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Thread: GFCI in unfinished basement on a 220v motor load

  1. #1
    DIY Retired Member walt_pittsburgh's Avatar
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    Default GFCI in unfinished basement on a 220v motor load

    I installed a 2P standard breaker to control both a Delta 220v cabinet saw and a Jet 220v planer. I have a wall outlet in an unfinished area of the basement (my workroom) with a 220v receptacle. It then has a rather short (approx 8-10ft) heavy duty extension with the correct 220v plug and receptacle I move between these two machines. Just depends on what I am working on. Typically it stays connected to the Delta Saw. Based on NEC, is a 2P GFCI required in this application?

    I have a concern that the motor characteristics may cause nuisance tripping. I noticed our furnace and an outdoor sewage pump are not connected to GFCI. I suspect it has something to do with they are both motors.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Don't take this as gospel, but I think it makes a difference if it is stationary equipment (direct wired) verses plug in. Although, in a potentially wet area, a GFCI has benefits, regardless.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Homeowner Thatguy's Avatar
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    You are not the only one worried about nuisance tripping.
    http://www.docstoc.com/docs/56726888...Patent-7292420
    The background info starts on sheet 6.

    Motors have capacitance from the windings to the grounded motor shell. The current caused by this capacitance can eat up a lot of the 5 mA leakage current "budget" that GFCIs have.

    You can measure leakage current and thereby infer capacitance with just a DVM, a resistor and a small fuse; you don't need a capacitance meter.

    "Unfinished basement" probably means "concrete floor", and concrete is a semiconductor and not an insulator, so you probably have some cause for concern.
    I guess one way around this problem while still maintaining reasonable personal safety and using a GFCI or not, is to periodically test that your equipment is properly grounded. Let's say once/month?
    Are your machines double insulated?

    BTW, if your breaker nuisance trips occasionally with these machines you might try using a longer and/or smaller gauge power cord as a troubleshooting aid.
    Last edited by Thatguy; 10-08-2010 at 12:19 PM.

  4. #4
    Senior Robin Hood Guy Ian Gills's Avatar
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    From personal experience I have never had a GFCI false trip when I have used one on sump pumps and refrigerators and even saws.

    I have had AFCIs trip though with saws.

    So count yourself lucky your basement is unfinished which requires GFCI for the 120 volt circuits rather than finished which might require AFCI.

    Nevertheless I do not think one is required for 220 volt circuits even in an unfinished basement. A dryer does not need one, for example. Nor does the AC unit which is outside in the rain.

    I'd try the dual pole GFCI if you are worried. It will be expensive though.
    Last edited by Ian Gills; 10-08-2010 at 01:17 PM.

  5. #5
    DIY Retired Member walt_pittsburgh's Avatar
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    Default Update on my GFCI Question

    Quote Originally Posted by walt_pittsburgh View Post
    I installed a 2P standard breaker to control both a Delta 220v cabinet saw and a Jet 220v planer. I have a wall outlet in an unfinished area of the basement (my workroom) with a 220v receptacle. It then has a rather short (approx 8-10ft) heavy duty extension with the correct 220v plug and receptacle I move between these two machines. Just depends on what I am working on. Typically it stays connected to the Delta Saw. Based on NEC, is a 2P GFCI required in this application?

    I have a concern that the motor characteristics may cause nuisance tripping. I noticed our furnace and an outdoor sewage pump are not connected to GFCI. I suspect it has something to do with they are both motors.
    Thanks to those who have replied so quickly. To clarify a few points. Both machines, which weigh several hundred pounds each, are on mobile bases so they do not have direct steel contact with the concrete floor. The basement is undergound on one side (front of house) and ground level on the other (rear). I can walk out from my workroom to a patio on the back side. The workroom has a finished drop ceiling and finished drywall on one side (common to the game room). I realize the 2P GFCI will be close to $100. I am just trying to get into compliance with NEC.

  6. #6
    Electrical Contractor jbfan74's Avatar
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    Only 120volt receptacles are required to be gfci protected.
    Yes I am A Pirate-Jimmy Buffett

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    Electrical Contractor Jim Port's Avatar
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    I am not sure about some of the issues raised in post 3 above, but the UL allowance for acceptable leakage on motors is about 1/10 of the level that a GFI should trip at. You should not be having issues with sump pumps, freezers etc tripping a GFI. If you are the problem appliance needs to be repaired or replaced. The old exceptions for appliances in areas that needed GFI protection have been removed. GFI protection is now required even for the ceiling mounted receptacles in a garage. Commercial kitchens even require GFI protection for the refrigerator.

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