transfer switch for off grid power

I recently purchased a manual generator transfer switch (like one here: http://reliancecontrols.com/ProductDetail.aspx?30216A ) and wanted to hook it up to where I have my off grid inverter power feeding into an IOTA ITS 30-R automatic transfer switch wired to the normally closed connection. My generator would be wired to the normally open connection, overriding solar power when started.

The output of the IOTA switch would then feed into the Reliance manual transfer switch and connect to the six breakers in my main panel.

My question is how do I wire the Reliance transfer switch for neutral and ground when connecting to my main panel? My main concern is creating a grounding loop from solar power (DC is grounded at negative terminal) conflicting with the transfer switch neutral and ground tying into the main panel.

I'm sure someone has done something like this before, so any suggestions would be appreciated.

Comments

  • CariboocootCariboocoot Posts: 17,615Banned
    Re: transfer switch for off grid power

    Must be having a senior moment as I don't see why you need two transfer switches to change your AC feed between generator and inverter.

    A transfer switch has one output and two inputs. The output goes to the AC breaker box. One input goes to the inverter's output, one goes to the generator's output.

    If you have one of the inverter/chargers it has AC IN which means it has a built-in transfer switch.

    Ground wiring should not be affected by any transfer switch, as all grounds should be connected together at all times and terminate in a single Earth ground point. The only time you get in trouble with this is using an MSW inverter which can not have the AC neutral-ground bond. In that case you leave the bond out and let the neutral "float". Check to make sure the generator doesn't already have this bond in any case, as you don't want two such connections.

    Again, I don't understand what you're trying to achieve with two transfer switches. Is grid power available as well?
  • czyhorseczyhorse Posts: 42Solar Expert
    Re: transfer switch for off grid power

    Sorry...forgot to clarify.

    My main breaker panel is set up for utility grid power. I'm attempting to have a central switching point to divert power to selected breakers when utility power is lost. The manual switch is to divert from utility power, and the IOTA is to switch from solar power to generator power when necessary.

    My off grid is solely for emergency backup.

    Hope that makes sense....
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: transfer switch for off grid power

    Yes, that fills in the missing pieces. :D

    So your manual transfer switch will change the critical load(s) between utility power and emergency back-up. The auto switch will change the emergency back-up feed between generator and inverter. Or you might want to have the auto switch change the critical loads to back-up and manually swap between inverter & generator. Whichever works better for you.

    Now, what have you got for an inverter? That will also be important to the equation.
  • czyhorseczyhorse Posts: 42Solar Expert
    Re: transfer switch for off grid power

    My inverter is an Exeltech XP1100. My solar and utility grid systems have separate ground rods though, therefore I don't know if my plan will work.
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: transfer switch for off grid power

    Okay, so not an inverter-charger. You could really automate this project with one of those.

    Are you sure 1100 Watts is a large enough back-up? That auto switch has a 60 Amp capacity (for two sides) on 120 - that's 7200 Watts. You should make sure that the Exeltech isn't trying to feed that much when the emergency power kicks on. Basically your inverter is capable of handling "one outlet worth" (not even full capacity there). What are you trying to protect? Refrigerator?

    Sorry to sidetrack.
    So you'll hook up the auto switch to handle power coming either from utility or emergency sources.
    The emergency sources being either the inverter or the generator, which you'll select manually with the other transfer switch.

    Keep in mind the utility, auto switch, and second transfer switch are designed with two poles for handling 240 VAC whereas the inverter is only 120 VAC - one pole. Which your generator is I don't know. I mention this because if you have the Exeltech's output connected to the wrong input side on the auto switch the wrong thing, or perhaps nothing, will be powered up when it changes over. You do not want to try to supply both sides of the 240 input on the auto switch with the inverter's 120 VAC output.

    Grounds. I don't know how you have it wired now, but there's no reason I can see that both systems can't share the same Earth ground point. A separate post for the inverter isn't necessary; you should be able to connect its ground to the house system. If anyone knows why not, they'd better speak up now before he follows my advice and possibly does something wrong.

