Source
r/electrical•
centrallcomp

If you have an American-style duplex wall outlet at 15 Amps with 120V, what is the maximum Wattage you draw from EACH INDIVIDUAL outlet?

Question. I can't seem to find a straight answer for this from any online sources. If I Google this answer, the first statement I get is "Most electrical wall plugs are 1800 watts depending on the breaker size. Most breakers are at 15 amps supplying 120 volts, or approximately 1800 watts.":

https://www.ius.edu/environmental-health-safety/files/power-cord-safety.pdf

Does this mean a duplex can support a maximum CUMULATIVE wattage of 1800W across both outlets, or can I plug in two 1800W devices on each outlet at the same time with a total of 3600W for the entire duplex (barring the 80% rule)?

Posted Jan 2, 2022, 7:00 AM UTC

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CPerryG•

It’s cumulative. The wire and breaker feeding that duplex is most likely rated for 15 or 20 amps… 1,800 watts is 15 amps at 120 volts. So, 15 amp circuit you get 1,440 watts and 20 amp circuit you get 1,920 watts (both are 80%). If you are trying to get over 1,440 watts off the duplex make sure it’s rated for 20 amps.

3
centrallcompOP•

(Looks at 1300W PSU connected to an overclocked computer)

Welp, I guess I'll have to get some extension cords to connect everything else. I appreciate it. How can you tell if a circuit has 15A or 20A?

-4
wifimonster•

Are you actually using all 1300 watts that power supply can give? Most power supplies for computers are oversized by quite a bit

Also, keep in mind that's 1300 DC watts. At full load, you'd actually using something like 1700 AC watts due to efficiency.

8
centrallcompOP•

It's close to around 1150 Watts. I do prefer to have some headroom in the event of a loss of efficiency.

2
wifimonster•

You may want to rethink using extension cords if these other devices your plugging in are also going to be using 1000+ watts. Fire hazard.

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[deleted]•

[deleted]

1
MonMotha•

Most modern PC power supplies in the kilowatt range meet at least 80+ Gold specs. This standard requires 87% efficiency at 100% output load on 115V input, so you'd only be pulling about 1500W from the wall with a 1300W power supply loaded to the hilt.

That's still a lot of power, though and loads a 15A circuit to nearly it's maximum recommended continuous usage rating.

2
CPerryG•

Check breaker for branch circuit amperage, and outlet will have a horizontal slit coming off the vertical slit on the left side of plug if 20 amps, no horizontal slit is 15 (layman’s terms).

1
connogordo•

Your UPS is not drawing 1300W. That is what the battery is rated for when you lose power. When you have your computer plugged into the UPS it is drawing the wattage of the device you have plugged into it + an insignificant amount to keep battery charged. Your computer/electronic loads will not overload the circuit/outlet, no matter how bad ass.

1
Soviet_Canukistan•

Welp guess Imma burn my house down for the 'gram? Sorry. And good on you for seeking answers. But "one weird trick" won't get you out of a house fire.

1
knipex_addict•

Where’d you get the 1150 watts from?

2
centrallcompOP•

LN2-cooled PC.

1
knipex_addict•

Sorry I meant what type of meter are you using to check your current draw?

2
Nullclast•

He's not, his power supply goes up to that, hell probably only ever really pull 600-800. People buy giant power supply's not actually knowing what they'll need. Going up to 1000 would likely require 2 large gpus in sli being overclocked running at 100% capacity.

3
MonMotha•

Folks running sub-ambient cooling off the PC supply can really load things up more than you'd expect. Peltiers are not efficient, for example, and can easily be had in sizes that pull a couple hundred watts just on their own.

The other reason for a large power supply in a PC is to handle the bursty current draw that's inherent in modern performance PC parts. They're thermally limited, but that means that, for a very short time, they can drastically exceed their steady-state thermal envelope, and this is useful for interactive performance. Modern HEDT CPUs from both Intel and AMD can easily exceed 300W transiently. Of course, this doesn't matter much when it comes to supply circuit sizing.

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centrallcompOP•

It's mostly just looking at component wattages rated by the manufacturer and adding them up, then adding any wattages drawn by components that can be monitored via software. If you do extreme overclocks on the CPU/GPU, you can easily go 100-300W above their rated wattages.

That is why I think using an extension cord to plug devices like the monitor to into an outlet on a different circuit might be ideal.

1
SamuelSmash•

OP get a cheap kill a watt meter and try to measure the power consumption of your PC under the worst possible scenario you could create.

You will very likely not even go over 600W.

If you PC actually managed to draw over 600W for anything longer than a few minutes you will even notice that the room begins to warm up.

2
knipex_addict•

You should definitely get a “kill-a-watt” meter, you need your VA and Power Factor to find your actual wattage, taking the nameplate ratings and adding them all together is not how you find wattage. Similar to your electrical panel, you don’t add all of your breakers together to conclude what your amperage is at.

1