Grid tie system with small critical loads battery backup

[Hedges]

By the way, I would put interlocked backfed breaker in main as well, in case I wanted to supply some of those loads.
It does mean you don't see when grid returns.

I've since implemented Load Side Tap instead - 200A main breaker only or meter main, fan out after that to main loads panel, inverter, backed up loads panel.

My system doesn't have the double current in N issue because my inverter is fed by main panel (with its own N), then feeds output of inverter through same conduit back into main panel, then out to sub-panel.

 

[timselectric]

Also, your drawing still shows two neutrals at the center (sub panel) equipment.
I would have a tap there, so that there's a single neutral to each piece of equipment.

 

[timselectric]

I would also use a trough, instead of conduits. To simplify everything.

 

[skyking1]

how do you make the neutral connection in the trough? It's making sense now, but I won't backfeed a breaker in the main panel. I'll make sure I get what I want in the critical loads subpanel and be happy with that. Power is quite stable where I am building, better than what I have now. I have made do with a few extension cords and a Honda 2000, this will be the lap of luxury by comparison.

 

[timselectric]

how do you make the neutral connection in the trough?

A standard terminal block or Polaris type connector.

 

[Hedges]

I used split bolt inside a conduit body. Also wrapped it but since it is zero volts I wasn't concerned about pointy ends poking through tape like I would for L1/L2.

I like Polaris. By selecting sufficiently oversize, I'm able to slip insulation through connector (of the type open on both ends) and set-screw onto a 1" section of exposed conductor after removing insulation in the middle. A 2-port connector supports 4 ends that way.

Tim - grounding lug in trough? I'm thinking lay-in lug, connect to middle of ground wire.

Should Skyking use Polaris for Neutral as well? That would support one more end for the lug. Or daisy-chain through ground bar in sub panel? One more wire back to lug?

My new setup has multiple panels I'll interlock and backfeed with #2 from inverter. One gets primary power 2/0 (and ground #4) through a different conduit. I'll stitch the neutral and ground (make some loops) to ensure it always has a path together with L1/L2. The conduit path is already a loop.

 

[mciholas]

mciholas said:
Another conduit goes from backup to inverter, carries one neutral, one ground, and two sets of hots (inverter load, inverter grid). These will generally be in use at the same time for normal operation (backup on inverter load, inverter grid either sucking power during dark or pushing PV back to grid during day).

This is also either /or.
(Referring to neutral currents only)

That makes no sense. The inverter decides, moment by moment, if the grid path sinks or sources power. Power *WILL* flow in *BOTH* grid and load lines at the same time. It *HAS* to that's the whole point of a grid interactive inverter. The combined neutral from the inverter will carry both the grid and load neutral currents mixed together. Is that what is intended?

At any given time, current only flows in one direction on a conductor.

Sure, at the nanosecond level, that is always true in every wire. In fact AC is defined as always changing direction.

None of this advise makes any sense to me. I'm advised not to have neutral loops, but you guys are creating one neutral for TWO circuits with this layout. I also can't believe the "put it in a trough" changes anything. How do the electrons know or care what box they are in?

Simple question: is my latest wiring diagram "right"? If not please explain *exactly* how it would change. There are four neutral things to connect: main neutral bar, backup neutral bar, inverter grid neutral, inverter load neutral. Now tell me how they are connected.

Mike C.

 

[timselectric]

Tim - grounding lug in trough?

I use a ground bar. It keeps everything simple and clean. Also handy for future additions.

 

[timselectric]

The combined neutral from the inverter will carry both the grid and load neutral currents mixed together.

It won't
The inverter is either a source or a load, at any given time.

I also can't believe the "put it in a trough" changes anything.

It simplifies the installation. And gives you a place for the tap.

How do the electrons know or care what box they are in?

Echolocation (sonar)
Maybe?

There are four neutral things to connect: main neutral bar, backup neutral bar, inverter grid neutral, inverter load neutral. Now tell me how they are connected.

Actually 3

 

[mciholas]

It won't
The inverter is either a source or a load, at any given time.

The single neutral line to the inverter is carrying the neutral currents from the GRID input/output (varies) to the inverter *AND* the LOAD output.

The single neutral between main and backup panels is carrying the neutral currents from both the inverter GRID input/output (varies) *AND* the backup panel if it is in grid mode.

NEC 200.4(A):

Neutral conductors shall not be used for more than one branch circuit, for more than one multiwire branch circuit, or for more than one set of ungrounded feeder conductors unless specifically permitted elsewhere in this Code.

