OT: How Do You Determine How Much Power Something Uses?

[WearyOne]

By some other posts on here a while ago, I believe there are some very knowledge electrical people here! And I have an OT question in that regard. Please don't laugh-- I have a lot of knowledge about some things, a little knowledge about others, and no knowledge about electrical stuff!

How do you determine how much power an item draws? Trying to not overload a circuit. Is it amps, watts, something else, or a combination of things?

And the numbers on the circuit breakers (i.e, 30), what are those?

Thanks!

Pam

[Phreak4u]

Most everything is rated by watts. In some cases they list the amps that a product will draw. The romex used is buildings is rated at 600v and 20a average. in houses unless otherwise specified, it will be a little less amperage. (15a) So say you have a clock radio, lamp, and your cpap, all plugged into one outlet. You're good to go. If you overload a circuit, the breaker will pop immediately and you'll know at that point you need to find another outlet on a different circuit.
With all the stuff I have in my computer room( and there's quite a bit of it) running I've yet to overload the circuit.

Marc

[WearyOne]

Thanks, Marc. It might have made more sense if I detailed just a little. We live in a tri-level house, my home office is on the main floor. My husband stays upstairs most of the time and freezes me out in the winter because, as we all know, hot air rises and it's hotter upstairs. I want to use a space heater around my desk. (Frozen hands don't type very fast!) Anyway, we've got so much stuff hooked up everywhere, I'm afraid of flipping the circuit that I plug the space heater into (same circuit as my computer, etc.) Was just trying to avoid my computer going off in the middle of working if the heater was too much for the circuit and flipped it off. Don't have another outlet in the room I need it in that's on a different circuit, that I can tell. (Upstairs, we already have to make sure his HDTV and computer aren't on at the same time I use the hair dryer, or that circuit flips.)

I have two space heaters. One is 1100 watts and doesn't list amps. The other one is 1500 watts and 12.5 amps. If the "30" marked on an individual circuit breaker is amps, then this 12.5 amps would be almost half of what that circuit is designed to carry, right? Or am I totally not understanding this. Or do space heaters just take too much juice to be on the same circuit as my office stuff?

[dwood003]

Circuit breakers are rated in amps.
Small appliances are usually rated in watts.
To convert watts to amps divide the voltage into the watts.
1000 watts divided by 120 volts would be 8.3 amps
Breakers sometimes become weak and trip prematurely.
Whats the problem?

[Wulfman]

If you have the owners' manuals, the information should be in those......if not labeled directly on the products.
In many cases, the information and owners' manuals can also be found on the Internet.


Den

[Phreak4u]

Circuit breakers are rated in amps.
Small appliances are usually rated in watts.
To convert watts to amps divide the voltage into the watts.
1000 watts divided by 120 volts would be 8.3 amps
Breakers sometimes become weak and trip prematurely.
Whats the problem?

Thanx Dwood...I couldn't remember the math conversion....

[WearyOne]

Circuit breakers are rated in amps.
Small appliances are usually rated in watts.
To convert watts to amps divide the voltage into the watts.
1000 watts divided by 120 volts would be 8.3 amps
Breakers sometimes become weak and trip prematurely.
Whats the problem?

Thanks, dwood, this does help educate me!

I just don't want to flip the circuit that my computer is on, and I know space heaters probably take a lot of juice. But I'm freezing down here in the winter when my husband is home, because he gets too hot upstairs, if I'm comfortable downstairs. I know, I could just try it and see, but I'd rather just know beforehand.

The one upstairs always flips when I use the hair dryer if his HDTV and computer are also on at the same time, so we have to watch that. Since you said that breakers sometimes become weak and trip prematurely, a visit from an electrician may be in order just to check things out, especially since the house is 28 years old.

We just had a 28-year-old heat pump/furnace system replaced in October, so money's rather tight now for any major electrical stuff.

[Goofproof]

Circuit breakers are rated in amps.
Small appliances are usually rated in watts.
To convert watts to amps divide the voltage into the watts.
1000 watts divided by 120 volts would be 8.3 amps
Breakers sometimes become weak and trip prematurely.
Whats the problem?

Correct! Items that produce heat draw quite a bit of power, also their turning on and off cause large voltage drops and spikes, so it best if they are on their own circuit breaker, and not hooked up to the computer line or costly T.V.s. Most people don't worry and just plug them in anyway. The problem comes from circuits that are heavily loaded in the first place.

Using a 1800 watt heater (12.5 amp) on a normal house breaker (15 or 20 amp), works fine, but when hooked to a line that's already running the fridge or microwave, or toaster oven, this causes a overload. Hooking more than one room heater to the same breaker overloads the wiring unless the circuit is designed for the heavy load. (30 amp) or more. Items that run larger motors, also are easy to overload by adding a heater (food disposer). Don't run the heaters on a extension cord unless it rated for more than the power of the heater. Jim

[WearyOne]

Circuit breakers are rated in amps.
Small appliances are usually rated in watts.
To convert watts to amps divide the voltage into the watts.
1000 watts divided by 120 volts would be 8.3 amps
Breakers sometimes become weak and trip prematurely.
Whats the problem?

