Ground wiring technique?

I plan to put a number of panels up on my roof, and as I understand it, they each need to have their frames grounded, in such a manner that if I remove one panel for any reason, the others will remain grounded.

Each panel has a ground icon embossed into the aluminum frame near a small, threaded hole. This hole is way too tiny for a standard 10-32 or even 6-32 grounding screw, so I think I'll have to drill it out larger. But I wanted to ask how exactly people have been making the ground connections. It would seem most efficient to daisy chain between all the panels, crimping two wires at a time into lugs, with one wire going to the previous panel frame, and the other wire going to the next. I can't find lugs, however, that look like they're rated to take two, #10 conductors.

I guess I could crimp a single conductor into a lug, then solder that to a wire that goes between all the panels. I would hate to use lead solder, though. And it would be more work. Surely, there must be a standard solution to this?

Comments

  • System2System2 Posts: 6,290 admin
    Re: Ground wiring technique?


    How about using silver solder? good looks and only slight surface weathering.

    brad

    The above is only my rambling, doubtlessly long-winded opinion.
    You're welcome to it, but I cannot attest to it's accuracy.
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Ground wiring technique?

    Grounding PV module frames can be a complicated undertaking. The aluminum frame is typically anodized, a chemically bonded finish that's something of an insulator. Thread-cutting fasteners and/or star washers are required for a good metal-to-metal connection, but corrosion between dissimilar metals can be a problem. This doodad is apparently the NEC approved solution.

    Here's a related article from John Wiles. Noted Wiles' alternative solution:
    If the module grounding is to be accomplished with a 14–10 AWG conductor, then the ILSCO lug is not needed. Two number 10 stainless-steel fl at washers would be used on the 10-32 screw and the copper wire would be wrapped around the screw between the two flat washers that would isolate the copper conductor from contact with the aluminum module frame.

    HTH,
    Jim / crewzer
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Ground wiring technique?

    "I plan to put a number of panels up on my roof, and as I understand it, they each need to have their frames grounded, in such a manner that if I remove one panel for any reason, the others will remain grounded."


    roderick,
    it is not necessary to have each individually done as a short daisy is feasable as long as it does not windup zig zagging your roof. it must seem to flow in a direction going towards the downlead for your ground. in fact that doodad is perfect as you could run a solid wire run rather than individual connections with lugs, which amounts to more of a resistance in the path. when a pv is removed just unscrew that ground lug to keep your wire run intact for the rest of the pvs. if it is not a smooth flow towards the ground, like when using 2 series runs of pvs, you could use a terminal block and combine the 2 with the wire going to ground. in fact, one of those wires could be a continuous run from the pvs(running through each doodad lol) and through the terminal block and straight to the ground with the second string's ground attaching to the terminal block. if terminal blocks aren't viable for you, run each string to ground with its own ground wire, but connected to the same ground rod. in cases where 2 rods are to be used you must use a bare solid copper wire buried in a straight line(if possible) to connect each rod electrically together using at least #6, but if you use a larger wire for the ground wire then use that size or bigger for this underground interconnection. no sharp bends should be on either the ground wire or ground rod interconnections as this presents a weak point to the wire with the possibility of lightning jumping off from that point. i hope this helps you, but if you have anymore specific questions concerning this please ask.
  • FrankFrank Solar Expert Posts: 54 ✭✭✭
    Re: Ground wiring technique?

    The manufacturer should have provided hardware and instructions on how they want the module grounded. The doodad is pretty cool (but expensive). My panels use a cupped washer and stainless steel self-tapping screws.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Ground wiring technique?

    frank,
    not all of them provide the hardware. unisolar doesn't anyway.
  • System2System2 Posts: 6,290 admin
    Re: Ground wiring technique?

    Thanks, everyone!

    I double-checked the box that the panels came in, and at least for these Mitsubishi modules, there is no included grounding hardware.

    The doodad looks like it would be ideal, but the other poster was right, they are expensive, especially compared to just a couple washers, even stainless washers. They rival the cost of the wire itself!

    The silver solder idea is a nice one. I think no matter what, I'll have to do some small amount of soldering. I might end up using plumbing solder, which I think doesn't have lead, either.
  • BB.BB. Super Moderators, Administrators Posts: 30,494 admin
    Re: Ground wiring technique?

    By the way, soldering is considered to be a big no-no in connecting ground wires... In a lighting strike the solder is blown right out of the joints. -- from what I have read. Only use mechanical/crimp type connectors.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Ground wiring technique?


    bb's right i had forgotten about the resistance factor with solder. when
    lightening hits the joint it might travel elsewhere. Of course i've had
    lightening blow fuse's out and jump the gap where fuse wire was
    and still fry the electronics.

    brad
  • BB.BB. Super Moderators, Administrators Posts: 30,494 admin
    Re: Ground wiring technique?

    And lastly, using plumber's solder implies another possible issue too... Plumber's typically use acid as part of the fluxing operation. Works great at cleaning the metal... however, it leaves acid behind (and in the strands up into the wire jacket that cannot be cleaned out) and causes corrosion fairly quickly.

    Only use rosin type flux/solder for electrical connections.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Ground wiring technique?

