A question about electicity for physics buffs/ electricians

[JVS]

Well not so much a question as an issue for discussion. My brother and I were talking about turning on the air-conditioner. The topic of electricity consumption came up. We were wondering how one would go about calculating the maximum possible electic consumption of a power outlet. Any ideas on this?

[JPJones]

1. Suck amps out at the limit of the circuit breaker n/t

[Syncronaut Seven]

26. Congratulations!

You are the proud owner of either a 15 Amp or a 20 Amp branch circuit. If it's 15A you can draw 12A (80%) continuous, If it's 20A you can draw 16A continuous. That's what the NEC says anyway.

If you're running an AC unit you can usualy get away with 12,000 BTU on a 15A circuit, 16,000 BTU on a 20A circuit. Providing there are no other loads and you're not at the end of a long string of outlets.

[Squeegee]

39. Power...

A 110 volt circuit drawing 20 amps would be 2200 watts of *power*.

[Syncronaut Seven]

40. Nominal Voltage in the US is 120V

Not 110. It's pretty much standardized. Makes a difference. You will also find 208, 240, 277 and 480 in commercial and industrial buildings.

[Squeegee]

43. So in essence...

... you will want to turn on your 240 Volt 40 Amp electric range instead. ;)

[0rganism]

38. Or shunt around the breaker and pull amps until the wiring melts

YMMV ;)

[Don_G]

2. P=I/R

If you don't have the math background, I would guesstimate the maximum rating for the outlet/circuit breaker plus 15% for a power load of no more than 10 to 45 minuets a day.

Far less if you have Aluminum wiring or need to plug in a Welder from time-to-time.

[JVS]

4. No. I mean if I wanted to use as much electricity as I possible.

24 hours a day. The discussion turned from how much could the AC use to how much could be drawn out total

[Syncronaut Seven]

41. 80% forever

100% for a couple of hours depending on ambient temperature. The breaker may or may not trip at this level. The breaker will trip sooner on a hot day.

125% for a few minutes.
150%-175% for a few seconds.
200%+ nearly instantaneous triping results.

[JPJones]

9. P=I^2*R; P = VI; P = V^2/R

I don't know what I/R would be.

[Rabrrrrrr]

15. Yeah, I/R isn't a real quantity

(though I'm sure someday, in some kind og quantum thirtieth-dimension particle physics with strings and callypigian mermaids, there will be found a spot where I/R is essential, and in which electrons move back in time and create warped space toroids with baryon emissions. And Geordi will need a reverse polarizer to fix it.)

[JPJones]

3. For example, 120 volts, 10 amps, gives you 1200 Watts

Do that for an hour, and you've used 1.2 Kilowatts hours of energy. That costs you about a dime. You will have caused about 2 pounds of carbon dioxide to be released into the atmosphere, by burning coal or natural gas at the power plant.

[JVS]

6. Ok. I knew a plug was 120V but didn't know the Amps

Any suggestions on ways to draw maximum current from the outlet?

[Rabrrrrrr]

10. You will draw maximum current, for a dt amount of time, if you

just take a wire and shove it into both holes in the outlet.

That's the only way to maximize the current draw; but it will only last about dt seconds because it'll trip the breaker.

Now, if you really want to be a bastard, you'll remove the breaker and replace it with a wire. And then go shove your wire into the outlet.

[JVS]

14. Isn't defeating the breaker a fire risk?

Wouldn't that essentially turn the entire circuit into a fuse that will break when some part of it burns/melts away?

[Rabrrrrrr]

20. Ddn't say it was safe, said it would draw the maximum possible current

:-)

Of course it's unsafe. But if he doesn't burn his house down, he might very well create a brownout in his neighborhood, and that's gotta be worth some street cred.

[JPJones]

23. If this were high school, the next thing that would happen

would be that you'd be stuffed into a locker.

