AFCI/LDCI A.C. cord problem

13670 Views 7 Replies 3 Participants Last post by Greg Sparkovich, Sep 19, 2007

Greg Sparkovich

Discussion Starter · Sep 15, 2007

Hi,
Can an AFCI device on the cord of an air conditioner detect a fault or arcing condition on the circuit it's plugged into?
I would have thought 'no'.
(BTW, the cord label says 'AFCI', not 'LDCI')
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The reason I ask is that when an air conditioner is plugged into a new receptacle that was recently installed, the AFCI trips on the AC unit's cord.

I plugged it into the 'old' receptacle (on an extension cord!) and it worked just fine.

So ...I plugged my tester into both receptacles to be sure they were both wired properly. It turns out the 'old' receptacle wasn't grounded.
so I thought that there must be a problem between the hot and ground in the AC unit and that this would trigger a trip in the AFCI protection when the AC unit was plugged into a grounded receptacle.

To quickly check my theory, I used a 3-prong adapter in the grounded receptacle -making sure that the metal terminal for the screw didn't touch the receptacle (IOW, I created a non-grounded condition on the 'new' circuit without taking it apart). It still tripped the AFCI protected cord. That seems to indicate that the problem is between the hot and the neutral after all -but before the AFCI protected cord???

I took everything apart and checked for a loose connection and the voltage maybe fluctuating or being different between the hot and the neutral vs. ground -but when I tested with my multimeter, it seemed to be getting a steady 112 volts from the hot to both the ground and neutral.

This is a mystery to me. What am I missing here?

Thanks in advance for any ideas or trouble shooting suggestions.

Peace,
Greg

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Joe Momma

· #2 · Sep 16, 2007

AFCI protection has nothing to do with the ground, such as GFCI protection does.
AFCI looks for small 'spikes' in the waveform of AC voltage indicating an 'arc' in the circuit.

This new circuit you had added was wired poorly, perhaps a staple driven too tightly, or a nail to hang a picture pierced the wire. Neither of which would happen if the circuit were run by a pro.

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MDShunk

· #3 · Sep 16, 2007

Does this air conditioner receptacle happen to be part of a multiwire branch circuit? I've been reading lately about loads on other phases of a multiwire branch circuit screwing with the neutral of that branch circuit "just enough" to confuse an AFCI/LCDI plug on another leg into tripping.

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Joe Momma

· #4 · Sep 16, 2007

How does an LCDI differ from a GFCI? anyone know the characteristics differences?

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MDShunk

· #5 · Sep 16, 2007

Joe Momma said:
How does an LCDI differ from a GFCI? anyone know the characteristics differences?

I'd sorta like to know myself. I did try to look the other night to see what the trip point of an LCDI was, and couldn't come up with anything. What I did find was that most or all cord-end LCDI's are made by no-name manufacturer's in China, so a quality issue might be the main culprit on many of these mysterious tripping air conditioner LCDI's.

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MDShunk

· #6 · Sep 16, 2007

Hey, I just found this document, which is pretty interesting regarding LCDI's. http://www.fireshield.com/04_0301TechNotes.pdf

It seems LCDI cord ends use shielded cable for the cordset, and it's looking for leakage to the shield. The document includes this chart:

I'm curious enough now to maybe see if I can still get one of those little 89 dollar window air conditioners at WalMart and tear the cord and the LCDI apart.

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Greg Sparkovich

Discussion Starter · #7 · Sep 17, 2007

MDShunk said:
Does this air conditioner receptacle happen to be part of a multiwire branch circuit? I've been reading lately about loads on other phases of a multiwire branch circuit screwing with the neutral of that branch circuit "just enough" to confuse an AFCI/LCDI plug on another leg into tripping.

I believe this could happen ...alas this is a new circuit, the only location run on new 12/2 romex.

I guess what I don't understand is that if it's a pinched neutral as JM suggests, how can an AFCI device on an A.C. cord detect a neutral/ground short on the branch circuit when the neutral and ground are eventually going to the same bus bar 25 feet away?
I understand that if it were an AFCI breaker, it could sense a problem in the entire circuit, but since this is a cord, I would think that it can only detect problems that occur *after* it -in the device it's protecting. How is that an incorrect assumption?

Thanks in advance for any help answering my question; I appreciate the time.

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Greg Sparkovich

Discussion Starter · #8 · Sep 19, 2007

I finally got back to trouble shoot this morning.
Happy to say the problem was the cord/AFCI device.
I disconnected the breaker and neutral in the panel and did not get continuity between the neutral and the ground. For good measure, I connected an AFCI breaker to the circuit and put a 100watt load on the circuit. No problems.

Meanwhile, the AC unit stopped working at all.

The whole thing is still a mystery to me though -which is annoying.

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