Sub Panel neutral bonding (2025 Update)

I agree using the 3 wire system and bonding the neutral and ground is the most practical solution. But be aware, if that third ground/neutral wire should fail open, there will be a dangerous condition in the outbuilding. Everything that was ground, can become energized.

mark

It just means you have to be careful when you make up those connections but if you are careless, you shouldn't be doing your own wiring anyway.

If there is a total of 10' or more of steel in contact with that concrete footer you have a Ufer (concrete encased electrode) and that is far better than the rods you drove. In fact with a Ufer, you don't even need the rods. You should be using a #4 or larger to connect the Ufer, Rods only require a #6. That should tell you something right there. If I was doing it I would have run another #5 rebar around the footer, tying all of the down rods together and then you have serious contact with the concrete and a stronger footer.

I think if you read that description I provided of how they detect the loss of the grid, the answer is almost certainly not. They are looking for stability in voltage, freq, power factor and it's unlikely a typical home generator is going to fool it. Especially with variable load, which you'd have when a fridge cycles on, etc. Of course that description looks like it's for a bigger solar install than a home one, but the home ones have to comply with regs and must use similar techniques. Most interesting in that was that the inverters described there actually deliberately screw with the grid when they think they may be in an island situation, the idea being that you can't perturb a true grid, but if the "grid" is an island with just some other solar sources, you can and then other inverters will see the deviation and shut down too.

The question is what dioes the generator/inverter think of having power supplied to the output?? Now, if you could iso;ate the "clock" a small inverter would do the job - all it would produce is the "sync" signal. You could produce that from the sound output of a cell phone or tablet - - -

A slightly broader view - the requirements for grounding-bonding on a service entrance are much tougher than past the service. Assume an overhead drop and EMT service entrance. The EMT from the meter can to the service panel is likely to be connected through concentric/ecentric knockouts at each end. That is not allowed for bonding and the meter can and EMT section are then not "grounded". Around here the practice was for the GEC exiting the panel to go through a ground clamp on the EMT then to the electrodes. That bonded the EMT but left the meter can. The bond between neutral and meter can is then critical. The EMT riser above the meter is connected through a hub, which is good for bonding.

I am too lazy to look it up, but I think if the EMT between the meter can and service panel does not have concentric/ecentric knockouts, an EMT connector through the right sized hole is also not an approved bond and a "grounding locknut" (not an ordinary locknut) or other means has to be used.

The EMT between the meter can and service panel is in parallel with the neutral wire but that was not considered a problem here.

If PVC conduit is used, more likely now, the bonding problems go away, but bonding the neutral to the meter can is then also critical.

The way I read Terry's post there is a utility meter separated from the panel by 1/4" of plywood. Sounds like a service panel, not a feeder-subpanel. Or that discussion may be in addition to a "new panel" at a separate shop building run off of a 3-wire feeder. Neutral-ground bond and earthing electrode(s) apply to both. More stringent bonding (above) only applies to a service.

I would want a Main Bonding Jumper in a service panel (is required in a separate building 3-wire feed subpanel). For a service with no MBJ in the service panel the bonding (as above) on the ?metal pipe? from the meter can is a particular question.

We had them when I was a kid.

We had a visitor with an intention tremor. Watching him try to stab those buttons when his finger was shaking was painful.

"That much", is likely a world of difference compared to the normal grid and would be instantly detected.

Maybe.

He didn't say "screw with the grid" and he actually explained what he meant.

"For the active anti-islanding function, we use a technique called Slip Mode Frequency Shift. This varies the reactive power output of the inverter. The goal of this protection method is to destabilize an islanded feeder by trying to influence the frequency. This diagram, from the IEEE 1547 testing procedure, shows how we test the anti-islanding function in the inverter.

We intentionally force the frequency out of spec and push against the grid, so we can properly detect and dissolve the island. We actually turn the anti-islanding function off, create an island, turn the anti-islanding function back on, and test the ability to disturb the island within two seconds. In our tests, we actually do it much faster."

You could try to fool a grid tie inverter with another inverter. You don't even need a generator inverter, you could use a car battery and an inverter. If it worked, you could keep the battery charged from the solar power. I doubt it would work. It would depend on the actual anti-islanding methods used in the particular solar inverter. And then there is the problem of how does a typical battery inverter or generator inverter react when the solar inverter is fooled into thinking the grid is there, powers up, connects and tries to put power into the "grid", which in this case is just a small inverter or generator? I would think that would produce a condition that if it didn't blow up the other inverter/generator, would result in conditions that the grid tie inverter would recognize as not right and it would shut down.

That is still flowery rhetoric for saying an unclocked inverter will go nuts. I think if it got a stable clock it would run.