Advanced Level Grounding Discussion for All-in-one Solar Power Systems

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[williamfigueroa]

Just wanted to congratulate you. Even licensed electricians get this subject wrong. I’m a master electrician with 23 years experience in the field and I see this confusion with the earth ground way too often. Thanks for spreading the right information on your channel. Keep up the good work.
Great video!

[john_in_phoenix]

This is a very complicated subject that even has many professional electricians scratching their heads. I would encourage more in depth coverage of the subject (that even I get lost on).

[wgoode]

One, That's how many ground/neutral bonds we need. With grid power input on an inverter or multiple inverters in this case. And that is already done at your main panel or meter panel. One ground location per service structure, now requiring two rods a minimum of 6 feet apart at the first means of disconnect. And in a separate structure (out building) sub panel or even a sub panel in your house never interrupt or divert your neutral or insulated ground from going back to the power company transformer. Meaning never give it an alternative path (ground bond to secondary ground rod) from getting back to the power company transformer. Because your sub panel in a separate structure does now require a ground rod also. And that's death waiting to happen if bonded. For example, your "incoming" ground, 4th wire, in any sub panel is a "ground fault current path" back to the transformer if the neutral gets broken or is shorted to either hot leg and, it must be insulated, not bare. Only your main service entrance wires from the meter to first means of disconnect can use an uninsulated ground. All this is another reason why separate auto transformers should never be used and should be banned if grid power is used on the inverter. In low frequency inverters with their own transformer they are protected if a neutral is lost, the inverter will shut down output AC power. But not separate auto transformers. Ever wonder why there is no breaker or disconnecting means on a neutral, death is why. Neutral IS A CURRENT CARRIER all the way back to the transformer and from there, all the way back to the generator at the power station. And ground rods just dissipate some of that current draw on its way back and keeps the voltage at zero between neutral and ground. It takes a completed loop to use electricity. If you interrupt that neutral path back to the transformer and send it to ground you can be shocked and everything attached to your ground bars in your sub panel will be energized. Be safe. Everyone has this false sense of safety when it comes to grounds, ground this, ground that, ground here, ground there when in fact a ground can be just as much deadly as it is safe. Mike Holts videos are great to watch he shows you exactly how people are being killed by not understanding neutral/ground bonds and ground fault current path. Great video and topic Will.

[samdorchester]

I am no electrician but I was in the dairy industry and when wiring a milking parlor all sub panels ground and neutral wires were to be separated. If they were not it caused a condition called stray voltage which harmed the animals. If I remember right the only place they are connected is at the main panel because all power eventually the power goes back to the power stations. We did have some cases where there was power coming back to the farm by the ground wire, then the power company would have to add more pole grounds. This probably don’t shed any light on the subject but that was my experience in grounds and neutrals.

[ashforkdan]

After a lighting strike that went up my ground rod and fried my inverter I talked with a home power engineer and explained how the ground here has coleagy "water proof ash" 12 inches down and the rain sits on top of it and the lighting hit the ground and went up my ground rod and straight to the inverter. He said to disconnect it and only use the battery ground. It's been 28 years now and lots of lighting but no more problems.

[cotandiet]

Introduction: Each inverter has its own current flow path, each one needs a reference ground point and a short current path. Two of them are combined to make a split phase system which shared the neutral wire. In this split phase system, current flows from each hot wire of it's own inverter and return back itself through the neutral wire. The ground is for reference point and a short current flow path. If the voltages of two hot legs are different, there will be current flow from one inverter to the other, does not matter you have one or two ground-neutral bond(s).
1. For transfer mode (Inverters using power from grid to supply power to the main panel by built-in relays), ground-neutral bond should be at the first panel (after the meter). This was already done when you have electric meter installed. The inverters are using ground-neutral bond from grid, this is correct. Do not create any ground-neutral bond to any panel in your house.
2. For off-grid, the ground-neutral bond should be at the inverters (grid neutral wire should be disconnected). If in case there is a short, the current flow will be terminated at the inverters. Remember, ground-neutral bond is used for reference point and short current flow path. One ground-neutral bond will work, but two are better. Current loop occurs only if your neutral wires are so small and two inverters are mounted far apart (long distance). For conclusion, keep the ground-neutral bonds on all inverters. You cannot count all inverters have bonding as multiple points, it is still single point of bonding because they are together as one power source.

[cybertrk]

This is why right to repair is important, actual board schematics need to be public even just for safety of the end user.

[danfitzpatrick]

I made a video showing this ground /neutral issue last year on my channel. The neutral should only be bonded at the main panel but there is still an issue with these inverters and the only way this could be fixed in my thoughts is upon transfer the ground and neutral bond should change it's state at that point.
I was in contact with the MPP solar engineers and they even watched my video, but I couldn't get them to understand the issue.
The reason these are wired like this (I was told) is that these are shipped to many places with varying code requirements.

[ShaleAudio]

I agree and this was a concern I had recently when setting up a system, because there are many systems that don't specify this but when you test you find it to be true. This is exactly the reason why the NEC says not to have a neutral ground bond in sub panels

[TerrydeAlaska]

The neutral and ground are tied together and bonded to the transform on the pole. The neutral and ground are tied together and bonded to metal and connected to a ground rod at the main service disconnect feeding your house. The inverter would normally float the neutral ground connection on pass-through of utility power and bond them on an outage and switch internally to disconnect from utility power to inverter power (produced from the batteries) and also in the same switch tie the neutral to ground. This is why it's important to ground all metal cases on an inverter. It's great to see you diving so deep on this issue.

