMS is the equivalent DC value

W = integral of 1/b-a(integral (V(t)*A(t(t) dt) for periodic loads (if I remember right)

VA is frequently used to specify the starting power of motor loads and is used to size generators to run that load. You cannot use 746 W/HP to size a generator for a motor load. Watts is used for resistive and DC loads.

Beandip · Jan 2, 2008, 12:42 PM

Originally Posted by KeepItSimpleStupid

VA and Watts are a little different.

W = V * A for DC and Resistive AC loads
W = V * A * Cos (Theta) for reactive sinusoidal loads
V and A are RMS values
RMS is the equivelent DC value

W = integral of 1/b-a(integral (V(t)*A(t(t) dt) for periodic loads (if I remember right)

VA is frequently used to specify the starting power of motor loads and is used to size generators to run that load. You cannot use 746 W/HP to size a generator for a motor load. Watts is used for resistive and DC loads.

The original post was probably referring to standard US AC power, thus I stuck to the basic W = VA for Resistive AC loads.

KISS · Jan 2, 2008, 01:10 PM

I know, but you used W=VA, which isn't necessarily true. If you had said W=V*A for resistive loads, I would not have made my correction. It's just you will find units of VA on some nameplates.

Stratmando · Jan 2, 2008, 04:52 PM

I have worked with many helpers that have too much ego to ask some basic things. The poster asked How many. I gave that answer, and how to figure. I didn't dig out the calculator. It is in my head like 1.732(square root of 3), white blue to green, blue white to red, white orange to black, orange white to yellow. Bad Boys R Our Y G But Violet G willingly(The resistor color code), and probably thousand others. I think the resistor needs to be updated. Female techs I know, actually use that same memory thing.
EDIT. Just reread post, didn't say Voltage. I assumed 120, will let poster do math from there, also that it was posted in Sept?