Circuit breaker questions AC

verdigo
verdigo Solar Expert Posts: 428 ✭✭
I finally pulled the trigger last night on ordering an inverter. (Took a couple of beers). Anyway it is an Outback GVFX3648. The E-panel has 60 amp breakers for both AC in and AC hot out. I have installed a sub-panel in the shed for shed loads and to make inverter connections to. It will be a 240 volt service. Just not sure how to connect the e-panel to the sub-panel.

All I can find at local stores are 30 amp breakers for the 120 volt slots, or is it ok to just connect the hots directly to one leg of the sub-panel's in-put from the house. Come to think of it I need some help on those connections as well. The e-panel's wiring diagram just shows the "AC hot out" and the "AC hot in" 60 amp breakers "to house loads".

When making the connections to the house I plan on installing a new breaker box. It will one of these http://www.ebay.com/itm/130784077360?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 and using one of these http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=141197649457 to manage critical loads and ensure anti-islanding. The existing box's main breaker is bad and can not be had anymore. Currently back-feeding a 100 amp breaker.

Of course I could just be way off in my thinking altogether.

Thanks

Dennis

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Circuit breaker questions AC

    Dennis I think you're a wee bit confused. Or maybe I am.

    The output of the GVFX is 120 VAC. To get 240 VAC from it you need an autotransformer. Otherwise you connect to only one side of the 240 VAC split-phase service, not both. (This for AC IN and AC OUT).

    The anti-islanding function is built-in to the inverter. AC IN is bi-directional, allowing AC to charge batteries and feed loads on AC OUT whenever there is insufficient sun to power things. When inverting the unit will power loads on AC OUT and send power to AC IN to back-feed the grid if 'SELL' is active.

    You might want to study Outback's manuals a bit more.
  • verdigo
    verdigo Solar Expert Posts: 428 ✭✭
    Re: Circuit breaker questions AC

    Yeah. Confused is a good word for it, but not about using one leg for the 120 volts. I am supplying the shed with 240 volts to it's own breaker box or what i am calling a sub-panel. I understand that I am only dealing with one leg of the 240 volts that I am running to the shed for my 120 volt connections. I may add another inverter later on to get to 240 volts. Probably not, but maybe.

    I am just having trouble finding 60 amp 120 volt breakers to make the connections to the sub panel. The e-panel has two 60 amp breakers. One on the input/bi-directional circuit and one on the output/off-grid circuit. The inverter's max output is 30 amps @ 120 volts in back-up or off-grid mode. The inverter's max input current however is 60 amps for it's by-directional circuit. I am guessing it needs up to this much current for the battery charging function?

    Maybe the simplest way to approach this question is to just ask "How do I connect my e-panel to my house loads?". While the inverter does have a built in transfer switch it will still backfeed the grid from the batteries unless the house main is switched off if both connections originate from the house's breaker box.

    What I am envisioning is that I am always selling power until the grid goes down. I then go to the houses breaker box and switch off the main breaker. I then switch on another breaker that back-feeds one leg of the house's breaker box which will have most if not all of the 120 volt circuits. When the security light comes on outside that is not on the house's meter, I switch off the back-feeding circuit from the inverter and turn the main breaker back on. This is what I am trying to do. Just ordered the inverter last night, and don't have the manual yet. It's such a nice weekend though. 65 degrees. I wanted to get ahead on the wiring.

    Thanks again

    Dennis
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Circuit breaker questions AC

    Okay 60 Amps @ 120 Volts is 7200 Watts. No way is one GVFX going to supply that. Obviously the E-panel was spec'ed for a pair of inverters not a single one. To carry that kind of current you'd need 6 AWG wire. That probably isn't what you'll be using. And that is an important point because the purpose of over-current protection is to kill the power before the Amperage heads into 'fry the wire' range. Needless to say a 60 Amp single pole 120 VAC breaker is not standard for any household wiring, so there's no surprise you can't find one.

    Frankly I'd change out the breakers in the E-panel if you're not going to run two parallel stacked inverters. Series stacked for 240 VAC will not double the current; it will still operate in the <30 Amps range (loads notwithstanding). The inverter will fault long before either of the output breaker trips. The large input breaker is designed to handle full load current (30 Amps) plus full charger current (about 75 Amps DC if I recall).

    How the wiring would normally look is something like this:

    MAIN SERVICE <---> GVFX ---> CRITICAL LOADS

    It sounds like you are wanting to use the GVFX to power 1/2 of the whole service when the grid goes down? In that case you really should use an external transfer switch to swap the line connected to the GVFX AC IN to the AC OUT (when grid power is down only AC OUT is energized by the inverter). So you'd have something like this:

    MAIN SERVICE <---> TRANSFER SWITCH NC <---> GVFX AC IN
    MAIN SERVICE <---- TRANSFER SWITCH NO <---- GVFX AC OUT

    Note the two positions on the transfer switch: Normally Closed, running most of the time in bidirectional mode with the inverter's AC IN and Normally Open, running when grid is down in monodirectional mode with the inverter's AC OUT.

