Grounding Question

nastynasty Solar Expert Posts: 35 ✭✭
Hello
Does this look right for grounding? Do I need a bond between the neutral and ground? If so can I make it from ground bus to the negative tie point? There is also going to be a Morningstar 300 inverter that will be wired into the AC load panel with a transfer switch between it and the other 1000w inverter that has a GFCI. Any advice would be appreciated. Hopefully the picture is clear.
Attachment not found.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grounding Question

    Ah, another notorious GFCI outlet inverter.

    Do not connect the neutral to ground at the AC panel. There is already a N-G bond in the inverter, before the GFCI.

    If you are going to add a MS 300 later, you will need to bond one of its AC OUT leads to ground, and switch both AC lines and the ground connection to the AC load center. Otherwise you will run into the ground loop problem that keeps cropping up on the forum; where an alternate path exists around the GFCI detection on the neutral line.

    You will probably end up pulling the GFCI outlet from the inverter, replacing it with a normal one, and putting in one neutral-ground bond in the distribution box. Any ground fault protection can then be added at the point of use.

    These built-in GFCI outlets seem to be no end of trouble, even when they work right.
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Re: Grounding Question

    Normally, most people put a heavy jumper wire from the battery ground bus to the earth ground rod (or ground bus common in your drawing).

    Connecting the AC output to earth ground ("white wire" made into AC neutral) is done to meet the electric code.

    For very small AC systems--it is debatable if grounding the AC output White Wire is really needed or not for safety.

    This gets into the questions of why earth ground...
    1. Ground to allow the use of only one terminal breakers in "hot side" (black/red wire) of wiring. The difference between a single breaker on 120 VAC wiring vs dual ganged breakers for 240 VAC wiring with two hots. For a 300/600 watt inverter and 14 awg wiring--There will never be a need for a fuse/breaker in the output (5 amps maximum will never trip a 15 amp breaker).
    2. Shock hazard--A floating output AC TSW inverter (like the MorningStar) will never shock anyone if one lead is touched (like touching one terminal on a battery--no current flow). If you earth bond one lead making a white/neutral lead, then touching the other black lead can cause a shock.
    3. If you have static electricity or lightning in your area--A grounded neutral will help shunt "high voltage" on the AC output to earth ground.
    4. A few devices work better with a grounded neutral... Florescent tube fixtures start better; Some spark type gas ignition systems (store/water heater/etc.) need a grounded neutral to sense the flame.
    5. If GFI outlets are installed (probably not recommended for MSW inverters--may cause false trips), I would install them at the outlet where used instead of the main inverter output (for a cabin/home). If you have a GFI trip at the sink, a single GFI on the inverter output will kill all AC power to the cabin--Leaving you in the dark (if you have AC powered lighting).

    If this is a small system with only a couple of connections (charging laptop, a few lights, radio, etc.)--floating the AC output would be fine.

    If this is a cabin and permanent wiring (especially if it may grow later and/or you have lightning in the area), I would concider bonding the AC output white wire and making it a grounded neutral.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nastynasty Solar Expert Posts: 35 ✭✭
    Re: Grounding Question

    Thanks for the replies. So if I remove the GFCI from the big inverter and hard wire it and the MorningStar to a transfer switch and then to the distribution panel I can use GFCI outlets and be good to go? Will I still need to ground one hot wire in both inverters and then to the common ground bus along with ground from distribution panel ground bus?
    Quote: For a 300/600 watt inverter and 14 awg wiring--There will never be a need for a fuse/breaker in the output (5 amps maximum will never trip a 15 amp breaker). Are you saying I shouldn't use breakers in distribution panel when I use the MorningStar? I was planning on using a transfer switch between inverters and common breakers. Sorry if I'm being dense I just want to get it right.
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Re: Grounding Question

    You do not need to use any breakers... The output of the inverter is less than the maximum current capability of the wiring (and in the US, 14 awg/15 amp rated wiring is the smallest standard AC circuit). I believe the MonringStar TSW 300 watt inverter has something like a 3 ap fuse recommended for their output wiring--But that is significantly less than the 10 minute 600 watt rated output (3amps * 110 volts = 330 watts max).