Isn't sharing the neutral between two circuits on the inverter a violation of this clause? It doesn't matter if the wires are all in one conduit or not.

If I did this, does the neutral have to be rated for the combined circuit ratings? 120 amps?

Actually 3

No, my inverter has a neutral connection for the GRID and the LOAD that are separate.



Thus I have main panel neutral, backup panel neutral, inverter grid neutral and inverter load neutral. 4 points.

Again, simply tell me how you wire those four points together and not combine neutral current from two circuits and without creating a neutral loop? I can't see anyway to do this.

The simplest would be to send every neutral to the backup panel neutral bar. Main neutral, inverter grid neutral, inverter load neutral all go to the backup panel neutral bar making it the single point neutral. That would be equivalent to a stand alone neutral bus bar where the backup panel to bus bar neutral wire is zero length.

The separate inverter neutrals are basically tied together at both ends, so that's electrically one wire so they will share current and not be segregated. Tis does mean the main to backup neutral is combined with backup panel and inverter grid current.

I am going to be wiring this up in a few days, so I am keen to figure this out.

Mike C.

 

[timselectric]

The single neutral line to the inverter is carrying the neutral currents from the GRID input/output (varies) to the inverter *AND* the LOAD output.

Either/ or
Not and
The inverter can't be a source and load, at the same time.

The single neutral between main and backup panels is carrying the neutral currents from both the inverter GRID input/output (varies) *AND* the backup panel if it is in grid mode.

Correct, but it's still one circuit from one source.

NEC 200.4(A):

Neutral conductors shall not be used for more than one branch circuit, for more than one multiwire branch circuit, or for more than one set of ungrounded feeder conductors unless specifically permitted elsewhere in this Code.

It's not two circuits. It's two optional sources for one circuit.
The interlocks keep them from being used simultaneously.

No, my inverter has a neutral connection for the GRID and the LOAD that are separate.

Most of the newer hybrid AIO's have a single neutral bar.
Your should be internally common. (Please verify)
You have two options.
1. Only use the input neutral terminal. (Assuming that it's the larger one)
2. Run both to the terminal block in the trough.
(#1 would be my choice)

Again, simply tell me how you wire those four points together and not combine neutral current from two circuits and without creating a neutral loop? I can't see anyway to do this.

See above

The simplest would be to send every neutral to the backup panel neutral bar.

I wouldn't do that. Because you can't isolate the backup panel for maintenance.
Without shutting down the inverter. And there may be times when that would not be desirable.

The separate inverter neutrals are basically tied together at both ends, so that's electrically one wire so they will share current and not be segregated.

Again, this would be parallel conductors. (Not recommend)
And requires keeping the backup panel neutral bar active, when maintenance is done. (Unless you also shut down the inverter)
A warning label would be needed.

I am going to be wiring this up in a few days, so I am keen to figure this out.

Hopefully this cleared up some questions.
I would definitely use a trough. It makes everything simpler and looks much cleaner.

 

[Hedges]

The electrons in L1, L2, N, and (in the event of a fault) G all want to be in the same box. They know if the others aren't with them.
(Trust me in this - I See Electromagnetic Fields!)

Either/ or
Not and
The inverter can't be a source and load, at the same time.

Correct, but it's still one circuit from one source.

It's not two circuits. It's two optional sources for one circuit.
The interlocks keep them from being used simultaneously.

With interlock of sub-panel set to "grid", it can put 60A in neutral.

The inverter has 2 load ports, second one could be set to supply a load, could also be single-phase and put another 60A in neutral, 120A total.

(Of course, inverter could charge its batteries and draw 60A, that ought to be in L1/L2 only, zero in neutral. But it is a Black Box, don't think we're allowed to assume zero neutral current.)

So I think either size neutral wire for 120A up to where it branches (possibly at neutral bar in sub-panel), or run separate neutral from Main to Sub and from Main to Inverter.

Mine is separate because inverter is connected through separate conduit branch. I'll run inverter grid and load connections through a single conduit, Red, Black, White, Green, Black Red.

 

[timselectric]

With interlock of sub-panel set to "grid", it can put 60A in neutral.

This would also require the interlock in the main panel be set to bypass.

The inverter has 2 load ports, second one could be set to supply a load, could also be single-phase and put another 60A in neutral, 120A total.

The breaker feeding the circuit will also limit the neutral current.
You can't have more current on the neutral, than what is on an individual leg.

 

[robbob2112]

You two guys are so freaking smart about all this stuff it makes me realize just how far I have to go.

Years of experince I guess.

I did a bunch of different things in the Navy 30 years ago and do things around the house, but for the last 30 I have been riding a desk working at a computer otherwise.

 

[Hedges]

This would also require the interlock in the main panel be set to bypass.

The breaker feeding the circuit will also limit the neutral current.
You can't have more current on the neutral, than what is on an individual leg.

I don't think so. Main panel doesn't have an interlock.
It has 60A breaker feeding sub-panel, and 60A breaker feeding inverter.

If inverter gets load attached to Load2 port as well, that could carry 60A bypass on L1, and sub-panel could carry 60A on L1.
That's 120A on L1, 120A on N.

 

[timselectric]

Main panel doesn't have an interlock.

It should, in this situation.

If inverter gets load attached to Load2 port as well,

There has been no mention of using the load 2 port, up to this point.

But, that would change everything.
You could upsize the neutral for the first section. But I'm not sure if it would get passed an inspection.
Electrically it would be fine. And wouldn't be confusing to anyone else working on it.
I usually try to follow industry standard practices. Because you never know who might be working on it next. Even if that someone is me, I don't want to have to remember something odd. I get enough of that, following others. lol

 

[timselectric]

There should not be any reason to not have an interlock in the main panel.
The only reason for switching to bypass is for maintenance on the inverter.
I don't see any reason to ever want both on.

 

[skyking1]

main panel interlock? please explain that @timselectric , how does my installation require one of those? normal operations for me are one breaker pair does the grid tie, and the other feeds the critical subpanel.
EDIT: Your post above cleared that up, thank you.
What I keep seeing is, this critical load panel is not an automatic fail over the way people keep drawing it. It has an interlock breaker set that requires human input.
I know this is a nice discussion but it has gone in the weeds for me. It is no longer on topic. My topic.
I don't want too much.
I want to be out of town and not have the food spoil, and if I am home I want 3 circuits of light switches to work.
I want to provide power to a 1/3 HP hydronic pump.

 

[mciholas]

The inverter can't be a source and load, at the same time.

The inverter can be a load to the grid and a source to the backup panel at the same time.

This is such a basic thing that it is freaking me out you aren't seeing that.

Maybe you are doing some magic semantic handwave that a device with TWO 240 VAC connections is somehow ONE circuit. I just don't see any justification for that interpretation.

There are times the grid port will load more power than the load port puts out (say grid charging battery). There will be times the grid port is loaded less than the load port (say some PV or battery but not enough to power all the backup, deficit from grid). And hopefully, commonly, the grid port will source power while the load port also sources power (excess PV input). The grid and load connections can go basically all over the place power wise.

The inverter can and *must* be able to operate as a source and a load at the same time. This is fundamental to its operation.

Correct, but it's still one circuit from one source.

No, it is two, grid and load.

It's not two circuits. It's two optional sources for one circuit.
The interlocks keep them from being used simultaneously.

There is no interlock on grid and load to the inverter. They both operate at the same time.

There is no interlock that prevents the inverter from using the grid connection while the backup panel uses the grid.

Thus the shared neutral in those connections crosses two circuits.

The only interlock is the backup panel can be powered from the main panel or from the inverter load output. That is the only interlock in the system.

Most of the newer hybrid AIO's have a single neutral bar.

Your should be internally common. (Please verify)

It probably is, would be odd to be otherwise.

You have two options.
1. Only use the input neutral terminal. (Assuming that it's the larger one)
2. Run both to the terminal block in the trough.
(#1 would be my choice)

#1 violates the wiring diagrams in the inverter manual. They always show the load neutral connection being used. Not following the manual violates the certifications.

#2 creates a neutral which has a loop. The loop is closed at the inverter with the grid neutral and load neutral are assumed to be internally connected.

Hopefully this cleared up some questions.

Not really. I'm far more confused now than when we started because I don't actually understand what you think is the right connections and/or what you are telling me violates code, the manual, or both.

Mike C.

 

[Hedges]

Only reason for interlock on main panel is if you want to feed one of its loads from the inverter, during a grid failure.
e.g. operate the garage door, finish the load of washing that is all soapy, before hanging clothes out to dry.

Your interlock on sub-panel can be a bypass, direct to grid, for inverter repair. Normally fed by inverter so you have UPS for critical loads.
If you never connect anything to Load2, neutral won't be overloaded. Inverter will charge with L1/L2, zero current on N. I used two separate N wires, so they won't be overloaded regardless.

My concern with relying on inverter is there are failure modes that can leave it shut down. In some ways, grid is a more reliable supply for freezer.
I would like a deadman switch that falls back to grid if inverter output is off.