# Power - When does the room go *boom*?

Discussion in 'FAQs' started by nolatron, Jun 4, 2007.

1. ### nolatronMember

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One thing that has never been my forty is electricity.

I'm trying to find out what's the best way to see if my office will safely handle everything I want to plug in without overloading it and setting it a-blaze.

My office/layout room has 5 AC outlets and is on a 15amp circuit in the breaker box. I have two computers, 3 LCD monitors, scanner w/psu, DSL model, wireless router, printer, and ceiling fan typically running 24/7 already in the office already.

How would I go about calculating what the office is capable of safely running without overloading the circuit?

Speaking of which, when one says "overload the circuit" (ie: don't plug 20 strands of xmas lights into one circuit), is that "circuit" referring to plugging way too much into a *single outlet* in a room, or to the entire circuit that powers all outlets in a room? Example: Is plugging 2 strands of xmas lights into 10 outlets in a room just as bad as plugging 20 strands of lights into a single outlet?

I'm starting to make a list of all the power supplies in the room and what I probably expect to have to see what my total volts/amps/watts usage would be.

If any further info needed to help me figure out, let me know.

Thanks!
2. ### ezdaysOut AZ way

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To start with, you'll have to determine if all those outlets are on one circuit. They probably are since that's normally the way they wire up a room. Plug in a lamp in one outlet, then find the ciruit breaker for that outlet and turn if off. Now go plug the lamp in all the other outlets to see if they're also off. If they are all on one circuit, you are limited to whatever the breaker is rated for, like probably 15 amps total for all outlets.

I took a few measurements, a while back and came up with these numbers:

One computer running with one LCD monitor = 1.2 amps. The monitor alone was 0,2 amps so your computers will draw about 3.0 amps total. Now my laser printer draws 5 amps while it's warming up, and that has to be considered.

Then there's the lights, and your scanner which you should be able to read the label on it and see what the power draw is. You should have amps to spare, but remember, each outlet may be rated at 15 amps, but the limiting factor is the breaker rating. You may also find that the circuit that goes to your office may also go to another room and you have to add the stuff in that room as well.
3. ### nolatronMember

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Seems like I basically need to watch my Amp load on that single breaker circuit, regardless of the voltage/wattage of items plugged in are.

As far I know so far the office is the only thing on that circuit as well. I'll test it out like you said to be sure.

4. ### ezdaysOut AZ way

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Yeah, you have to be careful how they distribute the circuits. My office is on one circuit, but that includes the lights. My train room is on another circuit, but it shares it with a bedroom and part of the hallway. Sometimes they'll put the lights on one circuit and the outlets on another one. The only way to tell for sure is to flip one breaker and see what doesn't work. Shortly after we moved in, some cement workers tripped a GFI circuit out on the back patio, and it took forever to find that the GFI was hidden behind some stuff in the garage on the same circuit.:curse: :curse:
5. ### nolatronMember

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Hah! I had exactly this happen to me at the new house, but it was the outlet on the front porch. Then one day I noticed a little grean light glowing in the garage of the tripped GFI.
6. ### 60103Pooh Bah

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Most of your equipment should have a rating in Watts. This may be a peak requirement, e.g. startup, or continuous. Divide walls by 120 volts to get amps. Now keep those amps under 15. For example, a 100 W light bulb will be just under 1 amp. You really want to be a bit below the 15 amp limit.
In our house, the living room and part of the kitchen are on the same fuse. We have an electric fireplace in the living room and if that's on, we can blow a fuse by using a kettle or toaster in the kitchen.
7. ### TriplexActive Member

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You think that's confusing? In my place, the living room light is on a different circuit from everything else. When the power goes out, every other circuit shuts down except that one. Sometimes, it goes out with the others... if the whole city block or more has a power failure. Once, there was some work being done - can't remember exactly what, but the power was being shut off to each house on the block in succession. First, all the lights went out except that one. Then they came back. Then that one went out. It's wired to a circuit in another house.

So, make sure your place wasn't wired by my electrician!
8. ### ezdaysOut AZ way

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About twenty some years ago I wanted to move an oven in a house we just bought. I flipped the breaker and saw the light go out and proceeded to cut the wires to it. Kapooww!!! I got a big arc, but fortunately my cutter were insulated. I went back and checked the wiring and found that they wired one leg of the 220 circuit to one breaker and the other leg was crossed to a different 220 breaker.wall1 I think your electrician gets around...:curse::curse:
9. ### nolatronMember

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/me hopes my 5yr old house got wired all nice and pretty like

Tonight I'll be taking note of everything in the office I have, plus what I expect to have with the layout. I have a feeling my XP computer power supply is gonna be a Amps hog.

I post up my findings.
10. ### nolatronMember

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Ok, here's everything in the room:

The stuff at the top is pretty much what runs 24/7 (and the green amp load). If I'm looking at this right, if everything currently plugged in hit max amp load based on the power supply it would hit 27A.

Toss in expected layout items and it 37 amps.

This just doesn't look...right...or safe.. heh.
11. ### ezdaysOut AZ way

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I don't know where you got your numbers from, but I think they're way too high compared to what I measured. I had an ammeter in the circuit and turned things on and off and I got 1.2 amps for a computer and the 19" LCD.
12. ### nolatronMember

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Yeah, the pc and gm300 list 5amps but I think that's at max load. the PC is 420watt power supply. and the power supplyfor the GM 300 scanner is a Astron RS-7A power supply.

I"m replacing my two old LCD's with a new 2nd 19" LCD so that'll drop off those two numbers too.

Everything I copied right off the power supplies "output" rating label.
13. ### JR&SonMember

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You dont need Output ratings
You need input

JR&SON
14. ### JR&SonMember

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Better yet
You can pick up a fairly inexspensive "inductive" amp meter.
Go to the breaker box and check it.

JR&SON
15. ### nolatronMember

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Doh! I think I left my brain at work today

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17. ### ezdaysOut AZ way

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No, not really. It is rated for 9 amps at full load, but you are not pulling a full load. Rating and actual are sometimes off by a lot. The 9 amp rating just means that it can pull up to that, but it can also pull a lot less depending on your load. As I said, my LED monitor is pulling around 0.2 amps, or 200 milliamps, far less than your rated 1.2 amps.

Now, just one word of caution. If you're not familiar with using test equipment such as a meter, it might be smart to have someone who has done this before to help you. Measuring current means that you have to actually break into the wiring and put your meter in the circuit. If you are using a clamp-on type meter, it is non-intrusive, but you still have to separate the wires so you can clamp onto a singe wire, not both or they will cancel themselves out and you'll read nothing. Measuring voltage can also be dangerous, so be careful.
18. ### nolatronMember

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I picked up one of those "kill-a-watt" items. Plug into a wall outlet, then plug in your equipment. It'll give you all kinds of ratings on what it's drawing from the circuit.

Not a professional measuring item by any means, but I think it should suit my needs.

P3 International

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