Mobile power system inverter and grounding

[WyoSoular]

I’m building a mobile power box with a 200ah LifePo4, Victron Phoenix 1200 Inverter, and a Renogy 60am MPPT. The goal is to charge either via solar or a/c. My question is related to proper grounding. With this being mobile I’m assuming I leave the inverter wired as a floating Neutral as it comes from the factory. I have some unistrut framing inside the box to mount things.

I’m wondering if the earth/chassis ground of the Phoenix inverter should go to my internal metal frame work along with the battery negative? Or with the floating neutral do I not want anything tied together? Just confusing information out there on this subject. Or do I not do any ground at all since nothing to ground to externally.

 

[Bobert]

I am interested to hear what the experts have to say about this issue. I believe the best thing to do is to ground all the devices to the “chassis” and don’t bond the neutral to the ground similar to how a small generator would be setup.

 

[WyoSoular]

I am interested to hear what the experts have to say about this issue. I believe the best thing to do is to ground all the devices to the “chassis” and don’t bond the neutral to the ground similar to how a small generator would be setup.

There seems to be a lot of contradictory info on this and very little help from the manufacturers. I would assume since this is acting like a generator so to speak it would simply be a floating ground and yes I would take the ground lug of the inverter to the metal frame and any other devices would share the frame ground. But then you wonder if the battery should also have the negative to ground to the same frame. Also will a GFCI outlet connected to the inverter output even work without a “real” grounded ground?

By the way this is all being installed in a Dewalt - Tough Chest Mobile Storage unit.

 

[Bobert]

There seems to be a lot of contradictory info on this and very little help from the manufacturers. I would assume since this is acting like a generator so to speak it would simply be a floating ground and yes I would take the ground lug of the inverter to the metal frame and any other devices would share the frame ground. But then you wonder if the battery should also have the negative to ground to the same frame. Also will a GFCI outlet connected to the inverter output even work without a “real” grounded ground?

By the way this is all being installed in a Dewalt - Tough Chest Mobile Storage unit.

A gfci will trip if it detects electrons taking a different path than between hot and neutral. My guess is that without a bonded neutral the gfci will still give a measure of protection against serious shock under limited circumstances, but no protection from a direct shock from the outlet itself. For instance if I cut a cord in half and plug it in to the gfci and grab onto the bare wires there will be no flow of current between myself and the ground because the neutral is not bonded to the ground and the ground of the power box is not connected to the “earth” the gfci would not trip as none of the electrons going through the GFCI would take an alternate path. however if components or wiring were to be damaged or malfunction in such a way that the case of the power box became “hot” the gfci would protect you from a shock between a device plugged into the gfci and the hot box.
The only way to fix that is to bond the neutral to ground (frame) and drive a ground rod and connect to that at which point you are no longer a portable system and you cannot connect to a system that is already bonded as it will cause other problems.

 

[WyoSoular]

A gfci will trip if it detects electrons taking a different path than between hot and neutral. My guess is that without a bonded neutral the gfci will still give a measure of protection against serious shock under limited circumstances, but no protection from a direct shock from the outlet itself. For instance if I cut a cord in half and plug it in to the gfci and grab onto the bare wires there will be no flow of current between myself and the ground because the neutral is not bonded to the ground and the ground of the power box is not connected to the “earth” the gfci would not trip as none of the electrons going through the GFCI would take an alternate path. however if components or wiring were to be damaged or malfunction in such a way that the case of the power box became “hot” the gfci would protect you from a shock between a device plugged into the gfci and the hot box.
The only way to fix that is to bond the neutral to ground (frame) and drive a ground rod and connect to that at which point you are no longer a portable system and you cannot connect to a system that is already bonded as it will cause other problems.

So with the risk of shock on a floting ground system such as with gas generators or solar or battery systems like this you’d think there was a safety device that’s a available to offer better protection other than GFCI? Maybe an ARC fault breaker on the output of the inverter? Anyway much searches on this topic seem to all be in discord as to the “right” way to have a portable system not tied to a grid or earth ground rod.

 

[dcg9381]

I'm studying this with the EG4 implementation that is "mobile". Here's what SS has to say about it:

EG4 Official Neutral Ground Bond Thread.

In this video, Brayden from EG4 dives into Neutral-Ground Bonding scenarios and how they are affected by different use cases.

diysolarforum.com

 

[WyoSoular]

I'm studying this with the EG4 implementation that is "mobile". Here's what SS has to say about it:

EG4 Official Neutral Ground Bond Thread.

In this video, Brayden from EG4 dives into Neutral-Ground Bonding scenarios and how they are affected by different use cases.

diysolarforum.com

Interesting but yet not the right info for a Victron Phoenix in a off grid standalone situation. They were always tying to grid or a fixed ground in all 3 scenarios. At home I could run a wire to my home ground rod or a
AC outlet ground and thus be earth grounded. Or I invent a floating ground shock protection device to put inline?

 

[MiSh]

I’m building a mobile power box with a 200ah LifePo4, Victron Phoenix 1200 Inverter, and a Renogy 60am MPPT. The goal is to charge either via solar or a/c. My question is related to proper grounding. With this being mobile I’m assuming I leave the inverter wired as a floating Neutral as it comes from the factory. I have some unistrut framing inside the box to mount things.

