Page 1 of 2 12 LastLast
Results 1 to 10 of 16

Thread: 480 Volt twist lock plug

  1. #1
    Join Date
    Apr 2008
    Posts
    364

    480 Volt twist lock plug

    I'm getting some machines in that are plug and play.. they have 480Volt twist lock plugs. The concept is to allow one machine to be unplugged and a different machine plugged in its place. Here is my question.. is it safe to unplug the units with 480 Volt at the plug? Seems to be a no brainer to me that an arc flash potential exist. Am I over cautious?

  2. #2
    Join Date
    Mar 2010
    Location
    Lake of the Ozarks
    Posts
    981
    Quote Originally Posted by cornbread View Post
    Am I over cautious?
    I think so if you are using the appropriate size and configuration of cord and plug and also not plugging and unplugging while the equipment is on.

    1N73LL1G3NC3 15 7H3 4BILI7Y 70 4D4P7 70 CH4NG3.

  3. #3
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    33,515
    There is arc flash risk, how much depends on several factors and won't necessarily the same at every receptacle.

    A 20 amp receptacle should have less incident energy available at the receptacle then there is at the service simply because the resistance of the branch circuit conductors will have a limiting effect, the longer those conductors the more limiting effect there is. There can still be a pretty significant incident energy available though, it just will be less then upstream at the feeder or service level.

    Is still a good practice to not plug items in under load.

    Some receptacle/ plug designs may offer better protection then others as well.

    Some places you do see a disconnect ahead of the receptacle and the proper procedure is supposed to be to turn the disconnect off before inserting or removing the plug.

  4. #4
    Join Date
    Jul 2006
    Posts
    2,430
    Quote Originally Posted by luckylerado View Post
    I think so if you are using the appropriate size and configuration of cord and plug and also not plugging and unplugging while the equipment is on.
    Agreed, most plugs aren't rated for "load-break" but are OK to disconnect while energized. Put up some "Turn off equipment before unplugging" signs.

    What's the current involved?

  5. #5
    Join Date
    Aug 2004
    Location
    Northern illinois
    Posts
    15,657
    It is hard to give you a good answer to this question.

    I will say this. I was in a plant a few years ago that had many dozens of machines hooked up this way. Each of the receptacles was labeled with the IE. None that I saw even made it into single digits. That suggests to me the risk associated with unplugging under power on these receptacles is quite low. But to reduce that risk even more it would be best to turn off the power to the receptacle first.
    Bob

  6. #6
    Join Date
    Apr 2008
    Posts
    364
    Just ran some calcs and look like the worse case is 2.6 cal/cm^2. I'm working with the operation folks to have the SOP include flipping the breaker off before plugging and unplugging. Appreciate everyone reply!

  7. #7
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    33,515
    Quote Originally Posted by zbang View Post
    Agreed, most plugs aren't rated for "load-break" but are OK to disconnect while energized. Put up some "Turn off equipment before unplugging" signs.

    What's the current involved?
    Quote Originally Posted by petersonra View Post
    It is hard to give you a good answer to this question.

    I will say this. I was in a plant a few years ago that had many dozens of machines hooked up this way. Each of the receptacles was labeled with the IE. None that I saw even made it into single digits. That suggests to me the risk associated with unplugging under power on these receptacles is quite low. But to reduce that risk even more it would be best to turn off the power to the receptacle first.
    I have greater concerns over what happens when plugging a cord in that happens to have a fault in the equipment then I am about unplugging one while it is loaded.

  8. #8
    Join Date
    Dec 2012
    Location
    Placerville, CA, USA
    Posts
    18,377
    Quote Originally Posted by kwired View Post
    I have greater concerns over what happens when plugging a cord in that happens to have a fault in the equipment then I am about unplugging one while it is loaded.
    A valid concern. In which case you should probably turn off the breaker.
    I believe that plugs and receptacles that are listed with an HP value in addition to current are in fact rated for load making and load breaking.
    If just amps and "tungsten" rated, you can make and break compliant lighting loads but not motors.

    Sent from my XT1585 using Tapatalk

  9. #9
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    33,515
    Quote Originally Posted by GoldDigger View Post
    A valid concern. In which case you should probably turn off the breaker.
    I believe that plugs and receptacles that are listed with an HP value in addition to current are in fact rated for load making and load breaking.
    If just amps and "tungsten" rated, you can make and break compliant lighting loads but not motors.

    Sent from my XT1585 using Tapatalk
    What about the millions of 5-15 and 5-20 receptacles that get motor loads plugged into them? I've never seen one that is HP rated that I can recall.

  10. #10
    Join Date
    Jan 2009
    Location
    Maryland
    Posts
    12,028
    Quote Originally Posted by kwired View Post
    What about the millions of 5-15 and 5-20 receptacles that get motor loads plugged into them? I've never seen one that is HP rated that I can recall.
    They are HP rated. It is part of their listing.

    page 467. http://www.ul.com/wp-content/uploads...White-Book.pdf
    "Electricity is really just organized lightning." George Carlin


    Derek

Posting Permissions

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