1 phase 460v cond. motor? - Page 3
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  1. #27
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    Quote Originally Posted by timebuilder View Post
    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."
    Timebuilder I have wondered this for some time now - about the seperate neutral 4 wire range and dryer cords.

    I understand what you mean about not using ground as current path.

    At the dryer electrical connection there is a jumper from ground to neutral so what did this really accomplish?

  2. #28
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    Quote Originally Posted by SBKold View Post
    At the dryer electrical connection there is a jumper from ground to neutral so what did this really accomplish?
    The intention of that equipment jumper was to place the chassis of the dryer at the same potential as the "grounded conductor," which we routinely call the "neutral" conductor.

    (Note: the NEC refers to the "hot" wires as the "ungrounded" conductors, the neutral as the "groundED conductor, and the ground wire as the "groundING conductor. They are working on changing the verbiage for most grounding conductors to BONDING conductors, since the purpose of an Equipment Grounding Conductor is to "bond" the metal parts to the panel via wires and conduit so that any short results in the overcurrent device being opened, which cuts off power to the offending appliance.)

    Today, we use a separate conductor that is intended to carry NO current unless there is a fault, and that is the fourth wire. It eliminates the possibility that the cabinet can become energized due to neutral currents in the circuit. This raises the level of safety, which is what the code is all about.

    Does that help?
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  3. #29
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    Quote Originally Posted by jarganda83 View Post
    Has anyone ever ohmed out a single phase motor and got 3 similar resistances?
    Yes. It is usually caused by a winding-to-winding short circuit.
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  4. #30
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    Quote Originally Posted by timebuilder View Post
    Yes. It is usually caused by a winding-to-winding short circuit.
    But the resistances were that way on the old and the new motor. The new motor runs within it's rating.

  5. #31
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    Quote Originally Posted by jarganda83 View Post
    But the resistances were that way on the old and the new motor. The new motor runs within it's rating.
    I would have to see the method used. Perhaps that would explain it.

    A three phase motor would have the same resistance for all windings. Are you perhaps talking about a three phase motor??
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  6. #32
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    Quote Originally Posted by timebuilder View Post
    I would have to see the method used. Perhaps that would explain it.

    A three phase motor would have the same resistance for all windings. Are you perhaps talking about a three phase motor??
    I agree, something is not right here. Either you have a 3 phase motor, your meter is not working properly, or your not ohming it out right. Was the motor completely disconnected and isolated when you took the readings?

  7. #33
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    Quote Originally Posted by timebuilder View Post
    The intention of that equipment jumper was to place the chassis of the dryer at the same potential as the "grounded conductor," which we routinely call the "neutral" conductor.

    (Note: the NEC refers to the "hot" wires as the "ungrounded" conductors, the neutral as the "groundED conductor, and the ground wire as the "groundING conductor. They are working on changing the verbiage for most grounding conductors to BONDING conductors, since the purpose of an Equipment Grounding Conductor is to "bond" the metal parts to the panel via wires and conduit so that any short results in the overcurrent device being opened, which cuts off power to the offending appliance.)

    Today, we use a separate conductor that is intended to carry NO current unless there is a fault, and that is the fourth wire. It eliminates the possibility that the cabinet can become energized due to neutral currents in the circuit. This raises the level of safety, which is what the code is all about.

    Does that help?
    Thanks for the reply and explanation. My conclusion is then it is a backup conductor to the single grounding conductor we used in the past. Because depending on which conductor has the least resistance for the neutral currents it may be using either one.

  8. #34
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    Quote Originally Posted by SBKold View Post
    Thanks for the reply and explanation. My conclusion is then it is a backup conductor to the single grounding conductor we used in the past. Because depending on which conductor has the least resistance for the neutral currents it may be using either one.
    With today's four wire cord, you do NOT hook up the strap. They want NO connection between the neutral and the equipment grounding conductor. The strap was only used when there were only three wires.
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  9. #35
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    I ohmed the new motor right out of the box. The motor only has 3 leads, black, yellow and brown. I just checked from one lead to another. I checked the old motot the same way, with the motor leads off.

    I guess there is a chance my meter was wrong, but I ohmed a different motor the same day because I wanted to compare numbers and it was about right. The only difference was the voltage. The old and new motor were 460 single phase. The compared motor was 208/240 single phase.

    I knew somthing was up...

  10. #36
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    Quote Originally Posted by timebuilder View Post
    With today's four wire cord, you do NOT hook up the strap. They want NO connection between the neutral and the equipment grounding conductor*. The strap was only used when there were only three wires.
    *In the dryer.

    There IS a connection between the neutral and ground, but that ONLY happens at the service entrance panel.

    Just to be 100% clear.
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  11. #37
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    Quote Originally Posted by jarganda83 View Post
    I ohmed the new motor right out of the box. The motor only has 3 leads, black, yellow and brown. I just checked from one lead to another. I checked the old motot the same way, with the motor leads off.

    I guess there is a chance my meter was wrong, but I ohmed a different motor the same day because I wanted to compare numbers and it was about right. The only difference was the voltage. The old and new motor were 460 single phase. The compared motor was 208/240 single phase.

    I knew somthing was up...
    A single phase motor that uses a run cap has three wires, and two windings. One is a run winding, and the other is usually referred to as an "aux" winding, which has a function similar to a start winding. The brown wire goes to the aux winding.

    What readings did you measure?
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  12. #38
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    Quote Originally Posted by jarganda83 View Post
    I ohmed the new motor right out of the box. The motor only has 3 leads, black, yellow and brown. I just checked from one lead to another. I checked the old motot the same way, with the motor leads off.
    Essentially Black is common, Yellow is run, and Brown is start...Brown to yellow "Should" have the most resistance. Black to Brown the second highest, and Black to yellow the least...A volt meter can pick up on a shorted motor, a grounded motor is a different animal...A short is a broken wire...A ground is a crack in the lacquer in the windings causing power to "leak" to ground...You need meg-ohm meter for that...The OP got blasted by a grounded motor, a shorted motor would blow the fuses or the breaker...

    BTW most of this is my experience, there is no hard fast rule on wire colors, the schematic or hook up diagram doesn't lie...
    "Overkill is an often underrated achievement", Will Hayden -- Red Jacket Firearms

  13. #39
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    Quote Originally Posted by R123 View Post
    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.
    Couldn't agree more R123.
    Mechs who rely on a multimeter to test resistance to ground (earth) run the risk of killing themselves or worse, their paying customer.

    Here are a couple of links of links to the type of meters we're talking about:

    http://www.hioki.com/product/field.html

    http://www.myflukestore.com/c538/meg...p?currency=USD

    They may be expensive but how much is your life worth to you and your family?
    Mistakes are a part of being human. Appreciate your mistakes for what they are: precious life lessons that can only be learned the hard way. Unless it's a fatal mistake, which, at least, others can learn from. Al Franken, "Oh, the Things I Know", 2002

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