Wiring a second and third subpanel

wrdaigle
wrdaigle Solar Expert Posts: 65 ✭✭✭✭
I am about to embark on a wiring project and could use some advice. I need to connect my shop/garage to my existing off-grid system. I would like to have 2 different subpanels in the shop:
  • One subpanel (30A, 240V) that is connected to the Inverters
  • One subpanel (30A, 240V) that is connected directly to my 12kW Kohler generator for running a table saw and air compressor.

I have an outback system with PS2 power panel and an X240 configured for 240V output regardless of whether I am running on one or two inverters. Right now I have a 100A subpanel for the house connected to the AC out legs of the PS2.

My plan at this point is to connect the first shop subpanel directly to the PS2 output legs just like the house panel is wired. Is this my best bet, or is there a benefit to wiring it into the house subpanel?

I plan on connecting the second shop subpanel directly to the AC IN legs on the PS2 so it has a direct link to the generator. Sound like a reasonable plan?

How about neutral and ground wires??? Do I need to run these from the house to the shop. The shop has an existing ground. If I need to run one or both of these wires, do I need to make a wire run for each subpanel, or could I make one wire run and link the 2 subpanels in the shop?

Bill

Comments

  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Wiring a second and third subpanel

    Hrmm. Well first thing I see is that you have a 100a panel (house) connected to the inverter's AC OUT. If you tap the sub off the house, you still only have a 100a max load connected to the inverter. If you tie the sub directly to the inverter, you have 130a max load connected to the inverter.

    I dunno the inverter specs so I don't know if that's acceptable.

    The next thing is the neutral to ground bond. That should happen at only one place. If it's happening at the house panel, then you should not tie neutral to ground anywhere else. If you tap the sub off the house then you wouldn't have to worry about it - just don't tie neutral to ground in the sub.

    If you tied the sub in at the inverter, then since the neutral and ground would be bonded at the house panel end of the wire, it'd be the same deal there - don't bond them in the sub panel. No extra bond or ground needed.


    Tying the other sub to the AC IN in on the inverter may be a different story, but probably not.

    If the neutral is bonded to ground on the output side of the inverter - does that mean that neutral is bonded to ground on the AC input side as well? I.e., does it pass through? Probably.

    If so, then when AC IN is connected to AC OUT inside the inverter, then the neutral and ground, being bonded on the AC OUT side (at the house panel) would also be bonded on the AC IN side - and so you would not want them bonded at the sub or the generator on the AC IN side.
  • wrdaigle
    wrdaigle Solar Expert Posts: 65 ✭✭✭✭
    Re: Wiring a second and third subpanel

    Thanks for the reply. I've already modified my plan a bit since I posted, but your response brings up a few more questions.

    I am no longer planning on installing a third subpanel. Instead I'm just going to install one (shop) subpanel. If I need to power it with the generator, I will run it through the inverter's transfer switch, just like the house is wired now.

    Don't worry, at no point will I have an opportunity to draw 130A from my inverters (they wouldn't like that). My Outback system has a built in load center. The AC OUT bars are connected to the inverters via a 50A breaker. The 100A breaker on my house subpanel isn't really doing much since the 50A breaker in the load center would get thrown well before I get to 100A.

    Your comments about bonding neutral to ground prompted me to do a little investigation. My previous statement about the bond occurring in the load center was not correct. In fact it doesn't appear to be bonded in the load center or the house subpanel. I checked the resistance between ground and neutral in both places and there doesn't appear to be a bond anywhere. Is this problematic??? It's been running this way for years (I'm the second owner).

    The load center is a bit of rat's nest. I'm in the process of putting together a wiring diagram so I'm 100% confident about what is connected to what. I will post the diagram with a few questions once I get it together.
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Wiring a second and third subpanel

    Depends on if the inverters are designed to have neutral and ground bonded. Some are, some aren't.

    What about the generator? Some have neutral bonded to ground by default, so you might have a situation where you do not have a neutral->ground bond when running on inverter, but do have them bonded when running on the generator.

    The building should be grounded in any case, and the neutral should be bonded to that ground if the inverters allow it.