AFCI and a soft start tool

[ActionDave]

Got me my first real AFCI head scratcher.

Is there any thing in a "soft start" saw that would trip an AFCI?

The saw comes up to speed extra slow so that is why I call it a soft start. It works on a GFCI protected circut so IMO that rules out a problem with the tool.

Circut checks out. Use any other tool on the same circut- table saw, skill saw, drill motor, air compressor, etc. and the breaker holds.

 

[Pierre C Belarge]

There may be a compatibility issue with the AFCI device and the saw. I would contact the manufacturer of the AFCI and explain it to them. Make sure you have the information on the nameplate of the saw handy for them. They are usually helpful with these types of issues.

 

[Jraef]

The way an AFCI works is entirely different from a GFCI, in fact you can get both features in the same breaker because they are so different. So the fact that your saw would not trip a GFCI s not unusual.

An AFCI detects an arcing fault by responding to a current flow profile that is consistent with an arc; essentially rapid rise rates (gulps) of current in each cycle that have a steep front; as opposed to a relatively smooth sine wave increase. Depending on what the saw mfr means by "soft start", that could look just like an arc current profile to the AFCI circuitry. Assuming it is a universal motor in the saw, they may be using SCRs to ramp voltage to it using phase angle firing, which delays the turn-on of the SCRs within each cycle as a way to reduce the RMS current getting to the motor. That sudden steep fronted rise in current when each SCR turns on may be close to the very kind of thing the AFCI profile is designed to look for.

 

[ELA]

What is the manufacturer of AFCI?
Some are better at discriminating a true arc than others.

 

[ActionDave]

The way an AFCI works is entirely different from a GFCI, in fact you can get both features in the same breaker because they are so different. So the fact that your saw would not trip a GFCI s not unusual

Rodger that. The fact that the saw won't trip a GFCI ruled out a pinched wire or some such problem. However, I was under the impression that AFCI'S did contain ground fault circutry but at a higher threshold than the 5ma of a GFCI. (ref to underlined. I assume can was meant to be can't.)
I am inclined to agree with you that the problem is in the soft start technology, but I must admit the only thing I know about SCR's is what the letters stands for.

I've heard so much talk about AFCI problems. I never had any till now. I'm becomimg a believer that they are lousy.

What is the manufacturer of AFCI?
Some are better at discriminating a true arc than others.

SqD HOM120.

 

[Jraef]

Rodger that. The fact that the saw won't trip a GFCI ruled out a pinched wire or some such problem. However, I was under the impression that AFCI'S did contain ground fault circutry but at a higher threshold than the 5ma of a GFCI. (ref to underlined. I assume can was meant to be can't.)

I don't do residential work so my knowledge came from training seminars I attended, it could very well be that manufacturers have decided to include GFI in them as standard since it's probably only a small incremental increase in cost to do so. All the necessary hardware would already be there I imagine.

I am inclined to agree with you that the problem is in the soft start technology, but I must admit the only thing I know about SCR's is what the letters stands for.

Do a search for "SCR Phase Angle Firing " if you want a better understanding.

I've heard so much talk about AFCI problems. I never had any till now. I'm becomimg a believer that they are lousy.

I think they have their place, but like anything else new, they tend to get applied where they shouldn't be in the early stages of implementation.

SqD HOM120.

The Home Line is not their best effort IMHO.

 

[iwire]

It is my understanding all listed AFCIs include GFP in the 30 to 50 milliamp range as part of the protection scheme.

 

[electricmanscott]

I've heard so much talk about AFCI problems. I never had any till now. I'm becomimg a believer that they are lousy.

Welcome to my hell.

 

[ELA]

AFCI's do include a 30-50ma GF protection in addition to the arc detection circuitry.

Dimmers also use "phase firing" and the AFCI's are supposed to be designed not to trip on their signature.

The larger current coupled with the fast rise times of the control circuit produce a broadband noise signature. AFCIs look for noise in multiple frequency bands. (20Khz, 35Khz and 55Khz center frequencies) in the QO115AFCI breaker.

I would suggest trying a different brand AFCI to see if it holds. If you must use the AFCI you have, and have to make it work on the saw circuit, then an EMI filter between the saw and the AFCI may help. If you use an EMI filter look for a higher quality unit (larger inductance values) with a good low frequency attenuation figure.

