AFCI breakers tripping every 7 days

[hmk123]

We have a new addition to our house with its own subpanel. Since it is a bedroom the outlets and lights are on their own two 20Amp AFCI breakers. We now narrowed it down to these two AFCI breakers tripping every 7 days at roughly the same time (from the time they were last reset). In the beginning we did not pay close attention but it always seemed roughly a week. Now it tripped again this evening, 7 days (within the hour) since we last had to reset it. It has been doing this even when the new room was not occupied and there was practically no load. Yesterday I disconnected the Smoke Detector because I thought it might do a self test every 7 days. But it still went out today. We have three dimmers on there and they control recessed lighting as well as one ceiling lamp with 3 or 4 light bulbs. Initially while no one was living there, there was no other load (yet a week later they had tripped). Now there is a small refrigerator in the room, plus a TV, a cable box, a micro wave, toaster and a lamp (there is also a Gas Fire Place with low voltage ignition). One would think that it has to be a device that keeps track of time and does a certain function every 7 days that will trip it. Have you ever heard of such a thing? Are recessed lights that touch the insulation known to cause any trouble? I just don't know of any device in that room that has a circuit that does things on a weekly basis (on the 7th day) after it was turned on. And we replaced both breakers once.

[Mikey]

I gather they trip 7 days after reset, not on a particular day? Do they both trip at the same time? I don't know enough about how an AFCI breaker works to say whether this is a possible explanantion, but I'm wondering if there's something happening on the service side of these two breakers that makes the AFCI breakers think there's an arc fault on the load side?

[hmk123]

Yes, they do both break at the same time. There are three AFCIs in the panel. The two outer ones break at the same time. The middle one stays. They used to be all 15s and we replaced the two outer ones with 20s. The one in the middle is actually used for the 2 outlets in the bathroom. One would think they need to be GFCI but they are not. There is one GFCI outlet near the wet bar. I just double checked and the fridge and toaster, etc, are not on one of those two AFCIs that keep tripping. So only the bedroom outlets and lights are on those two AFCIs. One is for the lights, the other one for the outlets. If this week is an indication, you can almost set your clock based on it. I talked to Square D (who makes our breakers) and the guy talked about a leak current that can trip them. But I assume that is not something that builds up over time, right? And how would it always need exactly a week? Again, the strange thing is this already happened when there was no one living in there yet and there was only occasional load on it. And yes, it is not the same day every week. It is 7 days to the hour after your reset them.

[Mikey]

By "inner" and "outer" I assume you mean the 3 breakers are in line on one side of the panel's 2 columns of breakers. If so, try swapping one of the outer 20A breakers with the inner 15A -- just unplug them and interchange their positions. This will place the now-outer 15A and 20A breakers on the same leg of the panel, and perhaps tell us if it is in fact something to do with the service, if the 15A breaker starts to act up.

[alternety]

Are those dimmers by chance the kind that can be controlled remotely over the power line? Do you have any household automation components installed?

Is it possible to remove everything from the circuits (unplug any thing in the outlets, unscrew bulbs, etc.) for 7 days to see what happens? Use some extension cords from other circuits (being careful about loads so you don't trip other breakers). If it still fails you now know it is not a faulty load that you know about. If it does not happen, put things back one at a time until it happens.

You said there were three in a row and the two outside ones trip. That probably means they are both on the same leg of your power service. It may be useful to exchange the wire of one tripping breaker to the non-tripping one.

[hmk123]

We do not have any household automation installed. But I will check to see if the dimmers could be controller remotely. Do they contain any circuits?

Using extension cords is a good idea. I think we will try that. What about the dimemrs? Do they need to be uninstalled? They seem to have a little light in there when they are turned off.

Would it make sens to try AFCIs from a different manufacturer?

Swapping the AFCIs might also be a good try (using the other leg). Also, a friend said I should put a night light on the 15 A one currently in the middle and see if this trips it, too.