    Some of this stuff is a bit hard to explain over the internet. :blush:
  • dwhdwh Posts: 1,332Solar Expert
    Re: transfer switch for off grid power

    The key thing is the neutral -> ground bond. That should be done in the main panel. It should NOT be done anywhere else.

    So make sure the neutral and ground are not bonded in the Reliance box (they almost certainly won't be, but make sure).

    Make sure the neutral and ground are not bonded anywhere else - not at the generator and not at the inverter. Depending on the generator, neutral might be bonded to ground at the factory. If so, then you need to "lift" (disconnect or remove) that connection or bonding jumper.


    Then there is the inverter...

    According to the Exeltech XP1100 manual:

    http://www.exeltech.com/downloads/xp600-1100manual.pdf

    "WARNING: The AC neutral lead is bonded to chassis through the barrier terminal strip connector located on the back of unit. Chassis must be bonded to earth ground through the external ground connector located on the rear of the unit.
    (See Appendix C)"


    You DON'T want the neutral bonded to ground in the inverter because it is already happening in the main panel. Appendix C shows a "bonding strip" installed across the neutral and ground terminals in the inverter. You need to remove that bonding strip.


    As for the grounding...the manual also states:

    "The Negative or Positive terminal of the battery (DC Source) must be bonded to earth ground. It's recommended that it be to the same earth ground used for AC ground."

    No problem.



    So you lift the neutral-ground bond in the inverter and run the hot and neutral to the Iota. You run a ground wire from the ground terminal to the ground bus bar in the Iota.

    Same with the generator - make sure neutral and ground are not bonded, run the hot/neutral to the Iota and run a ground wire from the gen frame to the Iota ground bus. The gen frame is required to be grounded if you are feeding a building with it.


    Then you run hot/neutral from the output of the Iota - along with a ground from the Iota's ground bus - to the Reliance and hook up the Reliance to the main panel according to the Reliance manual.



    The only question is the ground rods. You say there are more than one and the DC negative is grounded to the second rod. If that second rod is far away at the PV array then no problem. If it's right next to the main panel ground rod, then you should really have everything going to just the one rod.
  • sprintmansprintman Posts: 16Registered Users
    Re: transfer switch for off grid power

    I am planning to do a similar thing. While I don't have my panels yet I do have my manual generator transfer switch which ties into my homes panel and will control 6 circuits. My plan will be to run these circuits on solar every day and go to grid only if I have to. I've hopefully determined my panel needs based on the estimated daily demand of these 6 circuits. Just as a note of clarification, I plan no use of a generator I will just hook my inverter into this switch instead.
  • tmarchtmarch Posts: 142Solar Expert
    Re: transfer switch for off grid power
    sprintman wrote: »
    I am planning to do a similar thing. While I don't have my panels yet I do have my manual generator transfer switch which ties into my homes panel and will control 6 circuits. My plan will be to run these circuits on solar every day and go to grid only if I have to. I've hopefully determined my panel needs based on the estimated daily demand of these 6 circuits. Just as a note of clarification, I plan no use of a generator I will just hook my inverter into this switch instead.

    Is there a automatic transfer switch made that would basically use PV power until grid power is needed?
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: transfer switch for off grid power
    tmarch wrote: »
    Is there a automatic transfer switch made that would basically use PV power until grid power is needed?

    :confused: If you've got grid, why would you have off-grid PV power? It's really expensive per kW hour.

    Grid-tied solar works seamlessly with the grid. All household needs supplied by PV if enough is available, grid power used if not, surplus PV power sold back to grid if allowed by the utility.

    But yes there are inverters which could be set up to utilize the grid as a "generator" and cut it in if battery Voltage falls below a set point.
  • ggunnggunn Posts: 1,972Solar Expert
    Re: transfer switch for off grid power
    tmarch wrote: »
    Is there a automatic transfer switch made that would basically use PV power until grid power is needed?

    You cannot power your protected AC loads with PV alone; you have to have a battery bank and an inverter that can deal with battery voltages to make it work. Be prepared for sticker shock.
  • SevenSeven Posts: 292Solar Expert ✭✭✭✭✭✭
    Re: transfer switch for off grid power
    :confused: If you've got grid, why would you have off-grid PV power? It's really expensive per kW hour.
    There are several reasons that come to mind. Not all of them would be accepted as rational.
    Hobby... building a PV system can be fun. It is always a learning experience. It is cheaper than building a hot rod. Some people just need to do something to keep them occupied.

    Independence/security.... Having just a few circuits that are off grid means that if something bad were to happen and the grid was lost you still have some power. This covers some storms, car accidents that hit poles, or even a huge rate hike.

    Going green.....Less usage from the grid is less usage.

    Is it cost effective when grid is there, no. Are there more expensive hobbies, yes. Sometimes people just want to say I did it just because. Having a working PV system is something to be proud of, for whatever the reason. If you have some spare cash and are in need of a hobby, PV lets you do something that is good for the enviornment, good for the mind and body, and is much better all around than going to a bar. That last part is what the missus tells me anyway.
  • rimzanrimzan Posts: 5Registered Users
    Re: transfer switch for off grid power

    I totally agree with you Seven
    Seven wrote: »
    There are several reasons that come to mind. Not all of them would be accepted as rational.
    Hobby... building a PV system can be fun. It is always a learning experience. It is cheaper than building a hot rod. Some people just need to do something to keep them occupied.

    Independence/security.... Having just a few circuits that are off grid means that if something bad were to happen and the grid was lost you still have some power. This covers some storms, car accidents that hit poles, or even a huge rate hike.

    Going green.....Less usage from the grid is less usage.

    Is it cost effective when grid is there, no. Are there more expensive hobbies, yes. Sometimes people just want to say I did it just because. Having a working PV system is something to be proud of, for whatever the reason. If you have some spare cash and are in need of a hobby, PV lets you do something that is good for the enviornment, good for the mind and body, and is much better all around than going to a bar. That last part is what the missus tells me anyway.
  • ChrisOlsonChrisOlson Posts: 1,807Banned
    Re: transfer switch for off grid power
    Must be having a senior moment as I don't see why you need two transfer switches to change your AC feed between generator and inverter.

    There is a logical reason to do this for an off-grid installation too. We have one:

    Attachment not found.

    The inverter feeds the "On Line" input and the generator feeds the "On Aux" input. The reason we have it is because if something happens to the inverter where it has to be pulled out of the system, the switch can be flipped so we can keep our power on while the inverter is pulled out. If you rely just on the inverter's AC2 input and internal transfer switch the power from the generator is still going thru the inverter and it makes it hard to service it or replace it if something goes wrong with it.
    --
    Chris
  • NorthGuyNorthGuy Posts: 1,925Solar Expert
    Re: transfer switch for off grid power
    ChrisOlson wrote: »
    The reason we have it is because if something happens to the inverter where it has to be pulled out of the system, the switch can be flipped so we can keep our power on while the inverter is pulled out. If you rely just on the inverter's AC2 input and internal transfer switch the power from the generator is still going thru the inverter and it makes it hard to service it or replace it if something goes wrong with it.

    I have a manual bypass too. It looks different but accomplishes the same function.

    XW Control Panel (which I don't have) has sort of a transfer switch made up from breakers, which let you feed the generator (or grid) directly to loads bypassing the inverter.
  • ChrisOlsonChrisOlson Posts: 1,807Banned
    Re: transfer switch for off grid power
    NorthGuy wrote: »
    XW Control Panel (which I don't have) has sort of a transfer switch made up from breakers, which let you feed the generator (or grid) directly to loads bypassing the inverter.

    Yes, the inverter AC Bypass. We don't have the XW Distribution Panel either. But I made a AC Bypass for it out of a SquareD QO Loadcenter with two 60 amp breakers and a SquareD QO2DTI interlock:

    Attachment not found.

    I have our backup generator hooked up to the AC Bypass. If something happens to the inverter and the Honda at the same time, I can flip the AC Bypass and keep the power on with the backup. Over the years I've learned that having backups to backups can help insure that Murphy does not rule the day. :D

    --
    Chris
  • ChrisOlsonChrisOlson Posts: 1,807Banned
    Re: transfer switch for off grid power

    The first photo of our transfer switch was an old one. It has changed with the XW system

    Attachment not found.

    We now have a 70 amp box for the generator with a breaker in it that turns off the power to the inverter's AC2 input. But the power stays on to the transfer switch "On Aux" input from the generator because it does not go thru that breaker. And then I added a generator disabling switch for servicing the generator, as well as a momentary SPDT switch for manual starting and stopping of the generator.
    --
    Chris
  • KnowledgeSpongeKnowledgeSponge Posts: 163Solar Expert ✭✭✭✭✭
    Re: transfer switch for off grid power
    :confused: If you've got grid, why would you have off-grid PV power? It's really expensive per kW hour.

    Can you clarify this please?
    Suppose someone GAVE you EVERYTHING" you needed for a high quality 2Kwh per day solar power system.
    What is the "Cost" per Kwh then?
    I know, unlikely scenario, but please play along for a sec.

    Or...
    Suppose you already have everything you need to generate 2Kwh in your garage but it's just sitting in storage.
    Is it cheaper to let it just sit there and use all grip power or would it be economical to put it to use and generate "Some" power in lieu of grid power?

    If you can go long enough and generate enough Kwh without having to spend more money, don't you reach a break even point after which you would actually see a savings?

    I ask these questions sincerely because I don't know. Everyone says "Solar Power is Expensive"....but is it "relative" or "Absolute" ?
    Is there some "hidden" costs I'm not aware of?
  • ChrisOlsonChrisOlson Posts: 1,807Banned
    Re: transfer switch for off grid power
    I ask these questions sincerely because I don't know. Everyone says "Solar Power is Expensive"....but is it "relative" or "Absolute" ?
    Is there some "hidden" costs I'm not aware of?

    It's all relative to grid power costs. It's costs more to live off-grid than it does on-grid if you want to maintain the on-grid lifestyle. Most people who live off-grid live pretty spartan and watch every watt because it costs lots of money to generate off-grid power.

    HOWEVER - it don't matter for somebody who's on-grid that wants to put in an off-grid power system if you forget the economics of it. Too many people get wrapped up in the economics and forget that there's other reasons for wanting to do it. You might do it just to generate some of your electricity. It's fun. It's a learning experience. It might be a hobby - and I know people who spend money on hobbies where the money spent is "wasted" one heck of a lot worse than spending it on a RE system for your home.

    There's a few that think they're going to save money on their utility bills by putting in a solar electric or wind power system for their home. Sure, they might save some money on the bill, but it's going to cost them more to do it than what they save. Once you throw the economics out the window and put a different reason to it, it's one of the more worthwhile and rewarding things you'll do.
    --
    Chris
  • NorthGuyNorthGuy Posts: 1,925Solar Expert
    Re: transfer switch for off grid power
    I ask these questions sincerely because I don't know. Everyone says "Solar Power is Expensive"....but is it "relative" or "Absolute" ?

    Everyone pays a different price. For example, Chris would have to pay over $100K just to connect to the grid. Or my electric company wants me to pay them $75/month if I decide NOT to use their power, just for a "privilege" of having an electric pole on my property. In such cases, solar power will be cheaper. On the other hand, if you pay $5/month for service and $0.10 per kWh, no way you can beat this with solar.
    Is there some "hidden" costs I'm not aware of?

    Since you're providing your solar power to yourself, there's no costs that you wouldn't be aware of. Unless you're a really good salesman ;)
  • BB.BB. Posts: 24,676Super Moderators admin
    Re: transfer switch for off grid power

    To figure out your $$$/kWH or what ever you like to use... It is really simple to estimate:

    (cost of hardware+cost of labor+cost of batteries+cost of battery+hardware repairs/replacements every ~10+ years for 20 year system life) / (number of kWH per year your system will generate * 20 year life of system)

    Similar to generated power estimated costs:

    (total cost of genset + costs of maintenance+oil) / (expected hours of life) = $$/hour of operation

    added to the cost of fuel:

    (kWH per year * Gallons per kWH * $/gallon for fuel) / (hours per year of operation) = $$/kWH fuel costs

    $/operational hour + $/fuel cost per hour = estimated generators cost per hour

    It will usually range in the ~$0.50 to $1.00 to $2.00 per kWH. $0.50 per kWH for off grid solar power is really inexpensive and usually only by people that get used hardware, do their own install/maintenance, and have a fair bit of luck (also called good planing and maintenance).

