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  1. #1
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    GROUNDED B PHASE

    Boy did i get a education on this one the other day.

  2. #2
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    Quote Originally Posted by VTP99 View Post
    Boy did i get a education on this one the other day.
    Well, please share what you learned.

  3. #3
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    Quote Originally Posted by bunny View Post
    Well, please share what you learned.
    Well he is still alive so I bet it was a valuable lesson.
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  4. #4
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    Quote Originally Posted by thegoodlistener View Post
    Well he is still alive so I bet it was a valuable lesson.
    Yes i'm still here but that 3 phase motor is toast.

  5. #5
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    Quote Originally Posted by VTP99 View Post
    Yes i'm still here but that 3 phase motor is toast.
    If the voltages between the phases are correct, you should be able to change direction and have no toasting of the motor.

    Maybe there is a more detailed explanation of the sequence of events???
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  6. #6
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    Quote Originally Posted by timebuilder View Post
    If the voltages between the phases are correct, you should be able to change direction and have no toasting of the motor.

    Maybe there is a more detailed explanation of the sequence of events???
    wolfdogs post # 22 after yours is the correct answer. Switch A phase with C phase to reverse but leave B alone.

    timebuilder,
    The "sequence of events" was i replaced a 3 Phase RTU blower motor, same as old one, and added a motor starter. I needed to reverse the direction so i just picked any two phases and reversed. The starter tripped out. I took my amp probe and found the amps on each phase were way out of wack. Like 5-2.5-0 on each of the 3 phases. I then reversed things back and used the other phase. Guess what all 3 phases even out and no tripping overload.
    I don't understand it completely myself and maybe wolfdog can explan it in more detail.

  7. #7
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    Quote Originally Posted by bunny View Post
    Well, please share what you learned.
    yes, please do.

  8. #8
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    “If You Can Dodge A Wrench You Can Dodge A Ball”

  9. #9
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    Well for one thing don't just reverse any two phases to reverse direction. Also a fused disconnect is a no no with the N.E.C.
    The word needs to get out about this type of service.

  10. #10
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    Quote Originally Posted by itsiceman View Post
    A phase top
    B phase bottom left
    C phase bottom right

    Yes that B phase is grounded and will read zero volts to ground but she is still HOT.

  11. #11
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    Quote Originally Posted by VTP99 View Post
    A phase top
    B phase bottom left
    C phase bottom right

    Yes that B phase is grounded and will read zero volts to ground but she is still HOT.
    You'll never forget the first time
    I remember going WTF too
    “If You Can Dodge A Wrench You Can Dodge A Ball”

  12. #12
    Join Date
    Jan 2009
    Location
    Central NJ
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    The voltage of a delta connected system from B phase to ground is actually 240V. The grounded or nuetral conductor is derived by grounding the midpoint of 2 windings. these systems are also referred to as Hi leg, Red leg, Wild leg etc. The reason is between 2 phases to ground the voltage is 120V , but the the third phase to ground it's 240V. There are a lot of these systems that are not marked. A clue is when you see a panel with every third space blank. In a 3 phase application they operate like any other 3 phase connected system. The NEC requires an overload protective device in every phase. That could be an overload heater in a motor starter, a fuse or a common trip circuit breaker. In NJ, PSEG has some delta systems in the older cities where 1 phase is insulated from ground, but the voltage between phases is 240V. PSEG also makes the hi leg phase C phase in the meter enclosure and we have to transpose that conductor from C phase in the meter enclosure to B phase in the panel as per NEC. These conductors and bus bars should be marked with orange tape, paint etc.

  13. #13
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    Oct 2009
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    God's country - Shenandoah Valley, VA
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    Correction

    SBEC,
    The type of service that you are referring to is a 4wire, mid point grounded Delta; VTP99 is describing a 3wire, corner grounded Delta. On this latter type, one phase is indeed grounded and is 0 volts to ground. However, the grounded phase is still current carrying just like a neutral is current carrying and is grounded. The drawing he attached is correct. This type of service is only found in commercial/industrial where there are only 3 phase loads.

    A 4wire, mid point grounded Delta service is "hot" on all phases; 240v between all phases, and 208v to ground on the "stinger" or high phase.

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