AFCI trip on new furnace

M

Mechy

Member
Location
Ohio
Occupation
Professional Engineer
New AC and furnace professionally installed 4 months ago. Once cold weather hit, the 20A AFCI breaker for the furnace tripped. Wiring to furnace is through metal conduit. Furnace is only device on the circuit. After 1st trip, installer checked wiring connections. After 2nd trip, next day, installer replaced ACFI with 20A GFI breaker. Stated the ACFI was likely reacting to variable speed blower motor looking like an arc fault.

Still also considering possible amp draw issue. Due to filter being directly against the furnace enclosure, I don’t have a handy place to drill to insert a manometer tap to check pressure rise across the blower. The prior unit had a little length of duct after the filter for inlet pressure and also a handy tapping hole near heat exchanger coils for outlet pressure. So I can’t tell yet if it was too much load on the motor. We’ll have a cold spell this weekend, so if it’s motor load, the new 20A GFI only breaker should trip.

I have found a reference, but it’s AI -not real intelligence, that supports the installers claim:

“High Frequency Capacitive Leakage
Many modern furnaces with variable speed blower motors may not be compatible with AFCIs. They can produce high-frequency electrical noise that triggers the breaker.”

If this is the case, I would have expected it to come up elsewhere in the forum unless it is such common knowledge that no one uses AFCI with a furnace. No mention of it in the furnace installation info.

NFPA 70, NEC 2023 article 210.12 seems to indicate AFCI is required: “AFCI protection shall be installed in accordance with 210.12(B) through (E). In 210.12(B) it lists various rooms, closets, hallways and the catch-all “Similar areas”. No mention of what constitutes a “similar area”. It provides exceptions only for fire alarms and arc welders.

The furnace is in an unfinished basement.

So I have 2 concerns. Only the first applies to this forum. The second is a question of law for local inspector.

1. Is tripping an AFCI a common, known, issue for brand new variable speed blower motors?
2. Question Monday for local electrical inspector: Is AFCI required by law for the furnace?
 
1) Happens all the time. AFCIs are the most useless garbage known to man. Never saved one life.
2) I don't believe it is, depends on what year code you are on and where you are.
2a) Why is the electrical inspector getting involved 4 months after installation?
2b) If he says you have to have an AFCI, change it out to a regular breaker as soon as you see his taillights! Last thing you need is for "no heat" while you are away and you come back to frozen plumbing!

-Hal
 
Mechy said:
1. Is tripping an AFCI a common, known, issue for brand new variable speed blower motors?
Click to expand...
VFD appliances are known to trip the GFCI function of DF breakers.

AFCI’s trip on everything else installed by untrained persons, especially commercial electricians attempting residential wiring.
Mechy said:
2. Question Monday for local electrical inspector: Is AFCI required by law for the furnace?
Click to expand...
Only if installed in a room that requires AFCI protection.
 
hbiss said:
1) Happens all the time. AFCIs are the most useless garbage known to man. Never saved one life.
2) I don't believe it is, depends on what year code you are on and where you are.
2a) Why is the electrical inspector getting involved 4 months after installation?
2b) If he says you have to have an AFCI, change it out to a regular breaker as soon as you see his taillights! Last thing you need is for "no heat" while you are away and you come back to frozen plumbing!

-Hal
Click to expand...
Thanks. Regarding 2a above: 4 months ago it had a AFCI breaker, when furnace wasn’t running. The GFCI was a change recommended days ago by the installer.
 
AFCI & GFCI Requirements vary depending on Code cycle and location. Likely neither is required.
Post #2 & #3 above give the best advice.
 
Mechy said:
NFPA 70, NEC 2023 article 210.12 seems to indicate AFCI is required: “AFCI protection shall be installed in accordance with 210.12(B) through (E). In 210.12(B) it lists various rooms, closets, hallways and the catch-all “Similar areas”. No mention of what constitutes a “similar area”. It provides exceptions only for fire alarms and arc welders.

The furnace is in an unfinished basement.

....
Click to expand...
The basement is not a similar area. There is no requirement for AFCI protection for the basement. There is also no requirement for GFCI protection for a hardwired furnace in a basement/

Put the furnace on a standard breaker.
 
I would put an amprobe on the furnace blower

. I have an new AFCI on a new microwave dedicated circuit for about 16 months now. It tripped the afci the first day and twice more in the first 6 weeks.
Hasn't tripped since. Fingers crossed.
 
Eddie702 said:
I would put an amprobe on the furnace blower

. I have an new AFCI on a new microwave dedicated circuit for about 16 months now. It tripped the afci the first day and twice more in the first 6 weeks.
Hasn't tripped since. Fingers crossed.
Click to expand...
The stakes are low playing Russian Roulette with a microwave. Unless you are hoping for frozen pipes and making a score on an insurance claim I wouldn't recommend putting central heat on an AFCI heading into winter.
 
