i had a problem like that and it turned out to be the breaker itself. not saying thats the problem- i think there is a way to see how many amps its pulling when ya pull the trigger.
do you have anything else ya may have forgot about pulling off of that circuit?

 

Replace the panel breaker with a new one of the same amp rating. It's easy to do and quite inexpensive.

Any change in lighting or continual load on that circuit recently? I've had that happen where a very small change (like an added work light) was enough to trip a breaker.

Are you running an iVac switch to turn on the shop vac automatically? Some of those have delays to prevent tripping.

Shop vac filter clean? Dirty filter = motor works harder.

 

I'm not that experienced in this area of troubleshooting, and with that being said, I would do the following:

-If you can get access to a clamp-on type ammeter, I would use it to try and determine the amperage draw when the breaker is tripped.
-The problem might be the breaker. I would try to test that (e.g. move the saw to another circuit or try another high load tool on the current circuit or swap the breaker with another in the panel or replace the breaker).

If the problem is the saw motor, could worn/damaged brushes cause this problem? Does this motor have a start-up or run capacitor? If so-that might be the problem. Perhaps the power switch is going bad? My understanding is that (generally speaking) components closest to the source of power are the most likely to wear out sooner because of the initial load on startup.

I'm sorry I couldn't be of more help with this issue. I'll be watching this posting and hopefully others more experienced than me will respond-so I can learn too! Good luck.

 

Between your saw and shop vac you're probably right at 20amps if not slightly over.

As silly as this sounds, breakers eventually start to "pop" easier if you set them off a lot. Probably time for a new breaker as well.

I had this problem in my last house and ended up getting another circuit run to separate things a little more.

 

I am betting that the issue is in the saw, especially since it only happens when the saw is "cold"-i.e. sat unused for a long period of time. If it was a problem in the breaker, I would expect that it would occur sporadically with increasing frequency as the breaker grew warmer from the increased current flow.

When you say it happens at start up, does it happen when you first power the saw on (squeeze the trigger) or on first contact with the wood?

 

Probably a combination of both.

A breaker is 5-6$ so it's cheap to eliminate that.

 

It sound to me that it is the capacitor on the motor. Electrolyitic capacitors go bad with time and when they do, motors will draw more current on startup.

 

Hi guys, thanks for the input. I'm leaning to think the problem is not the breaker as I can run my 2hp dust collector and planer on the same circuit without problem. I also run the table saw from the same outlet and that's cheap, old and clunky yet has never tripped the breaker. All my 110v outlets are on the same breaker and it's only the miter saw that trips it.

For my first experiment, I got home last night and just spun the blade manually to see if it's cold grease or something that is creating the initial resistance. I then pressed the button and the breaker tripped - note nothing else was on, not even the shop vac. After resetting the breaker the saw worked fine. I was in the shop for about an hour and a half (not using the saw) and tried it just before I packed up for the night and it worked fine again.

Tonight I'm going to go at it with the air compressor and maybe apply some oil if I can find a place to apply it.

 

Good, you've ruled out an overloaded circuit (shop vac unplugged), and ruled out mechanical resistance (bad saw bearing etc.). That's a good place to start.

Based on everything you've described here, I would still replace the breaker first.

Then you can start investigating the electrical system and brushes on the saw.

 

Shop vac filter clean? Dirty filter = motor works harder.

- pintodeluxe

That's what fixed it for me last year.

 

Shop vac filter clean? Dirty filter = motor works harder.

- pintodeluxe

While the vacuum will have to run longer with a dirty filter to clean the same mess, the motor will not work harder, in fact it will pull less current as a function of moving less air.

 

good reason to have DC and planer on sep circuits. You only got one circuit for the whole shop?

 

I have an earlier version that looks a lot like your miter saw and I've had if for a really long time but never had it trip the breaker. I wonder if you have a short in the miter saw somewhere?

 

An update!

It's been damn cold here in Houston over the last few weeks with freezing temps so I've not been in the shop. This weekend we're in the 70s so back to normal. I went back to the shop and this time used the air gun to give the saw a good blast around the blade and motor housing. A visible amount of dust came out of the motor housing. I then gave the area around the arbor a good squirt of WD40 and pressed the button. She started first time and didn't trip the breaker.

I suspect it's the dust that may have been interfering with the motor commutators (or something like that). Hence the trip on first activation and then normal operation but leaving time for dust to settle brings the problem back. I am slowly improving my dust collection so hopefully some upgrades combined with a bit more cleaning will mean this problem doesn't repeat itself.

 

I use portable dust collectors, never had a good setup for plumbing in more permanent solutions. To avoid kicking breakers or having to run cords all over the shop to get the tool and collector on separate circuits, I wired the line of outlets on each wall as duplex outlets so that the top and bottom outlets are on different circuits. That way I can plug tool and collector into the same fixture anywhere in the shop.