Battery Grounding

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Comments

  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Battery Grounding

    Interesting discussion...

    Home Power articles by Dankoff (HP #107, June/July 2005) and Freitas (HP #118, April/May 2007) seen to suggest grounding solutions similar to Wiles'. Are they all drinking at the same bar? ;)

    I can't answer the question about the why's and wherefore's of Wiles' expertise. But, he's widely published (i.e., IAEA, Home Power, Sandia, etc.), he trains and lectures, he consults (Solar Energy International, SEI), and he designs. In short, Wiles appears the be the guru of all things PV and the NEC.

    I agree that all of Wiles' accomplishments don't necessarily mean that he's always right. Look at what the JPL "experts" did with one of their Mars shots. But, if there's another expert that commands Wiles' level of respect and peer acceptance in this field, I'd like to know who he/she is.

    I like this opening comment from Freitas' article:
    "Ask ten renewable energy installers about system grounding and you'll likely get ten different opinions as to what the National Electrical Code (NEC) requires, and what the correct methods are to meet those requirements."
    Regards,
    Jim / crewzer
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Battery Grounding

    too bad he isn't here to discuss it with him seeing as how somebody accredited him. the proof is that he did address my initial inquiry and incorporated it into the rules, but he didn't go with my solution and imho he screwed up the answer. oh well.
    same bar? hmmm, maybe somebody slipped them something. they do seem to be beating the same drum.
  • System2System2 Posts: 6,290 admin
    Re: Battery Grounding

    So, I'm hanging my PV's off the southern peak of my shed roof. Thing is, the shed is clad both roof and all sides with steel. Guess I better ground that outer steel shell too.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Battery Grounding

    watchout as the nec man cometh, but has no bite in canada. now that does bring up something else now that you mention having an all steel building. what if you mount it on an all metal skyscraper? long way to ground i would think with no option of a seperate rod as wiles suggests. i know i'd get it attached to a beam that is surely attached to the other beams and grounded, but i don't know how they did your building wayne. if only a few stories high i would still ground the pvs with a ground wire and rod of its own, but if the building has its metal going to ground and a ground rod take your ground wire from the pvs to that rod and be sure it's tied to the electrical ground rod via underground tie.
  • System2System2 Posts: 6,290 admin
    Re: Battery Grounding

    Yeah, it's only single story, built just last month, especially to hold my winters firewood supply AND as a mount for the PVs. The PVs will have solid mechanical (metal all the way) attachment to the metal sheathing over the wood frame on concrete slab, building. PVs wired 24 volt, feeding MX-60, into 12 volt battery bank. The metal sheathing ends about 3 inches from the surface of the ground, so I had better connect everything to a common ground rod. I'm thinking the sheathing is thin, so a direct hit anywhere on the building would vaporize the area around the ground connection. In time, grass etc will grow up and be in contact with the sheathing all around the building. I know every time I hear of lightening, I'll be pulling all the switches. LOL
    Wayne
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Battery Grounding
    Living in the lightning capital of the US, I never understood the concept of grounding the PV frames, thats a couple hundred square feet of lightning attraction that at best will vaporize the ground wire and at worst cause your home to burn to the ground.

    In all my installations, with full written approval of the local inspectors my frames are left un-bonded to anything. the last thing I want is to be waving a flag at the next bolt of lightning to say HIT ME HERE and that is exactly what grounding the frames do.

    The problem with that theory is that it depends a lot on what else is in the area. If your pv panels are the highest object, grounded or not, they are very likely to get hit - and if the frames are not grounded, the nearest path to ground is usually through your system.

    We have seen ungrounded systems where the lightning flashed around all over the place seeking a place to find ground, and most of that was directly through the inverters. In the high static period you often get just before a strike, I have seen array wires sparking 4-6 inches to a grounded conduit.
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Battery Grounding
    So, I'm hanging my PV's off the southern peak of my shed roof. Thing is, the shed is clad both roof and all sides with steel. Guess I better ground that outer steel shell too. ...The PVs will have solid mechanical (metal all the way) attachment to the metal sheathing over the wood frame on concrete slab, building. PVs wired 24 volt, feeding MX-60, into 12 volt battery bank. The metal sheathing ends about 3 inches from the surface of the ground,
    Wayne,

    The 2005 NEC (section 690.43) requires that exposed non-current-carrying metal parts of PV module frames be grounded in accordance with section 250.134 or 250.136(A), regardless of voltage. 250.134 contains lots of discussion and cross references about permitted grounding methods.

    250.136 addresses “equipment considered effectively grounded”. Specifically, 250.136(A) considers electrical equipment secured to and in electrical contact with a metal rack or structure that is grounded per 250.134 to be effectively grounded. This probably addresses niel’s question above regarding skyscrapers.

    However, I suspect that the metal shell of your shed would not qualify as structural or as grounded. My take of the NEC is that you’d need a specific equipment grounding conductor from your array if you were to install your system in the U.S.

