Critical loads panel with 2 power sources, interlocked. Do I have the neutrals wrong?

[Rokkerhead]

Im planning out my setup of an eg4 12000xp supplying a critical loads panel. I’d like to backup the loads panel with grid in case of inverter failure. I’ve read that some guys use a manual interlock rather than using a more expensive transfer switch. I made this diagram of the system, however I’m not sure I have the neutrals correct. I have a neutral from inverter to CL panel. And I also put a neutral from grid to CL panel. This doesn’t seem right in my head though.

Would the neutral from main panel to CL panel need to be disconnected when running from the inverter? Maybe a transfer switch is a better way to go?

 

[timselectric]

It would be better to only have one neutral path. Preferably with a T-tap for the inverter. But it depends on how the wiring is ran. Because the neutral needs to run in the same conduit or raceway with the line side conductors being used at the time.
So the question is, how are you running the wiring?

 

[GuyG]

Maybe a transfer switch is a better way to go?

Most transfer switches don’t have switched neutrals anyway, in my experience.

Thinking that you need to run a neutral from main panel to inverter along with the phase conductors. You have a roundabout return path to the main as it is, but as Tim has pointed out you’d prefer for the return current to stay with the hots as much as possible.

 

[Rokkerhead]

It would be better to only have one neutral path. Preferably with a T-tap for the inverter. But it depends on how the wiring is ran. Because the neutral needs to run in the same conduit or raceway with the line side conductors being used at the time.
So the question is, how are you running the wiring?

Conduit from inverter to CL panel: L1, L2 to CL main lugs. Neutral to CL neutral bar. Ground to CL ground bar.



Conduit from main panel (100 amp breaker) to inverter: L1, L2 (grid inputs), neutral (inverter neutral bar), ground (inverter ground bar).



Conduit from main panel (second 100 amp breaker) to CL panel: L1, L2 to CL 100 amp breaker, neutral to CL neutral bar, ground from CL ground bar to main panel ground bar.



The eg4 12000xp uses the 100 amp grid input for battery charging and 100 grid bypass when inverter overloads (internal transfer switch).

 

[GuyG]

Conduit from main panel (100 amp breaker) to inverter: L1, L2 (grid inputs), neutral (inverter neutral bar), ground (inverter ground bar).

Your diagram doesn’t show any neutral direct from main panel to inverter. That’s what I was getting at.

 

[etekberg]

I think the drawing is fine. I only see one return current path in the drawing except in bypass. But your description has an extra neutral from main panel to inverter that isn't in the picture which is going to have current on it when not in bypass.

I wired mine like your drawing but used 2awg.

Ultimately I don't think there is a perfect solution other than using a switched neutral transfer switch.

 

[Rokkerhead]

Your diagram doesn’t show any neutral direct from main panel to inverter. That’s what I was getting at.

Ahh. That’s where I messed up. I guess I was thinking that the neutral path from inverter to CL neutral bar, and CL neutral bar to main would be sufficient.

 

[GuyG]

I forgot to ask whether your AC wiring is in metal or pvc conduit. If metal, you absolutely need to group the neutral and ground in the same conduit with the hots.

 

[timselectric]

Conduit from inverter to CL panel: L1, L2 to CL main lugs. Neutral to CL neutral bar. Ground to CL ground bar.



Conduit from main panel (100 amp breaker) to inverter: L1, L2 (grid inputs), neutral (inverter neutral bar), ground (inverter ground bar).



Conduit from main panel (second 100 amp breaker) to CL panel: L1, L2 to CL 100 amp breaker, neutral to CL neutral bar, ground from CL ground bar to main panel ground bar.



The eg4 12000xp uses the 100 amp grid input for battery charging and 100 grid bypass when inverter overloads (internal transfer switch).

Are the conduits metal?
If not, are they running beside each other?

 

[Rokkerhead]

I forgot to ask whether your AC wiring is in metal or pvc conduit. If metal, you absolutely need to group the neutral and ground in the same conduit with the hots.

Still just planning this out. Nothing installed yet. Setup will be in my basement. Would metal be preferable?

 

[Rokkerhead]

Are the conduits metal?
If not, are they running beside each other?

Just planning right now. Nothing installed yet.

 

[etekberg]

I forgot to ask whether your AC wiring is in metal or pvc conduit. If metal, you absolutely need to group the neutral and ground in the same conduit with the hots.

Ground wouldn't matter in this case.

Still just planning this out. Nothing installed yet. Setup will be in my basement. Would metal be preferable?

If the return conductor isn't included then there will be a residual magnetic field that will create eddy currents in a metal conduit and heat it up.

 

[Rokkerhead]

Ground wouldn't matter in this case.


If the return conductor isn't included then there will be a residual magnetic field that will create eddy currents in a metal conduit and heat it up.