hbiss said:
1) Happens all the time. AFCIs are the most useless garbage known to man. Never saved one life.
Click to expand...
Last week I was at three service calls to see why breaker was tripping two were 15A AFCi's, first one was a condo that had #12 Aluminum branch circuit wiring, several melted connections, the condo had been renovated and the electrician (not us) did not make proper AL/CU pigtails and the connections were oxidizing after 5 years. Fortunately they used AFCI's when they replaced the panel and it caught the issue before it became a fire.
Second one was a bedroom receptacle in a old house that was fed from knob and tube, someone had run wiremold off it to feed a wall switch and ceiling fan, turns out the fan hot was pinched energizing the entire run of wiremold, again AFCI was added probably when they replaced the panel in mid 2000's it was early style AFCI (which seem to work better).
I do agree I would never put a furnace on a AFCI, but I think they do have a place, its just not every place.
 
pipe_bender said:
Last week I was at three service calls to see why breaker was tripping two were 15A AFCi's, first one was a condo that had #12 Aluminum branch circuit wiring, several melted connections, the condo had been renovated and the electrician (not us) did not make proper AL/CU pigtails and the connections were oxidizing after 5 years. Fortunately they used AFCI's when they replaced the panel and it caught the issue before it became a fire.
Second one was a bedroom receptacle in a old house that was fed from knob and tube, someone had run wiremold off it to feed a wall switch and ceiling fan, turns out the fan hot was pinched energizing the entire run of wiremold, again AFCI was added probably when they replaced the panel in mid 2000's it was early style AFCI (which seem to work better).
I do agree I would never put a furnace on a AFCI, but I think they do have a place, its just not every place.
Click to expand...
High resistance connections won't trip AFCI's. They have no way of differentiating that from normal resistance loading. Often if this is the situation the hot connection eventually develops a ground fault and if anything the AFCI will trip on GFP component. Not all have a GFP component anymore so not sure if those will trip in this situation.
The situation you described with a conductor pinched and contacting wiremold - that also probably tripped on GFP function. All earlier versions of AFCI's did have a GFP component.

I still haven't seen "that place" where they are actually something useful. First thing is 120 volts just doesn't sustain an arc for long at all unless you intentionally keep feeding material into the arc. Otherwise is sort of no different than using an arc welder but not feeding your electrode rod/wire into the work, the gap will quickly grow too big and not enough voltage to sustain the arc.

277 volts tends to keep arcing much longer than 120. Yet they don't address this particular voltage for such protection.

It started out with a legitimate request to find a way to prevent certain electrical related fires. They came up with something that doesn't really address the real cause of most those fires- resistive heating where it shouldn't be. then it became a money grab from the manufacturers once they lobbied to get it into codes and kept lobbying to expand the requirements as time went on. They have nothing to lose by pushing this. No other organization has enough profit motive to do the necessary testing to prove it wrong or at least questionable to the code making panels.
 
pipe_bender said:
Last week I was at three service calls to see why breaker was tripping two were 15A AFCi's, first one was a condo that had #12 Aluminum branch circuit wiring, several melted connections, the condo had been renovated and the electrician (not us) did not make proper AL/CU pigtails and the connections were oxidizing after 5 years. Fortunately they used AFCI's when they replaced the panel and it caught the issue before it became a fire.
Second one was a bedroom receptacle in a old house that was fed from knob and tube, someone had run wiremold off it to feed a wall switch and ceiling fan, turns out the fan hot was pinched energizing the entire run of wiremold, again AFCI was added probably when they replaced the panel in mid 2000's it was early style AFCI (which seem to work better).
I do agree I would never put a furnace on a AFCI, but I think they do have a place, its just not every place.
Click to expand...
I agree with kwired. While the AFCI breaker may have sniffed out a problem that a normal breaker wouldn't it has nothing to do with the arc fault technology in the breaker. The ground fault circuitry, added to AFCIs because they suck otherwise, is what was effective. AFCIs are a fraud and a waste of money.
 
kwired said:
No other organization has enough profit motive to do the necessary testing to prove it wrong or at least questionable to the code making panels.
Click to expand...
You would think the code making panels would be smart enough to figure this out themselves. It's not like the mountain of complaints all these years has been hidden. It's almost like they are in on the fraud.

Has anybody ever written a PI to have all AFCI requirements stricken? And dozens of other companies and individuals to barrage them with the same for every new code cycle?

-Hal
 
kwired said:
High resistance connections won't trip AFCI's
Click to expand...
More accurately stated, load resistance wont trip any fuse, breaker, or xFCI device.
kwired said:
it became a money grab from the manufacturers
Click to expand...
Also true with 2-Pole GFCI expansion, regardless of appliance incompatibility.
kwired said:
First thing is 120 volts just doesn't sustain an arc
Click to expand...
AFCI’s never needed arcs, much less amps, to trip all the time for unknown reasons, to most electricians.
kwired said:
that also probably tripped on GFP function
Click to expand...
GFP is a downstream event only, which wont explain why AFCI trips on upstream events.

AFCI also trips on common-mode resistance, and power signatures, historically triggered by harmonic noise, appliances, or gadgets, especially those missing FCC certification from Amazon.com
 
ActionDave said:
AFCI breaker may have sniffed out a problem that a normal breaker wouldn't it has nothing to do with the arc fault technology in the breaker.
Click to expand...
Most xFCI devices are not designed to be durable, with unshielded integrated circuits, subject to damage without SPD, and Test-buttons subject to mechanical failure from exposure to the elements.

Lighting strikes 5 miles away, and xFCI is junk, never was suitable for service equipment, nor as a comparison to simpler thermal magnetic breakers.
 
Last edited:
You must log in or register to reply here.
Top