Would it be possible for a 120V coolant pump(nameplate 120V/60Hz/1.15A) to run for an extended period of time on 208V? I got a call to a machine shop that was having problems with a grinding machine. After metering out the terminal strip (listed on the print as 120V) I found that someone had taken power from the wild leg off the line side of the starter to feed the coolant pump switch.I am told that it has operated this way for at least 5 years since the equipment was brought into the building. After diagnosing the problem(pinched wire against enclosure) I hooked it up the way it should be and it ran fine, Machine operator tells me that the coolant flow is less now to the cutting tool.All I can think is that the higher voltage was turning the pump at a faster rpm.There were also indicator lights that were supposedly working on the 208voltage as well.
208 vs. 120V
- Thread starter nizak
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- Placerville, CA, USA
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- Retired PV System Designer
Depending on the load applied, the motor could well have been fine with the higher voltage. And yes, it might have run faster, depending on the motor design. An induction motor would have run with less slip, so slightly higher speed. A universal motor would run quite a bit faster so that the back EMF would be higher to match the applied voltage.
Indicator lights like neon would be OK, as would incandescent lights which were deliberately run at less than rated voltage to extend life and make them more vibration resistant. They would be dimmer with the right connection.
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- Licensed Electrician
What was the voltage of the high leg?
I would imagine running at a higher voltage would not make the motor windings happy.
I would imagine running at a higher voltage would not make the motor windings happy.
The subject of using the high leg of 240/120 3ph4w panel has been addressed on numerous occasions on this forum. A single pole breaker with a rating of 208 or 240v may be hard to find. As such I would start with the breaker which feeds the load to confirm that hat is is rated for the application. Second, would a 240/120 3ph4w panel have high leg single phase pole spaces not usable? Could it be that an electrician or tech not being familiar with this configuration have installed a 1p breaker in the open space assuming that he would be supplying the pump with 120v?
Just a thought.
Just a thought.
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- Licensed Electrician
That is not the question though. The question is will a 120V motor wired to a high leg run, and if it does will it run faster.
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- Placerville, CA, USA
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- Retired PV System Designer
And the definitive answer to both is "maybe". Depends on the motor!
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- Licensed Electrician
As I think about this some more-
Taken as stated it is clear that the motor will run connected to the high leg. I don't think the higher voltage would overcome so much slip that it would make a noticeable difference in flow.
I think the machine operator is being paranoid because you changed something or something on the pump end changed.
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- Licensed Electrician
Stand by while I grab my dictionary and look up the word definitive.
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- Placerville, CA, USA
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- Retired PV System Designer
You are assuming that the pump motor is an induction motor whose speed is primarily determined by the input frequency, minus slip.
Whether it is likely or not to be used in this case, a brush type universal motor will have a speed which is determined primarily by voltage, independent of frequency.
Being that the standard acceptable voltage range is +-10% of the NP voltage. As such I'm personally impressed that the motor evidently lasted as long as it did. Yes, I did attempt to address when it was applied with a high leg to neutral voltage as I had previously and instead of addressing that issue a theoretical discussion about what happen when a motor is run with an almost 60% over voltage. Any motor data that I have maxes out at +-15%.At +15% efficiency drops about 2-3 %, Power factor drops 15%, FLA increases about 3-5%, LRA +10%, starting and max torque about + 20%.
Now remember that this is at +15 voltage max which the highest data that I have which is slightly less that 140v and then 208v?
If FLA is up 3-5% then what would be the motor heating be at 208v since you are now at almost 60% overvoltage? Compare the heating watts.
I'm impressed that the motor has survived at all. I must have had one heck of a heat sink.
But the Op has shown little concern in regard as to why it was misapplied in the first place.
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- Licensed Electrician
Yes, I think that we do agree.
I wonder where this string of posts was leading. Why was a 120v motor supplied with 208v in the first place? What was the reasoning for justifying that the 208v-N was allowed by the NEC? Has the 1p breaker which feeds the load be rated at least 208v which I doubt there are any available or 240v. All of this avoided and the subject is how is a 120v motor affected when applied at almost a 60% over voltage. It must be home heck of a motor to have survived at all if all of the information that has been provided is accurate.
There was no 1 pole breaker feeding the pump. Someone had hooked up the equipment and when they landed the 3 wires in the machine disconnect the wild leg just happened to be the one that was tapped off the top of the starter in the enclosure on the opposite side of the machine that was feeding the 120V terminal strip. I suspect the used equipment came from a facility that had 208Y/120 power. In that case any leg individually would have been 120V. When I originally posted I never said that the install was NEC compliant nor did I say that the pump ran from a 1 pole breaker. My original question simply was about the pump running at a higher voltage.
208 vs. 120V
Interesting that you had referred to a "wild leg" in your OP which can only be derived from a 240/120 3ph4w system via a1p breaker which is a bit less than a 60% overvoltage:
"Would it be possible for a 120V coolant pump(nameplate 120V/60Hz/1.15A) to run for an extended period of time on 208V? I got a call to a machine shop that was having problems with a grinding machine. After metering out the terminal strip (listed on the print as 120V) I found that someone had taken power from the wild leg off the line side of the starter to feed the coolant pump switch.I am told that it has operated this way for at least 5 years since the equipment was brought into the building. After diagnosing the problem(pinched wire against enclosure) I hooked it up the way it should be and it ran fine, Machine operator tells me that the coolant flow is less now to the cutting tool.All I can think is that the higher voltage was turning the pump at a faster rpm.There were also indicator lights that were supposedly working on the 208voltage as well."
Also, the slip speed of a motor run at 10-15% over voltage will be down 15-20% which means that the motor will run closer to its synchronous speed and at 60% over voltage one would conclude the slip would be down even more. As such, yes, the motor would fun faster. Lowering the voltage where it should be would decrease the motor speed back to where it should be.
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- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
But even reducing the speed slip to zero would not make the motor run really noticeably faster in terms of coolant flow even if it was running at 5% slip at full load under normal conditions. And I do not think a properly working motor would do that.
If the motor was a large HP motor or was running at light load, a slip of 1% would be more common. So the difference in speed from normal voltage to 60% over would not be more than the difference between, say 3564 and 3600.
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- Licensed Electrician
I would tend to agree with you but since this forum seems to be shooting at shadows my response to the machine operators comment with regard to a decrease in coolant flow when the motor was supplied with the correct 120v was that there was more slip or a sightly less rpm. Another unknown is how the flow rate of pump itself will respond to a ever so slight reduced rpm. I would have to respect the machine operator that may be very sensitive of the coolant flow rate because he find the machine where you and I may not have a clue.
Again, to you and I a minute decrease in motor rpm would seem to be insignificant but we may not be sensitive enough to be able to actually see the results. We are also depending upon the "opinion" of the machine operator.
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- Location
- Simi Valley, CA
Just had a building burn up two 120v sump pumps before they realized that they were hooked to the stinger leg of a panel. Neither the leg nor the panel was marked indicating that there was a high leg.
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growler
Senior Member
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- Atlanta,GA
The question is, "would it be possible"? and the answer is yes. One of the reason I say yes is that this one probably did.
It's not a good idea, it's not code complaint and I doubt it's ever really good for the life expectancy of the motor but I have seen some motors that were still running after extreme abuse. If you go to some of the third world countries you will see things hooked up and actually working that will amaze you.
Nizak noticed the mistake made by others and he corrected it. If the motor goes out in a few months or years he may get a call to replace it.
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