Good to know. Thanks!

 

[timselectric]

Just planning right now. Nothing installed yet.

Perfect
The best option is to install a trough and put everything above it. (If possible)
This keeps all wiring together and gives you many options.

 

[Rokkerhead]

I think the drawing is fine. I only see one return current path in the drawing except in bypass. But your description has an extra neutral from main panel to inverter that isn't in the picture which is going to have current on it when not in bypass.

I wired mine like your drawing but used 2awg.

Ultimately I don't think there is a perfect solution other than using a switched neutral transfer switch.

I was thinking, don’t I need the neutral from CL panel to main for when the inverter is in grid bypass mode?

 

[GuyG]

I was thinking, don’t I need the neutral from CL panel to main for when the inverter is in grid bypass mode?

Yes. Rule of thumb is to always group together all current carrying conductors of the same circuit, which includes the neutral in most cases. It’s mandatory when using metallic conduit/raceways AND when entering metallic enclosures.

 

[Rokkerhead]

Updated diagram to better reflect conduit runs. Am I in need of a ground from inverter to CL panel? Or does the ground from inverter to main to CL panel satisfy that?

 

[timselectric]

I don't like the parallel neutral path. But if everything is in separate conduits taking different paths, you are limited on options.
And yes, an EGC needs to be ran in each conduit.

Without knowing the location layout of everything, it's impossible to guess what the best way is.

 

[Rokkerhead]

I don't like the parallel neutral path. But if everything is in separate conduits taking different paths, you are limited on options.
And yes, an EGC needs to be ran in each conduit.

Without knowing the location layout of everything, it's impossible to guess what the best way is.

The parallel neutral is what was tripping me up in my original post. When power is supplied to CL panel by the loads output of the inverter (via battery and eventual PV), you would think that you would want the neutral from main to CL panel disconnected (which obviously a manual interlock wouldn’t do).

But what about when the inverter is switched to grid bypass mode (via an internal transfer switch which happens automatically if inverter gets overloaded). Wouldn’t I need the neutral still connected from main to CL panel? Because now the CL panel is powered by the grid.

Due to space constraints, my inverter and batteries will be on one wall. And the CL panel will be on a perpendicular wall. The CL panel will be right next to the main panel. So, I was thinking of 2 runs of conduit from inverter. 1 to CL panel, and 1 to main panel (for grid input). That way I can stick with 3 awg THHN wire. I could use just 1 run for both but I think I’d have to bump up to 2awg and I’m not sure if the 12000xp lugs are big enough.

 

[timselectric]

I would still use a trough, but it is more expensive when you turn a corner and continue on another wall. Still it's a much easier way to wire everything and end up with a cleaner looking system. Putting it all in a single conduit would be a pain and would look terrible, in my opinion.

If you watch some of Engineer775's youtube videos, you'll see how much better a trough would work and look.

 

[Rokkerhead]

I would still use a trough, but it is more expensive when you turn a corner and continue on another wall. Still it's a much easier way to wire everything and end up with a cleaner looking system. Putting it all in a single conduit would be a pain and would look terrible, in my opinion.

If you watch some of Engineer775's youtube videos, you'll see how much better a trough would work and look.

I’ll have to look into the trough idea. Thanks for the info.

I think I’m going to ditch the interlocked feeder from the main panel idea. I need to get rid of that parallel neutral. I don’t want problems. Do you know if transfer switches are made that will switch L1, L2 and neutral? I really just want backup power to the CL panel if the inverter craps out on me.

 

[etekberg]

And yes, an EGC needs to be ran in each conduit.

Do you have an NEC reference? I think equipment grounds are fine as shown.

 

[timselectric]

I’ll have to look into the trough idea. Thanks for the info.

I think I’m going to ditch the interlocked feeder from the main panel idea. I need to get rid of that parallel neutral. I don’t want problems. Do you know if transfer switches are made that will switch L1, L2 and neutral? I really just want backup power to the CL panel if the inverter craps out on me.

Yes, just use a 3 pole transfer switch.

 

[etekberg]

I’ll have to look into the trough idea. Thanks for the info.

I think I’m going to ditch the interlocked feeder from the main panel idea. I need to get rid of that parallel neutral. I don’t want problems. Do you know if transfer switches are made that will switch L1, L2 and neutral? I really just want backup power to the CL panel if the inverter craps out on me.

Yes, they are made, but I think you are way overthinking this. If you are concerned don't use ferrous conduit. But even with ferrous conduit the unbalanced current is likely small. I've read in Canada you don't even have to bother for less than 200 amps.

 

[timselectric]

Do you have an NEC reference? I think equipment grounds are fine as shown.

No time to look it up, at the moment.
But I can guarantee that the NEC requires an EGC in every conduit.