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Thread: Fieldpiece SC680 Ohm Issues

  1. #1
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    Fieldpiece SC680 Ohm Issues

    Hello

    I have the Fieldpiece SC680 Multi Meter and I was wondering does anyone have any problems when they ohm out motors for continuity or resistance? I had ohm out a motor one day and it was a 3 speed motor so I test each lead to ground and it indicated that there was no grounding then I test each lead for resistance and all the readings was good but the motor would not start. So I did a visual and noticed that the winding was fried and thatís why the motor would not start. Iím I doing something wrong by not reading my meter properly? Or while performing my winding to winding test is there a percentage between each winding that I may have overlooked? Or my SC680 meter is bad?

    Thanks!

  2. #2
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    Most likely youíre meter is telling the truth but youíre misinterpreting the results. A motor winding can be burnt in a way that it still has continuity but canít carry current.

    For example, measure the resistance on an incandescent light bulb. Youíll notice the resistance doesnít correspond to the wattage. This is because when the filament is actually loaded it turns white hot and itís resistance goes up tremendously.

    For this reason, the best way to check a motor is by doing a loaded circuit test and not an ohmmeter test. You make sure the motor is receiving the proper voltage and then see if it is running or not. If not, itís bad or out on thermal overload (meaning itís bad or there is some external problem that needs to be corrected).
    "I think Quantum tunneling would work great... "

    "Call a technician for God's sake. Or we'll see you on the news or the Dark Side of the Moon."

  3. #3
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    Also when in doubt you can easily test your meter against known resistance to be sure you get a reading that makes sense. Also jiggle the leads and make sure you have no problems in the leads. Bad leads will take you down a hellish troubleshooting rabbit trail at the worst times imaginable. Donít ask me how I know this lol.
    "I think Quantum tunneling would work great... "

    "Call a technician for God's sake. Or we'll see you on the news or the Dark Side of the Moon."

  4. #4
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    Quote Originally Posted by JayMan7 View Post
    Also when in doubt you can easily test your meter against known resistance to be sure you get a reading that makes sense. Also jiggle the leads and make sure you have no problems in the leads. Bad leads will take you down a hellish troubleshooting rabbit trail at the worst times imaginable. Donít ask me how I know this lol.
    Thank you for the response!
    I was worried for a minute that I spent a lot of money on a meter that was defective! And I for got to add that I did test the end coming current to the motor and I was getting the proper voltage going in and thatís when I did my visual and noticed the windings was burnt. Iíve dealt with Fieldpiece for years and I never had a issue with them when it came their tools! So again thank you! Oh by the way I was testing a motor and it was a PSC motor 3 speed and I was testing each lead to ground and I was getting continuity to ground on each lead but the motor was still operating as normal is this a single that the motor will eventually fail even if itís still running? It kind of sounds like the same issue you just explain to me about the burnt blower motor was still able to show it had resistance but in this case the motor is operating but when I test each of the leads I was reading continuity to ground on each lead?

    Thanks!

  5. #5
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    Fieldpiece SC680 Ohm Issues

    Quote Originally Posted by cook42 View Post
    Thank you for the response!
    I was worried for a minute that I spent a lot of money on a meter that was defective! And I for got to add that I did test the end coming current to the motor and I was getting the proper voltage going in and thatís when I did my visual and noticed the windings was burnt. Iíve dealt with Fieldpiece for years and I never had a issue with them when it came their tools! So again thank you! Oh by the way I was testing a motor and it was a PSC motor 3 speed and I was testing each lead to ground and I was getting continuity to ground on each lead but the motor was still operating as normal is this a single that the motor will eventually fail even if itís still running? It kind of sounds like the same issue you just explain to me about the burnt blower motor was still able to show it had resistance but in this case the motor is operating but when I test each of the leads I was reading continuity to ground on each lead?

    Thanks!
    You should never under any circumstance have continuity from a motor winding to ground (ie the motor housing). If you do have a direct short then the breaker should trip unless the unit is not grounded, in this case you will be electrocuted as soon as you touch the unit.

    Are you sure you are taking your measurements the correct way? It would be extremely rare for a motor to be grounded and still run. It could potentially have a high resistance short, but how did you measure and what was the exact value?
    "I think Quantum tunneling would work great... "

    "Call a technician for God's sake. Or we'll see you on the news or the Dark Side of the Moon."

  6. #6
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    Quote Originally Posted by JayMan7 View Post
    You should never under any circumstance have continuity from a motor winding to ground (ie the motor housing). If you do have a direct short then the breaker should trip unless the unit is not grounded, in this case you will be electrocuted as soon as you touch the unit.

    Are you sure you are taking your measurements the correct way? It would be extremely rare for a motor to be grounded and still run.
    Well I made sure I turn the power off and I took the motor leads off the control board and went to common to ground and my meter made the beeping sound and showed continuity and I went down the line from low speed and then high and got the same results. So Iím assuming that the furnace is not properly grounded to the control panel?

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