Dimmable LV track light humming & grounded neutral

Discussion in 'Electrical Forum discussion & Blog' started by brador, Mar 7, 2011.

  1. brador

    brador New Member

    Messages:
    11
    Location:
    New York
    Hello--

    I'd like to have low-voltage track lighting installed but am concerned about reports of humming (the lights, that is), especially when the lights are dimmed. I have been told that beside the proper dimmer, the track should be wired with a "third wire dedicated neutral" (I assume grounded conductor..the white one) going back to the panel. Does this sound legit?

    Thanks all. Keep up the good work.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,814
    Location:
    New England
    Some incandescent bulbs tend to humm almost regardless of the dimmer used. It depends on the power supply of the low-voltage system and the type of dimmer. Haven't got specifics...hopefully, someone does.
  3. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,529
    Location:
    North Carolina
    post the specs for the transformer and you will get a better clearer answer
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,263
    Location:
    Cave Creek, Arizona
    Brador, the "grounded" wire is the green one. The white is the neutral conductor.
  5. Jim Port

    Jim Port Electrical Contractor

    Messages:
    156
    Location:
    Maryland
    Actually the green is the groundING cdonductor. The white is the groundED.
  6. It's all in the transformer. It can hum. The transformer might hum (not the lights). Talk to whoever talked to you about this. It's the transformer. Did I mention it's the transformer? It is that. Even with the (easily available) dimmer with the 3rd wire, it might hum. I've bought all the transformers I've ever come across, for this purpose. There is no way to know in advance if they will hum. It's a just an expense you have to live with.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,263
    Location:
    Cave Creek, Arizona
    The white neutral is "ground potential" but is incidently grounded by its proximity to the "ground wire" which does have a path to the "earth", as our neighbors across the pond call it.
  8. ActionDave

    ActionDave Electrician

    Messages:
    345
    Location:
    Colorado
    hj, I know you know your stuff, but you lost me here.
    The grounded (commonly referred to as the neutral), and grounding (green or bare) are both tied to earth at the service but separate everywhere else.

    What do you mean by this?
  9. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,529
    Location:
    North Carolina
    Through the years much confusion has started about the neutral a conductor that is intentionally connected to earth (grounded) and the grounding conductor that is also intentionally connected to earth (grounded).

    As defined in Article 100 of the NEC the term ground means connected to earth. There is no definition of neutral but neutral conductor is defined as a conductor that will carry current and connects to the neutral point of a system. The neutral point is defined as common point of a wye-system or the midpoint of one phase of a delta system.

    The neutral is a current carrying conductor that carries the unbalanced current of a system. In a 120 volt system the grounded (neutral) conductor carries as much current as the ungrounded (hot) conductor therefore is in no longer neutral. This is why the NEC has one complete Article on the grounded conductor (white or gray), Article 200 and another Article 250 that addresses the grounding conductor(green or bare).

    When teaching a new class about premises wiring systems (the wiring after the point of attachment from the power company) I start by asking the class if there is a ground wire anywhere on their automobile. The definition of ground in the NEC is, “The earth†therefore a car does not have a ground but instead a return path back to the battery. This is the same wiring as a 120 volt circuit, a wire from the power source (Power Company) back to the power source (Power Company).

    Both the grounded (neutral) and the equipment grounding conductor connects to the grounding electrode conductor which connects to earth at the service. Yes the grounded (neutral) conductor that carries the same current as the ungrounded (hot) conductor of a 120 volt circuit is connected to earth at the service. This grounded (neutral) conductor is carrying the same amount of current as the ungrounded (hot) conductor therefore it is not neutral although through the years everyone has learned to call it the “neutral†conductor. In the case of a 120 volt circuit it is not neutral but current carrying.

    They power company will connect the return of the primary which in most cases across America will be 7200 volts to the same midpoint as the secondary of the transformer (the 240 coming into our homes) and connect this to earth at the transformer. Yes the primary (7200 volts) and the secondary (240 volts) will have the grounded (neutral) conductor connected together and to earth at the transformer. This connection of the grounded (neutral) is connected to earth again at the service disconnect of the premises wiring.

    There is a big difference between the grounded (neutral) and the equipment grounding conductor. The equipment grounding conductor will carry current ONLY in the event of a ground fault. The grounded conductor will in most cases always have current as it is the return path of the circuit.
  10. MarkTLS

    MarkTLS New Member

    Messages:
    7
    Location:
    New Mexico
    Brador, Great question, i get this all the time. First of all does your track lighting fixture have a magnetic or electronic transformer? As you know if it has a magnetic transformer you are required to use a magnetic dimmer. It will make a buzz, although soft all the time. If you have a electronic transformer then a good quality electronic dimmer should do the job. Please let me know either in this forum or direct and I would be happy to go into more detail. Would love to know the brand of the track fixture and dimmer you are putting together. Also the lamp wattage and the top range of the fixture.

    Mark Scott
    Lead Lighting Designer
    www.TotalLightingSupply.com
  11. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    I think marktls gets to the root of the problem. General purpose low voltage transformers, such as for MR16 track bulbs, can tend to hum, and are not specfically designed to be dimmed, so a little more humming can occur.

    The ultimate solution might be to upgrade to LED, but that will require expensive power modules and dimmer controls. Depends on what that "mood" lighting is worth to you.
  12. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    988
    Location:
    NY State, USA
    Mark, another reply to a really old thread I see. Why would you reply to a thread like this asking the OP questions. There is a near zero chance they are still around to answer and the project is likely done. I know, you are providing info for future readers. Then WHY ask the OP questions?
    BTW, the OP signed out the minute he posted this question and has not been back since.

    I think the reason is so that you can get your business info seen on your sign line. Free advertising is great, isn't it?
  13. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    For 75 years, the main overhead POCO lines here were 2 wire or 3 wire if 3 phase to the mines.

    A year ago, they spent a fortune running a bare third conductor about 3 feet down from the crossarms everywhere.

    Why a return line now? Is it part of the switch to "smart" spy meters?
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Electrical Forum discussion & Blog track light issues Mar 9, 2012

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