1 ph motor, tripping breaker

[Clayton79]

Hello, wondering what your thoughts are, 1ph cap start cap run 1/2 hp 120v
Grizzly 18” drum sander (woodworking)

Trips breaker 20 amp.
Checked caps independently, with fluke 87V and they read good. Motor winding is .6ohm. And uncoupled runs and pulls 4.6amps. Hook up belt to drum and little blower exhaust fan, minus belt for feed table, oh and motor data plate says 11.3 ish can’t remember exactly for FLA

Hooked up to drum Pulls 45-46 amps obviously not for very long.
measured voltage at 3 way splitter where plugged into 12awg extension cord voltage is 119 until start then drops and stays at 77V.

A nearby table saw only drops to 114v
When doing same check

Will be calling grizzly tomorrow just wondered if I’m missing something

Tried loosening and tightening belt tension. Everything turns by hand ok.

Also ditched extension cord and plugged into outlet directly on side of house and same shutdown scenario.

I know there are smarter guys than I with more experience, curious what y’all think

Clayton.(ps Yes I am a licensed professional) let’s get that out of the way LOL.


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[ActionDave]

How old is the install?

Is the motor wired for 240V?

If you put an clamp on amp meter around one of the leads going to the starting cap does it drop out?

 

[gar]

201028-2345 EDT

Clayton75:

It possibly is the inertia of the load, thus much slower starting. This means that starting current, which is very high compared to running current, with the starting capacitor connected, lasts a long time.

During starting measure the voltage at the main panel. Hopefully you have a high source voltage, like 125 V, and at the main panel you see less than 10 V drop during starting. If this is the case, then run heavy wires to your motor to reduce voltage drop to less than an additional 5 V. This will reduce starting time.

Another approach is to change to 240 V, if your motor can be wired for 240.

I have a much larger motor on a DeWalt radial arm saw. With a 12" carbide tipped blade I have somewhat the same problem. But it only occurs if the motor has been just started, I stop it, and quickly restart. My breaker is a QO20, and branch wire is about 125' of #12 copper. At the motor I drop from 125 V at the breaker to about 75 V on startup at the motor, and it takes several seconds to drop out the starting winding.

.

 

[zbang]

Hooked up to drum Pulls 45-46 amps obviously not for very long.

You don't say explicitly- does the drum revolve freely? The other parts? Pretty much everything should easily move by hand. Often these sort of things are mechanical, not electrical.

 

[paulengr]

1. Disconnect then Megger the motor between the leads and the frame. That’s usually step 1. 500 V, 60 seconds, should be at least 5-10 megaohms. Your Fluke 87V vanity meter is not a substitute for a real insulation resistance tester. If it fails, your motor is fried. No reason to continue.
2. The potential relay or inertia switch is also often an issue. Depends on the type of motor if it has one but with two caps, pretty likely. Measure voltage across the start coil if you want but usually if you listen you can hear when the start coil drops out. Alternatively measure current on the start coil. It should last at most 2-3 seconds. No drop out, that’s your issue. This is so common often it is faster and cheaper to just replace all three (both caps and the potential relay) before troubleshooting as they are all around $20 each, or switch to a potential relay instead of an inertia switch. If it’s an inertia switch make sure the shaft spins freely by hand because it could just be stalling out.
3. Voltage drop might be your issue IF you are messing with extension cords. You need a minimum size based on load and distance.

Learn How to Size Your Extension Cords to Lengths of the Run

Learn how to size your extension cords to lengths of the run to avoid voltage drop from ruining your tools and overloading circuits in your home.

www.thespruce.com

On starting if you have a big enough cord it’s still not uncommon to see 20-25% voltage drop, even on large three phase motors. But don’t expect to use #16 household Christmas tree cords on power tools.

 

[kwired]

How old is the install?

Is the motor wired for 240V?

If you put an clamp on amp meter around one of the leads going to the starting cap does it drop out?

Or does it ever show current at all when starting? If not maybe malfunction of centrifugal mechanism or the switch it actuates and it is stuck "open". physically spinning the shaft when attempting to start may get it going in this case, and if that is what has failed it possibly can be spun to start it in either direction.

 

[synchro]

The run capacitor alone might provide enough phase shift to start the motor with light mechanical loads, but it would be short on torque to start with higher loads if the start cap is bad and/or not being switched in. Your 87V will not test the cap at anywhere near the operating voltage and so it could still be bad. I agree with Paul that it would be worthwhile replacing the caps, at least the start cap which is very likely to be electrolytic and therefore more prone to failure.

 

[Barbqranch]

Is this the original motor?

 

[Jraef]

...measured voltage at 3 way splitter where plugged into 12awg extension cord voltage is 119 until start then drops and stays at 77V.

My guess is what ActionDave alluded to, that you have it connected internally for 240V and are feeding it 120V, so the motor lacks torque and is basically stalling when you have everything hooked up to it. Peak torque varies at the square of the applied voltage, so with 1/2 voltage the starting torque is only 1/4 of normal. With the belts disconnected, even that 1/4 the regular starting torque is enough to make it appear to be running normally, but it can't accelerate a load.

 

[Clayton79]

It is the original motor, was factory installed. But will double check the capacitor diagram. I can spin all belts by hand easily. We are replacing Run Cap per Grizzly only 15$ . Will update when we try it.


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[GoldDigger]

The belts spin easily, but you should notice a lot more inertial resistance when you spin the drum. And once you spin it up it should freewheel for a longish time if the bearings are good.


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[Clayton79]

Ok. Thank you all for the great troubleshooting ideas. In the end, turns out it was a voltage drop issue, too long of an extension cord. Moved sander to receptacle directly under main panel in garage. And it worked fine. Next step run real power via large conductors to new sub panel in shop.

Just wanted to everyone who invested their time and thoughts to know “the rest of the story” thank you

Clayton.


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[kwired]

Ok. Thank you all for the great troubleshooting ideas. In the end, turns out it was a voltage drop issue, too long of an extension cord. Moved sander to receptacle directly under main panel in garage. And it worked fine. Next step run real power via large conductors to new sub panel in shop.

Just wanted to everyone who invested their time and thoughts to know “the rest of the story” thank you

Clayton.


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must take it a bit of time to get to speed when voltage is good? Often you can find that an extension cord limits the starting current enough to not trip a breaker on instantaneous trip function, but usually on high torque type loads.

 

[Jraef]

Ok. Thank you all for the great troubleshooting ideas. In the end, turns out it was a voltage drop issue, too long of an extension cord. Moved sander to receptacle directly under main panel in garage. And it worked fine. Next step run real power via large conductors to new sub panel in shop.

Just wanted to everyone who invested their time and thoughts to know “the rest of the story” thank you

Clayton.


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Thanks for letting us know.