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Electrical mystery?

Discussion in 'Landscape Lighting' started by Tim R., Dec 7, 2010.

  1. Tim R.

    Tim R. LawnSite Member
    Messages: 87

    Ok, so this is the same place I thought I was having inrush problems with before. Here is what is going on now and it is making me scratch my head.

    Some background:

    -Dedicated GFCI protected outlet.
    -Outlet is 6' from the panel.
    -there is an 1200 watt transformer dedicated to that circuit
    -I am using approximately 950 watts on this transformer
    -It is controlled by photocell

    Here is the issue:

    Currently the homeowner has to reset his breaker at his panel at night when he comes home from work to turn the lights on.

    The lights stay on all night just fine, the homeowner commented that they are on in the morning when he leaves for work, but sometime (either when the transformer is powering off or sometime during the day) the breaker trips. This happens everyday, Rain or shine.

    Any thoughts?

    *on a side note. I took all the circuits off the main transformer and split them up between two smaller transformers just before thanksgiving. I taped the photocells and let them run to see if I would get a fault. No dice, they ran for well over a week just fine until I uncovered the photocells on those units and am back to the same problem.....
  2. steveparrott

    steveparrott LawnSite Bronze Member
    Messages: 1,276

    It seems clear that the problem is not with the transformer since you tried a single transformer and replaced it with two smaller ones.

    Equally clear is that the problem is on start-up. The close (6 ft.) distance to the transformer maximizes inrush potential. The extent of inrush depends upon the current phase at start-up. If the sine curve is at zero then the inrush current can be as much as 80 times the nominal amperage. If the sine curve is at the peak then the inrush is minimal. If you turn the transformer (in your scenario) on and off ten times, there will be 2 or 3 times that the phase is near enough to the zero line to result in an inrush current high enough to trip a 20 amp breaker - that's only once or twice a week.

    The fact that the breaker is tripping every time on start-up tells me that the panel breaker is either loaded near its max (is it really dedicated to the transformer?) Or, that it's defective.

    A good next step would be to replace the panel breaker with a high-magnetic type (HM or HOM series). These breakers are designed to deal with inrush problems.
  3. Tim R.

    Tim R. LawnSite Member
    Messages: 87

    Thanks Steve,

    the problem is not on startup but rather upon powering off. When the circuit is energized they stay on and hold just fine.
    Posted via Mobile Device
  4. steveparrott

    steveparrott LawnSite Bronze Member
    Messages: 1,276

    Sounds fishy to me. I can't imagine a scenario where the breaker would trip after normal operation throughout the night.

    You state: "Currently the homeowner has to reset his breaker at his panel at night when he comes home from work to turn the lights on."

    Is it possible that he does this after dark, after the inrush already tripped the breaker?

    It is conceivable that when he manually resets the breaker he holds it in place long enough (only needs about 0.005 secs) so that the inrush doesn't trip it.
  5. RLI Electric

    RLI Electric LawnSite Senior Member
    Messages: 381

    What kind of panel? GE,Square D, Siemens?
    Did anyone change the breaker?
    Did anyone change the gfi outlet?
    Is there a in use cover on the outlet?
    Are there any other issues going on in the house?
  6. Tim R.

    Tim R. LawnSite Member
    Messages: 87

    Steve, he resets it when it is still light outside. I am not ruling out inrush, but why would it trip after or during the shut off cycle.

    Square d panel.
    New 20 amp breaker
    new gfci (twice)
    yes, in use bubble cover.
    Posted via Mobile Device
  7. emby

    emby LawnSite Senior Member
    from Ontario
    Messages: 380


    You might try this as well as those suggestions that Bob made.
    Ensure that your photo cell is correct. There are many different types and different rated PECU`s. Your issue could be as simple as an inventory blunder along the way of distribution and it could the wrong model. Swap it out and try another or even another brand.
    That is bizarre that its tripping on shutdown. Maybe the photo cell is defective.....

    There also was a bulletin out at some point this past summer about counterfeit Square D 20 amp breakers. Look to see if the 20 on the breaker handle is painted or not. If its not it might not be a real Square D.
    Let us know what you discover.

    Last edited: Dec 7, 2010
  8. RLI Electric

    RLI Electric LawnSite Senior Member
    Messages: 381

    Sorry but is it a Square D Homeline or a QO breaker. HUGE difference in the quality of the two. If it is a Homeline you unfortunately cannot change it out to a QO. If you are familiar with the two models I apologize for mentioning that to you, no disrespect meant. Ken may be on to something there too with the photocell. No real moving parts so one would think it can't go bad but they do.
  9. Tim R.

    Tim R. LawnSite Member
    Messages: 87

    Thanks Ken,

    I have another 900 watt transformer on another dedicated circuit with the same photo cell that is working fine. It is 175' from the panel, but nonetheless, the same. My two temp transformers are causing the same problem. They are a different brand, but the same result. I would think inrush, but it is tripping on shut down, not start up.

    Still hoping someone else out there has encountered this.
  10. steveparrott

    steveparrott LawnSite Bronze Member
    Messages: 1,276

    Panel breaker is still the number one suspect. I suggest changing the panel breaker - preferrably to high-magnetic type:
    Square D model 20A HOM120HM.

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