Xantrex MPPT Charge contoller and grounding

I just installed a Xantrex MPPT charge contoller using Midnite Solars MNDC disconnect power center. Now Xantrex is very clear that negative cannot be bonded to to ground or the GFP in the MPPT charge controller will be useless. This means that I cannot use the grounding block in the MNDC since that will effectively bond negative to ground. It also means that all of my ground connections go through the charge controller which has only 2 connectors. Do I need to use a shunt or ? in the MNDC250 to isolate ground from negative in order to use the grounding block in the MNDC?

On the AC side (which I have not done yet) I would have to assume that I can bond neutral to ground in the MNDC. Would this have any effect on the GFP protection built into the MPPT?

Thanks to all who respond...this forum is great!

Brian

Comments

  • Dave AngeliniDave Angelini Solar Expert Posts: 6,138 ✭✭✭✭✭
    Re: Xantrex MPPT Charge contoller and grounding

    Brian,
    It is easier if you look at it from the other way. The ground bar or UFER or whatever you DC ground is goes to the XWCC's GFCI. From there you can use whatever you have wired in your panel. All ground current has only one path thru the XWCC's GFCI.

    AC neutral bonding to ground only happens in one place and usually in your house panel. It does not effect your DC GFCI.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • bfitzgeraldbfitzgerald Registered Users Posts: 26 ✭✭
    Re: Xantrex MPPT Charge contoller and grounding

    Hi Dave

    Thanks for your reply but alas, I'm still confused. Here is what Midnite Solar says about the MNDC, grounding and GFP. This is from the MNDC manual posted on their web site. I wish I could draw a picture it would be easier...but if I run my system ground to the ground bus bar in the MNDC it sure seems like I have a negative to ground bond in the DC circuit. That's why I was wondering if I need to use a shunt or something to isolate battery negative from ground in the MNDC.


    Grounding
    There are various ground circuits that need to be considered in the renewable energy system. The MNDC chassis should be grounded to your earth ground rod through a 6AWG wire connected to the ground bus bar located in the top left section of the MNDC chassis. The MNDC ground bus bar will then become your primary system DC ground. The ground bus bar is also where DC lightning arrestors get grounded. It is advisable to use one of the ½” conduit knockouts to mount a DC lightning arrestor to the MNDC box. It is also common to have a DC lightning arrestor out at the PV Panels that are grounded through their own ground rod. In dry climates it is advisable to also run a ground wire from the PV panels to the MNDC ground. The MNDC ground bus bar is an ideal place to ground a DC-GFP when installed as well as the inverter chassis and the charge control chassis. Do the grounds first since they normally lie in the bottom of the chassis.

    Battery Negative connection
    The wiring diagram shows a 500 amp shunt. This is used to measure voltage drop across the shunt to aid in calculating battery state of charge. The shunt does not ground the battery negative circuit. If this shunt is not installed, then you may use the 5/16” stud directly above the shunt area as a battery negative tie point. Using this tie point will ground the battery negative to the chassis. Grounding the battery negative is not allowed when employing a DC-GFP device. The inverter side of the shunt or the 5/16” stud are also an ideal tie point for PV negative or other DC negative circuits.

    Brian
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,138 ✭✭✭✭✭
    Re: Xantrex MPPT Charge contoller and grounding
    Hi Dave

    Thanks for your reply but alas, I'm still confused. Here is what Midnite Solar says about the MNDC, grounding and GFP. This is from the MNDC manual posted on their web site. I wish I could draw a picture it would be easier...but if I run my system ground to the ground bus bar in the MNDC it sure seems like I have a negative to ground bond in the DC circuit. That's why I was wondering if I need to use a shunt or something to isolate battery negative from ground in the MNDC.


    Grounding
    There are various ground circuits that need to be considered in the renewable energy system. The MNDC chassis should be grounded to your earth ground rod through a 6AWG wire connected to the ground bus bar located in the top left section of the MNDC chassis. The MNDC ground bus bar will then become your primary system DC ground. The ground bus bar is also where DC lightning arrestors get grounded. It is advisable to use one of the ½” conduit knockouts to mount a DC lightning arrestor to the MNDC box. It is also common to have a DC lightning arrestor out at the PV Panels that are grounded through their own ground rod. In dry climates it is advisable to also run a ground wire from the PV panels to the MNDC ground. The MNDC ground bus bar is an ideal place to ground a DC-GFP when installed as well as the inverter chassis and the charge control chassis. Do the grounds first since they normally lie in the bottom of the chassis.

