DELTA 46-460 Suddenly Tripping GFCI

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David350

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Location
Dallas, TX
I have a Delta 46-460 that I've had for about 5 years now. I originally had it in a backyard workshop where it was not on a GFCI protected plug and I never had any issues. I moved to a new house in late 2021 and now use part of the garage for my workshop. I started turning pens again before this past Christmas and probably made about 75 pens and then without warning, my lathe started tripping the GFCI. The first time, I thought it was just a fluke, so I reset it and all was fine for 8-10 more pens over a week or so. It then tripped again halfway through a pen and I was unable to get it to work at all without immediately tripping the GFCI. I had it on a 15 amp GFCI protected outlet, so I hooked it up to a 12 gauge, 25' extension cord and ran it to a 20 amp GFCI protected outlet (different circuit of course). It immediately tripped that one as well, so I am assuming its not either of my GFCI outlets at fault.

I did some google searches and found that this seems to be a problem with the Delta's variable speed motor so I replaced the GFCI outlet upstream of my lathe's outlet with a regular 15 amp outlet and the lathe now runs fine again. I think I also remember seeing some threads a while back on this site as well with GFCI's and certain power tools. I'm just now going to have to watch running an extension cord off this one circuit outside the garage when its wet outside. I do not have a sink or other source of water in my garage. For those in different parts of the county, its code here to have garage outlets GFCI protected even if you have no garage sink, etc. It's probably to guard against the extension cord use outside in a wet scenario.

My question to those smarter than I, is why did this run perfectly for probably 25-30 hours of lathe run time with the GFCI before it decided it didn't like running on a GFCI? :) When it first started tripping the circuit, I was not using it any longer (motor warmer) than I have in the past, and it would also now trip when starting up from not running for a day, etc. Thanks in advance for any insight or suggestions on how to run it with a GFCI if that's even possible. David
 
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That lathe will not play right with a GFCI breaker or outlet. You say the motor is getting hotter would indicate that thyristor that is converting AC to DC maybe breaking down and at some time you may loose speed control with knob. It probably will still run but speed change can only be done with belts. Is it the type#1 or Type #2? Switches seem to be a big issue with that lathe. Not long ago someone here had an issue with the switch and he had a type #1 and could not get a switch so I think he adapted a type #2 switch to make work.
 
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jttheclockman said:
That lathe will not play right with a GFCI breaker or outlet. You say the motor is getting hotter would indicate that thyristor that is converting AC to DC maybe breaking down and at some time you may loose speed control with knob. It probably will still run but speed change can only be done with belts. Is it the type#1 or Type #2? Switches seem to be a big issue with that lathe. Not long ago someone here had an issue with the switch and he had a type #1 and could not get a switch so I think he adapted a type #2 switch to make work.
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I was able to convert a type 2 switch to fit and work with my type 1 lathe. The connections are all the same but the type 2 switch is positioned backward in the housing. I believe I posted pictures if anyone needs to look them up for reference.

I would say that the issue is more with the converter drawing too much amps. I dont know how available those are for replacement.
Just a thought though, it might be bearings that are, or have gone bad and causing the converter/motor to work too hard get the lathe to turn over. Just a thought.
 
Mortalis said:
I would say that the issue is more with the converter drawing too much amps.
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Disagree. A GFCI doesn't care about the magnitude of current.

Ordinary circuit breakers and fuses respond to the magnitude of current in the circuit, and trip if that magnitude exceeds the thermal capability of the wire in the circuit.. So ordinary circuit breakers and fuses exist to protect structures from electrical faults that can lead to fire.

Current flows out of the hot leg, through the motor, and back through the neutral, and normally, the current flowing in equals the current flowing out. Engineers describe this as 'the guzintas equal the guzoutas'. A GFCI measures the difference between those two currents, and if that difference exceeds the level of current that can trigger human heart problems, it trips;. So the purpose of a GFCI is to protect people from electrocution.

The 46-460 is variable speed lathe, and one of the characteristics of electronic variable speed power converters is that they generate parasitic harmonic currents - currents at frequencies that are multiples of the standard 60Hz line frequency. The sensitive differential measurement circuit in a GFCI can be confused if it sees currents at frequencies other than its design frequency, and there have been many posts in this forum about variable speed lathes triggering GFCIs. And a number of lathe manfacturers have gone on record saying that their machines should not be powered from circuits with GFCIs. However, there are ways to incorporate filtration into the design of a variable speed controller to minimize these harmonic currents.

The fact that the lathe operated normally for a while, and only recently has started tripping the GFCI suggests to me that there is a component (most likely a capacitor) in the speed controller that is aging, and as a result, its rating is drifting. As a result, an internal filter within the speed controller may be less effective in blocking those harmonic currents. And incidentally, the observation that the motor may be running a bit hotter also suggests that there could be abnormal harmonic currents.
 
monophoto said:
Disagree. A GFCI doesn't care about the magnitude of current.

Ordinary circuit breakers and fuses respond to the magnitude of current in the circuit, and trip if that magnitude exceeds the thermal capability of the wire in the circuit.. So ordinary circuit breakers and fuses exist to protect structures from electrical faults that can lead to fire.

Current flows out of the hot leg, through the motor, and back through the neutral, and normally, the current flowing in equals the current flowing out. Engineers describe this as 'the guzintas equal the guzoutas'. A GFCI measures the difference between those two currents, and if that difference exceeds the level of current that can trigger human heart problems, it trips;. So the purpose of a GFCI is to protect people from electrocution.

