Connecting inverter to ac system

[BillBerner]

Mates
So maybe this is a terrible idea, but...
I would like to connect my inverter to the existing 120v ac outlets on the boat.
Is it a terrible idea to connect the output of the inverter to the 120v bus bar or load side of the main breaker IF AND ONLY IF I use a battery on off switch between the inverter output and the 120v bus/breaker.
Guessing this can't be abyc approved because of potential of either back feeding 120v to the inverter if switch is not turned off while on shore power.
Could I use some sort of diode instead to prevent it instead of switch?
Would like to avoid cost of xfer switch.
Guessing that feeding 120v from both shore power and inverter simultaneously would be okay because it would essentially be a parallel not series load.
Eager to get told I'm wrong.
Thanks

Bill Berner
Hull 66
Stamford, CT

[KenKrawford]

Bill, that's exactly what I did with my inverter. Next time I'm on my boat I'll get you a couple of pictures to help clarify my process. Basically, what I did was isolate the starboard and port outlet circuits by cutting the copper bus bar that connects all the AC circuits. I then installed a double pole double throw ON/OFF/ON switch that allows me to switch between shore power and the inverter. The switch is rated at 20 amps/250VAC if I recall correctly and costs around $20. The ON/OFF/ON designation is important as it eliminates any momentary connection between BOTH the inverter and shore power. The switch has 3 terminals: 1 feed in from the inverter, 1 feed in from shore power and 1 output leg going to the outlets. It works like a charm. The switch eliminates any back feeding as it isolates the inverter and shore power .

[wolfe10]

The most "idiot proof" way to wire inverter output into your existing 120 VAC system is with a SUB-PANEL.

There are a lot of different inverters out there with a bunch of different features. I will cover an inverter with "pass through" feature, as this is the most common type of larger inverters.

Remove the hots AND THE NEUTRALS for those circuits you want powered by the inverter when you aren't on shore power or generator from the 120 VAC panel. Wire them to a new subpanel with individual breakers for each circuit you want to be able to power from the inverter (hots to the breakers, neutrals to the neutral bus). Run a ground wire from original panel ground to new subpanel ground-- you can separate out the grounds if you like, but this is not necessary. Run the 120 VAC inverter IN from one of the breakers on the original panel (assuming pass through feature-- a great asset).

Now, everything is automatic. When on shore power or generator, the pass through feature of the inverter powers those circuits. When no outside source of 120 VAC is available and you turn on the inverter, those circuits are powered by the inverter.

Nothing to turn on/off, no possibility of two sources of 120 VAC (Extremely dangerous), no powering the battery changer from the inverter or other "no-no's"

Brett

[BillBerner]

Great info. Thanks to both of you. I've already got a dumb inverter, with no built in xfer (pass thru), so I'll be going with Kens version.
Didn't realize such a double pole breaker exists. Sounds perfect.
Also, I actually found a xantrex automatic xfer switch for around 50 bucks which was less than I expected. But 20 is still less than 50!
Thanks again.

Bb

[wolfe10]

Ken,

Did you isolate the neutrals for those circuits as well?

Just want to make it clear for Bill.

[KenKrawford]

Brett, I did this project 7 yrs ago so the details are fuzzy in my memory but I'm almost positive I did isolate them as well. I'll re-confirm next time I'm at the boat.

[wolfe10]

Ken,

Yes, you want to switch both hot and neutral when changing sources of 120 VAC.

Brett