    Battery Negative connection
    The wiring diagram shows a 500 amp shunt. This is used to measure voltage drop across the shunt to aid in calculating battery state of charge. The shunt does not ground the battery negative circuit. If this shunt is not installed, then you may use the 5/16” stud directly above the shunt area as a battery negative tie point. Using this tie point will ground the battery negative to the chassis. Grounding the battery negative is not allowed when employing a DC-GFP device. The inverter side of the shunt or the 5/16” stud are also an ideal tie point for PV negative or other DC negative circuits.

    Brian

    I can't help you if you try to make this complicated. Someone elso can try to help. No there will not an extra shunt. Start from your ground bar go to the CC's GFCI then exit the CC to the MNDC and anything else you want grounded. If you do go to the MNDC first with ground (becausue it is easier) make sure that there is not a bond to (negative battery) anywhere.

    No ground connection is alowed on the negative battery NONE! Your shunt is there at the negative battery for current measurement! Do not feel bad as this can be confusing. Do it right or it will be worse than feeling bad! Good Luck!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • bfitzgeraldbfitzgerald Registered Users Posts: 26 ✭✭
    Re: Xantrex MPPT Charge contoller and grounding

    Thanks again for your reply. I get it, no bond to ground and battery negative. I do want to ground first in the MNDC as it also grounds the chassis. But by design using the battery negative terminal in the MNDC also bonds battery negative to ground if I ground in the MNDC. My original question was about how to get around this design feature. Am I still making this hard? Any ideas?

    Thanks

    Brian
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,138 ✭✭✭✭✭
    Re: Xantrex MPPT Charge contoller and grounding

    You should ask the manufacturer. I only have direct experience with Xantrex panels. Someone else???
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • bfitzgeraldbfitzgerald Registered Users Posts: 26 ✭✭
    Re: Xantrex MPPT Charge contoller and grounding

    Thanks Dave, I'll try that. In the meantime, does anyone else have any experience or ideas?

    Brian
  • wtwoods_azwtwoods_az Registered Users Posts: 18
    Re: Xantrex MPPT Charge contoller and grounding

    Hi Fitz: Hey, I have the same setup, MNDC-250 and XW SC (I have two). This is how I have it setup: BAT NEG to 500amp Shunt, which is isolated from DC Ground. From the other side of the shunt: DC NEG to SC #1, SC#2 and XW Inverter. SC#2 has the GFP fuse installed and is DC Grounded back to all of my gear, the metal cabinet and a ground rod. This works for me.

    You could use the ground stud in the MNDC to ground that box if you want - that's what I used it for, but like you said, you can't use it as a DC NEG distribution point unless you don't care about the GFP function. I wanted a shunt anyway, so for me it was the ideal DC NEG distribution point.

    Dave's right about AC ground: make sure that there is only a single AC ground point. If you install a sub panel, do not bond GND to Neutral. It is possible to create a parallel path for neutral current if this is done creating an unsafe condition with the potential for bad things happening.

    Take Care, Bill
  • mike95490mike95490 Solar Expert Posts: 9,572 ✭✭✭✭✭
    Re: Xantrex MPPT Charge contoller and grounding
    wtwoods_az wrote: »

    Dave's right about AC ground: make sure that there is only a single AC ground point. If you install a sub panel, do not bond GND to Neutral. It is possible to create a parallel path for neutral current if this is done creating an unsafe condition with the potential for bad things happening.

    Is there any distance limit on this idea? I've got a long run (about 400') from my inverter and power panel with ground, to a pumphouse, which currently has no ground rod, it's tied via neutral only, back to the inverter. At what point do I need a fresh earth ground? I'm going another 700' to ozone water filter at the tanks.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 32,612 admin
    Re: Xantrex MPPT Charge contoller and grounding
    mike90045 wrote: »
    Is there any distance limit on this idea? I've got a long run (about 400') from my inverter and power panel with ground, to a pumphouse, which currently has no ground rod, it's tied via neutral only, back to the inverter. At what point do I need a fresh earth ground? I'm going another 700' to ozone water filter at the tanks.

    That is the $64,000 question...

    I do not know how NEC treats this sort of grounding issue.

    The simple/safe enough way would probably be to keep the hot/neutral "isolated" all the way from the home to the pump house and keep the single AC ground tie at the home.

    Drive a ground rod at the pump house and ground the well casing+all exposed electrical connections to the ground rod.

    Another option would be to use an isolation transformer between the home and the well (or a second isolated inverter--typically TSW true sine wave type if off-grid) and send the isolated AC power from the home to the pump house and then ground the Neutral at the pump house. Obvously, this involves a lot of extra expense and possible extra power losses (isolation transformer, second inverter).

    The idea is to keep you electrically save at the pump house. Option one takes care of that pretty much--noting exposed can become "hot" with respect to local ground.

