Inverter Ground Connections

[Sunking]

FWIW, those canny electricians are also careful not to touch two wires at different potentials at the same time! If they do that the lack of a ground will not save them.

True, but being grounded is just as dangerous if not more dangerous.

Grounding objects is great, but people have no clue what it does. Many electricians have no clue. There are 7 reason to ground something.

• Provide a planned path for lightning to discharge into earth.
• Accidental contact with utility High Voltage lines, or utility primary to secondary faults during storms or accidents
• Provides a discharge path for static electricity.
• Minimize touch potential of metallic frames, raceways, and equipment chassis under fault conditions.
• Provides a PLANNED FAULT LOW IMPEDANCE fault path back to the source to allow fusses and breakers to operate efficiently and quickly.
• Provide a signal reference level.
• Short out cable capacitance in large industrial systems.

Also note Ground does not necessarily mean earth. It can be earth or any body in place of earth like your car, boat, plane, or spaceship. Under normal operating conditions a ground does absolutely nothing in a residential application. In your home it is used to keep lightning and utility high voltages out of your house, and a cheap efficient way to have over current protection devices like breakers and fuses.

Industrial does not use grounded systems, the use Un-grounded Delta, or Floating systems. They do so for two main reasons. Grounded systems are prone to unnecessary outages, and dangerous to personnel working with such high voltages. Imagine how much it cost and down time in something like a glass or plastic extrusion operation or a refinery and the power goes off. It would take you several days to clean out the equipment and get it back on line, not to mention can even destroy the equipment. Hardened cold glass in a extruder destroys the extruder it. Or loosing a million barrels of raw petroleum that had to be burned off because you could not distill it. People in industrial applications can die if power is lost.

[inetdog]

FWIW, those canny electricians are also careful not to touch two wires at different potentials at the same time! If they do that the lack of a ground will not save them.

[Sunking]

The inverter's manual says there is a risk of electrical shock if the inverter is not grounded.

That is CYA Lawyer Talk. No mobile battery Inverter requires any ground whatsoever. All that is required is a GFCI. If you do Ground it greatly increases your chances of being electrocuted. Every Battery powered mobile Inverter has GFCI circuits. Even a 1000 watt Invferter could not possible operate a standard house 20 amp circuit? Why you ask? Because 1000 watts is only 8 amps at 125 volts.

Electricians have a neat little trick when they work on stick built homes wired with Romex and plastic boxes. They work on the wiring bare handed on live circuits. How do they do it? They know what they are doing, and disconnect the house ground while they work so they will not be shocked.

Some which are immune to the pain will test for a live circuit with their fingers. They touch their pinky finger to a grounded case, and then touch a live wire to see if it is hot. As long as the current does not run through their heart or brain, they are not injured. But that only works on voltages of 300 volts and less. Otherwise you could burn off a finger or hand. But it would not kill you.

[SunEagle]

And while we are clarifying, a transfer switch of some kind (or mechanically interlocked breakers or a single male inlet that gets one female cord or the other) is required whenever there will be the possibility of a grid connection and an inverter connection to feed the same wiring at different times.
A typical transfer switch will only switch the ungrounded conductors (one wire for straight 120, two wires for 120/240). But if there is a bond between neutral and ground on the grid/shore supply side to comply with NEC, then the transfer switch must have an extra pole to disconnect the house neutral from the grid neutral so that an MSW inverter that requires an isolated neutral can be used.

Thanks for the clarification. I believe I have one of those transfer switch on my RV.

[inetdog]

There are technically 2 grounding systems. One is for the metal equipment enclosure and panel frames. The other is associated with the neutral wire in an AC system or Neg wire in a DC system.

I think you and I were talking about the first one concerning the chassis. And Sunking was talking about the second which is not required for the GFIC protected inverters to work.

And while we are clarifying, a transfer switch of some kind (or mechanically interlocked breakers or a single male inlet that gets one female cord or the other) is required whenever there will be the possibility of a grid connection and an inverter connection to feed the same wiring at different times.
A typical transfer switch will only switch the ungrounded conductors (one wire for straight 120, two wires for 120/240). But if there is a bond between neutral and ground on the grid/shore supply side to comply with NEC, then the transfer switch must have an extra pole to disconnect the house neutral from the grid neutral so that an MSW inverter that requires an isolated neutral can be used.

[SunEagle]

The inverter's manual says there is a risk of electrical shock if the inverter is not grounded. Still, I see you are correct about GFCI. I clearly didn't understand how they operated before this prompted me to look it up. Thank you.

There are technically 2 grounding systems. One is for the metal equipment enclosure and panel frames. The other is associated with the neutral wire in an AC system or Neg wire in a DC system.

I think you and I were talking about the first one concerning the chassis. And Sunking was talking about the second which is not required for the GFIC protected inverters to work.

[createthis]

Mobile inverters do not need or require any ground. Nor should you use one. All you need and it built into the inverter is the GFCI, and GFCI needs no ground.

