Tablesaw motor tripping breakers - Woodworking Talk - Woodworkers Forum
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post #1 of 16 Old 05-21-2019, 11:58 AM Thread Starter
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Tablesaw motor tripping breakers

I've had occasional intermittent trouble with 240 circuit breakers tripping since I got my Powermatic 65 tablesaw. Yesterday I couldn't get my bandsaw to start up. Replaced the breakers and no better result. Unplugged the tablesaw and the bandsaw was fine. Plugged the tablesaw in and the breakers tripped.

What have I got? Someone suggested I take it to a motor repair shop.

Thanks, folks!
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post #2 of 16 Old 05-21-2019, 12:42 PM
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Quote:
Originally Posted by ChuckBarnett View Post
I've had occasional intermittent trouble with 240 circuit breakers tripping since I got my Powermatic 65 tablesaw. Yesterday I couldn't get my bandsaw to start up. Replaced the breakers and no better result. Unplugged the tablesaw and the bandsaw was fine. Plugged the tablesaw in and the breakers tripped.

What have I got? Someone suggested I take it to a motor repair shop.

Thanks, folks!
The repair shop is probably a good idea if the smoke is still in the motor.

“Everything we hear is an opinion, not a fact. Everything we see is a perspective, not the truth.”
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post #3 of 16 Old 05-21-2019, 01:42 PM
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if things are "normal" when the table saw is unplugged, sounds like a short in the plug/cord of the table saw.
which would explain the 'intermittent' part as well.


if the band saw is/is not plugged in, and the breakers trip as soon as you plug in the table without even starting the saw, that's even more suspicion on the plug/cord.
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post #4 of 16 Old 05-21-2019, 02:33 PM
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You might check to see if a stray wire is touching the case of the motor. If not then I would take it to a motor shop.
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post #5 of 16 Old 05-21-2019, 02:52 PM
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typically there is a start winding and a centrifugal switch in the motor, the switch is on at rest and cuts out as rpms build
if the motor has an accumulation of sawdust in it it can prevent the switch from resetting when the motor is off
i religiously blow out my table saw motor, obviously it didn't work as well at i thought
this is the sawdust buildup i found when my saw failed to start, it just hummed
you can see the little wire heading into that mess, i blew it out and it has worked for a couple years

my 60s era bandsaw has an old washing machine motor on it that has an intermittent centrifugal switch problem
no dust/dirt in it, just a sticky switch, i have to smack the motor with a board if it fails to start

i'd start there before you take it in to be repaired

also check out the capacitor hanging off the side of the motor, google how to check it

edit: reread your post...
if the breaker tripped when you plugged in the saw, not started the saw, look for a short in the cord/switch
use a multimeter to check between the 2 poles and the ground on the plug, should be an open circuit
if there is any resistance to ground start looking at the plug or switch
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post #6 of 16 Old 05-21-2019, 04:44 PM Thread Starter
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I opened up the switch cover to find this. Looks like one of the incoming legs gets hot at the terminal.
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post #7 of 16 Old 05-21-2019, 07:15 PM
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should be able to make short work of that problem..... (ouch)


look like it's a smidge too close to the grounding screw. is that arcing on the ground screw rim?
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post #8 of 16 Old 05-21-2019, 10:54 PM
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To me, it looks as though the wires in the right of the picture have improperly crimped terminals. Go get some new yellow terminals and solder them to the wires. Probably less than $5.

Also make sure that the screws holding the terminals aren't too long and barely touching the metal of the box.

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post #9 of 16 Old 05-21-2019, 11:53 PM
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Also check that box clamping bar. It looks like it was way too tight and crimping the cable. That induces heat and can easily lead to connection failure
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post #10 of 16 Old 05-22-2019, 12:20 PM Thread Starter
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Quote:
Originally Posted by TomCT2 View Post
look like it's a smidge too close to the grounding screw. is that arcing on the ground screw rim?
Tom, are you seeing that the green grounding screw has arcing? I hadn't spotted that. So when the lid is on the heads of the fried screw and the green ground screw are too close?

Not being electrically proficient I wonder, if that is the problem, why the issue was intermittent over the past several years. And I guess I could slip a piece of rubber inner tube between them for insulation?
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post #11 of 16 Old 05-22-2019, 12:23 PM Thread Starter
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Also check that box clamping bar. It looks like it was way too tight and crimping the cable. That induces heat and can easily lead to connection failure
Thanks for that spot! I can back that off a turn or so by now. It's been in that position for 3 or 4 years so it isn't going to go anywhere.
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post #12 of 16 Old 05-22-2019, 12:57 PM
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the problem with the overheating theory is - nothing has melted.....

the screw that bonds the two green grounding wires to the box looks to have some scarring along the ridge.

the crimped terminal looks to have some bright copper thread(s) sticking out. I suspect a couple strands from the wire were "too long" and projected through the terminal crimp - and are close enough to the head of that screw the voltage arced and shorts out. the soot/blacken bits on the crimp are more classic of shorting out than over heating.

I'm also suspecting the crimped terminal that is blackened is on the side of the switch going to the saw motor. it has no voltage when the switch is off.
when you _push in_ on the switch to start the saw, the cover flexes and the back of the switch is physically pushed close enough to the ground screw to arc, short, trip the breaker.

I would move the two green wires to the screw in the lower left corner of the box - and completely remove the screw current used on the green wires.

alternative: not 100% sure, but that looks to be a standard depth box - they make "deep" boxes that would have more distance from back of switch to box. that would mean unwiring everything to swap the box out - no biggie but more time/effort.

much better to fix the problem than the "stick something in to insulate" approach.
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post #13 of 16 Old 05-22-2019, 05:00 PM
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another idea .....

Turn the terminals over so the wires are on the bottom. That will give more clearance between the box and the terminals. Relocate the ground screw to the lower right corner screw IF they will under that screw.....?

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #14 of 16 Old 05-23-2019, 12:24 AM Thread Starter
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Tom, you NAILED it!!!

I recall that when I restored this saw getting that box together was a challenge! As I look at it now I simply need a deeper box. I;ll check on a deeper box tomorrow. Good news is that I have the room under the fence rail.

I am simply relieved beyond words!! Over the 4 or 5 years since I restored it the saw would occasionally try to start and acted under-powered and then the breaker would go. I thought it was the motor!

I cannot than you all enough! This forum 1) has been quick to reply, 2) doesn't back away from difficult problems, and 3) never makes me feel as dumb as I am for asking the questions I do!!

You are AMAZING!!!
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post #15 of 16 Old 05-23-2019, 12:45 AM
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I was a breakdown engineer for many years before I retired. Those metal box clamps are a major cause of wiring failure because they allow the wire to be squeezed so tight that it almost breaks. this causes overheating to the extaent the wire will melt or even catch fire.

nylon glands are much better, although even those can be overtightened by enthusiastic amateurs.
my favourite method of retaining smaller cables inside boxes is to use a cable tie, hand tight, inside the box, then mild hand pressure on the gland nut just enough to stop the cable tie from slipping through.

as said above, wire strands must NOT protrude through crimp terminals.

Last edited by sunnybob; 05-23-2019 at 12:48 AM.
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post #16 of 16 Old 05-23-2019, 08:34 AM
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don't cha' just luv' it when Plan B comes together . . . (g)
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