    However, if there is a Hot/Ground short or a Neutral/Ground short--you may not see it. The high resistance ground path between the pump house and the home may not trip the breaker if a short occurs.

    So, that then leads you to running a ground wire from the shed ground rod to the home ground rod. That would take care of a hot to ground short and trip the circuit breaker.

    Another option is a Ground Fault Interrupter on the Home to pump house circuit. that would detect leakage currents--but may not be practical... Many larger systems have more than 5 milliAmps of leakage current and you will get false trips.

    Unless an isolated transformer/system (option 2) will work for you--option 1 + tying the ground rods together probably makes the most sense.

    If you are in a lighting prone area--you may have problems no matter what you do (sort of separate solar power at the pump house).

    And leakage current can be an issue with "isolated ground"... At an old theme park I installed some equipment. I had a wire grounded at the tank and the system power 50' away and there was > 60 volts AC between them (I figured out after I got shocked touching two "grounds").

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • wtwoods_azwtwoods_az Registered Users Posts: 18
    Re: Xantrex MPPT Charge contoller and grounding

    Hi Fitz: I was about to reply and then I saw Bill's post. He pretty much covered everything. I was going to describe option #1 which he did as well.

    The only thing I would like to add is that it sounds like your equipment at the pumphouse isn't grounded now? Wow, no matter what else you do, let's fix that so we have you around for a long time. ....

    With the distances you mentioned, sounds like you don't live in downtown. Must be a nice ranch?

    Bill Woods
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,138 ✭✭✭✭✭
    Re: Xantrex MPPT Charge contoller and grounding

    Mike,
    Follow the single neutral bond rule! Always! It is the best way if you do not follow the rule to damage electronics! You do not want to hear the stories I could tell from jobs I have come in on late in the game! Lightning even more stories!

    At long distance, all local ground bars/UFER's need to be tied with a decent #6 and down to the ground that the main panels neutral bond point is using.

    There are some exceptions but at that point you are in the lightning damage specialty business and, they are not always right either.

    What are you doing to treat the pond water? RO?
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • mike95490mike95490 Solar Expert Posts: 9,572 ✭✭✭✭✭
    Re: Xantrex MPPT Charge contoller and grounding
    wtwoods_az wrote: »
    The only thing I would like to add is that it sounds like your equipment at the pumphouse isn't grounded now? Wow, no matter what else you do, let's fix that so we have you around for a long time. ....

    The remote pumphouse, is only "grounded" via the neutral wire, which is grounded way back at the power shed. 400' of #6 ground wire is not something I want to add to existing underground conduit, but a new ground rod is easily feasible. At least it's a 240V pump, so there should be no current flow in the neutral . L1 & L2 (both #6 ga) )handle all the main current, so only the timer (3W) and ozone system (60w) are 120VAC and have current on the existing #6 neutral .
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • mike95490mike95490 Solar Expert Posts: 9,572 ✭✭✭✭✭
    Re: Xantrex MPPT Charge contoller and grounding
    Mike,
    Follow the single neutral bond rule! Always! It is the best way if you do not follow the rule to damage electronics! You do not want to hear the stories I could tell from jobs I have come in on late in the game! Lightning even more stories!
    At long distance, all local ground bars/UFER's need to be tied with a decent #6 and down to the ground that the main panels neutral bond point is using.

    Does that mean pulling a new bare #6 wire for 400' ? I've got 3, #6 insulated in the conduit now, I don't know if I can pull another one at this point.
    photos at page 3 & 4 http://tinyurl.com/LMR-trenches
    There are some exceptions but at that point you are in the lightning damage specialty business and, they are not always right either.
    at least I'm in a low lightning area, with tall hills around this wiring.
    What are you doing to treat the pond water? RO?
    Triple-O ozone filter, bubbles ozone from bottom of tank, and has a mesh filter bag to collect gunk. Folks in the area like them. Likely add a 0.5 u carbon filter for drinking the ozonated water.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • wtwoods_azwtwoods_az Registered Users Posts: 18
    Re: Xantrex MPPT Charge contoller and grounding

    Hi again Fitz:

    I just came in from the backyard - it is 113 just now, the joy of Arizona in July, looks like a storm coming in from the East. I was pulling a CAT5 cable for my monitoring software and I was thinking about your install. I figured that you already had your wire run and I know what a pain it is to try to pull thru another conductor, especially the distances you are talking about. If it was me, I'd pull the neutral/ground connection and sink a 10 foot ground rod into the ground and ground all the pumphouse stuff to that. I'd also put at least one Delta Lightning Arrestor at the pumphouse (available from our sponsor: http://store.solar-electric.com/deliar.html) and another back near the main. Dave and Bill are very knowledgeable and probably the BEST way is 4-wires all the way to the main panel, I just don't know if that is feasible for you at this point.

