main panel humming

Discussion in 'Electrical Forum discussion & Blog' started by beekerc, Dec 1, 2008.

  1. beekerc

    beekerc IT Consultant / Network Engineer

    Messages:
    94
    Location:
    Seattle
    I noticed last night that my main circuit breaker panel is humming. no, it knows the words, it just chooses to hum instead. :D

    it's a square-D HomeLine, 42 slot, panel. I have a 200A residential service and has 27 breakers installed. 16 on the left and 11 on the right, if that makes any issue (i can provide an aggregate ampacity for each side if it will help). it's not a loud hum, but it is noticable from 3 to 5 feet away and i'm pretty sure it wasn't there before i activated a bunch of circuits, which I did right after the rough-in.

    is this a dangerous condition that needs immediate attention?
    or
    is this a condition that can be corrected? and if so, how?
    or
    is this something that cannot be fixed, and if not, what is the cause?

    Thanks
    B
  2. jar546

    jar546 In the Trades

    Messages:
    432
    Location:
    USA
    Turn each circuit on and off until the sound disappears. There is your problem circuit.

    If that does not work then you may have to change your main breaker to get it to stop. This sound is not necessarily normal but does happen from time to time.

    If that does not work then you may have a problem with harmonics and may have to re-evaluate the size of your neutral on your panel.

    If your panel is a Federal Pacific Stab Lok then it should have been changed years ago, nevermind what I posted above if it is.
  3. beekerc

    beekerc IT Consultant / Network Engineer

    Messages:
    94
    Location:
    Seattle
    One thing i forgot to mention is that if i apply pressure against any pair of breakers, the hum goes away, or is minimized. but the breakers are already snug and the pressure is over the plastic "hinge" side, not the stab-lock side.

    ugh. this is a brand new panel.

    another thing to mention is that i added a ground/neutral bus bar on one side. jumpered it to the existing on with a 6 gauge naked copper. also, now that i think about it, as i originally posted, there are 16 breakers on one side, and 11 on the other, could that imbalance have anything to do with the hum? ordinarily i wouldn't think so, but there is so much i don't know about electricity.

  4. jar546

    jar546 In the Trades

    Messages:
    432
    Location:
    USA
    Too much data processing equipment probably causing a harmonics problem.
  5. jamiedolan

    jamiedolan New Member

    Messages:
    28
    Location:
    Wisconsin
    another thing to mention is that i added a ground/neutral bus bar on one side. jumpered it to the existing on with a 6 gauge naked copper.

    Are you combining your neutrals and grounds on the same bar? I strongly suggest you separate your grounds and neutrals onto separate bars, and isolate the neutrals. Then if this is your main disconnect / SE, then use a bonding jumper to the neutral bar.

    If you have neutral connections on that bar that you have connected with the 6 gage copper, then that is a problem. If it is just a ground bar, then it may be ok.

    A neutral path needs to be able to carry the same amount of current as the hot, so you must size them the same. For 200A service, that would mean 1/0 or 2/0 to connect that additional neutral bar, pretty big difference from 6 gage.

    I don't want to come off sounding mean here, but you need to be more careful than this. Running neutrals through an undersized wire will cause it to overheat and damage your panel and start a fire. And your #6 is way undersized for your panel. Plus if it is a neutral connection, then it can not be bare copper.

    Why did you add this additional bar? Can you post photos?

    It would likely be safest for you to get an licensed person in to work on this.

    Jamie
  6. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    What would be the difference in combining the two on the same bar or keeping them separate and bonding the two bars together?

    This is very true if the ground bar is connected directly to the enclosure. In this case the enclosure become the path for current flow from the added bar to the grounded neutral coming in from the utility.