[Raphael_Hofmann]

I know from the Victron Inverters, that there is a ground relay, that automatically bonds ground and neutral in inverter mode.
The relay opens, once a AC input is connected. But the ground relay can also be disabled in software.

[noelburns]

Thanks Will as I have been of grid for thirty years and to earth at inverter and distribution panel made no sense and equipment suppliers were vague about this also. All information I read or watched stated to ground but I decided for the reasons you outlined to use the "floating earth" at the equipment end. Using the Inverters internal GN bond. And to quote part of Chris's comment " The reason we don't bond them in subpanels isn't to avoid ground loops, it's to avoid neutral current being carried on the ground conductor". Finally getting some sense on this important issue.

[justvisiten]

You have such great skills (I am in awe of your verbal skills) and insight in explaining what you are talking about but as an old retired master electrician, I just cannot understand all of this without schematics and symbols. And words seem to often fall short on tecnical problems. When I went into programing industrial automation, honestly words just could not much help. However, fortunately my limitations are not universal, and keep up the great work. And ground faults seem to be such a misunderstood problem and for good reasons. Let us all try to help each other stay safe! Says the old arc flash safety trainer.

[Vigo]

I'm glad you're working through this. I'm totally comfortable with DC systems but have to work my brain pretty hard to figure out grounding issues during this brainstorming phase of an offgrid system i hope to build in the coming months.

[teotwawki_je]

I had in interesting time getting it 'right' on a UK barge. Although our 240V single-phase is simpler, the occasional use of shoreline utility power needed extra thought. We ended up not bonding N to E within the boat as that often caused the onshore utility outlet, or the on-board RCD before the inverter input to trip. All Earths are connected onboard & with the DC -ve of both 12V & 48V systems. But while diagnosing the tripping we ended up with a 3-way switch to govern how the on-board earth connects with the shore-line earth. In one position it is a direct connection, in the other position it goes via a galvanic isolator. The mid-position provides isolation (just for testing, with the all-in-one configured to not use bypass). It's all stable & reliable now.

[davidhyman]

Grounding is a multifaceted beast, and has many different implication as whether it is AC or DC and/or even RF. An electrical diagram will show many items tied to ground rather than draw out the wiring for a ground wiring path. In AC circuits it typically refers as a chassis ground to bleed of static and provide a path of least resistance when/if the device has a short.

When we get to Inverters and especially the All-in-one units, it is recommended we treat them as a sub-panel. This Video shows the wiring and use of the sub-panel giving detail for ground and neutral connections. The ground wire is to provide a chassis ground to the cabinet of the invertor. When the AC loads are connected to the Inverter with a sub-panel the ground is still for Static and Chassis connections and not a current wire, the sub-panel passes the ground back to the main service panel and connects to earth with its bonding. The bonding of the main panel to earth is primarily to prevent lightning entry.

When you connect your batteries to your invertor they are completely isolated from all AC connections and bonding. On your Battery you can have a Negative Buss Bar to connect all the DC negative connections together. Never connect the batteries to earth ground, should the invertor generate a short you could send AC through the batteries and have an explosion.

Off-grid systems are wired with a sub-panel also, but as it does not have a main panel with a ground bonded to create the static/chassis connection we need to connect this panel to a ground rod to give that static/chassis connection. We DO NOT bond this panel! Again the Ground and Neutral in this sub-panel are NOT connected. Your Neutral wire is a current carrying wire to complete the circuit, the ground is for Static/Chassis and helps the circuit trip when there is a fault.

When paralleling units in a 120v configuration, connect only the Line1 together and then only connect the Neutrals together. Your Neutral is your return current wire in powering the circuit.

[stevejagger]

This is an excellent article on grounding, with particular attention to lightning protection, a much neglected aspect of all types of solar pv installations.

[McTroyd]

I'm no electrician, but I was always taught that, so long as you only had one ground for a common rail, it didn't matter which ground point it was. Ground loops are only an issue when multiple points are grounded differently, and there's potential between them due to the varying resistance. On a small system like this one, I'd probably stick with an earth ground in the panel so all my disconnection points are in one place. If all the (edit: ground points) are connected together, and only one point is actually grounded, I don't know that it matters. 🤷‍♂️👍️

[michaelcotherman]

Great explanation and demonstration, this is much better than a 'code-parrot' just repeating NEC ad-nauseum... You showing and talking through the thought process is extremely helpful to all viewers. Ground loops that close with that big of wire are not nearly as bad as ones with a long run between them, and would probably never have any issue in your lifetime, but for continuity(pun intended), following a standard is best. Thank you for your work.

[lunatik]

Personally, only the generator (floating ground) will connect to AC input,
but usually genny only drives a floating charger connected directly to the battery, multiple chargers if the load requires.

Ground is a local reference and 2 different grounds may not be the same reference aka ground loop.
The power company may have 100 to 150 KV on the pole and taps on a transformer for a specific circuit.
A transformer may supply multiple circuits.

A transformer with 220 secondary and dual (180 phase shift) 110 secondary circuits with a center tap, the new (CT) ground reference is different from the input ground. One would not want to tie the input and output grounds together.

The power company knows you are going to ground your breaker box and designs their system accordingly.
When using solar/ grid tie configuration, the equipment should handle any grounding issues.
If one was completely off grid, from a purely safety perspective it would be prudent to ground the box to a copper rod,
however, once done, the solar panel may increase the likelihood of becoming a lightning rod if not otherwise present.
Letting ground float might offer some protection.