PMA grounding for safety?

Discussion in 'Connecting to the Grid' started by Mark Zinn, Jan 13, 2013.

  1. My hydro project is at a point where I need to pull 3 #8cu thwn conductors through an underground pvc conduit from the PMA to a GTI in the house.

    Question: Should I also pull a grounding conductor and connect the frame of the PMA to the house grounding system?

    If I understand correctly, the 2011 NEC Art. 250-30(B) states that the PMA is a separately derived system with no grounded (neutral) wire and thus should not be connected to the house grounding system, even though the plug and play GTI will be grounded to the house grounding system through the 3-wire plug.

    The NEC further states that the PMA should be separately grounded to a ground rod to stabilize the voltage, minimize static buildup, lightning, etc. and all equipment related to this system shall be bonded to it.

    If this is correct, I will pull a grounding conductor from a ground rod installed at the site, through a lug on the frame of the PMA, to the main disconnect at the GTI in the house (since it is part of the separately derived system), and terminate it there.

    Some how it all makes sense, but doesn't sound right.

    Does anyone have any thoughts or maybe some guidance on PMA system grounding?
  2. leamywind1

    leamywind1 WindyNation Engineer

    Hello Mark, From what I understand and how we do it is the PMA is bonded to the tower by all of the mounting hardware. So grounding the tower should be good enough with it's own ground rod.Once entering the building all DC components are to have their own grounding via another ground rod and ground wire. On the AC side of things the home ground is used. Now it all goes out the window as the code was written for UL items. If your plug and play is a China GTI just use the ground from the plug for the inverter chassy as it is and do not have the DC ground touch the inverter so the A/C ground and DC ground are seperated. Any potential from the PMA/tower will got to it's own ground, any potential from the DC components will go to their ground, and any potential from the AC side will go home to the main electrical AC ground
    I also am assuming your PMA is putting out 3 phase wild A/C? If your area even approves of the inverter i would check with your local inspector if you are intending to go through all the red tape with permits and inspections. If not this set up should work fine as you are covered on all sides. I would think it can't be more redundant then that?
    This is a great question. Please post more information if you find out otherwise.
  3. Thanks Larry, I was hoping to get a response from a fellow electrical guru. Yes, I have a SuperAmp PMA with 3p./3w. ac output. I agree that the two grounding systems should never be connected together. Potential induced on one would be induced on the other.. lightning, for instance could be disastrous to the house wiring.

    My house footer is sitting directly on a limestone ridge. I can only drive a ground rod about 3'. I could drive it at an angle according to the NEC. However, at the PMA site I can get the full 8' straight down, so I think that's going to be the plan at this point. Wire is expensive, but I think I have enough for 4 wires back to the disconnect. If I pull all 4 at once it will be much easier than adding one later, and I'll have a spare if one of the phase conductors ever goes bad.

    It's sometimes difficult to obtain specific info needed, so thanks again. Good to know I'm on the right track.
  4. leamywind1

    leamywind1 WindyNation Engineer

    Good luck and please keep us posted with production.:)

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