    A grounded conductor or neutral if you please in a 120 volt circuit will carry the same current as the ungrounded or hot conductor. In a multiwire circuit the neutral will carry only the unbalanced current between the two circuits contained in the multiwire circuit

    I don’t think that anytime someone is doing or saying something that is to help someone else that it is mean.
    Your advice of under sizing a conductor and you concern that it might cause a fire is a gallant gesture on your part and you should be commended for your efforts.
    If the added bar is for nothing but the equipment grounding conductors then the #6 is fine. In Table 250.122 we are told that a #6 will safely carry the fault current of a 200 amp circuit. This is all this bonding jumper would have to carry.
    Again if this added bar is connect directly to the panel enclosure then he wouldn’t even need to install the #6 as the enclosure itself would safely carry any fault current.
  7. beekerc

    beekerc IT Consultant / Network Engineer

    Messages:
    94
    Location:
    Seattle
    ref posts 5 & 6 regarding the neutral/grounding bar and the 6ga wire.

    The bar itself is made by Sqaure-D for their HomeLine breaker panels.
    This is a main panel so the grounds and neutrals are connecting (is "bonding" the right word to use here?) to the same bus bar.
    The 6ga naked jumper wire was indicated by the electrical guy at my local McLendeon's Hardware, who is a retired licensed electrician.
    The installation was done by my neighbor, a licensed electrician, he does more commercial than residential, but licensed is licensed.
    i take some pictures this evening and post them.

    my understanding was the for a main panel, neutral and ground could bond to a common bus bar, however, for sub-panels, neutral and ground had to be kept separate.

    how would you go about isolating grounds and neutrals in a main panel? there would have to be two separated bus bars on each side of the panel. they would need to be isolated. but wouldn't they all ultimately connect to the grounding wire that exits the panel?
  8. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    You are correct that that the equipment grounding (bare or green) can land on any terminal bar in the service equipment and this bar has to be connected/bonded to the bar that has the incoming neutral from the meter. This bond/connection can be made with the screws that is used to mount the bar to the panel.
    What you can’t do is install a bar in the service equipment and land the grounded/neutrals from the branch circuits on it.

    In the picture below you can see by the arrows that by landing the grounded/neutral conductor on the added ground bar the return current must follow a path across the panel enclosure in order to get back to the neutral incoming from the utility.
    The panel enclosure is now part of the path and is carrying the full amount of current of that circuit.

    [​IMG]

    This is a good example of something that will work even though it is very, very dangerous. It is this same principle that Jeff posted a link to about Isaac.
    This is the same installation that some of the moderators of this site have made the statement that they couldn’t believe that an electrician would use a uninsulated conductor for a current carrying conductor.

    As to the remark you made about the person that installed your grounding bar having a license, I have seen this type of improper installation 100s of times by licensed electricians. This is one of the tools I use to help mandate and keep updating the requirements for continuing education for license holding electricians as well as certified electrical inspectors.
  9. beekerc

    beekerc IT Consultant / Network Engineer

    Messages:
    94
    Location:
    Seattle
    in my panel, there is a factory installed terminal bar on each side of the center (hot) bus - presumably for wiring convenience - however, this bar only extends from just below the master switch, to about half way down the length of the hot bus. The additional bar was added on the right side, directly below the factory installed terminal bar, screwed to the back of the panel and jumpered to the terminal bar directly above it, so the current path stays on the same side of the panel.

    I'm assuming that the factory terminal bars are properly connect to the whatever neutral/return/ground they need to be. the panel was installed by a different electrician and that installation was permitted and inspected.

    Attached Files:

  10. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    Those factory installed terminal bars are to be used for all the white/gray grounded/neutral conductors in the circuit wiring.

    With or without the #6 jumper the grounded/neutral conductors can not land on that bar if that bar is connected directly to the back of the panel enclosure. With or without the #6 jumper between the two bars should a grounded/neutral (white or gray) conductor land on that bar that is directly connected to the back of the panel enclosure the enclosure (the metal box holding the breakers) is carrying current.

    Again, just because an electrician installed it and an inspector inspected it in no way changes how those little electrons are going to travel. The path those electrons travel is a matter of physics that can not be changed by any person.

    This is one of the best reasons for education to continue for anyone in the electrical field. Electricians and electrical inspectors are, believe it or not, humans and subject to all the laws of human nature. It is human nature to be lazy and to become complicit in our every day routines. If it works it must be right is the mind set of most people in all trades.
  11. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    I'd use a garden hose to isolate the noise source. You need someone on the distant end to signal you when the hose end is on top of the noise.

