Dont want to die in a fire but want to use my computer more.
March 20, 2008 3:10 PM   Subscribe

Possibly arcane question about my computer and AFCI circuit breakers.

I moved not all that long ago into a brand new condo (new construction, that is) and as per code the bedrooms all have AFCI circuit breakers on the outlets rather than GFI breakers. Sounded fine to me. Except that since I live alone I'm trying to set up one of the "bedrooms" as an office/den/whatever which, of course, requires my computer be in there. The problem is that the computer, with insane high end video card and so forth, confuses the AFCI circuit breaker and nuisance trips every single time I try to plug in the computer. Every. Single. Time.

I can plug an HDTV, XBOX 360, DVD player, satellite TV receiver, DSL+router, monitor, printer, and telephone in to a power strip and one of the outlets in here with no problem whatsoever. But if I unplug all of that crap and plug in my computer - by itself, no peripherals, etc - the AFCI breaker trips instantly. I can use the computer perfectly well on any non-AFCI breaker but try to plug it in to any of the bedroom outlets and BOOM.

I've looked a bit online and this appears to be a not completely unknown issue with higher end computers and AFCI breakers in new construction. Has anyone encountered this problem themselves and figured out a way around it that does not involve replacing the AFCI breaker with a GFI breaker?

Some kind of uninterruptible power supply? A super magic electrical doohickey that modulates the power draw so the idiot AFCI breaker doesn't interpret my computer as a dangerous arcing condition? A different brand of AFCI breaker which plays better with other children? If so, which brand? Sacrificing a chicken to the AFCI breaker? Help?

Right now I've got a bright orange heavy gauge extension cord strung from my power strip in the AFCI breakered office through the middle of the room and out into the hallway. The hallway, of course, has regular old circuit breakers rather than AFCI breakers. This is untenable in the long or even medium term. Like I said, I know I can replace the AFCI breaker with a regular circuit breaker and it may work just fine but I'm uncertain exactly how that comports with the fire code or whatever. There's gotta be a reason there are AFCI breakers in the bedrooms. Or is it just a crappy nuisance requirement?
posted by Justinian to Home & Garden (12 answers total) 1 user marked this as a favorite
 
Maybe a UPS/power conditioner with a transformer in it would help. If the computer circuit were electrically isolated from the wall side through a transformer, the AFCI breaker might not see the "characteristic waveform" that makes it trip. Just a guess, though.

Also, I don't know about consumer-type household breakers, but breakers around here have adjustable short-term and long-term trip setpoints that can be adjusted. That's for overcurrent, though, I don't know if 'sensing an arc condition' has an adjustable setpoint. You could call an electrician and ask - they probably wouldn't charge you just to tell you over the phone if that sounds like something fixable or not.
posted by ctmf at 4:17 PM on March 20, 2008


You might try replacing your PC's power supply with a new one that has active PFC (Power Factor Correction). PFC is intended to reduce the higher harmonic noise on the power lines generated by the high frequency switches in the power supply. Many cheaper power supplies only have passive PFC which is not as effective. Every switching power supply will have slightly different noise characteristics. You want to find one that doesn't cause false tripping of your AFCI breaker. Unfortunately it might be a case of trial and error finding a supply that will work for you. Here is one example I found in a quick search although I can't vouch for it.

As ctmf said, it is possible that using a UPS between the wall and PC may help, except that most moderately priced uninterruptible supplies pass AC power directly through except when the AC main power fails. So that isn't going to filter anything for you. What you would need is what is called an online or true UPS that always conditions the power going to the PC. These are usually in the hundreds of dollars. It would be cheaper to replace the PC power supply if you are comfortable with doing that.

The breaker has a microprocessor inside that looks for the signature of an arc fault. The software algorithms for difference brands of breakers will look for slightly different noise patterns. So the other alternative is to replace your AFCI with a different brand device.
posted by JackFlash at 4:50 PM on March 20, 2008


Thanks guys. I have seen some references that certain brand AFCI breakers work better with computers than others; specifically the "Square D" brand breakers. I have to go to home depot tomorrow anyway so will probably pick up another brand AFCI breaker and a normal breaker while I'm there. If changing the brand works that's probably the easiest solution with the least change to the status quo.