    I have no idea about what the CSA Canadian Electrical (CE) code requirements might be.

    HTH,
    Jim / crewzer
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Battery Grounding

    wiles (not applicable to you wayne, but there may be something similar for you) does say the pv frames and their mounts need grounded for the record. anyway wayne, the type of building you specify is difficult to ground properly as each piece of metal would need to be bonded electrically and that's quite a task for sure. if there is a metal beam that goes from the top and down the sides to the concrete, now that would be worth bonding if needed and tying to the ground rod, otherwise i would skip grounding the building itself and just place a couple of small lightning rods at the top ends of the building with ground wires and ground rods if you wish to do anything at all with it this being in addition to the pv frame grounding and tied together at ground. remember that more than one rod needs bonded together underground with at least #6.
  • System2System2 Posts: 6,290 admin
    Re: Battery Grounding

    Great info, thanks a lot guys, you've been a great help. Much of it, I kind of guessed at, not knowing for sure where I was going, but now have a rather firm idea and plans. The top of the rack is bolted tightly to the metal shell, for the full length of the building, so I'll ground the rack and add a couple of lightening rods for good measure and bond all gnd rods together. Sound good?
    Thanks a lot
    Wayne
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Battery Grounding

    sounds good. go for it.
  • icarusicarus Solar Expert Posts: 5,117 ✭✭✭✭
    Re: Battery Grounding

    No offense guys, but you have gotten far into the land of black magic for most of us simpltons out here.

    The original question was why or why not to ground the neg side of the battery bank. Here is my take. (Some of this is covered in other threads, so apologies for duplication.) My system and that of our neighbor(s) are all small (~150watts, 12vdc) off grid systems where NEC, CSA, doesn't really matter. We want safety and reliability. The answer as to grounding the DC side of things was answered for me lately as a result of multiple failures of a electronic voltage control unit on the genset. Mitsubishi's local people didn't do squat about identifying the problem. After the fourth failure in 3 or 4 years on my neighbors system, I was able to get some useful information out of Mitusbishi. It turns out that when you ground the batteries, and expecially if they share ANY ground wire with the AC side, you introduce a ground loop that will fight the electronics in the control unit.

    Since in small systems there is no electrocution hazzard from the batteries, and the potential fire danger is abated by proper fusing etc. grounding the batteries is not only unneeded, but potentialy harmful. That said, it is suggested that for lightning protection, the frames of the panels should be grounded, as well as any battery box that is metal where the batteries sit.

    This is the way that I have revamped my system. Since my panels are mounted on the house, if I get struck, I have all kinds of other trouble to contend with.

    This seems like a common sense pragmatic approach, without too much NEC conflict getting in the way. I'm curious to see what you guys think.

    Once again thanks everyone for your input. I find myself reading deeper and deeper into the forum, learning more than I should. I know just enough to be dangerous. (And killing time that I should be doing something else!)

    Icarus
  • sanitariusanitariu Solar Expert Posts: 33 ✭✭
    Re: Battery Grounding

    This is old thread but i will post how i did grounding.

    Attachment not found.

    This is my solar setup. I did not make lightning rod only ! I do not believe that attracting thunders is good.
    4 X 240watt Luxor, Victron Energy Multiplus Compact 24 volt 1200VA, electrodacus solar controller, 8 x WB-LYP160AHA LiFeYPO4 3.2volt
  • BB.BB. Super Moderators, Administrators Posts: 28,879 admin
    Re: Battery Grounding

    You did not ground the negative battery bus?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Battery Grounding
    BB. wrote: »
    You did not ground the negative battery bus?

    Just a guess.... maybe there is a DC GFP in the Victron. If you follow the Midnite Classic instructions, you do not ground the negative battery bus.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • sanitariusanitariu Solar Expert Posts: 33 ✭✭
    Re: Battery Grounding

    No i did not make battery negative grounded.
    Actually DC part do not have grounding. Only metal parts (chassis) of devices like morningstar controler, victron inverter, panel frames.
    Reading again Victron inverter manual says:

    "120V models: The neutral conductor of the AC output circuit of the Inverter is automatically connected to the safety ground during inverter operation. This conforms to National Electrical Code requirements that separately derived from AC sources (such as inverters and generators) which have their neutral conductors tied to ground in the same way as the neutral conductors from the utility tied to ground at the AC breaker panel. For models configured with a transfer relay, while AC utility power is present and the Inverter is in bypass mode, this connection (the neutral of the Inverter’s AC output to input safety ground) is not present so that the utility neutral is only connected to ground at your breaker panel, as required.

    230V models There is no connection made inside the Inverter from either the line or neutral conductor to safety ground"
    4 X 240watt Luxor, Victron Energy Multiplus Compact 24 volt 1200VA, electrodacus solar controller, 8 x WB-LYP160AHA LiFeYPO4 3.2volt
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Grounding

    None of the quoted section of the Victron manual has anything to do with the DC side.