    Bill sweating in AZ:cool:
  • BB.BB. Super Moderators, Administrators Posts: 32,612 admin
    Re: Xantrex MPPT Charge contoller and grounding

    Lift/don't connect the AC Neutral from the home to your pump-house ground--keep the AC Hot and Neutrals floating all the way back to your home.

    Is this a 120/240 H-H-N split phase system? Or is everything 120 VAC at the pump house? If the pump is 240 VAC and you have a 120 VAC light? Perhaps switch to a 240 VAC light and float the Hot/Hot leads, and use the Neutral as your bond between the pump house ground and the home ground.

    Otherwise, trench another ground wire (and perhaps bury 2-4" ABS sewer pipe so you can pull other-stuff if ever needed again...

    4pm and 72F degrees here south of San Francisco Ca. (has been a pretty cool summer so far for us).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,572 ✭✭✭✭✭
    Re: Xantrex MPPT Charge contoller and grounding
    BB. wrote: »
    Lift/don't connect the AC Neutral from the home to your pump-house ground--keep the AC Hot and Neutrals floating all the way back to your home.
    Is this a 120/240 H-H-N split phase system? Or is everything 120 VAC at the pump house? If the pump is 240 VAC and you have a 120 VAC light? Perhaps switch to a 240 VAC light and float the Hot/Hot leads, and use the Neutral as your bond between the pump house ground and the home ground.
    Otherwise, trench another ground wire (and perhaps bury 2-4" ABS sewer pipe so you can pull other-stuff if ever needed again... ......-Bill

    I wish I could. It was $5K to have 2 backhoes trench and refill. That's just not going to happen again. In the 900' trench, there is about 2 miles of pipe, (waters & electrics) and I'm just going to have to try to pull a ground wire in the existing conduit. I think I can pull a bare wire, insulation may make it too thick to wedge in there. Maybe I'll score a trench and drop a 1/2 conduit 12" down, and hope for the best .
    And looking back at a photo I took of the panel, I've got an inspector that wants a ground at each panel. I remember hearing we had to ground the panel to the building ufer ground. At least those 2 grounds are only about 6 ' apart. and won't have much potential build between them.

    powered by XW6048, so it's a split phase system, w/240V pump.

    I'll look into putting a couple Deltac arresters at the pumphouse too.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 32,612 admin
    Re: Xantrex MPPT Charge contoller and grounding

    If it is a 240 VAC pump and you have no 120 VAC items to run--you could rewire the neutral to be a safety ground instead. If you want a little 120 VAC at the pump house--you could wire up a switch and step-down transformer for 120 VAC when needed...

    Otherwise, I think that NEC would require 18" deep minimum--perhaps renting a small trencher would be be "good enough"...

    Regarding grounding the panels--I assume that you mean to Neutral/Bond in each panel. That is usually what we are trying to avoid. When this is done, significant amounts of AC current are now starting to flow through your safety ground.

    And, if the safety ground takes a different path than the neutral/hot wires--that is actually a violation of NEC code. Basically, all current carrying "circuit sets" need to pass through the same hole/conduit/metal box right next to each other.

    You do not want to (for example) pass A hot wire through one conduit/opening and a neutral/return wire through another conduit/opening. Because, you now have a differential magnetic field between the two wires (outbound and return) and can magnetically induce currents in the steel box/conduits... Causing localized heating (assuming the currents are high enough).

    So--the second box (presumably powered from the first box) should have a "floating/isolated" neutral bar... But the metal box itself should be safety grounded per NEC requirements.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,138 ✭✭✭✭✭
    Re: Xantrex MPPT Charge contoller and grounding

    Mike,
    This problem, and it is a big problem when you are the utility happens to people who are doing all the construction and just don't have the time. It can really take a chunk out of your wallet if your luck runs out!

    I will go back and read all this again but I can give you advice on what I have done for similar remote arrays and pumps.

    Your lucky that this does not have to run all time, I am thinking it is unatended and only used when you are "there"?

    If that is true, you have time to do this right? You want both systems at the same ground potential. The only way to do that is to bond them. The arrestors should be installed ASAP along with the local ground system. A #6 bare (minimum copper) wire even 2 inches under the soil must be added. Until then you should keep the two systems completely isolated if you even think there is going to be lightning.

    Some of that monsoonal stuff has creaped into all areas of California at one time or another. Our good friends in Arizona never mind helping us out here, do you guy's?
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

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