Correct! Items that produce heat draw quite a bit of power, also their turning on and off cause large voltage drops and spikes, so it best if they are on their own circuit breaker, and not hooked up to the computer line or costly T.V.s. Most people don't worry and just plug them in anyway. The problem comes from circuits that are heavily loaded in the first place.

Using a 1800 watt heater (12.5 amp) on a normal house breaker (15 or 20 amp), works fine, but when hooked to a line that's already running the fridge or microwave, or toaster oven, this (causes a overload. Hooking more than one room heater to the same breaker overloads the wiring unless the circuit is designed for the heavy load. (30 amp) or more. Items that run larger motors, also are easy to overload by adding a heater (food disposer). Don't run the heaters on a extension cord unless it rated for more than the power of the heater. Jim

Jim, thank you! I thought I was beginning to understand from the other great posts before yours, and then reading yours, by Joe, I think I've got it! I was also wondering about the turning off/on that these heaters do, and you clarified that as well. I now feel educated enough to intelligently figure out where to plug this thing in, and not plug it in!!

Thanks, all for your help!

[Goofproof]

Also depending on how you house is wired, the outlets tend to share the same circuit breakers, meaning just having two heaters plugged into different outlets doesn't mean they aren't running on the same wire and circuit breaker. You need to know what wire and outlets are hooked together. That's where X-Ray Vision comes in handy. Remember the person who wired your house was trying to make it as easy on themselves (and Cheap), as the laws (Codes) allow. Like Government work, lowest bidder. That's why when I run any thing new that uses a lot of power, I add another circuit just for it. (big A/C units, Compressor, Welders ECT)

[GumbyCT]

Most appliances are clearly labeled as to power consumption, just follow where the wire goes into it.
The only thing I plug into my computer line is a UPS.

Space heaters and hair dryers draw a lot of power as do vacuums.

Space heaters are also the source of many house fires in the winter. When the temp drops people turn up the heaters and you can't see it or feel it but if the wires in the walls are bad and over heat, you have trouble. If a fire start inside the wall, by time you find out, it is way too late.

House fires increase drastically during winter bc people are trying to stay warm.

Do your self a favor, either get an electrician to check your place out or move the computer up to the heated room. I think oil heat will be cheaper than electric this year too.

Better yet get a laptop low power consumption and if the circuit breaker trips you are all set.

You get cold, move upstairs. Done.

[billbolton]

How do you determine how much power an item draws?

The simplest method is to buy an in-line power meter and plug the appliance(s) concerned into it and see how much energy it is actually using.

I can't point you to a specific US example, but here in Australia these devices are readily available for about AUD$30...

http://www.jaycar.com.au/productView.asp?ID=ms6115

... so I'd be very surprised if there is not something similar available in the US market.

If you want the formal method of calculating power consultion, this web site is good....

http://users.tpg.com.au/users/robkemp/P ... mption.htm

... the examples are worked for 240V mains power but the formula and approach work for any mains voltage.

Cheers,

Bill

[WearyOne]

Wow, this is all such good information. I know there would be a lot of knowledge about this here.

Very difficult to move upstairs, as I have a big ergonomic setup--desk, movable keyboard tray, a keyboard that's completely split in half, and so on, plus my transcription equipment. I type for a living (transcribe tapes and digital recordings).

I've noticed before that there, in my opinion, doesn't seem to be a pattern as to what outlets/rooms, etc., are on what circuits. I've love to have an electrician come in here and map out the whole thing for me, you know, exactly what outlets are on what breakers. When we moved in the house, the breaker box was labeled in pencil as to rooms, and it was barely readable (and wrong, in one instance). I tried my best to figure it out, and I think I did a pretty good job, but I'm not confident enough to know it's 100% right. Guess I could turn one breaker off at a time, and then run around the house checking to see which outlets don't work with each breaker!

I was in an apartment fire as a teenager, caused by a faulty furnace in the apartment above us. My mom and I, and cat, got out fine, but lost everything (good insurance, though). (It was about 10 degrees outside.) Probably another reason I'm so cautious about this.

[fuzzy96]

just a little food for thought -....yes volts x amps+watts
watts/volts=amps
watts/amps= volts
if you use a circuit breaker beyond 90% of its rating(i.e. 30 amp breaker beyond 27 amp) almost any surge or spike will trip it. generally speaking 80 to 85% is all that a circuit should be normally loaded to. running a breaker too close to it's max and or tripping it severely shortens it's life.
your power company can give you rough figures on what appliances draw.

and if you really are bored and want to do yourself a favor--get a loud radio and plug it into each outlet one at atime and flip the breakers till it goes off. then mark the outlet cover with the corresponding circuit breaker. this saves tine and confusion and you can also see how many and which outlets are on the same breaker-- so you can better manage the load.

stay warm and safe

RICK

[WearyOne]

Just wanted to thank everyone again for your help and education. Went around yesterday and checked to see which outlets/lights were on what breakers. The box was labeled pretty well, but did have two breakers labeled wrong. And I was able to determine in the kitchen/my office/living room area (which is all on one floor), which outlets were on which circuits. Can't put the heater in my office, but if I really need to, I can run it from an outlet that's on one of the kitchen circuits into the office (with a high enough rated extension cord, of course)! (That particular circuit doesn't have anything running on all the time except a coffee maker clock!)

Anyway, thanks again!

Pam