[Rabrrrrrr]

25. Some of my asshole classmates used to do this experiment in class

In our electricity class. Except that instead of shoving a wire into the outlet, they'd plug in a soldering iron and set the tip on the cord and walk away. In a minute or so, there'd be a loud POP and all the lights would go out in the basement where the classroom was.

[Endangered Specie]

11. Get alot of 8 in 1 electrical outlets and connect heavy appliances...

Or go to a home depot and ask what various outlets can take wrt amps.

[JPJones]

12. Why on earth would you want to do that? n/t

[JVS]

19. No reason in particular,

[Endangered Specie]

7. What if your on a nuclear power plant.

[JPJones]

16. No CO2 produced by nuclear power.

You make some nasty radioisotopes, though.

[Endangered Specie]

29. I know that...

wanted to know how much of the radioactive stuff you get though.

[flowomo]

5. just keep plugging shit in until the fuse blows....

that's the limit

[vajraroshana]

34. LOL, that's what I was thinking too (n/t)

[Rabrrrrrr]

8. Check the rating of the breaker controlling that outlet - that's how much

No math needed at all. :-)

But first, a correction: outlets don't consume power. They are merely interfaces for the electrical pathway between your appliance and the nearest transformer. :-) Appliances consume the power. (though for the total purists out there, I realize that the outlets themselves actually do consume some fractional amount due to not being super-conductors, but that's splitting a very small hair).

The easiest way to tell is to go to your circuit breaker, look at the fuse or breaker that controls that outlet, and see what amperage it's rated at. Usually in a home they're 15 amp breakers. When I was engineering at a factory that electric ovens, we used 600 amp fuses. Big.

Anyway.

So whatever that breaker is rated at, that's the maximum amount that you can send through any outlet; and, considering you probably have a number of outlets connected to the same breaker, the actual amuont of amperage you can send through one outlet will be less than the breaker is rated at, unless you turn off everything else (because the breaker will trip when TOTAL power consumption of all outlets/lights/etc. connected to that breaker goes beyond its rating).

Now, if you are talking purely theoretical - how much power can this outlet handle, assuming an unlimited supply and no breaker - meaning, how much power will it take to actually cause the outlet itself to melt/explode/shatter/catch on fire and cease functioning, then I can't answer you on that. I can only say, go run some tests.

[JVS]

13. What would be a good way to waste as much electricity as possible?

Assuming that I have a 15 amp circuit breaker. We knew that appliances consumed the power not the socket, but I had made an argument that there must be a limit to how much power one could draw through a socket. So we wanted to figure out an upper bound based on how much could be drawn through. Now that figuring that out has been made clear, it begs the question of how we could come up with a device to consume that much power.

[Rabrrrrrr]

17. You wanna waste as much as possbile, eh?

Find yourself a 120V * 15 AMP = 1800W device, and leave 'er running. Though you might be able to even stretch that another 10-15%, depending on the breaker. Couple hairdyers and an air conditioner (to cool down from the hair dryers, I guess) oughtta do it.

And you are definitely the winner in the argument about whether there is a limit. :-)

[JVS]

21. Yeah, Our scenario was to put the AC by the oven and let the oven heat it

[JPJones]

18. Well, it will be fun when the cops show up.

Looking for the growing lamps.

[JVS]

22. Do you think they'd arrest us?

[JPJones]

24. Not unless you were growing pot.

In George Bush's America, it is your God given right to waste energy. When we run out, we'll just invade another country.

[ProudGerman]

27. As an electrician, I've done some 'temporary' power set ups

Temporary is in quotes because the set up is let's say, less than safe.

On a constuction site, after the power company has made its hook up, I've had some serious amperage running through a single 20 amp commercial grade receptacle. Though not intentionally, or through my own doing. Power a single receptacle on a construction site, and the three ways will daisy chain like crazy. I've probably seen 60 or 70 amps going through a single receptacle before it just heated up and deformed, breaking the connections. Circular saws, battery chargers, hammer drills, and core drillers can suck down the amps.