    If you put your ear to a wall xformer, this is a 60 Hz hum. See if your panel hum is higher in freq.
  12. Cookie

    Cookie .

    Messages:
    5,658
    Location:
    .
    Maybe a breaker came loose and the humming is actually arcing from a loose connection? If the humming is constant what about using a thermal, if you have one, to see what the temps are on the breakers? (I am not sure if this will help you or not)
  13. jamiedolan

    jamiedolan New Member

    Messages:
    28
    Location:
    Wisconsin
    What would be the difference in combining the two on the same bar or keeping them separate and bonding the two bars together?
    Sorry, I worded that poorly, I should have explained, it was really just a suggestion / my preferance. If a external disconnect is ever added, it makes it an easy change over. Sorry I didn't state this more clearly.

    A grounded conductor or neutral if you please in a 120 volt circuit will carry the same current as the ungrounded or hot conductor. In a multiwire circuit the neutral will carry only the unbalanced current between the two circuits contained in the multiwire circuit

    So on a 200A panel, if one side "leg" of the panel was fully loaded with 120v loads, and there was nothing on the other side (I agree would not be likely to happen in the real world, but would be possiable), then the neutral would be required to carry 200A of return current, vs if the loads were perfectly balanced, it would not be required to carry anything.

    If the added bar is for nothing but the equipment grounding conductors then the #6 is fine. In Table 250.122 we are told that a #6 will safely carry the fault current of a 200 amp circuit. This is all this bonding jumper would have to carry.
    Again if this added bar is connect directly to the panel enclosure then he wouldn’t even need to install the #6 as the enclosure itself would safely carry any fault current.

    I might have misunderstood his setup, my impression was that this was being used as a current carrying correction, for neutral connections.

    If this was truely a second neutral bar, current carrying, then it would be required to be served with the same size conductor as the service, correct?

    Thanks
    Jamie
  14. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    I can agree with your preference and for the same reason that you mentioned., shows that the installer was thinking ahead.
    This is true and very unlikely on a residential service panel. But what we were addressing was the #6 used to bond the added equipment grounded terminal bar to the factory installed terminal bar. The grounded/neutral conductors would not be allowed to land on this bar that was added unless that bar was isolated from the panel enclosure. In this event the jumper would be required to be based on Table 250.66

    As I outlined above if this added bar is bonded or mounted to the enclosure then it can not have any white or gray conductors connected to it at all. This would make the enclosure current carrying.
    If the added bar was isolated then the jumper could have a bonding jumper not smaller than a #4 that bonded the two together but must be large enough to carry all current imposed on it.
  15. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,013
    Location:
    New England
    Maybe I'm all wet, but it seems the bus bar in a typical panel alternates one leg to the other, so as you filled it with CBs on one side, you'd essentially be balancing the potential load (but maybe not the real one). A 220 breaker doesn't reach across to the second column of breakers to make the electrical connection to the second leg.
  16. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    Sounds to me like you have got a pretty good handle on the arrangement of a panel’s bus bar.

    If the service lost one leg then every other breaker space in the panel would be dead.

    For the panels neutral to carry a full 200 amps the panel would have to be completely loaded and one leg of the service is lost or opened.
  17. Cass

    Cass Plumber

    Messages:
    5,980
    Location:
    Ohio
    Is the panel still humming or has the problem been rectified?

    Has it learned any new tunes???
  18. beekerc

    beekerc IT Consultant / Network Engineer

    Messages:
    94
    Location:
    Seattle
    as a matter of fact, i taught it Beethoven's "Ode to Joy". :)

    it's either not humming as loud, or the ambient noise level in the basement is increased slightly to drown it out.

    i will look into the case/bonding issue of the bus bar as well as the suitability of the 6-gauge jumper wire, although the two electricians who i have consulted (the one at the hardware store that sold me the bus bar extension and the copper wire, as well as my nieghbor who put it in) did not say anything to indicate that what was being done was not proper.

    on the other hand (ref my Dressing a Panel post) in the the process of decluttering the wire runs and shortening the ground and neutral wires, i may be able to pack everything on the factory bus bar and disconnect the extension rendering the base bonding issue moot.
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