Page 2 of 2 FirstFirst 12
Results 11 to 20 of 20

Thread: Need clarification

  1. #11
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    33,080
    Quote Originally Posted by Smart $ View Post
    He probably would if the MMC had a supply neutral. He said it does not,
    I must have missed that, time to use his PM as the neutral conductor I guess, then maybe the guy will learn why it is wrong. (did I say that?)

  2. #12
    Join Date
    Apr 2009
    Location
    Williamsburg, VA
    Posts
    4,244
    Quote Originally Posted by JohnnyBoy718 View Post
    Hello. My idiot foreman slash PM has tasked me with installing a hot water heater with a small pump. The heater is 3phase 480. The pump is 1phase 120 that draws nothing. I'm feeding the heater from an empty switch on an MCC board. What I was instructed to do is bring to bring 480 (3# 10's + 20 amp fuses) over to heater and to use one of the 277 legs to feed small step down transformer to feed pump. The problem I face is the primary side of the transformer requires a neutral. There is no neutral to be had in the MCC board it is only 3phase 480. The idiot I work is telling me to ground the neutral on the primary side of transformer. Any thoughts ???
    What exact transformer is he asking you to install? You need a 480 - 120/240V single phase transformer of the correct kva for the pump. Period. End of story. Connect 2 277V legs on the primary to get your 480V primary; you do not need a neutral on the primary side.

    btw, it's "water heater".
    Electricians do it until it Hertz!

  3. #13
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    33,080
    Quote Originally Posted by JFletcher View Post
    What exact transformer is he asking you to install? You need a 480 - 120/240V single phase transformer of the correct kva for the pump. Period. End of story. Connect 2 277V legs on the primary to get your 480V primary; you do not need a neutral on the primary side.

    btw, it's "water heater".
    secondary side does not need 240 volts capability

  4. #14
    Join Date
    Apr 2009
    Location
    Williamsburg, VA
    Posts
    4,244
    Quote Originally Posted by kwired View Post
    secondary side does not need 240 volts capability
    I'm aware of that, it's just that most 1ph 480V to 120V xfmrs do both secondary voltages and are cataloged that way.
    Electricians do it until it Hertz!

  5. #15
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    33,080
    Quote Originally Posted by JFletcher View Post
    I'm aware of that, it's just that most 1ph 480V to 120V xfmrs do both secondary voltages and are cataloged that way.
    A control transformer may not, and may be suitable for the application. Hot water circulation pump I'm guessing possibly only needs 50 maybe 100 VA transformer.

  6. #16
    Join Date
    Apr 2016
    Location
    new york city
    Posts
    3
    Quote Originally Posted by jumper View Post
    It is.
    I know its illegal , but what about it is unsafe ? I know your putting potential on the ground.

  7. #17
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    33,080
    Quote Originally Posted by JohnnyBoy718 View Post
    I know its illegal , but what about it is unsafe ? I know your putting potential on the ground.
    When current flows through a conductor there is voltage drop on that conductor. Shorter length of conductor maybe not that much but there is still some resistance in the conductor. When you have current flowing in exposed metal parts it will raise the potential of those items and anything bonded to them over earth and other objects that are at earth potential but not bonded to the items that are carrying current. This is why you can go to almost any premises wiring system and measure from the bonded objects to a probe out in the yard and at least measure a couple volts. Around swimming pools and similar things that is way too much and the reason they have all the equipotential bonding rules they have for those applications.

    The next reason is if you open the return path you are left with full circuit voltage between the components where the circuit was opened. Take a machine or appliance that is using the equipment ground to carry some of it's current and have some accidental opening of the EGC, this leaves all the metal parts bonded to the EGC at 120 volts or even 277 to other grounded objects, unless there is incidental bonding going on, then you may never notice but you still have current flowing via any path it finds rather then a designated grounded conductor.

  8. #18
    Join Date
    Oct 2009
    Location
    Austin, TX, USA
    Posts
    8,264
    Quote Originally Posted by JohnnyBoy718 View Post
    Hello. My idiot foreman...
    Do you call him that to his face? Does he read this forum?

    My dad used to have a sign in his office that read: The boss may not always be right but he is always boss.

  9. #19
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    33,080
    Quote Originally Posted by ggunn View Post
    Do you call him that to his face? Does he read this forum?
    He wouldn't be an idiot if he read this forum

  10. #20
    Join Date
    Apr 2009
    Location
    Williamsburg, VA
    Posts
    4,244
    Quote Originally Posted by JohnnyBoy718 View Post
    I know its illegal , but what about it is unsafe ? I know your putting potential on the ground.
    Again, you do not need a neutral on the primary side, nor need to use the ground as a neutral. 480 - 120V 1ph xfmrs of the kva rating you need (perhaps 100VA as kwired mentioned) are cheap, less than a hundred dollars.

    Short of pulling a neutral that you dont need, and cant connect to the MCC anyway, your other option is a 480V 1 or 3ph pump, which will probably cost more than buying a small step down xfmr and 120V pump.
    Electricians do it until it Hertz!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •