Off Grid solar and generator connecting the system

[EOWR]

I have a 1 Victron MultiPlus 48/5000/70 inverter charger 230 volt (not a MultiPlus 2) passing through a Victron Autotransformer and connected to a main electric panel at 110vt on each side and neutral to the neutral bar in the main panel. We now have a new diesel generator 240 volt floating neutral. I would like to power the main electrical panel through a Blue Seas AC Rotary switch 2 sources to 1 (Main electric panel), 2 position and off 65amp 240volt. The main panel is grounded to earth via large copper Rod. Generator to feed 2 hots and neutral to the panel via switch. Question #1. to keep both sources from having any issue with back feeding through the neutral Gen system and solar system could I switch neutrals in the Rotary switch for both systems and connect neutral to the grounding bar in the main panel? Since we use either the generator which is 12.5kw for big load usage including charging solar batteries through the main panel when required or we go through the solar system via the AC rotary switch and to the panel which is maxed at 5000kw. Never at the same time. Question #2 what would be the best solution for connecting these power sources? We are located on a remote Western Caribbean Island with no grid power so we are the power company.
The original installer has grounded the Solar Autotransformer, Inverter/ Charger and PV breaker panel together at a bar and then to a seperate ground rod which is approx 11' from the main Panel Grounding rod. Suggestions and Advice is greatly appreciated.

 

[BackCountry]

If I'm understanding you correctly, you're wanting to isolate the generator and solar system from one another, ie. never both at the same time?

If that's the case, I'd use a double throw heavy duty nuetral switching safety switch:

https://rexel-cdn.com/Products/A0F83F96-B5BA-4083-BB89-776600364A4C/A0F83F96-B5BA-4083-BB89-776600364A4C.pdf

That'll isolate either system.

If it were me; however, I would ditch the Victron setup (I've installed many Victron Multiplus systems) and get a Sol-Ark inverter. It'll control your generator automatically, and safe you from having a variety of equipment.

 

[EOWR]

Thank you for your helpful response. I have a marine grade AC rotary switch that I will use with the switched neutral. These switches are costly but this way I should not have any current flowing to the offline system. My concern now is since the main panel is used for the neutral and ground should the solar system's autotransformer, Inverter/charger and PV breaker panel keep it's own ground or would it be best to run it to the main panel? example the generator in online and powering the main panel and all loads depending on the situation I can either charge batteries from a breaker from the main panel or if it's in the day hours I still could charge the batteries directly from the panels but the ground would be in the main panel. What's your thinking on this. Thanks, EOWR

 

[jaggedben]

I'm not understanding either the system line diagram or what your exact concern is. You confused me when you said:

Since we use either the generator which is 12.5kw for big load usage including charging solar batteries through the main panel when required or we go through the solar system via the AC rotary switch and to the panel which is maxed at 5000kw. Never at the same time.

Do you never connect the solar system to the generator, or do you connect it to charge the batteries? Which is it?

I'm also confused if you are asking a question about whether you should switch the neutral (that is a choice) or about how to ground the neutral (that depends, in part, on the choice of whether to switch the neutral).

 

[BackCountry]

Thank you for your helpful response. I have a marine grade AC rotary switch that I will use with the switched neutral. These switches are costly but this way I should not have any current flowing to the offline system. My concern now is since the main panel is used for the neutral and ground should the solar system's autotransformer, Inverter/charger and PV breaker panel keep it's own ground or would it be best to run it to the main panel? example the generator in online and powering the main panel and all loads depending on the situation I can either charge batteries from a breaker from the main panel or if it's in the day hours I still could charge the batteries directly from the panels but the ground would be in the main panel. What's your thinking on this. Thanks, EOWR

The neutral and ground should be bonded in the main panel. If your rotary switch also switches the neutral then there shouldn’t be a concern, essentially there are separately derived services.

 

[jaggedben]

The neutral and ground should be bonded in the main panel. If your rotary switch also switches the neutral then there shouldn’t be a concern, essentially there are separately derived services.

I think the NEC might disagree but I'm not sure if that's a critical issue here.

 

[synchro]

The following comments assume that you will be charging the batteries from the generator through a breaker in the main panel that feeds the AC-IN port of the MultiPlus. If this is correct, during charging I believe the AC-IN of the Multi-Plus will be connected to its AC-OUT port and then over to your neutral-deriving auto-transformer. If so, you'd need to switch the auto-transformer derived neutral to keep it from "fighting" the generator neutral, which would result in undesired neutral currents. This is an additional reason to switch the neutral beyond the need for preventing currents through multiple N-ground bonds.

The original installer has grounded the Solar Autotransformer, Inverter/ Charger and PV breaker panel together at a bar and then to a seperate ground rod which is approx 11' from the main Panel Grounding rod.

Even when switching the neutral, you should eliminate any bond from the auto-transformer derived neutral to ground, because then the auto-transformer neutral could still fight the generator neutral through multiple N-G connections. The separate ground rod you mentioned probably does no harm as long as it's just connected to the EGCs (equipment grounding conductors) and not bonded to neutral.

Question #1. to keep both sources from having any issue with back feeding through the neutral Gen system and solar system could I switch neutrals in the Rotary switch for both systems and connect neutral to the grounding bar in the main panel?

Perhaps this back feeding you mention is related to what I brought up at the beginning of this post, but without a diagram to reference it's not clear.

 

[ggunn]

...to keep both sources from having any issue with back feeding through the neutral...

How would that happen? Most transfer switches do not switch the neutral and have the N-G bond on the load side of the switch.

 

[tortuga]

Guanaja Island ?

I think I am going to need a site visit for this one and I'll get you all fixed up I promise, Ill waive all my fees in exchange for round trip plane tickets for two and a honeymoon suite on the beach for a week .

 

[BackCountry]

I think the NEC might disagree but I'm not sure if that's a critical issue here.

There are a lot of things the NEC wouldn’t agree with in this situation, agreed!

 

[BackCountry]

The following comments assume that you will be charging the batteries from the generator through a breaker in the main panel that feeds the AC-IN port of the MultiPlus. If this is correct, during charging I believe the AC-IN of the Multi-Plus will be connected to its AC-OUT port and then over to your neutral-deriving auto-transformer. If so, you'd need to switch the auto-transformer derived neutral to keep it from "fighting" the generator neutral, which would result in undesired neutral currents. This is an additional reason to switch the neutral beyond the need for preventing currents through multiple N-ground bonds.



Even when switching the neutral, you should eliminate any bond from the auto-transformer derived neutral to ground, because then the auto-transformer neutral could still fight the generator neutral through multiple N-G connections. The separate ground rod you mentioned probably does no harm as long as it's just connected to the EGCs (equipment grounding conductors) and not bonded to neutral.


Perhaps this back feeding you mention is related to what I brought up at the beginning of this post, but without a diagram to reference it's not clear.

I didn’t read it the way you did, but I see what you’re saying.

The AC in does indeed close AC out as a shoreline scenario so that AC in takes the load.

This is why the neutral, if switched, shouldn’t allow any through current because the only “load” transferred would be open on the other side with the transfer switch aimed at the generator. It is a little backwards.

It would seem like perhaps the cleaner way would be to switch grid or generator up stream from the multi plus, of course the voltage sounds like the issue here.

 

[ggunn]

Something that keeps coming up in this thread is the alleged possibility of some sort of current backfeed through the neutral if the switch does not interrupt it, but I am struggling to understand how that could happen. Any current flow has to have a return path; you cannot have current flowing in a single conductor without one. What would the return path for this backfed current be?

 

[BackCountry]

Something that keeps coming up in this thread is the alleged possibility of some sort of current backfeed through the neutral if the switch does not interrupt it, but I am struggling to understand how that could happen. Any current flow has to have a return path; you cannot have current flowing in a single conductor without one. What would the return path for this backfed current be?

With the Multiplus isolated via a switch that opens the inverter charger and closes the generator, the multiplus’ inverter is now out of the picture.

Generator is on and closed to the main panel.

Main panel has a breaker in it to feed the multiplus which would simulate giving it grid power and thus it would transfer any loads (which there aren’t any, other than the charger itself because the loads are now opened at the transfer switch). The charger would work off of generator power, providing that the generator’s output voltage works for the input voltage of the multiplus, and there would be no neutral derived from the inverter because it would be off.

The only time the inverter can create a neutral and line current in this scenario is if the loads exceed the input amperage setting, then the inverter can assist; however, since the only load is the charger itself if the AC out of the inverter is opened — that factor is eliminated.

The logic would be AC in defeats inverter, thus no possible neutral “back feed.”