BTW, I must ask that you refrain from asking what breaker this circuit was hooked up to. We don't need to go into the fact that it was hooked straight into the lugs.

[Rabrrrrrr]

28. Nothing like being connected straight to the grid, eh?

"Breakers will be delivered in a few weeks."

[maggrwaggr]

31. you can blow up a transformer doing that

I work in commercial film production and we tie in frequently. If you don't know what you're doing, or if the location's electrical service is actually rated higher than the service can actually provide, you can blow up the nearest transformer, which needless to say is a pretty big deal.

I've only seen it happen once on my watch, but it was pretty dramatic. Shut down the entire neighborhood.

[Rabrrrrrr]

32. Believe me, I know

/me <-- electrical engineer

When I was a kid, seemed like at two or three times a year a squirrel would squirrel its way into the transformer running our block and send us all into a couple hours of powerlessness.

Shhhhh...zzzzzzzzllllzzzlzlzlzlzlzlzlzlzlzlzlzl.....SPA-KOOM! Fritz fritzx fritz glub glub whoooooooooooooooooooooooooooooooooo as everything powers down and the block becomes silent with no air conditioning sounds...

[maggrwaggr]

33. here's a weird one for you --

my sister lives in Texas and fire ants got into their transformer. Somehow, fire ants love the shit that's inside transformers. They eat it. But it didn't just go out, it caused some violent voltage fluctuations which caused every appliance in their house with a power supply to burn up! TV's, stereos, VCR's, computers, all went POOF! Surge protectors didn't even help.

Lucky for them their homeowner's insurance covered a lot of the damage.

[Rabrrrrrr]

35. Don't believe what you read - those damn fire ants

DO have technology. And they're watching us. Oh, yeah. They're watching. Just waiting for the moment to strike with their long-distance voltage fluctuators, EMP generators, silicon disruptors.

Seriously, though, I have heard of some similar situations of people getting not a voltage spike from lightning or anything, but something in the system, usually centered on just one house and not affecting houses nearby, that fries a bunch of stuff.

Electricity is bloody weird in the way it works. Yeah, it mostly conforms to the laws we've noticed and put down equations to model and predict, but not always. Every now and again it just does what it wants.

[BiggJawn]

30. Plug a TV into every outlet...

Tune them all to "FAUX NooZ" and "Murkan Idle" and oh, GAWD! Can't forget "SURVIVOR"!!!!

That would be the biggest waste of electrcity in the whole city!

[Trajan]

36. Isnt the UL rating of a standard duplex convenience outlet ...

about 30 instanteous amps ??? ...

A point I would make ...

You mention 'maximum possible electrical consumption of a power outlet' ....

Well: power outlets do not 'consume' power, since outlets do not use power, but only channel current to the load(s) by completing a circuit through to the load ... The actual 'electrical consumption of a power outlet' would be the heat generated by power dissipation caused by a current across its finite contact resistance combined with the inherent conductor resistance within the outlet itself: ... this internal 'impedance', which exists in all circuits due to the finite resistivity of all electrical conductors, is what is used to calculate the power dissipated within that circuit element ...

One might measure the total power consumption of the circuit thusly ...

Pt = Vt * It
Total power = Total Voltage * Total Current ...

These values relate to the ENTIRE circuit, not just the outlet ...

Due to Kirchoff's Voltage Law: EACH series element in a circuit exhibits a 'voltage drop'(IR Drop), of which all the voltage drops in a series circuit would sum together to equal the total voltage applied to the circuit ....

The implications of KVL is that ALL circuit elements, even simple conductors, will experience a power loss which equals the current through the conductor, squared, times the minute resistance of the conductor itself ... hence wires, switches, plugs and receptacles WILL generate heat that equals the amount of power calculated by the voltage drop these devices exhibit, the current flow through these devices, and the inherent resistivity across each device ...