It will be interesting if they trip again this Sunday at 8:45pm. Will be exactly 7 days. That's what it did last time. Am just wondering how it can be so precise without something "knowing" about time that then gets reset.

[hmk123]

I also just found out that there is an outside receptacle on the one breaker and it is a GFCI receptacle. Can that cause problems? Then again, I would not assume it to trip after exactly 7 days. Right now I suspect the dimmers to be the problem.

[alternety]

Smart dimmers will always draw some current. It is one of the issues with using them with fluorescent bulbs. Taking the bulbs out may or may not eliminate current flow, but it will stop any odd interaction between the dimmer and the bulb/ballast. The seven day thing says to me intelligence or some capacitor charging at a steady rate until it triggers something.

An automatic remote meter reading or an attempt at power company load balancing could trigger something. Do you have a plan that lets the power company control loads in the house. Do they offer such control and may be accidentally sending the signals and confusing something in the circuits? Explain the problem to the power company tech support.

Sacrifice a small mammal directly under the main power panel. It works best at the full moon; but in an emergency try it whenever you can. Repeat during the full moon if not effective. Do this will humming the mantra ohm ohm ohm and dance naked widdershins (counter clockwise).

Good luck.

[Mikey]

Has it always been Sunday at 8:45PM? Is there anything anywhere else in the house that happens at that time, like a lawn sprinkler starting up, water softener regenerating, etc.?

[hmk123]

So it is on the 7th day. Which means if it happens next on Sunday, the next time after that it will do it on Saturday. And when noone was living there we did not always reset it right away. So then again, it did it only seven days after the reset. Maybe it is indeed some capacitor that is charging. I will need to keep a close eye on it. In the beginning we just said: funny, it is roughly a week. Now we paid more attention to it and last time it was exactly 7 days to the hour. Will see if it is like that again. That's why I think if it is the power company it would not be based on when we reset it. But I will give them a call. The capacitor sounds more like it although the accuracy seems strange. I think we will take the lights out or replace the dimmers for now with regular switches and see if that helps. Thanks so far to everyone for the tips.

[Mikey]

Too bad it doesn't happen every hour, instead of every week -- this'll take months to track down .

[jadnashua]

Does your power company do electronic reading of your meter? I wonder whether a powerline superimposed digital command is going out at that time, requesting your meter to respond with the current reading...the resulting modulation of the power could be interpreted by the AFCI as an arc since the power would fluctuate. Not normally enough to see anything, but who knows...just brainstorming here.

[Mikey]

If there's additional space in the panel, I'd try adding two 20A conventional breakers and moving those 2 circuits to those breakers. Leave the AFCIs in place where they are, turned on. Wait 7 days and see what happens.

[hmk123]

If there's additional space in the panel, I'd try adding two 20A conventional breakers and moving those 2 circuits to those breakers. Leave the AFCIs in place where they are, turned on. Wait 7 days and see what happens.

Yes, there is room in the panel. That seems like a good idea and I should do that. My contractor mentioned something like that, too.

Also, as far as I know they do not do remote meter reading (yet). I think it needs to be something though that gets reset when resetting the AFCI breakers.

[Mikey]

I asked Square D customer service if a fault on the line side could trip an AFCI breaker. They said no. I didn't like that answer, so I did a little more research, and found the following block diagram of an AFCI (from http://www.iaei.org/subscriber/magaz...mblin_fig5.gif), which seems like it will trip the CB, regardless of which side the fault occurs on:



I then sent the diagram and the same question to the IEEE, which has a special arc-fault advice line set up. They said yes, based on that diagram. There is, of course, no guarantee that the diagram accurately describes Square D's breaker -- they could have incorporated a filter to prevent detecting fault signatures on the line side, for example. Depending on the sensitivity of the sensor, you may also need some load on the load side to complete the circuit through the sensor.

Shall we try for 2 out of 3? Anybody want to do the obvious experiment?