Few questions regarding automatic transfer switch

[Electry]

Planning to buy Giandel 3000W inverter which is missing N-E bonding and planning to add automatic transfer switch which would either connect shore or inverted live / neutral wires to main van breaker box. Breaker box has RCD and MCB. Would appreciate if these answers could be answered:

1. Is it necessary to have RCD between Inverter and Automatic Transfer Switch, even if there is one in breaker box after the switch?
2. Can both shore and inverter earths be connected together even if inverter earth is bonded to its neutral? Is shore earth affected by inverter's neutral (as N-E bond is made)?
3. Should shore / inverter AC earth be connected to vehicle chassis / negative 12V DC busbar?
4. Is there any safety risk with inverter still working when switched to shore power? Inverter output wires would still be live even when on shore power.

Thanks for answers

 

[time2roll]

No breaker needed between the inverter and transfer switch. No issues having power from both shore and inverter at the same time.
All my grounds are bonded including to the 12v chassis frame.

Not sure what the RCD and MCB stand for.

 

[Supervstech]

Ok...

There can be ONLY one N-Ground bond... one.
It cannot be in the inverter, UNLESS there is noplace else with one.

I usually unbond everything when I install a transfer switch, and have the bond in the transfer switch.

 

[Electry]

Ok...

There can be ONLY one N-Ground bond... one.
It cannot be in the inverter, UNLESS there is noplace else with one.

I usually unbond everything when I install a transfer switch, and have the bond in the transfer switch.

Theoretically there would be two separate N-Ground bonds (from shore and from inverter), but transfer switch should switch live and neutral so that it is using either shore or inverter with its own N-Ground, so in result maintaining only one N-Ground bond after the transfer switch. And this is where I'm not sure if N-Grounds could interfere somehow when shore and inverter are ONLY sharing the same ground (especially when inverter is turned on and N-Ground bonded whether shore power is connected or not).

 

[Zil]

The shore N/G bond is at the service entrance from the mains. When the transfer switch is "to inverter" the mains H/N is disconnected. The mains G should be connected to the RV chassis. It doesn't matter if that stays connected while on inverter. If you unplug from shore It also doesn't matter. The inverter case should be connected to the RV chassis.

 

[Electry]

The shore N/G bond is at the service entrance from the mains. When the transfer switch is "to inverter" the mains H/N is disconnected. The mains G should be connected to the RV chassis. It doesn't matter if that stays connected while on inverter. If you unplug from shore It also doesn't matter. The inverter case should be connected to the RV chassis.

Thanks for the answer. I have updated wiring diagram and connected all AC earths in shore breaker box which is then grounded to DC negative bus bar (and then to vehicle chassis). Could you look at the diagram and tell me if everything looks correctly? I mainly have these requirements for AC system:
1. Battery charger is ONLY working when shore power is connected (that's why it goes through separate MCB).
2. Everything else works either from shore / inverter (wiring is in breaker box after the automatic transfer switch).

Do I think correctly that no additional grounding near inverter is needed to prevent ground loops? I think I confuse AC / DC loads here - do I need to connect Inverter AC earth directly to shore breaker box earth AND separately connect inverter grounding point to chassis? Or can I just connect inverter AC earth to inverter grounding point and then just route that cable to shore breaker box earth (as at the end inverter still would be grounded to the vehicle chassis)?

 

[Zil]

There is only one battery to BusBar cable, but this is how I can show the connections.
Battery negative -> negative dc BusBar #1 -> inverter dc negative feed.
Battery negative -> negative dc Busbar #1 -> accessory dc fuse block negative.
Battery negative -> negative dc BusBar #1 -> shore power battery charger dc negative
Battery negative -> negative dc BusBar #1 -> MPPT charge controller negative.
Negative dc BusBar #1 -> chassis.
Inverter case lug -> either negative BusBar #1 or chassis. Same with the MPPT case lug.
Instructions state do not hook case lug to inverter feed negative terminal. I use chassis point as the wire would be longer to the negative BusBar #1.
A maximum of two main cables can be connected to one terminal of a heavy duty BusBar, along with one smaller wire.
I think there should be an ac ground wire to the transfer switch, most likely the case.
I think I would connect the shore ac ground wire to the chassis close to the point where the shore power enters the van.
Your diagram looks good.

 

[Electry]

Your answers are really helpful, thank you for helping me understand all of this. I'm using 220V 4 Pole 2 NO + 2 NC contactor as automatic transfer switch:

And it doesn't have require to connect earth.

Furthermore, I have few more questions regarding AC wiring:
1. Is RCD / GFCI in breaker box (after transfer switch) is enough? I know I need RCD + MCB for shore because I use separate shore only battery charger. Maybe there is a need to add additional RCD just after Inverter's N-E bonding (before transfer switch)? I'm not sure, as I saw various wiring diagrams with RCD and without.
2. Out of curiosity, what would happen if shore power is connected (which should be N-E bonded from shore mains, for ex. house outlet), and transfer switch would pass inverter live and neutral instead of shore (malfunction). In other words, battery charger would be powered from shore power, everything else from inverter at the same time. Whole system then would have 2 N-E bonds. Would the system be safe anyways? To my understanding, fault at battery charger (shore power) would trigger RCD in SHORE breaker box, and fault in fridge would pop RCD in the breaker box (after the automatic transfer switch)?

