Best way to wire in inverter to breaker panel?

Re: Best way to wire in inverter to breaker panel?

Oh--OK.

Several questions first... What Brand/model of AC inverter do you have?

Most MSW inverters cannot have their output connected to earth/green wire/bonded to neutral grounding (if battery is also negative or positive grounded too). This creates a short circuit through "most" MSW inverters and will let the magic smoke out.

And most TSW inverters have fully isolated AC outputs--So you can take one of the AC outputs, put a white wire on it, and connect it to the neutral/ground bus in the main panel. And the black wire output can connect to the bus bar/main breaker in the AC panel.

You need to read the manual for your AC inverter and grounding to ensure you do not make a costly mistake.

If the main panel's AC Current rating is equal too, or less than the AC inverter's maximum output current rating, then you can jumper both buses together so you can have 2x as many breaker positions for a 120 VAC only panel.

Make sure you "home run" each black wire out and white wire back to the main panel. You don't want to send out two "hot wires" and bring back one white wire as you would normally do with typical north American home's 120/240 VAC Split Phase power.

With two "black" phases from a 120 VAC only panel, the current from both hots add up and can overheat the neutral/return wire.

With 120/240, the neutral is the center tap of a transformer and will never carry more current than that of either of the hot wires.

Sorry--it is confusing to write this--and doubly hard to read and make sense not knowing your experience level with 120 vs 120/240 VAC circuits.

-Bill

Re: Best way to wire in inverter to breaker panel?

First note: Do not use battery clamps for connecting up your inverter's DC input power. Bolt everything together. Battery clamps typically do not make "good enough" electrical connections to reliably pass the current for a largish AC Inverter:

2,600 Watt inverter * 1/0.85 inverter eff * 1/10.5 volts battery cutoff * 1.25 NEC wiring/breaker derating = 364 Amp branch circuit recommendation

>300 amps is a lot of current to pass through anything but solid "bolt up" connections and very heavy copper wiring.

Back to the type of inverter question:

It is a MSW inverter, and they completely skip talking about AC Neutral Bonding (or not).

It may have a transfer switch--two pole would be my assumption--so the neutral is bonded to ground by the utility panel, but is not bonded if the inverter is operating and powering the main panel.

So--in your main panel, being completely off grid operation (?)--Your AC panel needs to have an isolated "neutral/white" wire power block (it looks like you can float it fro ground by cutting/lifting the bonding strap on the left of the bus bar.

So, bring the "black wire" from the inverter to your AC bus bars (jumpered together if you wish). And the "white wire" to the, now floating, return bus.

And wire up the rest of your system.

Note, if you ground bond the battery negative terminal with the rest of your grounding (inverter ground is probably just to the metal shell of the inverter and the metal box of the battery charger), this would be the "standard" method for DC grounding your system. Then you can put fuses in the positive bus connections to your inverter, battery charger, etc....

The following is an "advanced discussion" about grounding MSW inverters. There are lots of grounding/wiring issues with MSW inverters and how we "normally" connect AC and DC wiring. You can ignore this part just like 99.999% of the people do. However, if you are very concerned about (fire) safety, then you can read/discuss the following:

But the AC Inverter wires are now not floating (if the battery bus is grounded)--And if you accidentally short to ground either of the inverters Black OR WHITE wires, it can cause excessive current to flow and smoke wiring and/or AC inverter--so both inverter's outputs should be protected by a fuse or breaker.

In reality, you should treat the MSW Inverter's output like 120/240 VAC wiring. Each branch wiring should go through a pair of ganged breakers to cut of the power if either wire gets over current (as from a short to ground or hot to hot short). And not even use the return bus connection (except for green wire grounding--if needed).

If you do not ground reference the Battery Bus--Then both the Battery's DC Bus and Inverter's AC outputs are floating with respect to ground (more or less)--which is very commonly done to reduce the chance of a short circuit causing problems.

Still not "safe" from an NEC/Engineering sense, but very typical for such MSW inverter installations.

Floating power systems should have double pole/ganged breakers on their output wiring to protect both sides from shorts. If the return is grounded, then the ground referenced return wiring generally will not ever have any voltage above ground, so a return wire to ground short will not create excessive current, and does not need fusing.

-Bill

Re: Best way to wire in inverter to breaker panel?

