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Discussion Starter · #1 ·
I have a new Dewalt 15 Amp miter saw (DWS780) that trips the 20 amp breaker immediately almost every time. The pole barn was just wired a month ago, by an electrician, and all the plugs are installed correctly. I've tried plugging the saw in, by itself, on two different designated outlet circuits and both trip almost every time. Did I get a faulty saw, or is it something to do with the wiring?
 

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If there is another circuit available, try that. It could also be low voltage at the barn. Try the saw at a receptacle at your house. If it works there, you may have a bad breaker serving that pole barn circuit.

Is the breaker in the barn panel a GFCI type? If so, it may be too sensitive. Those type of breakers are also affected by any small leakage on the circuit that can make them super sensitive to any motor load starting up. You need to check line current with no load connected to see if there is any low level ground fault. Pole barns and rain or high humidity can be problematic for GFCI receptacles and breakers.
 

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Remodel and New Build GC
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Is it a GFI breaker that trips.....

I have my portable on-site craftsman table saw that has the very same issues on a gfi circuit.

It will immediately trip the gfi on start-up....but every once in a while will start and run fine.

I have to extension cord it to a non-gfi when on site, and when at home I have a special non-gfi recep for it.

When running, I've tested it for any leak to ground and found none. Yearss ago, I posted this question on here, but found no answer.
 

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Discussion Starter · #4 ·
If there is another circuit available, try that. It could also be low voltage at the barn. Try the saw at a receptacle at your house. If it works there, you may have a bad breaker serving that pole barn circuit.

Is the breaker in the barn panel a GFCI type? If so, it may be too sensitive.
It tripped on 2 separate circuits in the barn and they are not GFCI breakers. I will try the saw in the house tonight.
 

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this be what your needing - time delay breaker












Long-Time Delay
Long-time delay causes the breaker to wait a certain amount of time to allow temporary inrush currents, such as those encountered when starting a motor, to pass without tripping. The adjustment is from 2.2 to 27 seconds at six times the continuous amps (Ir) setting.
 

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I have the exact same saw and the same problem on our outside receps. No GFCI installed yet - just regular ole 4 dollar breakers. No AFCI either.

Maybe the time delay breaker is the fix?

I mean, I don't know what options we have beyond that. It's a 20 amp circuit. Nothing else on it when I run mine, still trips every other cut.
 

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Discussion Starter · #9 ·
I tried the saw in the house and it tripped those breakers too. The barn panel is about 40 feet from the house panel. Neither are AFCI breakers.
 

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I would try pulse triggering it off and on until the speed increased enough that it wasn't such a big draw.
 

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How about a picture of the cord and plug attached to the saw.
You cannot defeat this plug. You must find your issue. What does the instructions say. It must tell you the electrical requirements.
Do not overthink this.
 

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How about a picture of the cord and plug attached to the saw.
You cannot defeat this plug. You must find your issue. What does the instructions say. It must tell you the electrical requirements.
Do not overthink this.
It's just a standard 3 prong plug for a 15A rated receptacle. The instructions don't say anything special, just a 15 A 1600 Watt saw. It does not specify start up current as being higher. Which would be weird anyway, since an outlet rated over 15A would be a different plug type and circuit requirement since 20A still strips.

https://usermanual.wiki/Dewalt/DewaltDws780UsersManual164255.892967632
 

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retired framer
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It draws 25 amps or more on start up, over sensitive breakers.
 

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Hey Nealtw, where are you seeing that?

Is it normal to expect a 20 amp circuit to carry 25 amps instantaneously?

Even the 80% headroom rule supposes we don't go over the rating of the breaker to provide for startup currents. There's no headroom at all here, when it's over 125% of the circuit rating, even with a dedicated 20 amp circuit if it's demanding 25 amps on start up.

Makes no sense to me. But then, I went to Oklahoma schools....so there's that.
 

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That motor does not use 15 Amps with the blade just spinning in free air. It uses 15 amps when you are trying to cut a maple 6x6 in a hurry.

But there will be a big spike in current, for a brief time when it is started. I would have that that would be below the breaker's threshold.
 

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Hey Nealtw, where are you seeing that?

Is it normal to expect a 20 amp circuit to carry 25 amps instantaneously?

Even the 80% headroom rule supposes we don't go over the rating of the breaker to provide for startup currents. There's no headroom at all here, when it's over 125% of the circuit rating, even with a dedicated 20 amp circuit if it's demanding 25 amps on start up.

Makes no sense to me. But then, I went to Oklahoma schools....so there's that.
what breaker mfr are you using ?
 

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what breaker mfr are you using ?
Square D, just like you suspected.

I mean, I can just put in a 25 or 30 amp breaker and move on with my life but, once again, I'm scratching my head about how things are rated.

If your saw pulls 25 amps at start up, and that's the most it will ever pull, then guess what? That's a 25 amp saw, in my world. That's the rating. To call it 15 amps because most of the time it's not in startup doesn't mean a damn thing to me, ha ha. Every piece of wood I cut will include startup current. Every cut.

But no...apparently not. And that just blows my mind.
 

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retired framer
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Hey Nealtw, where are you seeing that?

Is it normal to expect a 20 amp circuit to carry 25 amps instantaneously?

Even the 80% headroom rule supposes we don't go over the rating of the breaker to provide for startup currents. There's no headroom at all here, when it's over 125% of the circuit rating, even with a dedicated 20 amp circuit if it's demanding 25 amps on start up.

Makes no sense to me. But then, I went to Oklahoma schools....so there's that.
https://en.wikipedia.org/wiki/Inrush_current
 
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