A 'perfect' conductor, that which has zero resistance, would pass current without power loss (I^2 * 0 = 0) .... but such a conductor does not exist .... hence why power loss is exhibited universally by ALL circuits that draw current ...

In your case:

Pt = P1 + P2 + P3 (P1 = It^2 * Source Impedance; P2 = It^2 * contact resistance of the connection systems; P3 = the actual power usage of the load, in this case: the Air Conditioner)

IOW: Power Total = power loss through a voltage drop across the source impedance + power loss through a voltage drop at the power outlet and its connections + power used by the load

What this says is that: the total power used in the circuit equals the combined power dissipation of each series circuit element ... The outlet itself only 'uses' the power that is lost across it's contact resistance + it's conductor resistivity ... If one assumed 0.5 Ohms of resistance exists across the outlet itself ... and if the load draws 15 amps, this 'loss' would equal:

power dissipation at the outlet = ((15)(15)) * 0.5 = 225 * 0.5 = 112.5 WATTS dissipated as heat within the outlet alone ....

The safety rating of the outlet takes in consideration the ability of the outlet to dissipate this heat effectively without overheating and disintegrating (losing its physical integrity, and its ability to maintain circuit functionality) ....

Er ... we might call this 'melting' ....

Typically: .. safety rating values are double or half (as appropriate) of failure values ... SO: if a circuit element can handle 200 watts of power dissipation before it fails, it is given a rating of 100 watts ... Since receptacles possess a generally stable internal resistance, they may instead be given a 'safe current rating', which translates to a specific power rating ...

So: ... to CLOSE this essay ...

Ehem ... sorry ....

The maximum power that can 'safely' be used within THAT outlet would equal approximately 2 times the safe rating ... If the current flow through the outlet creates a power dissipation that exceeds the rating, you are treading into a dangerous range of operation .... if it approaches DOUBLE the rating, you may be approaching an imminent failure of the device, and possibly dangerous generation of heat and or fire .... (That is: if the breaker hasnt tripped, which is why we have breakers and fuses) ....

PS ... an anecdote:

I once worked on a specific program that used a large capacity, 3 phase, 400 cycle UPS as its primary system power source ...

It used three main cords to connect the UPS to the system itself ...

Each cord passed about 50 amps of current ....

One night: a janitor came to sweep the floor, and was using his broom near the power receptacles ....

He accidently bumped into one of the plugs ... which in turn caused ONE of the plug prongs to temporarily make 'poor contact' with the receptacle contact (IE caused a momentary increase in contact resistance) ...

Well: This contact resistance was already passing 50 amps of current, and when the resistance spiked: the instantaneous power disappation ( P = I^2 * R ) was too much for the plug to handle ... which simply exploded ....

Many of the techs were confused by this, but it makes perfect sense, since such instantaneous voltage drops carry with them a concurrent power spike .. in this case: a tremendous spike ...

Anyways .. I hope that helps .....

[JVS]

Thanks for the story

by "maximum possible consumption of an outlet" we really just meant to restrict the consumption by insisting that all power be drawn through one outlet.

Your answer puts it in terms of the physics classes that I took.

[Syncronaut Seven]

42. Can't do that Trajan

You'll confuse people. Most folks eyes glazed over by the third line.

When people ask me why the plugs on their grow lights get hot I just tell 'em it's magic. That usually satisfies them.

Now repeat after me "Hi my name is Trajan & I'm a recovering technophile."

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[camero]

44. 1.5 amps

take the amount of outlets in the circuit and divide it by the amount of amps at the breaker.

I used 10 outlets on a 15 amp circuit. Though you only use the amount of amperage that you draw from it. How many things are plugged in.

Simple ohms law. V=IxR

Some info here:http://www.grc.nasa.gov/WWW/K-12/Sample_Projects/Ohms_Law/ohmslaw.html

[Syncronaut Seven]

45. I'm sorry, is it

Hi, how are you?

or

How high are you?

I forget