The inverter's manual says there is a risk of electrical shock if the inverter is not grounded. Still, I see you are correct about GFCI. I clearly didn't understand how they operated before this prompted me to look it up. Thank you.

[SunEagle]

Mobile inverters do not need or require any ground. Nor should you use one. All you need and it built into the inverter is the GFCI, and GFCI needs no ground. Your Inverter cannot possible produce enough current to operate a Breaker unless it is extremely small breaker like 1 or 2 amps.

Maybe the confusion is what type of ground we are talking about.

I was talking about the inverter chassis ground terminal. I would imagine the same "ground grid" the pv panel frames and CC chassis ground terminal.

[Sunking]

Mobile inverters do not need or require any ground. Nor should you use one. All you need and it built into the inverter is the GFCI, and GFCI needs no ground. Your Inverter cannot possible produce enough current to operate a Breaker unless it is extremely small breaker like 1 or 2 amps.

[createthis]

What are you going to use as a "ground" if you take that inverter and use it somewhere not close to your home?

I won't. That's why it's nice that it doesn't require a ground. However, when it's at my house, having a ground protected GFCI is nice.

[SunEagle]

I'm not planning to grid tie it to the house system, but I was planning to attach the ground on the back of the inverter to the house ground, which is the point of this thread.

What are you going to use as a "ground" if you take that inverter and use it somewhere not close to your home?

[createthis]

That inverter can be used only in a totally isolated system from your home grid power so there is no need to worry about back feeding into the grid.

Like your Yeti the Go Power has a place to plug in the loads not provide power to your house panel which would be illegal and unsafe.

It can be used on a RV but might required a transfer switch as inetdog suggested but IMO would require some type of equipment grounding system and a rod if used in the field.

I'm not planning to grid tie it to the house system, but I was planning to attach the ground on the back of the inverter to the house ground, which is the point of this thread.

[SunEagle]

Interesting. When I read the original comment, I missed the MSW reference. So, pure sine wave inverters don't have this problem? Isn't it a really bad idea to feed power back into the grid without a grid tie permit/inspection anyway? The transfer switch seems like the way to go there.

Back on the topic of pure sine inverters and grounding... I ended up buying this Go Power 300W inverter: http://www.amazon.com/gp/product/B001539BCE

I'll do a review video on it in the next day or two, I think. My initial impressions are good. It's significantly heavier than the old inverter. Probably a good sign for longevity.

When it arrived, I wired it up and tested it without a ground connection. To my pleasant surprise it worked properly, even though the front sockets feature GFCI. I didn't get shocked when I touched the case carefully with a knuckle either. I'll wire up a cable to run the house ground to the case, eventually, but it's nice to know it operates like my old yeti 400 pure sine inverter without a ground if needed. Makes it a bit more portable that way. I didn't want to have to pack a 6 foot grounding rod and pound it into the ground every time I go camping.

That inverter can be used only in a totally isolated system from your home grid power so there is no need to worry about back feeding into the grid.

Like your Yeti the Go Power has a place to plug in the loads not provide power to your house panel which would be illegal and unsafe.

It can be used on a RV but might required a transfer switch as inetdog suggested but IMO would require some type of equipment grounding system and a rod if used in the field.

[createthis]

It is a very common problem when dealing with an RV that will have both an MSW inverter and a shore connection. The simplest way to avoid it is to get a transfer switch that switches the neutral too. That way the grid neutral can be bonded to ground as the NEC requires while the inverter neutral is isolated from ground.

If you are just running off the inverter at all times, then the best solution is to avoid the MSW inverters with that problem.
Or wire your space with an ungrounded neutral, which is technically an NEC violation.

Interesting. When I read the original comment, I missed the MSW reference. So, pure sine wave inverters don't have this problem? Isn't it a really bad idea to feed power back into the grid without a grid tie permit/inspection anyway? The transfer switch seems like the way to go there.

Back on the topic of pure sine inverters and grounding... I ended up buying this Go Power 300W inverter: http://www.amazon.com/gp/product/B001539BCE

I'll do a review video on it in the next day or two, I think. My initial impressions are good. It's significantly heavier than the old inverter. Probably a good sign for longevity.

When it arrived, I wired it up and tested it without a ground connection. To my pleasant surprise it worked properly, even though the front sockets feature GFCI. I didn't get shocked when I touched the case carefully with a knuckle either. I'll wire up a cable to run the house ground to the case, eventually, but it's nice to know it operates like my old yeti 400 pure sine inverter without a ground if needed. Makes it a bit more portable that way. I didn't want to have to pack a 6 foot grounding rod and pound it into the ground every time I go camping.

[inetdog]

Is that a common error when migrating a circuit from grid to battery? What's the proper way to connect it?

It is a very common problem when dealing with an RV that will have both an MSW inverter and a shore connection. The simplest way to avoid it is to get a transfer switch that switches the neutral too. That way the grid neutral can be bonded to ground as the NEC requires while the inverter neutral is isolated from ground.

If you are just running off the inverter at all times, then the best solution is to avoid the MSW inverters with that problem.
Or wire your space with an ungrounded neutral, which is technically an NEC violation.