How to properly connect a 120v inverter to 240v service panel(only using 120v)?

[BB6-213]

I got absolutely ridiculed on Reddit asking this question, so maybe I will have better luck here.

I have a 5kw 120v SRNE inverter powering a standard residential 100a 240v service panel. The dryer is propane, and I have no use for 240v, so I need to get 120 only on L1 and L2.

I have read that it's possible to pigtail the hot to both legs of the main breaker, but could have issues with branch circuits. Is there a way to locate a branch circuit, and how can I make this work without issues?

 

[Mattb4]

You can jumper L1 and L2. Since you have no 240vAC branch breakers in the panel you will not have to remove them. Typically a label would be added to the front of the panel stating "120vAC only".

 

[Mattb4]

Just to be sure you understand the only power going to that panel will be from your 120vAC AIO and not from another source. For instance you can not have 240vAC being fed in off a transfer switch because of the jumpers shorting the L1 and L2 legs. Also you can not supply "AC in" back to your AIO from the panel.

 

[BB6-213]

Just to be sure you understand the only power going to that panel will be from your 120vAC AIO and not from another source. For instance you can not have 240vAC being fed in off a transfer switch because of the jumpers shorting the L1 and L2 legs. Also you can not supply "AC in" back to your AIO from the panel.

The home is fully solar, no other powersource, so that should rule out that issue.

By jumping both poles of the main breaker, would I have any issues with the potential hot neutral on a branch circuit? That is the only thing concerning me. All circuits are 15a or 20a, mostly led lighting and outlets. I just don't want to fry anything, trying to make it as safe as possible.

 

[hwy17]

The concern you heard about is probably about MWBCs.

 

[Mattb4]

The home is fully solar, no other powersource, so that should rule out that issue.

By jumping both poles of the main breaker, would I have any issues with the potential hot neutral on a branch circuit? That is the only thing concerning me. All circuits are 15a or 20a, mostly led lighting and outlets. I just don't want to fry anything, trying to make it as safe as possible.

The L1 an L2 poles on your main breaker should not be connected to the neutral bus. None of your branch circuits should have a neutral wire as a power lead (GFCI breakers will have a neutral wire for detection purpose). The only concern is if you need a NG bond. This might be done by your AIO when operating as inverter or not. If not you would NG bond at panel. You also will want a good earth ground (ground rod outside and bare copper cable indoors running to panel) in your system with both the panel and the AIO chassis grounded to it.

 

[ChrisG]

Be careful with MWBCs. You can overload neutral on those circuits. Typically would be in a single run with black/red/white/ground with black and red on different phases/breakers. Would only energize one of them, not both if only feeding 120v to panel. Under normal 240v split phase the neutral on the MWBC is canceled or at leased reduced amps. If only feeding 120v the neutral will have to carry both 120v hots though it. Think of it as Black 15a/Red15a/Neutral 15a return with 240v. If using 120v only on the MWBC it’s Black 15a/Red 15a/Neutral 30a return…will burn up.

 

[再生可能 エネルギー]

I have read that it's possible to pigtail the hot to both legs of the main breaker,
but could have issues with branch circuits. Is there a way to locate a branch circuit,
and how can I make this work without issues?

I am puzzle about what you call "issues with branch circuits"
since each L1 and l2 branches are independant circuits (no 240V appliance)?

Could using two separate main circuit breakers instead of a dual main circuit breaker
would be recommended or not, or would make any difference?

 

[Mattb4]

Be careful with MWBCs. You can overload neutral on those circuits. Typically would be in a single run with black/red/white/ground with black and red on different phases/breakers. Would only energize one of them, not both if only feeding 120v to panel. Under normal 240v split phase the neutral on the MWBC is canceled or at leased reduced amps. If only feeding 120v the neutral will have to carry both 120v hots though it. Think of it as Black 15a/Red15a/Neutral 15a return with 240v. If using 120v only on the MWBC it’s Black 15a/Red 15a/Neutral 30a return…will burn up.

No it will not burn up. The power supply is only the AIO. You can not exceed its loading. And the wires feeding the main panel from AIO should be sized appropriately.

Let's say you are powering 2 hots of 15 amps. The 30 amps combined on the neutral (and the hot) to the AIO has to be in the load capacity or a overload condition happens.

 

[HighDesertOffgrid]

The concern you heard about is probably about MWBCs.

Those Multiple Warhead Ballistic Cats have gotten me on more than one occasion.