375matt wrote: »

I'll get the clamps off and bolt em up. Knew I'd take some heat on that one! All I had at the time. Batteries are c&d kct 450 amp hour wired in parallel now as 2 each 12 volt banks. I believe that makes it 900 amp hours now?

Yep.

Some fuses and breakers/switches from our host:

High Amperage Inverter Fuses & Breakers
Battery Accessories & Maintenance (high current battery switches)

The inverter does have its own grounding lug wire. Charger has its own grounding wire and the square d load center has its own grounding lug. Am I correct to bond these 3 together n out to grounding rod using # 6 copper? Do I need to put a 4th ground in from the negative of the battery terminal as well?

Yes, but these (should) only be grounding the metal boxes... Not any of the electrical +/- DC or AC wiring (other than the green wires).

If this is fixed installation with metal skins, water pipes, lightning in the area (a whole 'nother kettle of fish), then you should connect the battery negative with a heavy wire directly to the ground rod too (all grounds connect together in one place--the ground rod).

Do not ground bond the AC Neutral (white wire) to any grounds/green wires. The Battery grounding provide a return path through the AC inverter if the white wire is grounded (most likely for MSW inverters). Smoke and all kinds of other fun will ensue if this is done.

Looking at the panel removing the green screw in the picture below on the neutral bar isolates the ground from it. If I have the screw in it bonds the neutral and ground using the panel.

If you use the bus bar for your AC return wiring--Yes, this is the correct way to handle the situation (AC return should be treated as if it too is AC Hot--which it is, in a way).

I am also looking to put in a manual transfer switch when I find one. I assume that i just keep it inline with my other wiring but Im not sure if there would be any issues with the generator neutral ground being bonded? Its a champion 3500 watt. This is off their website so it appears i'm good there:
Most Champion Power Equipment generators have a "floating neutral", meaning that the neutral circuit is not connected to the frame or to earth ground. This also means that both legs on the receptacle are hot legs, which is normal for floating neutral generators. As a result, there is no specific hot leg and neutral leg wiring arrangement for the generator winding connection to the receptacle. The floating neutral configuration is common for applications such as connection to a recreational vehicle and connection to home power where the transfer switch does not switch out the neutral to ground connection.
http://www.cabelas.com/generators-accessories-champion-3500-watt-generator-1.shtml

Yes, small AC generators (less than ~3.5kW) have a floating AC output.

You could, if you wanted, ground a "white wire" at the genset and use a two pole AC transfer switch. This will have a grounded neutral when the generator is running, and a "floating" MSW neutral when the AC inverter is running--pretty much copies how RV parks/vehicles handle the setup.

There is probably no really good reason to even bother ground the AC "White"--It is not going to do much (unless, you have lighting in the area).

There are a couple of manual one one automatic AC Transfer Switches here (you have the transfer switch "turn on" when the generator starts--I think this one has a 15 second delay to allow the genset to stabilize before being hit with the loads:

Transfer Switches and Generator Auto Start Accessories

-Bill

Re: Best way to wire in inverter to breaker panel?

Yep--Very important to understand and ask if something is not clear when dealing with these power levels. Large battery banks scare me about as much as working with a 10,000 amp limit 120/240 VAC pole transformer when connecting up to the home AC line drop (i.e., a lot).

I try to use "open" neutral when typing about "broken" (unconnected) electrical connections.

Floating tends to just not mean "referenced to earth ground or nearby metal frame work (such as car chassis). But I could understand how somebody would confuse a floating neutral or "floating outputs" (not ground referenced) vs a broken connection back to the center tap of a pole transformer, genset, or 120/240 VAC inverter.

-Bill

Re: Best way to wire in inverter to breaker panel?

OK, that is Vmp=30.7v and Imp=8.14a

If you connect that panel to a ~14.5 volt battery bank, the output wattage will be around 8.14a*14.5v=118watts into battery bank.

If you use a MPPT charge controller, the typically peak wattage will be around 250w*0.77derating=193watts into battery bank. Or about 193w/14.5v=13.3a into battery bank nominal peak current.

Kind of expensive to throw a XW 60 amp MPPT charge controller at this bank with only a 250 watt panel--but if you are going to use more panels later--It certainly will work fine now, and support more panels later.

-Bill