how much power can be safely drawn from two household outlets?

Howdy
I have a bunch of computer/computer related things getting power from the same two outlets. The list goes:
--Compaq Presario computer
--an older (circa 1999) HP computer --a 19-inch monitor --cable modem --Samsung laser printer --Canon photo printer --HP flatbed scanner --speakers with subwoofer --charging cradle for a cordless phone --a Linksys router --charging cradle for a USB price swiper --power adapter for a USB hub
Just wondering if all this together will stress my wiring or otherwise be dangerous? I'm running all of this off a power strip and an APC UPS (which I guess draws a bit of power on its own).
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BTW I live in the US.
On Sat, 04 Jun 2005 06:01:13 GMT, Trevor Smithson

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On Sat, 04 Jun 2005 06:04:09 GMT, Trevor Smithson

One 15 amp circuit in the USA will support 1800 watts of resistive load (15 x 120)00. Computer equipment is a complex load with less than 100% power factor. Let's assume your p.f. is 80% so now you are limited to .80 x 1800 or 1440 of real power watts. Derating this further, will give you even less since you never want to load up one circuit to 100% ampacity.
If you had a simple device like Watt's Up, you could measure your actual load just before the UPS. It will vary depending on what printers are powered up, but for the most part, the devices you mentioned present pretty much of a constant load. If you don't have a true power Wattmeter, you can get a very rough approximation by adding up the watts for each device as stamped. Just a guess here, but the laser printer probably consumes the most power when warming up and actually printing, the computers and the monitor will come in 2nd, espcially if it's an older CRT monitor. Put your hand on the top and in the back. Does it run hot? The heat you feel indicates heavy power use and possible wasted power. Printers only consume significant power when they come off standby. The hubs, cordless phone, and router, have minimal power consumption.
I have similar equipment in my office. Based on a long life of experience with this stuff, you would be much better off with two circuits for your office equipment. If you are just limited to the one, however, it probably won't be dangerous. The question is... What else is on that circuit (bathroom lights, window air conditioner?) If you a tripping the breaker due to overloads, you will need to do something about it.
20 Amp circuits are also common and preferred whenever possible. You will have a 33% increase in capicity to 2400 resistive watts vs. the 15 amp circuit. The ampacity of the circuit is listed on the breaker (or fuse).
Beachcomber
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Thanks much for your reply. Since I live in an apartment I doubt my landlord would let me have an electrician wire a second circuit. Maybe...I've been here 5 years, plan to continue living here...so he might. The reason I ask is that sometimes the lights in my office/spare bedroom will dim when the laser printer starts up. That Samsung is a new addition, and I guess it put me close /over to what my wiring/circuits can handle.
I'm not sure what else is on the circuit, but I do not get dimming when my A/C (which is is another room) comes on, or when I turn lights on. The dimming also doesn't happen when I use the photo/inkjet printer, but of course it's a much smaller printer. You mentioned monitor age might be a factor; mine is a KDS purchased in 2003, I think. It's a CRT.
Oh, I have not had any breakers tripped. Just the dimmed lights phenomenon.
On Sat, 04 Jun 2005 07:05:46 GMT, not snipped-for-privacy@xxx.yyy (Beachcomber) wrote:

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wrote:

Overload or not, that flickering when the laser printer's fuser starts cycling on and off can drive you nuts. Try to get a dedicated outlet for that if possible. Also, The laser printer is your largest load on your list of equipment when it's online and printing. Also, since most of your equipment uses Switch-Mode Power Supplies, there is a large non-linear component to your load; an instrument like the aforementioned "Watts Up" will not give your accurate results because it measures RMS. It will not indicate the full actual load applied. Additionally, the NEC requires circuit ampacity to be rated for 125% of the rated load when the load is continuous plus the non-continuous portion:
210.19(A)(1) "Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Where a branch circuit supplies continuous loads or any combination of continuous and non-continuous loads, the minimum branch-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the non-continuous load plus 125 percent of the continuous load."
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I had the exact same issues (dimmed lights) when I got my first Apple NTX Laser Printer way back around 1994. That sucker had the pickiest power requirements I've ever seen and I had to give it its own circuit, even it meant running a heavy duty extension cord across the room. I believe it had something like 7 separate power supplies within and God help you if you wanted to run it on an alternative source of power like an alternator.
The new Watt's Up claims to be fairly accurate, even with complex loads. It will also give you a value for the power factor. If you don't have a $3000 precision scientific wattmeter just laying around, it's certainly better than just guessing.
Also, if you need to find out what else is on your office circuit, just flip the breaker off and see what else has stopped working.
When you design your own house, put in two dedicated isolated ground 20A circuits for your office equipment. You can even have the funny looking hospital grade orange receptacles with little pilot lights in them for the ultimate in coolness.
Beachcomber
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You can go with the load calcs, or , if you have your own circuit breaker panel inside your Apt. without bthering the LL, you can have someone place an ammeter on the circuit with all you're equipment on, and measure just how much draw you have on each circuit and take it from there. 1 Solution is, If the conduit used in the apartment is Pipe (EMT) it wouldn't be too difficult to upgrade the circuit to accomodate your demand., but there are other solutions like changing the light fixture wires to another unloaded circuit, Or Easier yet, try placing a Compact Fluorescent Bulb on it and see if it still dims when your laserjet kicks on. Roy
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If the UPS is carrying the load you are OK. It will shut down long before you will trip a 15a breaker.
On Sat, 04 Jun 2005 06:01:13 GMT, Trevor Smithson