 

[ricardocello]

Multi Wire Branch Circuits are a way for the electrician to run one less cable, saving a few pennies. I hate them.
My kitchen had one 15A mwbc for the dishwasher and the lights.
Had to combine them into one 15A circuit to put in a GFCI breaker when I extended the circuit outside.
Fortunately, LED lights and modern dishwashers can easily fit on a single 15A circuit.

To the OP: I don't see any in the photo you attached.
An MWBC will usually have a red wire and a black wire going into adjacent breakers, and only a single white neutral wire from the same cable.
NM-B 14/3 or 12/3 w/Ground round wire usually.

 

[BB6-213]

Multi Wire Branch Circuits are a way for the electrician to run one less cable, saving a few pennies. I hate them.
My kitchen had one 15A mwbc for the dishwasher and the lights.
Had to combine them into one 15A circuit to put in a GFCI breaker when I extended the circuit outside.
Fortunately, LED lights and modern dishwashers can easily fit on a single 15A circuit.

To the OP: I don't see any in the photo you attached.
An MWBC will usually have a red wire and a black wire going into adjacent breakers, and only a single white neutral wire from the same cable.
NM-B 14/3 or 12/3 w/Ground round wire usually.

Thank you all for the wealth of information.

All of the breakers are just a single black hot, the only red wire was for the double pole washer which was eliminated. There are red wires on the light switches, but that is the only place I have come across red.

After jumping the main, would it be best to move half of the breakers to the other bus or just leave them in the column configuration?

 

[Mattb4]

...

After jumping the main, would it be best to move half of the breakers to the other bus or just leave them in the column configuration?

Electrically speaking it is the same. Depending on your panels cover plate if the breaker knockouts are not removed yet it likely would look better.

 

[HighDesertOffgrid]

Electrically speaking it is the same. Depending on your panels cover plate if the breaker knockouts are not removed yet it likely would look better.

Sensible. Current inverter could only output 50 amps even if voltage drops to 100v. Would you concur, Dr. Matt?

 

[ricardocello]

I got absolutely ridiculed on Reddit asking this question, so maybe I will have better luck here.

Thank you all for the wealth of information.

You are welcome, this isn't Reddit!

 

[Mattb4]

I am puzzle about what you call "issues with branch circuits"
since each L1 and l2 branches are independant circuits (no 240V appliance)?

Could using two separate main circuit breakers instead of a dual main circuit breaker
would be recommended or not, or would make any difference?

In the US we run 240vAC split phase. This means that there are 2 hot wires and a neutral. In other countries they operate with 230v single phase that has only one hot and a neutral. The 2 hot wires are 180 degrees apart electrically so that if connected together you get 240vAC but by themselves connected to the neutral wire you have 120vAC.

Branch circuits are simply the individual breakers in a distribution panel and their wires going to loads. If they come from only one leg (L1 or L2) they are 120vAC. If they feed from both L1 and L2 you are feeding 240vAC to the loads.

 

[Hedges]

Be careful with MWBCs. You can overload neutral on those circuits. Typically would be in a single run with black/red/white/ground with black and red on different phases/breakers. Would only energize one of them, not both if only feeding 120v to panel. Under normal 240v split phase the neutral on the MWBC is canceled or at leased reduced amps. If only feeding 120v the neutral will have to carry both 120v hots though it. Think of it as Black 15a/Red15a/Neutral 15a return with 240v. If using 120v only on the MWBC it’s Black 15a/Red 15a/Neutral 30a return…will burn up.

5kW inverter is 40A at 120V. One MWBC with two 20A circuits sharing a single 12 awg neutral could be seriously overloaded. 2x current, 4x power dissipation in wire, 240 degrees C rise. Guaranteed to melt the insulation.
Do check for them. if found, you can wire both red and black to a single 120V 20A breaker.

 

[ChrisG]

No it will not burn up. The power supply is only the AIO. You can not exceed its loading. And the wires feeding the main panel from AIO should be sized appropriately.

If he had a 6000w inverter feeding only 120v and both MWBC are on 15a beaker for each hot and each hot was maxing 15a (vacuum on one and griddle on another), that neutral is going to get toasty.

 

[Mattb4]

If he had a 6000w inverter feeding only 120v and both MWBC are on 15a beaker for each hot and each hot was maxing 15a (vacuum on one and griddle on another), that neutral is going to get toasty.

Looking at his panel I do not see any MWBC, do you?

 

[ChrisG]

Looking at his panel I do not see any MWBC, do you?

lol. No. For some reason I didn’t see the picture posted show up in my feed. Weird.

Ok, all is well!