Page 1 of 4 1234 LastLast
Results 1 to 13 of 48
  1. #1
    Join Date
    Jan 2010
    Posts
    6,611

    GROUNDED B PHASE

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

  2. #2
    Join Date
    May 2003
    Location
    Utah
    Posts
    735
    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
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,724
    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.
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  4. #4
    Join Date
    Jan 2011
    Location
    Boston, MA
    Posts
    461
    Quote Originally Posted by bunny View Post
    Well, please share what you learned.
    yes, please do.

  5. #5
    Join Date
    Mar 2007
    Location
    wedged in freezer shelf
    Posts
    7,068
    “If You Can Dodge A Wrench You Can Dodge A Ball”

  6. #6
    Join Date
    Jan 2010
    Posts
    6,611
    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.

  7. #7
    Join Date
    Jan 2010
    Posts
    6,611
    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.

  8. #8
    Join Date
    Jan 2010
    Posts
    6,611
    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.

  9. #9
    Join Date
    Jan 2009
    Location
    Central NJ
    Posts
    29
    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.

  10. #10
    Join Date
    Oct 2009
    Location
    God's country - Shenandoah Valley, VA
    Posts
    382

    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.

  11. #11
    Join Date
    Mar 2010
    Location
    Southeast Michigan
    Posts
    40
    Well for one thing don't just reverse any two phases to reverse direction.
    How do you change direction then? I have only seen this configuration once and had no problem changing direction. Dont understand how it would toast motor if proper voltage. Motor is still being energized on all three legs.

  12. #12
    Join Date
    Aug 2006
    Location
    Ohio
    Posts
    2,072
    I have never seen it. Is this a regional thing?

    I need to look into this.

  13. #13
    Join Date
    Mar 2010
    Location
    Southeast Michigan
    Posts
    40
    Quote Originally Posted by zw17 View Post
    I have never seen it. Is this a regional thing?

    I need to look into this.
    Just very old system not used in new construction the building I seen it in was pre WWII.

Page 1 of 4 1234 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event