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On Sat, 04 Jun 2005 10:45:37 -0400, snipped-for-privacy@aol.com wrote:

Just another thought... If it were me, I would remove the laser printer from the UPS and plug it a separate outlet (ideally on a different circuit and perhaps use a good surge protector device).
The function of a UPS is mostly to keep your computer going during a power failure and give you time to save your open files and do a normal shutdown. A laser printer on that line is going to take up a lot of the capacity of the UPS with no real benefit to you.
Beachcomber
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I run my monitor, main PC, router, and cable modem off the UPS. During the one long power outage I've experienced since I've had the UPS, the UPS battery lasted about 10 minutes. More than enough time to log out of my work VPN, save things and power down gracefully.
On Sat, 04 Jun 2005 15:25:00 GMT, not snipped-for-privacy@xxx.yyy (Beachcomber) wrote:

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As others have noted, little power consumption with all those devices together. The wall receptacle is probably rated for 15 amps. Moreso, it is probably powered by a 20 amp circuit. With so many devices, then a power strip is probably being used. That $3 power strip (that should have no surge protectors as even the UPS manufacturer suggests) must have the one component essential to power strips - a 15 amp circuit breaker. IOW long before ae load can cause wiring problems, that circuit breaker would trip. Again, a power strip without that circuit breaker: replace it for human safety reasons.
Do incandescent bulbs dim or brighten when powering up this system or any other heavy appliances? If not, the you probably have a very healthy wiring system. But again, multiple appliances on one receptacle should be powered through a power strip that has an all so necessary 15 amp circuit breaker.
Trevor Smithson wrote:

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Yes, the lights is the room with my computer equipment dim just a bit briefly, when the laser printer fires up.

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And do lights elsewhere in the building brighten when the UPS is powered?
Trevor Smithson wrote:

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As a side note...can someone here give me a quick primer on electrical terminology. You know, amps, volts, watts, ohms, joules...or a link to a webpage would be great too.

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wrote:

Give this a shot, navigate down to, and through, the electricity stuff.
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
May not be up your alley.
j
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Yes, the lights is the room with my computer equipment dim just a bit briefly, when the laser printer fires up.

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The wall receptacle is probably rated

Are 20A breakers and 20A wiring that prevalent? Most panelboards I see (North of the USA) are chock full of 15A breakers.
j
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Here in the South USA, typically 15A for lighting circuits and 20A for recepticals. (Thats the way I install them, and what I have seen in almost all the homes that I have worked in anyway.)
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Anthony

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| |> Are 20A breakers and 20A wiring that prevalent? Most panelboards I see |> (North of the USA) are chock full of 15A breakers. |> | | Here in the South USA, typically 15A for lighting circuits and 20A for | recepticals. | (Thats the way I install them, and what I have seen in almost all the homes | that I have worked in anyway.)
I see that in lots of homes around here in WV (considered by some to be part of the south).
My plan for my future house is to just go with 20A across the board, while still keeping all lighting on separate branch circuits apart from all the receptacle branch circuits. Switched receptacles intended for table lamp use will be on the lighting circuits.
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The circuit breaker will protect the wiring as long as the circuit breaker is good and the wiring is done well (e.g. no loose connections in wiring, no loose connections where cords plug into outlets, etc.). The circuit breaker is probably fine. If you have, and are comfortable using, a voltage tester, you could plug in some big loads (some 300W - 500W torchiere lamps, heater, hair dryer, etc.) on your power strip and see how much your voltage changes at the power strip with the load ON versus with the load OFF. Post the info here (Watts & type of load, voltage with load OFF, and voltage with load ON) and you can get some opinions on whether the numbers sound reasonable or not. You could also give some indication of how far the outlet is from the panelboard. If you use lighting as a load for this test, you can also try shaking and wiggling cords and connectors and watching to see that the lighting stays constant. This is a mild indication that there is not some intermittent connection that may cause trouble if your cords gets bumped/disturbed as they likely will with normal use.
Laser printers are notorious for causing light dimming. They will draw huge current (30A is a number I believe I've heard kicked around) for brief periods for internal reasons (heating toner I believe). Apparently many of them will do this regularly, every 20 - 60 seconds. That huge current draw will cause a brief voltage drop at the load end of the circuit, which can cause lights on the same circuit to dim. Your a/c will be on a different circuit, which is the reason you don't see it causing dimming of those lights. If you want to find out what all is on your computer outlet circuit, turn off the breaker. Obviously, the lights on the circuit will go out. A voltage tester or portable lamp (or portable anything) will tell you which outlets are on the same circuit. You may want to keep them in mind, and not plug a heater into one of those outlets some day.
j
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