Off Grid Grounding the right way…

[Stevevan58]

Hi new to the group, still confused about grounding my main system.
Im more interested in the “right” way to do things, not what is minimum code.
I have an off grid cabin, 12k hybrid inverter, 5-SOK 48v rack batteries, feeding my 100a main panel. Honda7k inverter genny wired into my inverter to charge my batteries.
House is wired normal AC. My electrician hasn’t installed any earth ground. Should I have him do it?
Thanks for any advice, sorry about asking same question. Just can’t seem to find any real answer to why or why not to have an earth ground on an off grid house.

 

[robbob2112]

Sorry a novel and more topics than you asked.

The why to have a ground is safety. You want your GFIC outlets to work and you don't want a shock so you need a ground.

You need one earth ground system. This can be a single rod or two rods 6ft apart connected by an unbroken #6 or bigger bare wire connected to the main panel. In the main panel there should be a Neutral-Ground bond in there. Sometimes generators have a N-G bond for when you are off-grid... but that is usually on larger systems. If it does you need to make sure there is only one of these.

The grounding system (i.e. the ground in your main panel) should be connected to all your inverter and other equipment cases and if the battery rack is metal to it. You do not connect it to the negative pole on your battery. This is so you can't get a shock from a difference of potential when touching any two things. This EGC (Equipment Ground Conductor) should also be run in the same conduit as your current carrying conductors out to your array. Out at the array it attaches to the pv panel frames, any metal racking, the combiner box if it exists. If you have multiple strings you can use just one EGC split off to each set of frames... You do NOT connect the PV negative wire to the EGC. The idea of all of this is also that there is no difference of potential so you can't touch two things and get a shock.

One reason to ground the panel frames - the hybrid inverters have a tendency to push AC voltage out the PV wires and if the frames aren't grounded you can get a shock.

All PV wires in or attached to a dwelling MUST be in metal condiut... this can be as MC cable, EMT, rigid, or FMC.. PV wires are sized 156% of expected current. i.e. 30amps generated at panels, 30a * 1.25% * 1.25% = 46.875a - so PV wire rated for 45amps outside and in the conduit you can stick with PV or you can switch to THHN and use the NEC standard chart - 8awg ... most commonly done is 10awg which in PV wire is rated at 40amps... but when you switch to THHN in conduit it is 30amps... so you have to upsize the wire.

Note - also use a DC isolator like the IMO brand - this positioned right outside the house - it cuts off the PV from the inside equipment and can be worked thousands of times without damaging the switch. The plastic IMO uses is self extenguishing so if there is a short that causes a fire inside the box it will go out as soon as the heat source is removed. The plastic the import knock-off makers is generally just standard ABS plastic and will burn and keep burning once lite.

All PV conduit must be labeled as such as are any boxes containing PV wires.

You do NOT want a second rod out at the array. A nearby lightning strike travels as a voltage gradient in the ground and if there are two rods one will rise several thousand volts and the easy way to lower potential will be through your pv wires and equipment to the other ground rod.... Then once it passes the first rod it will hit the second rod and repeat the process in reverse.

If you array is any distance from the house you want to use a SPD at both ends of the PV wires between the house and the array. If it is on the roof use a SPD at the house entrance for the wires. The midnite solar SPD are top notch and highly recommended.