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As the title states, I have a house and a shop both with 240 feeders coming from the grid.

grid feeders

I have solar panels and a solar inverter in the shop.

Solar Inverter

Shop main breaker box

inverter panel

The solar inverter is powered by panels, a 48v battery bank and the grid (fed from the main breaker box in the shop). It draws from the panels first, the batteries second and if the batteries' voltage gets too low it will pull from the grid to charge them. I have a 2 120 legs and a neutral coming from the main to the inverter and the same, 2 120s and a neutral leaving the inverter to the subpanel which is powering most of the shop as well as sending a 240 aerial to a subpanel in the house which feeds most of the 110 circuits.

Ariel messenger

Main and subpanel in the house

Solar subpanel in the house

Both the main breaker box in the house and the shop have ground and neutral combined. The subpanel in the house being fed by the inverter fed panel in the shop has an isolated ground bus.

I tried giving the inverter fed panel its own ground bus but the results were not good. Which later dawned on me, was probably because its not actually a subpanel.

So in the house, the solar fed subpanel is getting its ground to its isolated ground bus from the main panels shared ground/neutral bar which is I assume is attached to a ground rod outside.

In the shop the main panel doesnt seem to have a ground. Just a 3 cable feeder, the neutral being attached to the ground/neutral bar. Which I have a ground wire running from and going to the inverter's panel's ground/neutral bar.

My question is, is it dangerous that neither panels in the shop have any way to go to ground? Why did the main panel not have a ground rod? Should I install one?

I know this is a complicated setup and I truly appreciate any insight.

Thank you.

-Dusty

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    Who's your electric utility? I take it both the shop and the house have their own meters, or do they share a meter on a pole somewhere? Sep 18 '21 at 17:40
  • All those wire nuts outside the panel need to be inside a box of some sort.
    – FreeMan
    Sep 18 '21 at 19:00
  • Also, can you get us the model number of your inverter please? Sep 18 '21 at 21:37
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    OK so you have 1 electric meter and one of the breakers in the main panel powers a feeder from the house to the shed. Does that feeder have 3 wires or 4 (separate ground and neutral)? Was it installed prior to 2008? Also, how about the new solar feeder going the other way, 3 or 4 wires? Sep 19 '21 at 0:20
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    Armorlite 125-ft 10/3 Solid Aluminum MC Cable Sep 19 '21 at 20:26
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Ok, first, let's get some terminology straight so we are talking the same language.

  1. There's a difference between grounding (or earthing) and bonding. The purpose of grounding is to provide a low impedance path for induced transient currents, such as lightning strikes, transformer faults and other electrical noise safely to the physical earth itself. The purpose of bonding is to ensure that all metal parts of electrical equipment and metal piping systems in your building are connected not to the Earth, but to the neutral conductor coming from the transformer. This is to ensure that a ground fault (when a hot wire touches the metal chassis of a piece of equipment) makes a short circuit to neutral in order to cause the circuit breaker or fuses instantaneous trip mechanism to nearly instantly open.

So this is why the neutral bus in your main panel or disconnect is either bolted or attached by a wire or strap to the metal chassis of the panel enclosure. So when a ground fault occurs, say in your washing machine, the fault current travels through the third prong on the plug, through the green or bare copper wire, back to your panels neutral or ground bar and then down the neutral wire on your service drop and then to the transformer where the current originated. It's a common misconception to think they this current dissipates into the ground. Electricity must make a complete circuit to flow and the resistance of the earth from your panel to the transformer on the pole is so high it might as well be considered infinite.

Now, it's very important that this neutral to chassis bond only occur at one point in your electrical system. By code, that is to be done in whatever enclosure contains the main disconnect for that building. That could be a meter socket with a main breaker built in, a fusible disconnect or a main breaker load center (what you have). Any sub panels down stream from your main panel must have an appropriate sized equipment ground run with the feeder conductors and the EGC and neutrals must remain isolated in the sub panel. If you were to bond the neutral in the sub panel, neutral current would take parallel paths on both the feeder EGC (including metal conduit if used) as we as the neutral conductor, proportional to their impedance respectively. This is a hazard for electrocution because ground wires are not expected to have current passing through them under normal circumstances.

If I understand correctly, you have a standalone PV system that is NOT utility interactive, correct? If so, you'll want to follow the manufacturers instructions for neutral bonding and grounding. Regardless, all grounding systems in your home and also buildings with common metal systems (like underground pipes) all need to be bonded. And each separate building must have it's own grounding electrode. Rebar, ground rods, etc.

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  • His system isn't truly standalone either -- it's capable of pulling power from the mains, but not pushing power back up, as far as I can tell. Also, the OP appears to have 2 service entrances run from a "maypole" with the meter on it, so it's natural that the OP would have N-G bonds at each SE point Sep 19 '21 at 1:07
  • You're correct about the bonding at each building if their fed from a "farm service" via triplex cable, although this is not standard practice today. Today we install discos or a panel usually on a board and two posts, do the neutral bond there and then run quadplex or underground conduit with EGCs to each building.
    – DrSparks
    Sep 19 '21 at 1:13
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    Yeah, the modern style is to run feeders to each building from a service disconnect at the maypole as that gives better control over stray earth current, and stray earth current makes for unhappy cows Sep 19 '21 at 1:14
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    In either case, the OP should refer to manufacturers instructions. It's important to understand that electrical current returns to it's source with regards to understanding fault current paths. A utility interactive inverter has a pure sine wave generator that matches the grids sine wave phase. I don't think the OP has this system and would need to be approved and inspected by the electrical inspector and utility engineer.
    – DrSparks
    Sep 19 '21 at 1:15
  • I greatly appreciate the information DrSparks and Mr Eel but unfortunately the manufacturers instructions are lacking. manualslib.com/manual/1954554/… Sep 19 '21 at 18:17

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