Oh and also, could inverter case lug be connected to inverter AC output earth and then connected to chassis? Whole connection would look like this: Inverter AC Earth -> Inverter case lug -> Shore breaker box earth busbar -> Chassis point?

 

[12VoltInstalls]

connected all AC earths in shore breaker box which is then grounded to DC negative bus bar (and then to vehicle chassis)

Shorepower provides the green/bare/earth through the service pedestal it plugs into.
N and G should not be bonded in the RV panel

Can both shore and inverter earths be connected together even if inverter earth is bonded to its neutral?

No, read below:

Ok...

There can be ONLY one N-Ground bond... one.
It cannot be in the inverter, UNLESS there is noplace else with one.

I usually unbond everything when I install a transfer switch, and have the bond in the transfer switch.

You show a transfer switch. It should switch four wires if 50A, 3 wires if 30A

So if you have a 50A cord you have four wires, if 30A there’s only three wires.
if I understood your inverter- that has three. A 50A RV panel has 4 wires. A 4-pole transfer switch will let you switch the hots, neutral, and the ‘earth.’
Only three poles needed for a 30A RV system. I think you have 30A shorepower?
@Supervstech
So you should have the RV panel not bonded, the shore power cord wired into the transfer switch, the inverter bonded and wired into the transfer switch, and that feeds the RV panel. The appropriate N/G bond is always maintained.

 

[Electry]

Shorepower provides the green/bare/earth through the service pedestal it plugs into.
N and G should not be bonded in the RV panel

No, read below:


You show a transfer switch. It should switch four wires if 50A, 3 wires if 30A

So if you have a 50A cord you have four wires, if 30A there’s only three wires.
if I understood your inverter- that has three. A 50A RV panel has 4 wires. A 4-pole transfer switch will let you switch the hots, neutral, and the ‘earth.’
Only three poles needed for a 30A RV system. I think you have 30A shorepower?
@Supervstech
So you should have the RV panel not bonded, the shore power cord wired into the transfer switch, the inverter bonded and wired into the transfer switch, and that feeds the RV panel. The appropriate N/G bond is always maintained.

Yes, Im using 3 wire shore plug (its usually 16 amps in Europe).

About N-E (or N and G) bonding - I think you misunderstood me. I'm not bonding N-E at RV panel. I'm only bonding it at inverter (as it doesn't do that internally). Then I'm passing inverter's EARTH (which is again, bonded to inverter's neutral) to "shore" breaker box earth bus bar. Then "shore" breaker box earth bus bar is connected to vehicle chassis. Maybe my naming is confusing. That "shore" breaker box is inside RV. I just want to keep "shore" and "internal" AC breaker boxes separately.

About switching part - take a look at slide 9 of Mobile System grounding ebook over there https://diysolarforum.com/resources/grounding-made-simpler-part-4-mobile-systems.159/ . Inverter maintains N-E bond even with shore connected. Transfer switch only switches hot and neutral. Earths are always connected together. My wiring diagram shows the same - transfer switch switches only hot and neutral. Earths from shore and inverter are connected together at "shore" breaker box and then grounded to vehicle chassis.

I have updated wiring diagram, maybe it will look clear now

 

[12VoltInstalls]

Then I'm passing inverter's EARTH (which is again, bonded to inverter's neutral) to "shore" breaker box earth bus bar. Then "shore" breaker box earth bus bar is connected to vehicle chassis.

Ok.
As long as there is no N/G bond in the shorepower panel.

take a look at slide 9 of Mobile System grounding ebook

Earths from shore and inverter are connected together at "shore" breaker box and then grounded to vehicle chassis.

there is the ebook drawing
Circuit-wise yours is the same, but the book has a safety ground at the transfer switch

I think I would connect the shore ac ground wire to the chassis close to the point where the shore power enters the van.

I’m not certain shorepower bare/Grn/ground should be connected to the chassis here. I think it should go to the ac distribution panel only, the bare/grn/ground not adding the vehicle to a potential electrical fault path, and I’d use a transfer switch that would switch the grn/bare

 

[Electry]

Ok.
As long as there is no N/G bond in the shorepower panel.

View attachment 81981

there is the ebook drawing
Circuit-wise yours is the same, but the book has a safety ground at the transfer switch


I’m not certain shorepower bare/Grn/ground should be connected to the chassis here. I think it should go to the ac distribution panel only, the bare/grn/ground not adding the vehicle to a potential electrical fault path, and I’d use a transfer switch that would switch the grn/bare

Could you explain shorepower panel? Are you referring about shore power coming from campsite should be NOT N/G bonded OR that bond should not be made in #1 breaker box (referring to breaker box in wiring diagram). Because it's not, as per my wiring diagram.