    If you ever plan on installing a larger inverter and/or a backup AC Genset, then having breakers already there will help limit the cost/work of upgrading.

    Also, it is sometimes nice to break even smaller installations into several circuits... At least two would be my recommendation. One for lighting and a second for everything else. You could even have a third circuit for stuff you only want to turn on manually (i.e., TV, games, etc.) or a small circuit for running cell phone chargers, a couple lights, alarm system, etc.

    Usually, those types of options are easier to do during installation vs adding later. You can "home run" multiple circuits (one to lights, another to outlets, outside outlets, etc.) and put them all together (for now) and add a box+breakers later.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grounding Question

    You can ground one leg of each inverter providing they both are entirely separate from one another on the AC side. It is easier to get around this by making one neutral-ground bond at the distribution panel and leave the inverters "floating". That way whichever one is supplying the AC will have the connection while in use.

    What Bill was saying about the AC out on the 300 Watt inverter is that the inverter's capacity in Amps is way below 15, so the breaker will never trip before the inverter faults. You can use them to expedite wiring, but they aren't actually going to provide any circuit protection because the current can never get that high (600 surge Watts / 115 Volts = roughly 5 Amps).
  • nastynasty Solar Expert Posts: 35 ✭✭
    Re: Grounding Question

    I do plan on having three circuits like Bill said but without breakers how do I wire them if I dont have breakers? My 1000w inverter manual states peak output is 25A. I am not understanding what Bill means by "home run" and "put them all together". Thanks once again. Is a transfer switch between the inverters the best way to select between the two? The 300w will be used the majority of the time, probably 80-90% of the time. Thanks once again for your help. If there was a solar installer that I could get to travel to my place I would definitely go that route.
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Re: Grounding Question

    Home run (one set of wires from each load back to the power source--sometimes called a "star" pattern):
    [FONT=fixedsys]Battery Bank ================load1
                 +
                 ================load2
                 +
                 ================load3[/FONT]
    

    Daisy Chain (one set of wires from power source to first load, then to second load, then to third load):
    [FONT=fixedsys]Battery Bank =========+==========+=========load3
                        load1      load2[/FONT]
    

    With the Home Run, you can can wire all three leads together (wire nuts, bus bars), or wire to a panel (with breakers, one for each run), or even "light switches" so you can turn on and off specific runs (loads/appliances/lighting/outlets).

    Most "good inverters" can source upwards of 2x their rated power (for a few cycles to a few minutes). So your inverter can source 1,000 watts continuously and 2,500 watts for a short period of time (starting a motor, etc.).

    It does get a bit more confusing with AC power... There is something called the "power factor" that, more or less, is how efficiently the current is used by the load.

    An induction motor may use only 0.66 (~66%) of the current for turning the motor... the rest of the current is moving in the wire, but not doing any work... So, a 300 watt motor may need:
    • VA (Volt*Amp) = Watts/PF = 300 Watts / 0.66 = 455 VA

    So, it is possible in the above case to pull ~300 watts from the battery bank but drive 450 VA to the load.
    • Power/Voltage = Amps = 300 watts / 120 VAC = 2.5 amps (assuming PF=1.0)
    • Power/(voltage*PF) = Apparent Amps = 300 watts / (120 VAC * 0.66 PF) = 3.8 Amps (this is current flowing through the wire supplied by the inverter)

    Induction Motors, many power supplies and battery chargers, many CFL type lamps, etc. can have "poor" power factor... In the range of 0.50 to 0.70 -- Ideally, all devices would have PV~1.0 (or 0.95) as this is the most "efficient"--But it does cost extra money to achieve this for many devices.

    Anyway, it is not unusual for a motor/AC/ and other devices to easily draw 3-5x their rated load on startup (first few AC cycles to a few seconds for starting a compressor, as an example). Generally fuses and breakers are rated to pass starting surges for a few seconds before they blow/trip (45 amp surge on a 120 VAC 15 amp circuit was common with the older computer equipment I used to work with in decades past).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Re: Grounding Question

    Regarding two inverters (high power and low power as an example)...