I’m wondering if the earth/chassis ground of the Phoenix inverter should go to my internal metal frame work along with the battery negative? Or with the floating neutral do I not want anything tied together? Just confusing information out there on this subject. Or do I not do any ground at all since nothing to ground to externally.

You indicate you will be charging via solar or a/c. I'm assuming by a/c you mean a battery charger plugged into a wall outlet? If that's the case, won't you have a n/g bond connection from the breaker panel thru that a/c connection to the power box? That may throw a little different 'wrench' into your plan.

 

[WyoSoular]

Your correct on the A/C charge. But since when charging with A/C I would isolate the battery from the inverter with a disconnect switch. But also since not an RV type setup I’d never be using the system while charging

 

[Bobert]

Your correct on the A/C charge. But since when charging with A/C I would isolate the battery from the inverter with a disconnect switch. But also since not an RV type setup I’d never be using the system while charging

How do you normally use your power box?
If the ground from the house is connected to the frame of your box and the neutral from the house is connected to the neutral output of your box you will have bonding from the house even if there’s no “hot” connected to the box.

I have a travel trailer that is outfitted with a 3500w 120v output AIO. When I am connected to shore power I have a neutral ground bond through that connection even if the breaker is off or the power is out, What I haven’t figured out is what to do when I am not connected to anything. I would like for the external GFCI outlet to be effective but even if I bond the ground I doubt I can get enough coducuctivity from the tires and stands to trip the GFCI but it would still work for the GFCI outlets inside the camper. I am considering wiring a manual transfer switch so that position A would leave the neutral unbonded and allow shore power input to the AIO and bonding from that source wether power is on or not. position b would disconnect the wires from the shore input plug and bond the ground to neutral. This would work to prevent a double bond but would require remembering to use position b for bonding when no connected to shore power. Another possibility would be to use a lithium battery charger to charge the batteries and bond the camper “permanently” In this case the ac input would never actually directly power anything in the camper.

 

[WyoSoular]

How do you normally use your power box?
If the ground from the house is connected to the frame of your box and the neutral from the house is connected to the neutral output of your box you will have bonding from the house even if there’s no “hot” connected to the box.

I have a travel trailer that is outfitted with a 3500w 120v output AIO. When I am connected to shore power I have a neutral ground bond through that connection even if the breaker is off or the power is out, What I haven’t figured out is what to do when I am not connected to anything. I would like for the external GFCI outlet to be effective but even if I bond the ground I doubt I can get enough coducuctivity from the tires and stands to trip the GFCI but it would still work for the GFCI outlets inside the camper. I am considering wiring a manual transfer switch so that position A would leave the neutral unbonded and allow shore power input to the AIO and bonding from that source wether power is on or not. position b would disconnect the wires from the shore input plug and bond the ground to neutral. This would work to prevent a double bond but would require remembering to use position b for bonding when no connected to shore power. Another possibility would be to use a lithium battery charger to charge the batteries and bond the camper “permanently” In this case the ac input would never actually directly power anything in the camper.

The power box is 100% off grid unless I need to recharge without solar and have to use the home A/C. The inverter is factory set to floating ground and I’ve left it that way so far woth no ground wire attached. If I charge the batteries the inverter would be shut off and the battery positive lead disconnected with a switch.

 

[dcg9381]

Interesting but yet not the right info for a Victron Phoenix in a off grid standalone situation. They were always tying to grid or a fixed ground in all 3 scenarios. At home I could run a wire to my home ground rod or a
AC outlet ground and thus be earth grounded. Or I invent a floating ground shock protection device to put inline?

Pretty sure that's not the case. They discuss a "mobile" case (which is my case) where you now need to install a bond screw and alternate firmware for "mobile" use.

 

[Bobert]

The power box is 100% off grid unless I need to recharge without solar and have to use the home A/C. The inverter is factory set to floating ground and I’ve left it that way so far woth no ground wire attached. If I charge the batteries the inverter would be shut off and the battery positive lead disconnected with a switch.

If you never connect the ac output of your inverter into the house wiring system you could bond the grounds and neutral at the inverter and then ground the box to the earth for better function of your GFCI. The bonding really doesn’t accomplish much unless you earth ground and need complete GFCI protection but of course you are no longer mobile in that scenario. I believe most portable power sources have a floating neutral. This is to avoid the accidental double bonding situation

 

[dcg9381]

If you never connect the ac output of your inverter into the house wiring system you could bond the grounds and neutral at the inverter and then ground the box to the earth for better function of your GFCI. The bonding really doesn’t accomplish much unless you earth ground and need complete GFCI protection but of course you are no longer mobile in that scenario. I believe most portable power sources have a floating neutral. This is to avoid the accidental double bonding situation

The trick comes in applications that are sometimes grid tied and sometimes not grid tied. As I understand it the current run of EG4 6500 inverters have a relay that handles this bonding based on if they're charging from grid power or not. I haven't looked into how other inverters handle it.

Generators can be floating neutral (or not). I'd address it case by case. I don't know about other power sources (such as "power bank" type deals).

 

[WyoSoular]

Pretty sure that's not the case. They discuss a "mobile" case (which is my case) where you now need to install a bond screw and alternate firmware for "mobile" use.

They’re specific to their devices and their mobile system discussed still has the possibility of being connected to a/c for supply and earth ground in a panel. Unless I misunderstood. The Phoenix Inverter is very different from their system also.