I still think the better way to do this is to put the generator ahead of the multiplus and let it manage it as needed. I’m assuming the reason this is not desirable is the OP may have loads that exceed its capacity:

https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-inverter-charger--800VA-5kVA-EN.pdf

 

[jaggedben]

Something that keeps coming up in this thread is the alleged possibility of some sort of current backfeed through the neutral if the switch does not interrupt it, but I am struggling to understand how that could happen. Any current flow has to have a return path; you cannot have current flowing in a single conductor without one. What would the return path for this backfed current be?

I agree, but the issue of current circulating through the autotransformer is probably real. I'm not familiar enough with the Victron to comment on details, but the systems I've installed that use autotransformers to derive a neutral automatically disconnect it when connected to the grid. Here the generator derives the neutral when in use so disconnecting the autotransformer needs to be accounted for.

 

[synchro]

I still think the better way to do this is to put the generator ahead of the multiplus and let it manage it as needed. I’m assuming the reason this is not desirable is the OP may have loads that exceed its capacity:

I agree that this would be preferable since you wouldn't need a transfer switch, and the MultiPlus would be operating the way it's normally used. But then, as you say, it would be likely that the OP could not utilize the full capability of his generator.

Below is the simplified schematic of the MultiPlus 48/5000/70:


The OP must have his MultiPlus programmed such that the relays do not ground the N "neutral" in order to allow split-phase 120/240V operation.

According to Victron the AC out 1 port provides:
"Automatic and uninterruptible switching
In the event of a supply failure or when the generating set is switched off, the MultiPlus will switch over to inverter operation and take over the supply of the connected devices. This is done so quickly that operation of computers and other electronic devices is not disturbed (Uninterruptible Power Supply or UPS functionality)."

AC out 2 port functional description:
"Auxiliary AC output
Besides the usual uninterruptable output, an auxiliary output is available that disconnects its load in the event of battery operation. Example: an electric boiler that is allowed to operate only if the genset is running or shore power is available."

Therefore both AC outputs will be internally connected to the AC input if a generator voltage is present at the "AC in"port. And so if there's a neutral forming autotransformer on the output of the MultiPlus, its L1 and L2 terminals will be connected by the MultiPlus to the generator when it's supplying voltage to the AC in port. Hence, you would want the transfer switch to connect the neutral for the main panel to the generator's neutral during generator operation, and disconnect it from autotransformer's neutral.

I think there could be a problem with having the AC input of the Multiplus fed from a breaker in the main panel when the transfer switch is connects the MutiPlus AC output to the main panel. That's because it would be externally connecting the AC output directly to the AC input forming a loop around the MultiPlus, possibly with unpredictable and undesirable results. Therefore, I think the MultiPlus should be fed with a separate small panel directly off of the generator instead of from the main panel. That way the output of the MultiPlus can never feed back to its input no matter what position the transfer switch is in.

 

[synchro]

Something that keeps coming up in this thread is the alleged possibility of some sort of current backfeed through the neutral if the switch does not interrupt it, but I am struggling to understand how that could happen. Any current flow has to have a return path; you cannot have current flowing in a single conductor without one. What would the return path for this backfed current be?

I agree, but the issue of current circulating through the autotransformer is probably real. I'm not familiar enough with the Victron to comment on details, but the systems I've installed that use autotransformers to derive a neutral automatically disconnect it when connected to the grid. Here the generator derives the neutral when in use so disconnecting the autotransformer needs to be accounted for.

On the generator, the stator winding is tapped at a halfway point to connect its output neutral conductor. The OP is using a center-tapped autotransformer to derive a neutral for an inverter that has a two-wire L-L output, but no neutral. But the L1-N and L2-N voltages derived by the autotransformer and the generator from the same L1 and L2 will not be identical because of practical reasons, and so if you connect their neutrals a current will flow. How much current there will be depends on the amount of mismatch and the impedance that's present at the neutral terminals of these two devices.

The return path for the neutral current in the OP's case is the L1 and L2 that the generator and inverter/charger both share when the generator is connected to the input of the MultiPlus. That is because the inputs and outputs of the MultiPlus are not isolated from each other. See the schematic in my post above for further detail. If the inverter and generator were two independent sources that had no L1,L2 connection like the OP has using the MultiPlus bi-directional inverter for battery charging, then no switching of the neutral would be needed.