    If there is no DC GFCI (as vtMaps suggests) then the negative battery terminal should be grounded.
  • sanitariusanitariu Solar Expert Posts: 33 ✭✭
    Re: Battery Grounding

    Strange but I still think different...
    If your generator says it needs a ground, ground it. If your inverter says it needs a ground, ground it. If your batteries do not have a factory sticker that says "ground the negative terminal", do not ground them because "Buba" says to. Unless "Buba" has a new inverter to give to you when your inverter burns up.
    Actually even NEC allows floating DC side. If i ground negative on the battery ... bad things can happen on my inverter if neutral on the inverter is connected to ground which is on any cheap inverter...
    4 X 240watt Luxor, Victron Energy Multiplus Compact 24 volt 1200VA, electrodacus solar controller, 8 x WB-LYP160AHA LiFeYPO4 3.2volt
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Battery Grounding
    sanitariu wrote: »
    Actually even NEC allows floating DC side.

    True enough. And when you have a floating ground, for safety the NEC requires fuses or breakers on BOTH positive and negative wiring.
    sanitariu wrote: »
    If your batteries do not have a factory sticker that says "ground the negative terminal", do not ground them because "Buba" says to.

    My flooded lead acid batteries do not have a factory sticker on them that says "this side up" Fortunately, I took Buba's advice and did not install them on their sides.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • sanitariusanitariu Solar Expert Posts: 33 ✭✭
    Re: Battery Grounding

    Yes i have 125A fuses on negative and positive side above on the picture.
    Still these grounding stuff is a little black magic for me... I hope i did it good enough.

    "Buba" was just a joke :)
    4 X 240watt Luxor, Victron Energy Multiplus Compact 24 volt 1200VA, electrodacus solar controller, 8 x WB-LYP160AHA LiFeYPO4 3.2volt
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Grounding

    I should have never wasted all that time and money on getting an education.
    I see that now. Too late. *sigh* :roll:

    Trust in Bubba; don't trust in an engineer. We should put that on coins.
  • BB.BB. Super Moderators, Administrators Posts: 28,879 admin
    Re: Battery Grounding

    The DC + AC Neutral "grounding issue" does depend on the specific AC inverter... Most TSW inverters have isolated AC outputs--And you can ground DC negative and AC neutral safely. Most MSW inverters have non-isolated AC outputs and should never have the AC neutral + DC battery outputs ground referenced at the same time--Makes a short through the MSW inverter. Read the manual(s) to be sure (and not all will tell you if safe or not).

    Just out of curiosity--Can you take a Meter and measure the AC and DC voltage on the battery negative terminal for me? I am curious to see what the floating battery bank bus voltage is.

    Note: Floating Voltage readings are only 1/2 the story--A DMM has very high internal resistance an can read high floating voltages, but there may be near zero amps (i.e., static build up and relatively non-hazardous) or 10-100's of amps available--that would be a second test/require analysis of the hardware to know for sure.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sanitariusanitariu Solar Expert Posts: 33 ✭✭
    Re: Battery Grounding

    I will take measures with pleasure.
    Just explain me what do you mean with: "Can you take a Meter and measure the AC and DC voltage on the battery negative terminal for me? I am curious to see what the floating battery bank bus voltage is."

    If i understood correct i did the following:

    I put my meter to DC scale. Put negative on my battery and positive on my ground (green) cable at the inverter. It shows 0.01V
    I put my meter to AC scale. Put negative on my battery and positive on my ground (green) cable at the inverter. It shows 0.00V
    4 X 240watt Luxor, Victron Energy Multiplus Compact 24 volt 1200VA, electrodacus solar controller, 8 x WB-LYP160AHA LiFeYPO4 3.2volt
  • BB.BB. Super Moderators, Administrators Posts: 28,879 admin
    Re: Battery Grounding

    Thank you, sounds very good--Is that with the inverter running under load?

    No issues with that voltage reading. Almost sounds like there is a some sort of DC Negative to Safety/green wire ground somewhere in the system (could be wire, could be "something else").

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sanitariusanitariu Solar Expert Posts: 33 ✭✭
    Re: Battery Grounding

    Inverter is under load when i took probes.
    My inverter is true sine and have option "ground relay".
    According the manual:
    "Ground relay is useful when an earth-leakage circuit-breaker is part of the installation.
    When the internal transfer switch is open (inverter mode) the Neutral of the inverter is
    connected to PE. When the transfer switch closes (AC input is transferred to the output) the
    Neutral is first disconnected from PE."
    4 X 240watt Luxor, Victron Energy Multiplus Compact 24 volt 1200VA, electrodacus solar controller, 8 x WB-LYP160AHA LiFeYPO4 3.2volt
  • BB.BB. Super Moderators, Administrators Posts: 28,879 admin
    Re: Battery Grounding

    Nice inverter... That ground relay only applies to the AC "neutral/green wire grounding" side of the inverter.

    The DC side--Seems like it is grounded "somewhere/somehow" from your measurements (generally a good thing)--But I have no idea how or where (details can matter--a lot).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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