Bench milling machine tripping GFCI

[peter d]

It might be worth trying a regular circuit breaker, and a GFCI outlet.

How far is the breaker from the mill? I think longer wires between a GFCI device and the load increase the chances of tripping.

GFCI's can be finiky things.

About 50 feet. I'll give your idea a try.

 

[kwired]

GFCI's don't like long circuits because of leakage current due to capacitive effects on long circuits. 50 feet is not all that long to be troublesome, but give it a try anyway. I see much longer extension cords all the time that seldom have tripping issues - especially at construction sites.

 

[glene77is]

GFCI's don't like long circuits because of leakage current due to capacitive effects on long circuits. 50 feet is not all that long to be troublesome, but give it a try anyway. I see much longer extension cords all the time that seldom have tripping issues - especially at construction sites.

KWired,
I frequently see old houses with old 1940's romex where the leakage along a circuit of 50-100 feet will trip GFCI breakers.
Must install OBC GFCI at each receptical location.
By old 40's romex I refer to the rubber-composition wrapped in linen. Have not seen this effect from 50's (and later) using TW insulation.

 

[Jraef]

Why do you have a GFCI on a milling machine in the first place? Are you milling in the bathroom or outside in the rain?

 

[iwire]

Why do you have a GFCI on a milling machine in the first place? Are you milling in the bathroom or outside in the rain?

If it is a garage or unfinished basement and is 125 volt 15 to 20 amp it is required.

 

[Jraef]

If it is a garage or unfinished basement and is 125 volt 15 to 20 amp it is required.

Ah, I missed the "bench" part of this so it's probably small like you said, thanks.

Wait, garages now too? Not just the outlet near the washing machine? Man, I've been out of the resi business too long now to continue commenting on this stuff, too many changes to keep up with if you don't do it but once every 10 years. Time to shut up and leave it to the pros now. :slaphead:

 

[peter d]

Why do you have a GFCI on a milling machine in the first place? Are you milling in the bathroom or outside in the rain?

It's located in my dad's workshop which is in the basement. Originally none of the outlets in his shop were on a GFCI but I changed that. :thumbsup:

 

[kwired]

Wait, garages now too? Not just the outlet near the washing machine? Man, I've been out of the resi business too long now to continue commenting on this stuff, too many changes to keep up with if you don't do it but once every 10 years. Time to shut up and leave it to the pros now. :slaphead:

I have been in the trade since the 1987 code was in effect and dwelling garage receptacles were required to be GFCI protected then, so you are only a couple years behind on this one.

 

[ELA]

My dad purchased a small bench sized milling machine for making small parts. It's a Micro-Mark, not sure of the model. It's a variable speed model with an electronic power supply.

Anyway, I assemble all the controls and fire it up. The unit runs fine until about 10% speed on the controller, then it trips the Square D QO GFCI breaker. I'm thinking that the power supply is creating a lot of harmonics and other dirty power that is causing the GFCI to trip. Your thoughts?

As always actually measuring the leakage level would be prudent but those meters can be expensive for only an occasional use.

Totally possible that conducted EMI ("electrical noise" ) could trip a GFCI. You can search threads on Treadmills and find many instances of this.
When the manufacturer said it is a known problem did they explain what that meant? If it is tripping due to excessive leakage that would be very bad. However since it only trips at the 10% speed point I would suspect EMI becomes excessive at that level.

If you are interested in maintaining operation on a GFCI adding an EMI filter between the mill and the GFCI may help.

 

[steve66]

Why do you have a GFCI on a milling machine in the first place? Are you milling in the bathroom or outside in the rain?

Well, if his wife lets him keep the milling machine in the living room or in the dining room, she's a keeper

 

[glene77is]

It's located in my dad's workshop which is in the basement. Originally none of the outlets in his shop were on a GFCI but I changed that. :thumbsup:

Peter,
When does the 10% speed occur ?
As you increase from 0% speed to 10% speed ?
or
As you decrease from 100% speed to 10% speed ?

It was my passing thought that the EMI, being of much higher frequency than the 60cycle,
might leak through and out of the mill at a higher rate than the 60cycle.
That being because Electrostatic Coupling (capacitive coupling) is greater for higher frequency signals.

Is there any grease on the mill ? Could be conductive, or contain metal shavings.
Are there any metal shavings on the mill ?
Metal shavings could be conductive, and could contribute to capacitive leakage at EMI frequency.

Have you tried changing the cord-plug ? Check for strands of wire fraying.
My VOM has both milli-Volt and micro-Amp ranges. Have you tried such a VOM ?
Have you tried monitoring the voltage at the mill using an oscilloscope. ?

When your mind and all else is failing, Shoot in the Dark !
Try something different.