    You might be better off wiring your "low power" loads (cell phone chargers, laptop computer, TV, modem/satellite receivers, etc.) to the "low power" TSW inverter.

    And run separate cabling to your "high power"/less critical loads (washer, hand tools, electric mixer, etc.) to your high power (possibly MSW) inverter.

    Many hardware stores have "orange" outlets--You can put those on your "low power" wiring and use the standard white/ivory on the high power outlets (it was common to use orange outlets for battery/UPS backed outlets in our server/security rooms).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grounding Question

    We are talking AC wiring here, not DC.

    If you're leaving out the breakers you need three bus bars: one for ground and one for neutral as you would normally have, and a third one to tie all the "hot" wires to.

    As Bill mentioned, you may want to simply wire some things to one inverter and some things to the other. For instance if you have everything connected to the small inverter and someone switches on a heavy load, the lights go out. If you have the heavy load outlets wired separately to the large inverter that can't happen. You just have to remember to turn it on when needed. The small inverter can stay on all the time, or run in "standby" mode (although some loads may be too low current to switch it on).
  • ywhicywhic Solar Expert Posts: 612 ✭✭
    Re: Grounding Question
    We are talking AC wiring here, not DC.

    If you're leaving out the breakers you need three bus bars: one for ground and one for neutral as you would normally have, and a third one to tie all the "hot" wires to.

    As Bill mentioned, you may want to simply wire some things to one inverter and some things to the other. For instance if you have everything connected to the small inverter and someone switches on a heavy load, the lights go out. If you have the heavy load outlets wired separately to the large inverter that can't happen. You just have to remember to turn it on when needed. The small inverter can stay on all the time, or run in "standby" mode (although some loads may be too low current to switch it on).

    Wait.. so I can put a small MS300 into a panel and a larger inverter into the same box and leave the smaller MS300 on all the time??

    When I turn on the larger Xantrex 2000w inverter to drive a larger load (like my A/C) I can leave the smaller one connected on the same 110 circuit panel??

    I want to have all the outlets in my cabin going into 1 panel.. then feed it from that 1 panel from the inverter(s)..

    So I would feed the 1 'panel' with both inverters with no issues?? won't the larger inverter push juice back into the smaller inverter??
    (or am I over thinking this again??)

    ETA: Can I run the MS300 pure sine and add a 2300 MSW inverter (if I wanted too) to run the larger loads??
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grounding Question
    ywhic wrote: »
    Wait.. so I can put a small MS300 into a panel and a larger inverter into the same box and leave the smaller MS300 on all the time??

    When I turn on the larger Xantrex 2000w inverter to drive a larger load (like my A/C) I can leave the smaller one connected on the same 110 circuit panel??

    Not exactly: the AC outputs from the two inverters must be separate. Only inverters designed to be "stacked" can share AC output connections.
    I want to have all the outlets in my cabin going into 1 panel.. then feed it from that 1 panel from the inverter(s)..

    So I would feed the 1 'panel' with both inverters with no issues?? won't the larger inverter push juice back into the smaller inverter??
    (or am I over thinking this again??)

    If both inverters are true sine they can share common neutral with ground bond in the box, but the hot lines must be separated.
    ETA: Can I run the MS300 pure sine and add a 2300 MSW inverter (if I wanted too) to run the larger loads??

    Not together: AC outputs of those two are totally incompatible; hot and neutral both need to be separate.
  • ywhicywhic Solar Expert Posts: 612 ✭✭
    Re: Grounding Question

    I could bring the 2 separate HOTS into the box via breakers to the one 'backbone' to the outlets. (Keeping in mind the ground neutral mess and keeping all leads separate..)

    Run the MorningStar 300 Pure Sine all day long.. and if needed shut off / disconnect that breaker..

    Flip the other Xantrex Pure Sine inverter breaker ON for use with the hi-power load though correct..

    Go back to the other by switching it back..
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grounding Question

    Another caveat: if one of the inverters has GFCI output, don't connect it to the other.

    The usual way of using the two inverter system is to separate the AC loads into high and low Wattage, and never the two shall meet. If you switch between using just breakers there is always the chance of having both on at the same time. That would be bad.
Sign In or Register to comment.