    And $1 per kWH for fuel costs alone (or worse) is probably a good starting point. (~3.5 kWH per 1 gallon of gasoline / $3.50 per gallon gasoline)

    You can stretch the numbers (more efficient diesel, making sure you run the genset > 50% rated load, purchase used fork lift batteries and keep them well maintained, or purchase very inexpensive golf cart batteries and keep them maintained). Also, sizing the system to your needs--I.e., no larger battery bank / generator bank than you need. "Over-sized" battery banks and generators can be very costly (big battery banks cost a lot of money to replace, and big generators drink a lot of fuel per hour).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NorthGuyNorthGuy Posts: 1,925Solar Expert
    Re: transfer switch for off grid power
    BB. wrote: »
    It will usually range in the ~$0.50 to $1.00 to $2.00 per kWH. $0.50 per kWH for off grid solar power is really inexpensive and usually only by people that get used hardware, do their own install/maintenance, and have a fair bit of luck (also called good planing and maintenance).

    If everything went as planned, my cost would be within $0.25-0.30/kWh, but I did all the work by myself. In reality, it is a little bit more than this mostly because we consume less than I though and the cost of the system is still the same. So, when this cost get spread over the lower number of kWh, the cost/kWh goes up. If we consume even less, the cost per kWh will be even higher - just to show you how useless $/kWh is when appied to off-grid system.
  • ChrisOlsonChrisOlson Posts: 1,807Banned
    Re: transfer switch for off grid power
    NorthGuy wrote: »
    just to show you how useless $/kWh is when appied to off-grid system.

    Agreed. The location many of us have chosen for our off-grid homes, and the independence we have, is worth more than putting $/kWh to it.

    And don't forget that for people who live on the grid that an off-grid power system can help keep critical things alive during a power outage such as 'fridge, freezer and lights. There's no real way to put a $/kWh figure to that when your place is lit when the power goes out while while the neighbor's place is dark as a black hole at midnight.
    --
    Chris
  • waynefromnscanadawaynefromnscanada Posts: 3,009Solar Expert ✭✭✭✭
    Re: transfer switch for off grid power
    ChrisOlson wrote: »
    It don't matter for somebody who's on-grid and wants to put in an off-grid power system if you forget the economics of it. Too many people get wrapped up in the economics and forget that there's other reasons for wanting to do it. You might do it just to generate some of your electricity. It's fun. It's a learning experience. It might be a hobby - and I know people who spend money on hobbies where the money spent is "wasted" one heck of a lot worse than spending it on a RE system for your home.
    Once you throw the economics out the window and put a different reason to it, it's one of the more worthwhile and rewarding things you'll do.
    Chris

    How true! Couldn't have said it better! I never did waste electricity, although I always used what I wanted/needed, as long as it was available. That non-wasteful attitude made me a perfect candidate for an off grid system. Between my solar and the wee hydro system, I have all I need and often more. It's an incredible feeling to be independent of the grid, and awesome not being aware that all your neighbors could be without power. If I was 30 years younger, I'd definitely cut the wires to the grid, but now I realize the day will come, if I live that long, when I won't be able to look after my system and it will fall into disrepair. When/if that day comes, I'll be glad to have the grid. Right now, the ONLY thing I use grid power for is to run the mini-split heat pump on milder days when the wood fire would make things too hot but I still need a little heat. But even that, if the sun is shining, I do use solar to run it for heat, and free AC most of the Summer!
    So far Nova Scotia Power is letting me away with it, but they did come change the meter to one of the new digital types a couple of months ago. They suspected the meter was bad, or I had frigged with it because of the low recorded usage. But it didn't do them any good, usage still didn't go up. Hahaha
    All around me there are folks threatening to stick a $300 solar panel on their roof so they can do away with their $ 300 to $400 per month power bill (just under 14 Cents/kwh), but for the life of me, I can't figure out why they haven't done it yet. :D:D:D
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