The funny thing about it is that if you add enough inductance/capacitance (EMI filter) to prevent the nuisance tripping, will the breaker then trip on a real arc?

 

[ActionDave]

At this point the problem is just an annoyance, but it is the first time that I have experienced an AFCI problem that was the breaker and not a "housekeeping" issue with the circut.

Electricmanscott I now feel your pain and will join you in any rebellion you wish to lead.

 

[kbsparky]

The question I have is this: Does the saw trip on starting, or stopping?

I have seen numerous instances where a "chop saw" would start and operate just fine plugged into an AFCI protected receptacle. When the carpenter released the trigger, that was when the breaker tripped.

Seems that many such power tools have a built-in safety feature that uses a short burst of slamming the motor into reverse to slow down the blade (electric brake?).

That burst I believe makes the motor brushes come alive with a short-duration arc (can't blame `em for that -- there should be a lot of stress here trying to slow down that blade). This arc is interpreted to be a bad thing by the AFCI unit thus tripping the breaker.

So now we have one safety feature canceling out another safety feature with the electric brake tripping the arc-fault breaker. Which one wins?

It would seem that the politically motivated rules (put into the Code due to the efforts of industry paid lobbyists) are trumping common sense ... for now.

 

[ActionDave]

The breaker trips on start up. On a normal circut the blade will spin approx. 2 turns before reaching full speed.
On the AFCI circut it gets about one half a turn and trips.

 

[cadpoint]

I just have to wonder how:

"the circuit checked out"

:grin:

My thoughts are the AFCI is doing what its suppose to... not to get hung up with words or phrases:

The inrush is to much by the design of the motor and is working it,(the AFCI)!

 

[ActionDave]

My thoughts are the AFCI is doing what its suppose to... not to get hung up with words or phrases:

The inrush is to much by the design of the motor and is working it,(the AFCI)!

What person or property is being protected?
This breaker is not doing what it is supposed to do. It is stopping the saw from doing what it is supposed to do.

 

[cadpoint]

What person or property is being protected?
This breaker is not doing what it is supposed to do. It is stopping the saw from doing what it is supposed to do.

I can't beleive you stated that!

I frankly can understand why someone forgot why we have circuits on breakers, much less looking for certain types of faults via the use of certain types of breakers.

Plenty of progressive answers have been given, but to you I'm wrong, Man it's getting colder in here....

Until you truely test the line and Meggar or do an insulation test on that one circuit well I guess we won't know. A GFCI will let a pitch set of circuits through, it just on the other line, in respects to what works for an AFCI.

Here do this take your 18 volt battery (i'm thinking) Dewalt and plug the battery into the battery holder and plug it into your circuit in question.

If that doesn't trip, as the battery starts chargeing, plug the plug, the breaker trips and works as designed.

 

[ActionDave]

Well it's dark here. Every time the carpenter tries to use his saw the lights go out.

I don't think you're wrong in as much as you are saying that the motor on the saw is doing something that the breaker sees as a dangerous arc and is tripping, but there is no arc fault. Other motors with brushes work fine; said saw trips every AFCI in the house, and thanks to the '08 code there are a lot of them.

 

[ELA]

How important is it to get that particular saw working without tripping the breaker?

If it is worth the cost/effort you could try an isolation transformer dedicated to that particular load. Suggest also adding a GFCI to the secondary.

 

[ActionDave]

Thanks for the idea. I'd like to try the iso-xformer but for now everybody is managing with a few extra extension cords to the bathrooms.

I can't get over the fact that one can plug in a 25 year old Skill saw, pull the trigger and see a blue flame wrap around the brushes- no trip.
Plug in a new Hitachi soft start chop saw, won't even get one second of power- breaker trips.

 

[Steviechia2]

I have found that anything with a transformer ( usually with lighting ) will trip these afci's. I just did some trouble shooting on a job we did which had 3 lo-volt pendant lights. I removed the ground from the feed to lights and it did not trip the breaker. I put the ground back and it continued to trip. We use Seimens panels, I replaced this breaker with a Cutler Hammer and we have had no problems since.