Inverter to AC Panel Wiring

JRM

I'll try again - I think clicking on "New Discussion" erased my message.  I used to follow this forum but have been away.  Too much to get done and not enough time.  It looks like there have been some changes to the format.  I have a solar panel/battery storage off grid setup and have got to the point of connecting my 110 volt inverter to an AC electric panel.  Can I do this with a main breaker?  From images I have seen, this isn't necessary, and I can use a jumper to connect the breaker rails.  But I want to protect the inverter from an overload.  It does have fuses, but re-setting a breaker would be easier than changing fuses.

If I can use a main (input) breaker, how should it be wired, or does this even matter?  I think my basic question is whether a regular branch breaker will trip whether power is coming in or going out?  And this time I will save my message in case I don't post it correctly.

JRM

Photowhit

JRM said:

I'll try again - I think clicking on "New Discussion" erased my message.  I used to follow this forum but have been away.  Too much to get done and not enough time.  It looks like there have been some changes to the format.  I have a solar panel/battery storage off grid setup and have got to the point of connecting my 110 volt inverter to an AC electric panel.  Can I do this with a main breaker?  From images I have seen, this isn't necessary, and I can use a jumper to connect the breaker rails.  But I want to protect the inverter from an overload.  It does have fuses, but re-setting a breaker would be easier than changing fuses.

If I can use a main (input) breaker, how should it be wired, or does this even matter?  I think my basic question is whether a regular branch breaker will trip whether power is coming in or going out?  And this time I will save my message in case I don't post it correctly.

JRM

So If you want to protect your inverter from overloading, that would be a breaker or fuse between the battery bank and inverter. Most inverters will have internal protections/shutdowns to prevent this. Even if you had a breakers the internal protections might kick in before the breaker heated up enough to trip.

If you will only service the breaker box with the inverter, I'd connect at the main break, just for the ease of shutting everything down.

Is the breaker box 220 volt? this may require an additional connection so both 'side' of the 220 box are served.

BB.

Breakers (and fuses) are there to protect the wiring... They can also be nice to turn off circuits for service.

Breakers and wiring do depend on the size of the inverter (AC output current) and the rating of the panel itself.

For most of us, usually the panel is rated for way more current than a typical AC inverter can output... Say a 100 amp rated panel and a 3 kWatt / 25 amp @ 120 VAC rated inverter... So a "Main Breaker" is not needed--But still may be nice just to be able to kill power at the panel.

Assuming that your panel is a 120/240 VAC rated box... you can either jumper the input to the main breaker (L1 from inverter to the L1 and L2 main breaker inputs, or L1 to one pole of the breaker and jumper the bus bars in the box. I would suggest L1+L2 connections before the breaker as the rest of the box is wired "normally" so it does not confuse somebody later (say you upgrade to a 120/240 VAC inverter and/or backup genset) down the road.

There are distribution boxes that don't have a main breaker at all--So you could use one of those and wire directly from the inverter AC output to the distribution box--Save the price of a "main breaker" but lose the "master shutdown" to your panel/home/cabin.

The other issue to watch with 120 only wiring... Remember that L1+L2+Neutral north American wiring or 120/240 VAC split phase wiring--The L1 and L2 poles are 180 degrees out of phase to give you L1 to L2 at 240 VAC, and L1 to Neutral or L2 to Neutral at 120 VAC.

In a split phase installation, the Neutral only carries a maximum of the breaker rated current (say 15 amp circuit for L1/L2, then the Neutral only carries 15 Amps max or the difference of L1-L2 current).

For 120 VAC wiring on a 120/240 VAC panel, with the L1 and L2 jumpered together for 120 VAC only... Then the output current of L1 and L2 "add" together (L1+L2=Neutral current). Where this matters is if you use, for example, 14x3 ROMEX (14 AWG with Black, Red, White, and ground). This works great for carrying 120/240 VAC split phase current. But if you were to use the same 14x3 ROMEX on a 120 only panel, then the L1+L2 current adds up for the Neutral line. And your 15+15 amps max for L1/L2, add up to 30 Amps (maximum) for the neutral current--Way to much current for 14 AWG wiring.

So, in the case of wiring your home/cabin, only use 14x2 (and other sizes) only cabling--Do not used a "common Neutral" for two different circuits that you can do with a 120/240 setup.

That also suggests that if you have a 100 Amp 120/240 VAC panel wired for 120 only... That the max wattage of the panel will be reduced too. As an example 100 Amps * 120 VAC = 12,000 Watt max rating... A 120/240 VAC split phase power source would be rated for 100 amps * 240 VAC = 24,000 Watts (because the Neutral current adds for 120 panels and does not add for 120/240 split phase power).

But as I said earlier, most 120 VAC output inverters are going to be much smaller than the main panel max current rating so should not be an issue.

-Bill

JRM

Thank you for responses.  I was able to determine that my inverter does have overload protection that turns it off, although its directions about this are not very clear.  I assume this is separate from fuses that are described as providing short circuit protection and am guessing that turning the inverter off and then back on will clear the overload status.  I do think that a properly sized main breaker on the output side of the inverter would prevent the rest of my system from getting more power than the inverter is designed to produce, and I should be able to shut down the AC side of the system by turning the inverter off.   And since the inverter has its own overload protection, it appears acceptable to forego a main breaker and to use a jumper in the panel to add 110 volt circuits.  The inverter is wired to provide only 110 volt power.  It has three connectors (L1, L2, and L3), but L2 is a ground and L3 is the neutral, so it cannot provide 220 volt power.  This simplifies wiring while it also limits my future options.  Thank you again for the advice.

JRMunn