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    Weird temporary power issue

    Had a weird temporary power issue today at work, and wonder if anyone can shed some light on this for me. Our spider box started smoking things, chargers, lights, etc. I did a voltage test with my digital multi-meter, and was getting 190v hot to ground ("A" Leg) and neutral, and 60 volts neutral to ground. On "B" leg I got 102V to ground and neutral. I didn't have my wiggy on me to test with that, but the incandescent lamps were noticeably brighter and my charger was smoking, so I believe the reading. I thought the box had gone bad, but I tested the corded and the same issue. I tested the power out of the box prior to that, same issue. When I took off the incoming cap into the spider box, it was not all the way in, and was partly out. I tested that cord and all was well. I plugged it back in properly and all problems disappeared. I'm led to believe the problem was the cord cap was not all the way into the box, however I can't figure out why this would cause in any way 190v on either leg. No issues in the cord cap itself, and there are no issues with the neutral or ground at the panel it originates from. Any ideas?

    #2
    Originally posted by beachbumjeremy View Post
    Had a weird temporary power issue today at work, and wonder if anyone can shed some light on this for me.
    Our spider box started smoking things, chargers, lights, etc. I did a voltage test with my digital multi-meter, and was getting 190v hot to ground ("A" Leg) and neutral, and 60 volts neutral to ground. On "B" leg I got 102V to ground and neutral.
    I didn't have my wiggy on me to test with that, but the incandescent lamps were noticeably brighter and my charger was smoking, so I believe the reading. I thought the box had gone bad, but I tested the corded and the same issue. I tested the power out of the box prior to that, same issue.
    When I took off the incoming cap into the spider box, it was not all the way in, and was partly out. I tested that cord and all was well.
    I plugged it back in properly and all problems disappeared. I'm led to believe the problem was the cord cap was not all the way into the box, however I can't figure out why this would cause in any way 190v on either leg. No issues in the cord cap itself, and there are no issues with the neutral or ground at the panel it originates from. Any ideas?
    1. Please put in some line feeds to make your post more readable.
    2. No doubts about it, you had a compromised (or completely open) neutral connection into the spider.
    Where that compromise took place is the only question. And the answer is very likely the incoming cord connection.
    If it is anything but a twist lock, it is possible to have it sideways in the socket so that one or another pole (including neutral) is not making contact.
    Either change out the connector type or educate everybody about proper connection practice AND provide somewhere to strain relieve the incoming cord so that is does not pull on the plug. (A good spider box will have a way to do that.)
    If it is a twist lock already, then just educate yourself and others on the job to make sure it is inserted AND twisted.

    As for why it caused those voltages, with the neutral conductor floating, the 120V loads on the two legs form a voltage divider which sets the voltage on the disconnected neutral.
    If the loads are exactly balanced you will still get two 120V legs.
    If there is no load on one leg, the neutral will go to the voltage of the other hot and nothing will operate. But a small load plugged into the unloaded leg will probably die.

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      #3
      I fully agree with GD's assessment as the most likely problem, you had an open circuit condition in the neutral conductor someplace, your description of what happened is classic symptoms of this issue.
      I live for today, I'm just a day behind.

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        #4
        Originally posted by GoldDigger View Post
        If there is no load on one leg, the neutral will go to the voltage of the other hot and nothing will operate. But a small load plugged into the unloaded leg will probably die.
        I get that the neutral was floating, which was ultimately the root cause of the problem, but I do not understand this explanation. When the neutral is not making contact, and the circuit can not be completed, how can this lead to an increase in voltage due to an unbalanced load? Which resource should I use to understand this better, maybe with some illustrations or something?

        Comment


          #5
          Originally posted by beachbumjeremy View Post
          I get that the neutral was floating, which was ultimately the root cause of the problem, but I do not understand this explanation. When the neutral is not making contact, and the circuit can not be completed, how can this lead to an increase in voltage due to an unbalanced load? Which resource should I use to understand this better, maybe with some illustrations or something?

          I found this in my photobucket account, something I'm sure I answered a similar question with here before. Look at it and then ask more questions if you still have them.

          I live for today, I'm just a day behind.

          Comment


            #6
            When the lights get brighter, it's usually a neutral issue.
            I can build anything you want if you draw a picture of it on the back of a big enough check.

            [COLOR=red]There's no substitute for hard work....but that doesn't mean I'm going to give up trying to find one.[/COLOR]

            John Childress
            Electrical Inspector
            IAEI / CEI / C10
            Certified Electrical Inspector

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