    Does that help?
  • verdigo
    verdigo Solar Expert Posts: 428 ✭✭
    Re: Circuit breaker questions AC

    I was mistaken about the e-panel breakers. The are 50 amp. Yes. it does help. I have begun to look at some of the large transfer switches like this one. http://www.amazon.com/Reliance-TCA1006D-Generator-15000-Watt-Generators/dp/B000HRWGPS/ref=sr_1_3?s=hi&ie=UTF8&qid=1393110189&sr=1-3&keywords=generator+transfer+switches. Thanks for the help, and sorry for being so unclear in the first place.

    Dennis
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Circuit breaker questions AC

    Now the bad news:
    Legally you can not do it this way because it would allow the inverter's output to energize the utility lines should someone forget to turn off the main breaker. This requires some form of interlock to prevent the AC OUT from being active if the main is also on. It may be possible to fashion and acceptable means of this with your existing main service, depending on its design.

    This is why it is usually done with a sub-panel, allowing the inverter to do the auto-transfer in the event of an outage.

    Keep in mind that the inverter can really only handle two 15 Amp circuits.
  • verdigo
    verdigo Solar Expert Posts: 428 ✭✭
    Re: Circuit breaker questions AC

    Understood. I need it to be legal. The existing main service will be getting replaced anyway. The main breaker is bad and I am currently back-feeding a 100 amp breaker till I get an electrician to come and swap it out. I have been looking at "generator ready load centers" I believe there are options for manual or automatic transfer switches available for these. Are you familiar with these?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Circuit breaker questions AC
    verdigo wrote: »
    Understood. I need it to be legal. The existing main service will be getting replaced anyway. The main breaker is bad and I am currently back-feeding a 100 amp breaker till I get an electrician to come and swap it out. I have been looking at "generator ready load centers" I believe there are options for manual or automatic transfer switches available for these. Are you familiar with these?

    These are designed to cut the utility power and feed select circuits from generator input. In this case you'd be substituting inverter input for the gen. The thing is they come in numerous variations, based on the number of individual circuits and corresponding generator power. Look them over carefully.

    In this case you would again have an input line for the inverter and an output line from it, so the gen transfer switch becomes a bit redundant unless you power the AC IN from one pole and feed AC OUT to the opposite pole via the transfer switch. Something like this:

    MAIN L1 <---> AC IN (keeps batteries charged and back feeds when power is available)
    MAIN L2 ---> TRANSFER SWITCH NC ---> CRITICAL LOADS
    AC OUT ---> TRANSFER SWITCH NO ---> CRITICAL LOADS

    In this way when power goes down the inverter will feed through the manual transfer switch to power critical loads which would otherwise be powered by L2.
  • verdigo
    verdigo Solar Expert Posts: 428 ✭✭
    Re: Circuit breaker questions AC
    Now the bad news:
    Legally you can not do it this way because it would allow the inverter's output to energize the utility lines should someone forget to turn off the main breaker. This requires some form of interlock to prevent the AC OUT from being active if the main is also on. It may be possible to fashion and acceptable means of this with your existing main service, depending on its design.

    This is why it is usually done with a sub-panel, allowing the inverter to do the auto-transfer in the event of an outage.

    Keep in mind that the inverter can really only handle two 15 Amp circuits.

    I hate to be perceived as thick headed, but even with a sub-panel there would still have to be an additional transfer switch (outside of the inverter) to power the sub-panel/critical loads or they wouldn't be available during normal grid operation, so the breaker box and the interlock kit, (which necessitates the main to be off for the critical loads to be powered) that I posted links to in my original post should work and be legal?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Circuit breaker questions AC
    verdigo wrote: »
    I hate to be perceived as thick headed, but even with a sub-panel there would still have to be an additional transfer switch (outside of the inverter) to power the sub-panel/critical loads or they wouldn't be available during normal grid operation, so the breaker box and the interlock kit, (which necessitates the main to be off for the critical loads to be powered) that I posted links to in my original post should work and be legal?

    Nope.
    There's a transfer switch built in to the GVFX. Normally any critical loads connected to its AC OUT are powered by the utility whenever AC IN is active.

    The only reason for dividing it up the way I described is to reduce the current potential on the AC IN circuit (only has to be enough to power the inverter in charge mode as no loads would be carried on that wiring). Hence my original wiring description:

    MAIN SERVICE <---> GVFX ---> CRITICAL LOADS