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

One 15 amp circuit in the USA will support 1800 watts of resistive load (15 x 120)=1800. 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

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 phenomen>>

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

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."

If the UPS is carrying the load you are OK. It will shut down long before you will trip a 15a breaker.

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

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

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

The load you describe is not excessive. Your laser will draw ~5 amps periodically to heat the fuser. That periodic increase accounts for the lights dimming.

Ed

They have to heat up the fuser roller. Toner is basically black stuff and glue, and the fuser is what melts the glue to make the black stuff stick to the paper.

The few printers I've taken apart have an incandescent lamp to do this. It looks exactly like the 300 W and 500 W lamps that go in torchiere lights or work lights - a long glass tube with ceramic ends and a straight coiled filament - but it's as long as the width of a piece of paper. You never see the light because it's sealed inside the fuser drum when in operation.

Matt Roberds

Thank you. I wonder if the numbers I've heard (as high as 30A) are rampant exaggeration. The laser printers I have in mind would be corded 120V jobbies, for "commercial duty" in offices or the like.

j

The IBM 3800 that used 14" wide paper and moved 32" a second only used a 1600w fuser lamp. Lets not get too carried away about an 8.5" paper path that moves a couple inches a second. These things are just a few hundred watts (300-500)

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 > I run my monitor, main PC, router, and cable modem off the UPS.

Interesting. Thanks. In this case the 30A might be not such a ridiculous exaggeration, based on a couple of things. Assuming 120V then the nominal RMS current would be 13A RMS, which would correspond to a peak of appx. 19A. I understand the current into an incandescent can be a fair bit higher when first switched on (anyone have any comment on how much higher?). Maybe "as high as 30A" covers this kind of extreme case and 'peak' current.

j