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In my attic I have a relatively decent electrical circuit that runs a family room with a modest entertainment system, a home office with a monster PC, and a couple of ceiling lights. I've never had any problems with it before.

Recently I got a new laser printer that apparently draws a lot of current briefly when it comes out of sleep mode - enough to trip my UPS (the printer is not plugged into the UPS). I don't know if this is a dangerous situation, but it's unsettling and I'd like to fix it if possible.

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Could you clarify what you mean by "trip my UPS"? UPS is an un-interruptable power supply (battery backed-up mains voltage). So is your breaker tripping? Does the UPS just momentarily detect a loss of power from the outlet? etc. –  qes Nov 6 '12 at 17:18
The UPS appears to detect a dip in voltage and goes into battery mode for a little while. Sorry if my description above was misleading. The printer does not trip the circuit breaker in the basement. –  GXSmiley Nov 6 '12 at 17:53
Didn't realize laser printers are so power hungry. This answer on SuperUser explains Why you shouldn't attach laser printers or scanners to an UPS –  Tester101 Nov 6 '12 at 18:44
OMG 23A? I'm not an electrician but that seems awfully high for a single device. I mean, that would blow a typical residential circuit, no? –  GXSmiley Nov 6 '12 at 18:56
I used to have an HP LaserJet4 printer. I ran a separate circuit for it per the manual. That helped keep my lights from dimming too much. Recently I had an issue with a UPS that kept tripping. I found out that I could configure the UPS voltage trip sensitivity. Lowering the sensitivity solved my occasional tripping. Maybe your UPS has a similar feature. –  Scott Bruns Nov 7 '12 at 19:27
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3 Answers

To directly answer your question: no you cannot "boost" a circuit.

Every wire has a voltage drop, and according to NEC it can't be more than 5% at the outlet. Voltage drop is proportional to the length of the wire, resistance (which is dependent on the size of the wire), and current. In other words, as your load goes up, so does your voltage drop.

If your existing wiring is just on the edge of either load or size, then the current may be going up enough that it's below the UPS threshold and thus the UPS is switching to back-up power because it sees it as a brown-out.

If the cable is too small (typical is 14AWG for a 15A circuit, 12AWG for 20A) then the only thing you can do is either increase the cable size, or run a new circuit (and really, you're not going to pull out the old cable and run bigger cable, it's just as much work to run a new circuit so you might as well do that).

If the load is too high (eg, you're close to 15A) then the only thing you can do is run a new circuit, or decrease the load.

You could start by using a Kill-a-watt or similar device to measure power consumed by your PC, printer, TV, etc. This will help guide you to what is consuming too much power, and where (if you go this route) it makes sense to split the circuit up.

You mentioned lights; using LED or CFL bulbs may be a stop-gap to save some power, and is certainly one of the easier things you can do.

If it comes to it, there's ways to be creative about how to split the circuit up, without necessarily having to rip out a lot of drywall. You may be able to run a new cable halfway, and then splice in and split the circuit into two, starting from a light or receptacle. You may be able to find the wire underneath in the basement, and cut it and put in a junction box so the circuit from that point on is on the new circuit. It's hard to be specific here without actually being in your house.

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thanks for the great info. Do I understand correctly then that circuits come in different amperage ratings (you mentioned 15A and 20A)? If so, would it be possible to "upgrade" my existing circuit? Or is that likely to require rewiring? Also, would it be hazardous to just leave it? I don't foresee a rewiring job spanning 4 floors to be cheap :) –  GXSmiley Nov 6 '12 at 18:43
You can't run 20A on a 14AWG wire (it's against code and a fire hazard): you have to upgrade to a 12AWG for 20A. If you're going to do that, you might as well just run a second circuit (in which case another 15A 14AWG circuit would be fine). As I said, your problem sounds like too much current for the wire size, causing a voltage drop (if the problem was you were drawing over 15A, the breaker would trip) so even if you could, just changing to a 20A breaker wouldn't help at all. –  gregmac Nov 6 '12 at 20:47
You should have got an inkjet ... :) Wow - who would've thought you'd need to rewire to accommodate for a printer. It must be those large commercial ones yea? –  ppumkin Nov 7 '12 at 11:20
ppumkin, LOL no, this is the Brother HL-2270DW, a $150 desktop laser that's gotten great reviews. It really is unbeatable at the price, with a built-in Wi-Fi print server, two-sided printing, 27ppm speed, etc. I really think it's my circuit that's iffy rather than the printer. According to my UPS display, it's providing 115V at best, and when the printer powers up it momentarily drops to about 110V, which is just barely enough to trip the UPS. –  GXSmiley Nov 7 '12 at 15:01
I have this printer too and the lights in my basement dim noticeably when it prints. –  hereswhatidid Nov 7 '12 at 15:29
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If the printer has Wi-Fi, you can put it anywhere. just put it on a different circuit in another part of the house.

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It sounds like you don't know what you are doing with regards to electricity. It's ok. Most people don't. But that means you should probably not even consider anything like the "boosting" that you are requesting. Nothing short of rewiring your home with a heavier gauge would solve your problem safely. If you must do that, call a certified electrician.

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This is a fairly judgmental response for a do-it-yourself forum. Also, the statement "Nothing short of rewiring your home with a heavier gauge would solve your problem safely." is factually incorrect. –  alx9r Dec 8 '12 at 2:26
Thanks, Lars, but I never intended to do any rewiring myself. When it comes to DIY projects around the house, I have a long, proven record of failure :) –  GXSmiley Feb 27 at 1:33
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