If that doesn't work, I'll look into changing the power supply in the computer as suggested, but I'm definitely not going to buy a true UPS if it costs a few hundred bucks when replacing the AFCI with a $10 GFCI will almost certainly work. After reading more about AFCI breakers online I'm feeling more comfortable with simply replacing it with a regular breaker. It should be no different than how I've run computers for the last 25 years.
posted by Justinian at 6:37 PM on March 20, 2008


Just get a plain old outlet. You should never plug a computer into a GFCI anyway. If it switches off, you will lose whatever you're working on.
posted by kindall at 10:52 PM on March 20, 2008


Kindall, the AFCI is in a branch breaker back at the main breaker panel. Since 2002 the National Electric Code requires an AFCI breaker on all circuits that feed bedrooms. A GFCI is often found in single outlets in a bath or kitchen and protects only against electrical shock. An AFCI serves the entire circuit and protects against fires. The best solutions were presented above. An ordinary breaker should only be a last resort if nothing else works.
posted by JackFlash at 11:39 PM on March 20, 2008


Yeah, I'm going to try a different power supply first.

Since a licensed electrician will likely refuse to replace a code-mandated AFCI breaker with a regular breaker, is there a physical difference that would present problems with making such a replacement? Like do the wires connect differently such that I can't simply shut off the main power, flip all the circuit breakers to OFF, pull out the AFCI breaker, and push in the regular breaker? I suppose once the power is shut off I could take off the panel and inspect the wiring to make sure it's the same.

I hate working around live power, though, and I know the line in to the main breaker is still live .
posted by Justinian at 12:17 AM on March 21, 2008


You should be able to replace one with the other. First try a different brand of AFCI and if that doesn't work you can put in a regular breaker. Make sure you turn off the main breaker at the top of the panel first. Then use a volt meter to make sure that power is removed from the bus bars.

The two types of breakers are wired slightly differently. For a normal breaker, only the black hot wire connects to the breaker. The white neutral wire connects directly to the neutral bus bar. For the AFCI, the white wire must also go through the breaker for sensing. So it has a little pigtail attached. The pigtail goes to the neutral bus bar and the circuit white wire connects to the neutral side of the breaker. So the white neutral wire comes in from the house circuit, goes to the breaker, out the other side through the white pigtail which then connects to the bus bar. Just connect the new AFCI the same as the old. If you replace with a normal breaker, remove the pigtail from the neutral bus bar and connect the white circuit wire that was on the AFCI to the location on the neutral bus bar where you removed the pigtail. It is easier to disconnect and connect the wires to the breaker before you install it in the panel.

Don't try any of this stuff if you don't know what you are doing. Don't touch anything without testing with a volt meter. Touching an energized circuit could kill you.
posted by JackFlash at 2:39 AM on March 21, 2008


Thanks, JackFlash. I'm giving everything else a shot before replacing it with a regular breaker. Like I said in my question, I know that's a last resort.

I'm heading out now and picking up

A) A new power supply for the computer since I'm going to build a new one soon anyway.
B) A Square D single pole AFCI breaker
C) A Siemens Q120 single pole breaker

and will try them in that order. I will also try not to kill myself with electricity.
posted by Justinian at 11:05 AM on March 21, 2008


(I suppose AFCI breaker is redundant, kind of like PIN number)
posted by Justinian at 11:06 AM on March 21, 2008


I replaced the power supply with one that had active PFC and it is no longer tripping the AFCI. So the other answers would probably have worked, but this was the cheapest one that had no possibility of causing me to die a horrible electric death!

I have some spare breakers now in case something happens too.
posted by Justinian at 6:32 PM on March 24, 2008


Now that the question is resolved and nobody is reading this anymore, do I get to post ASCII pictures of bunnies with pancakes on their heads?
posted by Justinian at 6:33 PM on March 24, 2008


I'm still reading. Good to know the new power supply worked, for future reference.
posted by ctmf at 9:47 PM on March 24, 2008


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