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  1. #14
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    Quote Originally Posted by GT Jets View Post
    Now we're getting to the meat and potatoes.

    A higher end meter very well may have been able to prove the motor partially grounded. What make/model meter were you using?

    I agree that the ground issue needs to be investigated further. My bet is that the breaker panel the power is coming from has lost continuity with the ground stake at some point. Either that or it was never completed (both equally plausible).

    For god sakes be careful....
    The problem would not be with the grounding stake or rod. The ground path begins at the panel with the system bonding jumper, which connects the ground bar to the cabinet and the neutral. This is the ONLY point in a system where the neutral and grounding conductors meet, so as to avoid what they call "objectionable current," that is, where current typically is flowing through the ground conductors. That current should ONLY flow during a fault. That's why they changed from three wire to four wire plugs for dryers, because we used to tie the ground (cabinet) to the neutral at the terminals in the back of the dryer. Now, only the cabinet connects to the fourth wire, and never carries current until something in the dryer shorts to the cabinet.

    The grounding conductors carry fault current to the neutral at the panel, so as to assist the overcurrent device to open. The ground rod outside is there to take any lightning potential in the building wiring system to a low impedance earth ground, which only lightning uses as its sought potential. We can read voltage potential to ground because the building neutral and the utility transformer neutral (the center tap of the secondary) both tie to ground rods for lightning protection of the grid and structure.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  2. #15
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    Keep in mind all your electrical connections including ground is only as good as it's weakest or apparent connection. I your unit is grounded you may want to check the five or six screws on the fan guard to top cover since carrier uses screws with a rubber washer.

  3. #16
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    Quote Originally Posted by ararams View Post
    Keep in mind all your electrical connections including ground is only as good as it's weakest or apparent connection. I your unit is grounded you may want to check the five or six screws on the fan guard to top cover since carrier uses screws with a rubber washer.
    AND, the motor should have a grounding conductor going to the unit cabinet, under a machine thread screw, such as a self-tapping 10-32 screw. Green coloring is not an NEC requirement, BTW.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

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  4. #17
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    Jan 2012
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    Fresno, ca
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    Timebuilder, does this "bonding jumper" weaken when there is a large flow of current through it? The cc heater in the unit

  5. #18
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    Jan 2012
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    Sorry... the wire nuts that attatch the the cc heater leads were laying in water in the botttom of the unit. So, that did trip the breaker at the roof panel and at the breaker down stairs.

  6. #19
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    Quote Originally Posted by jarganda83 View Post
    Timebuilder, does this "bonding jumper" weaken when there is a large flow of current through it? The cc heater in the unit
    Generally speaking, no. It is sized by the manufacturer of the panel to be sufficient for its purpose.

  7. #20
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    When the unit "zapped" me it was only a tingle.

    So, if the unit was properly grounded I should have felt absolutely nothing?

    The breaker only trips when there is high amperage, right? So, if the short to ground in motor was very small then maybe it wasn't over amping?

  8. #21
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    Quote Originally Posted by timebuilder View Post
    AND, the motor should have a grounding conductor going to the unit cabinet, under a machine thread screw, such as a self-tapping 10-32 screw. Green coloring is not an NEC requirement, BTW.
    [ I energized this unit after installing the new cc heater and the cond fan grill zapped me. This unit was grounded. The cond motor is stud mounted. This motor came from the factory with just 3 leads (common, start and run) and no ground wire. ]
    These four statements confirm the ground was lost at the cfm grill to cabinet connection.

  9. #22
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    Quote Originally Posted by jarganda83 View Post
    When the unit "zapped" me it was only a tingle.

    So, if the unit was properly grounded I should have felt absolutely nothing?

    The breaker only trips when there is high amperage, right? So, if the short to ground in motor was very small then maybe it wasn't over amping?
    A short is an unintentional connection from line potential to a grounded body or conductor, bypassing a load. Shorts can carry significant amperage. There may have been a high resistance bleed of current from the windings to the motor hosing, and not a true "short."

    That said, there are several ideas to consider. For example, were you touching the cabinet when you touched the fan grille, or were you not touching any part of the unit except for the contact where you felt some current?

    In the first example, where you would be touching a grounded cabinet, and then with the other hand, you touched an improperly grounded motor that was leaking current to its housing, you were completing a circuit to ground, and the unit was grounded, yet the motor and fan grille were not.

    In the second example, if you were standing on a dry surface in work boots and you STILL could feel current, you narrowly escaped a deadly shock, probably due to the boots. In that situation, it would be likely that the unit is not properly grounded to the power system by an EGC.

    Bottom line is this: if the unit and its components were properly grounded, it unlikely that you would feel a current bleed from a defective motor, if that is the only contact, i.e, the hand that felt the current. If the motor had a real short, enough current would flow through the equipment grounding conductor back to the panel to open the overcurrent device.

    So, the answer is in exactly how you contacted the unit, and how well the unit and the motor are tied to the equipment grounding conductor.

    Remember, it only a takes an extremely small current flowing through your chest to send your heart into a fibrillation that only a cardiac device such as an AED, can correct.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  10. #23
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    Jul 2007
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    You really need to use a megger to check for grounded motors. If the motor has a very mild ground, the 9 volt battery inside your standard ohm meter isn't powerful enough to complete the circuit. A megger, which produces 250 or 500 volts, will be alot more accurate. There has been many times my high quality Fluke 87 won't show a ground but the megger will pick it up.

  11. #24
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    Jan 2012
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    Fresno, ca
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    You guys are absolutely right! When I got zapped I was repositioning the lid because I removed it to install the cc heater. The motor leads were still connected and the screws to the lid were not installed and the unit was supplied with power.... You guys are good.

    I know your right because I checked voltage at the grille and at the cabinet. I was not showing any voltage at the cabinet because it is properly grounded.

  12. #25
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    Quote Originally Posted by timebuilder View Post
    The problem would not be with the grounding stake or rod. The ground path begins at the panel with the system bonding jumper, which connects the ground bar to the cabinet and the neutral. This is the ONLY point in a system where the neutral and grounding conductors meet, so as to avoid what they call "objectionable current," that is, where current typically is flowing through the ground conductors. That current should ONLY flow during a fault. That's why they changed from three wire to four wire plugs for dryers, because we used to tie the ground (cabinet) to the neutral at the terminals in the back of the dryer. Now, only the cabinet connects to the fourth wire, and never carries current until something in the dryer shorts to the cabinet.

    The grounding conductors carry fault current to the neutral at the panel, so as to assist the overcurrent device to open. The ground rod outside is there to take any lightning potential in the building wiring system to a low impedance earth ground, which only lightning uses as its sought potential. We can read voltage potential to ground because the building neutral and the utility transformer neutral (the center tap of the secondary) both tie to ground rods for lightning protection of the grid and structure.
    I caught myself using an incorrect term, so I want to correct it for all of you. My bad.

    The jumper for bonding at the panel is the MAIN bonding jumper. The System bonding jumper is used where to have a transformer in a store (for example) where the service is 460v, and the transformer is there to supply power to the outlets, lighting, equipment, etc, that need 120v. In the transformer you have the SYSTEM bonding jumper, as it is a "separately derived system."
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  13. #26
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    Fresno, ca
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    Quote Originally Posted by jarganda83 View Post

    How could a single phase motor ohm out all the same? The motor only uses 2 legs of power. L1 to common, L2 to run cap to run, other side of run cap to start.

    ???
    Has anyone ever ohmed out a single phase motor and got 3 similar resistances?

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