The 46-460 is variable speed lathe, and one of the characteristics of electronic variable speed power converters is that they generate parasitic harmonic currents - currents at frequencies that are multiples of the standard 60Hz line frequency. The sensitive differential measurement circuit in a GFCI can be confused if it sees currents at frequencies other than its design frequency, and there have been many posts in this forum about variable speed lathes triggering GFCIs. And a number of lathe manfacturers have gone on record saying that their machines should not be powered from circuits with GFCIs. However, there are ways to incorporate filtration into the design of a variable speed controller to minimize these harmonic currents.

The fact that the lathe operated normally for a while, and only recently has started tripping the GFCI suggests to me that there is a component (most likely a capacitor) in the speed controller that is aging, and as a result, its rating is drifting. As a result, an internal filter within the speed controller may be less effective in blocking those harmonic currents. And incidentally, the observation that the motor may be running a bit hotter also suggests that there could be abnormal harmonic currents.
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Thank you for that explanation. I am definately not, I believe as I mentioned in the switch conversion thread, in no way an electrically minded guy. I can properly add an electrical outlet but would actually prefer to enlist the skills of a licensed electrician. Your explanation was clear and unassuming. I spoke out of my --- instead of my brain/mouth. o_O. My apologies if it mislead anyone.
 
monophoto said:
A GFCI doesn't care about the magnitude of current.
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I spoke too quickly, and need to clarify that statement.

A GCFI receptacle doesn't care about the magnitude of current. It's sole function is to compare the currents in the hot and neutral wires, and trip if they differ by too much, typically, by more than 0.005 amperes which is the roughly amount of current required to disrupt the electrical signals controlling the human heart.

However, it is sometimes possible to see GFCI breakers, especially in older homes. These are circuit breakers to which GFCI functionality has been added. They respond to both the magnitude of current and the balance between hot and neutral wire current. When GFCI protection was first developed (in the late 1960s), it was implemented in circuit breakers, and it was expected that they would be applied on circuits feeding receptacles in bathrooms and kitchens (where they were first required).

Later, as the cost of GFCI protection came down, ans as code requirements were augmented to add GFCI protection on outdoor, basement and garage receptacles, the GFCI function was moved to receptacles. It is still possible to buy GFCI breakers, but I think most new homes today are built with GFCIs in receptacles rather than putting GFCI breakers in the panel.
 
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monophoto said:
I spoke too quickly, and need to clarify that statement.

A GCFI receptacle doesn't care about the magnitude of current. It's sole function is to compare the currents in the hot and neutral wires, and trip if they differ by too much, typically, by more than 0.005 amperes which is the roughly amount of current required to disrupt the electrical signals controlling the human heart.

However, it is sometimes possible to see GFCI breakers, especially in older homes. These are circuit breakers to which GFCI functionality has been added. They respond to both the magnitude of current and the balance between hot and neutral wire current. When GFCI protection was first developed (in the late 1960s), it was implemented in circuit breakers, and it was expected that they would be applied on circuits feeding receptacles in bathrooms and kitchens (where they were first required).

Later, as the cost of GFCI protection came down, ans as code requirements were augmented to add GFCI protection on outdoor, basement and garage receptacles, the GFCI function was moved to receptacles. It is still possible to buy GFCI breakers, but I think most new homes today are built with GFCIs in receptacles rather than putting GFCI breakers in the panel.
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I have both. Got a bunch of breakers from a job we did for Merks. They were renovating the office building and we had to build these temporary panels that had outlets below for all the trades to plug into and instead of putting outlets in we used GFCI breakers. After job was done I took a bunch of them. Used them in my sisters house as well as mine. Nothing wrong with breaker as opposed to outlet except for convenance. This is code today that all temporary outlets have to be GFCI protected. Even home projects so if you are getting inspections done be aware. An electrical inspector walking through a job for rough-in work can issue a fine.
 
Some motor controllers, especially those with VFD (Variable Frequency Drives) are problematic when it comes to GFCI tripping. Of course you have some options to improve things without sacrificing safety or changing wiring to be outside of current electrical code. The easiest would be to hardwire your lathe into a circuit that does not have GFCI protection. This fixes the problem without removing GFCI protection on any outlets. Since you would no longer be able to unplug it you would probably want to have it wired into Safety Disconnect Switch so that you could still have a means to disconnect it from power without having to use a dedicated circuit in your breaker box.

Another option could be to add an isolation transformer to your lathe, but that would most likely be cost prohibitive. A 2kva isolation transformer would cost in the $800-$1000 range.

Dave.
 
If I were OP I would put a single outlet ( nothing else can be plugged into it)right next to his GFCI and plug the lathe in and be done. I would jump off the line side of that GFCI and you are good to go.
 
At the equipment design place I used to work for dedicated outlets on machines we used to use the "trick" of using a Locking outlet of the same NEMA rating as the standard Straight Blade outlets. It reduced the temptation so that one of our maintenance tech's could not plug a tool into the outlet "just this once".

For 15A/125V outlets, instead of the typical 5-15 NEMA configuration we used the L5-15 for both the outlet and the plug on our machine. It also made "accidentally" unplugging something a little less likely as well. - Dave

NEMA Configurations 15A.JPG
 
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