Lathe Trips Circuit Breaker

[David2011]

Maybe I've over-thought this. This is the last paragraph I typed but I moved it to the top. Could the motor's start capacitor be getting weak? It's 10 years old. I only have a volt meter; no way to measure peak startup power consumption.

This is the second lathe with which I've had this problem. In the low speed range it runs fine but it more often than not trips the circuit breaker in the high speed range. The lathe is a 1 HP Grizzly 9972Z. It's in a fairly new shop, attached to the existing house, with 12 GA wiring and a 20A breaker. The 100A breaker box is tied to the primary household breaker box, about 3 feet away, with large primary wiring as would be expected. I inspected all of the wiring after the electrician finished and have no reason to think this is an electrical fault. I believe it to be the same as with my last lathe in a different shop; just trying to spin up the chuck and spindle at the higher speeds is drawing a little more than the breaker can tolerate. The motor is a typical single phase motor with a centrifugal startup switch. The actual wire run from the breaker box to the lathe is probably no more than 25'-28' up a wall, across a ceiling and down to the outlet.

Running 10 Ga wire and a 30A breaker is the obvious solution but the wiring is in a room finished ceiling. The option that jumps out at me is to utilize a nearby 240V outlet. Inexplicably, the electrician ran 8 ga wire to all of the 240V outlets even though I specified 20A service to all but the welding machine outlet. At this point that's in my favor. Each 240V outlet is on a dedicated breaker. I could install a 30A breaker at the main panel in the shop. At the outlet I'm thinking of installing a small sub panel, supplying 20A 240V to the dust collector as it already has and a 30A 115V circuit for the lathe.

[NP317]

Measure your static AC Voltage is at the lathe. and during startup.
If incoming Voltage is running low, that could explain your problem.
Also, replace the circuit breaker with a new one. Breakers degrade with usage and they are not robust like a switch.
BTDT.
RussN

[Bill Shields]

I have several cheapo ROC / PRC motors pushing 40:years old, and several USA / European motors over 60 years old that have the original starting caps in them...and several USA Air cond units that have had their caps changed twice in 10 years....so who is to say?

Take russ' advice..

Change the breaker and check all connectors before you rip the motor apart.

Have a breaker in another circuit that you can swap?

[David2011]

I'll swap the breaker with another in the shop. They're all less than 2 years old and this is the first one that has ever tripped. Two have never even had a load on them. Easy enough to TRY to measure the voltage during startup but when it trips the lathe hardly moves. It's almost instantaneous. I'll check it first at the highest speed in the low rpm range.

[Bill Shields]

Take the chuck off and put the lathe in lowest gear possible ..or take the belt off the motor so that it is spinning nothing but itself.

It MAY be a problem in the reversing drum switch.

Put a couple of those in over the years to replace Asian manufactured.

[David2011]

On the voltage test at 560 rpm, the highest of the low speeds, the voltage dipped from 123 to 117 momentarily.
When I went to change belts I realized I had forgotten that I had a new belt. The original high speed belt that came with the lathe was so tight that no tensioner was needed and in fact I felt that it was far too tight. I put the new belt on in the 720 rpm position, set up the volt meter and to my surprise the lathe started up like it should have. The voltage never dropped below 119. Encouraged, I moved it to the highest speed of 2400 rpm. Instead of popping the breaker the lathe spooled up over 1-1/2 to 2 seconds to full speed. Again, the voltage didn't drop below 119. Seems the super tight belt was creating a huge load.

The bad news it that the bearings which seemed to be in marginal condition at 560 rpm confirmed that they're in need of replacement with a howl. I'll get some good replacements (not factory replacements) and that should take care of several issues including chatter when parting off.

[Bill Shields]

Ah...cheap bearings are the death knell of most everything that has rotating or oscillating or reciprocating parts.

[NP317]

Glad you defined some cures.
Happy repairing.
RussN

[Bill Shields]

Correct belt?

Belts of same first-glance apparent length and cross section can be different.

This is common with belts from Asia, which frequently do not use the North American common A, B or C section it V angle.

[David2011]

Bill, I noticed that with the replacement. It came from NAPA and has a slightly different cross section than the original belts but it still fits the grooves adequately. When I was a puppy I worked in industrial and oilfield supply and got a good education on belts through Gates. They covered cross sections, belt-to-pulley fit, balanced belt sets, O-rings and roller chains. Not much need for roller chain education outside of that business but the belt and O-ring part of the education has served me well more for hobbies than business as I moved on from that business.

[Bill Shields]

BTDT

however the difference is probably why it is so tight without use of the tensioner....

it does not take much difference to make up 3/4" of belt length

did you look up to see the belt designation that Grizzly shows?

3L320 or 3L290

[David2011]

Yes, I refer to the manual frequently. The belts that came with the lathe seem to both be original equipment. They’re both Asian in origin. The dates of manufacture are consistent with the date of the lathe’s manufacture. The shorter belt is for the low speed range. It’s not marked with its size that I can see. The longer original is marked Z787 which is at 31” shorter than a 3L320 by about an inch. The new belt is the closest that NAPA had, a 3L340. It’s close enough that the tensioner snugs it up with some space to spare. I don’t know if the previous owner ever used the high speed range; will have to ask next time I see him.