So it goes back to the transfer switch. Do I really need to switch ALL wires (hot, neutral and earth)? Because previously you said I would need 3 pole switch. Book says earths should be tied together and doesn't require switching. What is the difference?

 

[Zil]

No you do not switch earth/ground. I only suggest connecting the box that houses the switch onto earth/ground if it is a metal housing.
I think your diagram is correct as to all the circuits.

 

[12VoltInstalls]

So it goes back to the transfer switch. Do I really need to switch ALL wires (hot, neutral and earth)? Because previously you said I would need 3 pole switch. Book says earths should be tied together and doesn't require switching. What is the difference?

The difference is where it is possible though unlikely to have ground loops when grn/bare/grd become energized as if it were neutral in certain circumstances or faults.
diysolarforum.com resources pages 9 & 14 summarize this.
If you switch all three you can’t ever have a loop because you make the bare/ground sanctified holy to its source bond.

I’m not the expert here and I can’t recall but I believe that mobile systems are noted in NEC to not N-G bonded within the mobile unit/vehicle. I think that includes mobile homes. So switching all three solves it.

@Supervstech @smoothJoey or someone have quoted these sections in the past but I just killed 20 minutes and can’t locate the ref.
I could be wrong, don’t think I am.

This is even alluded to in an unrelated thread by another smarter-than-me guy:

The autransformers for Victron, Sunny Island, and Sunny Boy Storage (page 12 in link below) all switch the auto-transformer into the circuit when grid is switched out. SMA maintains neutral-ground bonding via grid connection (not meant for mobile), while Victron switches it (for mobile.)

The above smart characters can affirm or shoot me- just so as it gets done correctly

 

[Supervstech]

I dont see a reason to switch ground.
Multiple CONNECTED grounding locations is fine.
Multiple NEUTRAL bonded to ground locations is NOT ok.

 

[12VoltInstalls]

I dont see a reason to switch ground.
Multiple CONNECTED grounding locations is fine.
Multiple NEUTRAL bonded to ground locations is NOT ok.

Thanks.

So what about the shorepower shock hazard that I believe is called out with an NEC reference to not bonding and chassis grounding in a mobile home? Is that not applicable to towable or drivable vehicles, too? (I wish I could find that other thread!)

 

[time2roll]

Standard practice to not switch the ground in an RV transfer switch. All grounds are bonded including vehicle frame attached to the 12 volt negative.

Neutral-Ground bonding is a separate issue and should only be bonded at the power source.

 

[Electry]

I dont see a reason to switch ground.
Multiple CONNECTED grounding locations is fine.
Multiple NEUTRAL bonded to ground locations is NOT ok.

So looking at my diagram, is it wired correctly? I do understand that multiple neutral to ground bonds is a no-go, but I can't wrap my head in my case as hots and neutrals are switched. They only share the same earth.

For example I plug shore power. System is now N-E bonded from shore (assuming it is wired correctly at campsite). Does the inverter's N-E bond "exist"?

 

[12VoltInstalls]

For example I plug shore power. System is now N-E bonded from shore (assuming it is wired correctly at campsite). Does the inverter's N-E bond "exist"?

If using a transfer switch then, no, the inverter’s bond does not exist

 

[Electry]

If using a transfer switch then, no, the inverter’s bond does not exist

Thanks! Also, maybe you know an answer for this question? I just want to see if I'm thinking correctly.

What would happen if shore power is connected and transfer switch would pass INVERTER live and neutral instead of shore (malfunction). In other words, battery charger would be powered from shore power, everything else from inverter at the same time. Whole system then would have 2 N-E bonds. Would the system be safe anyways? To my understanding, fault at battery charger (shore power) would trigger RCD in SHORE breaker box, and fault in fridge would pop RCD in the #2 breaker box (after the automatic transfer switch)?

 

[12VoltInstalls]

Would the system be safe anyways?

The transfer switch should be of a quality that it won’t fall apart internally and do that. I believe listed transfer switches are all ‘wafer’ switches and catastrophic external damage is probably the only way they could fail this way.

I’ve looked for that freaking thread with the NEC mobile isolation reference but I can’t find it. As stated, I couldn’t locate. I’d like to know if I’m wrong. Or better: right!

What supervstech stated is true; that is the convention.
Since nothing further has been posted here and the diagrams concur with yours - run with it.

Whole system then would have 2 N-E bonds

Well because your arrangement is slightly atypical that could occur in that scenario.

But I can’t see that scenario happening with a listed transfer switch because like I said, internally they are sortofa a wafer disc or knife switch that is A/0/B mechanically locked to position internally. I haven’t taken one apart in a very long time and as I recall I have only disassembled one housed manual switch LOL

The household-sized or industrial switches are more easily observable by removing the flash cover, and they are even more simple - and huge.

A good switch won’t likely fail in that way