'96 SQT15MS- Panel breaker tripping

Hi All,

Back here after a few years trouble free-ish.
My 96 SQT 15 MS has started tripping the breaker at the electrical panel. I've been running on a 60A breaker for about 6 years now.
First time happened while doing a days worth of roughing with the main spindle around 50% most of the day.
It has happened a few times since then, so I switched to a 100A breaker.
The last breaker trip happened with no load while I was programming.

edit: After switching to the 100A breaker it has tripped twice with very little load.

It's been fine for the 15-20 hours I've ran since then.

Any thoughts on what might be going on?

Thanks for the help!

are you using D curve breaker? Your MDS B power supply is failing.

ManualEd said:

Hi All,

Back here after a few years trouble free-ish.
My 96 SQT 15 MS has started tripping the breaker at the electrical panel. I've been running on a 60A breaker for about 6 years now.
First time happened while doing a days worth of roughing with the main spindle around 50% most of the day.
It has happened a few times since then, so I switched to a 100A breaker.
The last breaker trip happened with no load while I was programming.

It's been fine for the 15-20 hours I've ran since then.

Any thoughts on what might be going on?

Thanks for the help!

Click to expand...

Just to be sure what you are saying, the machine hasn't tripped since replacing the breaker? Breakers can degrade over time, I've had to change out many over the 25yrs I've been running.

gmc1724 said:

Just to be sure what you are saying, the machine hasn't tripped since replacing the breaker? Breakers can degrade over time, I've had to change out many over the 25yrs I've been running.

Click to expand...

Sorry about that, I edited the post for a bit more clarity.
It has tripped twice with very little load since changing breakers.

noname777:are you using D curve breaker? Your MDS B power supply is failing.​

Click to expand...

My panel is a god awful old FPE Stab Lok, so I don't have any options for fancy breakers.
I've never even heard of a D Curve breaker to be honest.
I'll look into the power supply. I would really prefer if it wasn't a lathe-side issue...

you need to have a D-curve breaker, as it can tolerate momentarily high inrush AC current. It will trip eventually if you have something going on, but it should skip abnormalities related to servo amplifiers, digital power supplies and whatever needs huge inrush current to charge capacitors.