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ResConst · Jan 29, 2009, 06:22 PM

I am troubleshooting a bedroom archfault ciruit. It seems that any load placed on the circuit trips the breaker. As long as all the lights are off and nothing is plugged into an outlet everything works fine. Although, once a light is turned on or something (anything) is plugged in the breaker trips. I have tried running a new home run wire and checked all my lights and switches. Any tips would be very much appreciated.

KISS · Jan 29, 2009, 06:37 PM

Have you changed the switch feeding the light?

stanfortyman · Jan 29, 2009, 06:37 PM

I hate to ask a real obvious question, but did you try another breaker?
By this I mean another arc fault breaker.

ResConst · Jan 29, 2009, 07:03 PM

I actually bypassed the switch and wired directly to the devices. So when the breaker is on the light or outlet should be on.

ResConst · Jan 29, 2009, 07:10 PM

I have replaced the arch fault breaker. This is the second one. I don't think I could have two bad breakers in a row.

ballengerb1 · Jan 29, 2009, 08:24 PM

This is probably all to simple but it is possible that you actually have a fault and the breaker is doing its job? Have you considered trying to test adead short?

KISS · Jan 29, 2009, 08:24 PM

So, the short across the switch blew the breaker?

I guess what I would do in this situation is move the tripping circuit to a regular breaker and insert a milliameter in the ground lead. Basically your looking for greater than about 6 mA to trip the breaker.

ResConst · Jan 29, 2009, 08:32 PM

Yes, I doesn't matter what I have connected directly to the breaker. Switch or not it trips if there is any kind of load. I have tried inserting a normal 15 amp breaker and it works fine. What would greater than 6 mA mean?

ResConst · Jan 29, 2009, 08:35 PM

What is a dead short? I don't see how I could have a fault. I am running a brand new wire directly from the breaker to a light. No switch no junctions. This set up is just for testing purposes. It still trips every time I turn on the power.

ballengerb1 · Jan 29, 2009, 08:45 PM

Since reading your next few posts there is no dead short, the standard breaker held so there's no short.

KISS · Jan 29, 2009, 08:53 PM

A combo GFCI trips at about 6 mA. There should be no cuurent in the ground wire. I'm suspecting that there may be, meaning the AFCI is doing it's job as a GFCI.

The AFCI looks for a paricular signiture type of current waveform of an arc. A loose connection is what it's looking for. So a switch that lingers at the switching point or an accidental erosion of insulation when installing causes the same type of fault.

Make sure the bus bars are clean where the AFCI connects.

There are a few techniques:
1. Measureing (the ground currents)
2. Check for shared neutrals.
3. Substituion
5. Isolation using the binary search technique. e.g Divide in half. Remove last half. Is fault in last half. Then connect 3/4 of circuit. Then figure out if it's between 1/2 and 3/4 and just keep dividing.
6. Inspection

If you have to temporarily replace the feed going up the stairs or something to isolate the wire segment or feed it from another working outlet nearby.

e.g. swich the AFCI to another circuit nearby. Remove the feed from the broken circuit at the first link of the chain. Connect the segments together. This isolates the feed.

Use the binary search technique and replace the bad segment externally.

ResConst · Jan 29, 2009, 09:11 PM

A strange fact is that I also took the AFCI breaker and installed it for my smoke detectors and it did the same thing. It tripped immediately. I have four smokes on their own circuit all hardwired in. I don't know if this tells you anyting new or not. Thanks for the advice so far. It really is helping.

ResConst · Jan 29, 2009, 09:14 PM

One question. It might be a stupid one but I have to ask it. How would you have shared neutrals? Wouldn't you have to have your circuits totally screwed up to do that?

KISS · Jan 29, 2009, 09:29 PM

I'm thinking incorrect installation w/ respect to the pigtail and load neutral. See: AFCI guide to arc fault interrupters for home owners and home inspectors: how to buy, install, test, & inspect AFCIs

And this link: Applying and Using Arc-Fault Circuit Interrupters

Shared neutrals:

You might think it's difficult, but all you have to do is have a fixture or box fed by 2 different circuits and you picked the wrong one to return it to the panel.

Note that tha AFCI has 4 connections:
1. The buss
2. Load HOT
So far, so good. Just like a normal breaker. Now the fun part.
3. Circuit neutral goes to the screw on the breaker.
4. The pigtail goes to the neutral bus bar.

In a typical main panel ground and neutral are connected to the same bar. (there are exceptions)
In a sub-panel ground and neutral are separate. You MUST use the neutral bar for the pigtail.

ResConst · Jan 30, 2009, 07:07 AM

I did not know the ciruit neutral went to the breaker. This is probably my problem comletely. Right now the circuit neutral and the pigtail both are going to the neutral bar in the panel.

KISS · Jan 30, 2009, 12:26 PM

See what happens when you read the directions?

i.e. When all else fails, read the directions.

The GFCI looks at the difference of currents flowing in the hot and neutral. It does this, by DIRECTLY measuring the difference. One conductor is passed clockwise through a toroid and the return conductor counter clockwise.

With another winding, that difference can be amplified.

Shorted neutrals are handled in a different fashion. Both hot and neutral are modulated out of phase to the load. If for some reason the load side neutral is stuck at ground, the modulation can be detected because I won't cancel.

KISS · Jan 30, 2009, 01:31 PM

I'm surprised at the experts that answered. At least we were thinking simple, just not simple enough.

Looks like I was the only one who got it right.

I'll admit, I was a little misled by the ResConst handle.

stanfortyman · Jan 30, 2009, 01:38 PM

Sorry, but I find it ironic that someone who is "troubleshooting" an electrical circuit does not even know how to wire it. :(

ResConst · Jan 30, 2009, 05:01 PM

Its my own home that is having issues. I thought if it was something easy I wouldn't need to call an electrician. Thanks for not being helpful though.

stanfortyman · Jan 30, 2009, 07:04 PM

Oh goody. Another red box to add to my collection. :D :rolleyes:
Don't worry, I rarely give retaliatory reds. I don't put much stock in those popularity systems.

It wasn't meant to be helpful. I was stating an opinion. See my signature line?
Besides, between your name, the way you explained the original situation and the fact that you never mentioned this was your own home. I had you figured for another handymen in over his head.
Sorry if that is an easy assumption to make. It just didn't apply here is all.