    One of the big problems with solder and lightening, is the relatively low melting point of solder. It instantly melts, is blown away and leaves behind what can be the next thing to an open circut.
    Wayne
  • rplarryrplarry Solar Expert Posts: 203 ✭✭✭✭✭
    Re: Ground wiring technique?

    What about soldering and crimping is that acceptable?
  • BB.BB. Super Moderators, Administrators Posts: 30,494 admin
    Re: Ground wiring technique?

    Well...

    A properly done crimp is a better connection than solder. Also, if you vibration or movement of the wire/cable, if it is going to work harden and break, it will be at point where the solder stopped wicking up the wires (crimp connections will hold up much better to bending/vibration).

    If the connection must be soldered, then make sure that you only use solder & flux designed for use in electronics. And that the connections are clean and that you don't move the joint until it has hardened. And only use it as a supplement to crimp/mechanical connections in house mains wiring and grounding.

    -Bill.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Ground wiring technique?

    Point on soldering well-taken. There are two strings, but I can run one ground from each to a ground bar on the junction box.

    Normally, I wouldn't use plumber's solder on electronics, because of the corrosion mentioned, but I came to thinking: this is used to do copper pipes all the time, and the walls of those are no thicker than the hefty gauge ground wire.

    I'll still go with mechanical connections, given what was said about resistance and tolerance for lightning.
  • FrankFrank Solar Expert Posts: 54 ✭✭✭
    Re: Ground wiring technique?

    I would run panel grounds directly to a ground rod and not into a junction box. If you did get unlucky and experience a lightning strike you want to keep that energy as far away from any power wiring as you can and shunt it as quickly as possible into the earth.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Ground wiring technique?

    it appears i wasn't clear enough as frank is correct. you can use a terminal block, but it shouldn't be with your other connections at all as that is a deviation from the flow towards that ground and even if it doesn't deviate by some wild outside chance it induces an emp into your + and - leads, if you're lucky enough that it doesn't jump straight to them as wire insulations usually breakdown at about 600v. i was talking of using the terminal block in open air or even mounted to the frame of the last pv inline before going down to the ground. remember the flow i was telling you as it must flow from the pvs, either they be paralleled or seriesed like a daisy chain, always moving towards the ground as straightly and short as possible without any sharp bends. never route it near other wires if at all possible and never into or under a house.
  • System2System2 Posts: 6,290 admin
    Re: Ground wiring technique?
    niel wrote:
    . never route it near other wires if at all possible and never into or under a house.
    A thought that I would completely agree with. Interesting item tho - I understand that there are some provisions in the Electrical Code for some parts of Canada, to provide for a "proper" ground for the utilities input to new homes, which suggest a substantial length of heavy copper wire, to be placed on the earth, in the hole dug for the basement, then pour the concrete basement floor over it. Also, in Newfoundland, at least a number of years ago, their code required that the ground rod and it's wire, be in the earth, in the basement, before the concrete floor was poured. The only thing you saw on completeion, was the ground wire going down the inside of the basement wall and dissipearing into the floor.
    Can't help but wonder, just how high will a basement floor bulge up with several thousand PSI steam pressure under it?
    Wayne
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Ground wiring technique?

    that's not very wise of them to put a ground rod under the house as a direct strike has to continue through the house to get to the ground making everybody and all appliances in the house possibly within it's path. even a close by strike may follow a path into the house to go through that rod which is a low point of resistance to the earth. if it were me i'd challenge that law as a rod outside driven to below a level that the basement floor is at would be better by far. that way it doesn't go through the house, but around it. if they'd insist on keeping the law i'd drive one in from the outside that is longer than the depth of the rod under the house and interconnect them. it would then be more apt to follow the longer deeper rod placed from the outside(at least you'd hope it'll follow the second rod).
  • System2System2 Posts: 6,290 admin
    Re: Ground wiring technique?

    Hmm, should I run a separate ground and stake for the array frame?

    My inverter has ground fault detection on the DC input, and requires a ground from the array. I suppose that connection could go to some other ground, but that seems to go against the intent of the inverter's protection.

    I am also concerned about running another ground stake into the ground, which would lead to a multi-point ground, and again, may confuse the GFI on the inverter. The inverter is mounted outside, about 4 feet away from the service panel, which has the earth ground connection for the house. Moreover, it seems that the inverter ties the negative lead of the array to its chassis, which is tied to earth ground. I don't like the idea of making that lead attractive to lightning, but it seems I have no choice.

    Possibly I'm a fool, but I'm not terribly concerned about lightning protection. While I'm sure they occur sometimes, ground strikes are rare in the valley, and my roof is single-story. I would think the first targets for lightning would be the 2-story houses on either side of me, the TV antenna on the roof of one of them, the three 50' Cypress trees in front of my house, or the 60' redwood of the neighbor two doors down. Fortunately, none of these are in the path of the sun, or else I probably wouldn't even be here asking these questions.

    Your thoughts are enlightening (no pun intended), more are welcome.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Ground wiring technique?

    just how accessable is the main utility ground rod to your pv system ground? if it is possible to run the ground wire from the pv system to that point that would be best. as to the connection into the box do what you have to do as i had said not to route near other wires if at all possible. their design forces you to do it.
    if the utility ground is too far away or not convenient for your pvs to run to i do recommend the 2 seperate rods and interconnecting them underground to make them as one. this is fine that the rods could even be on opposite sides of a home as long as the bare solid heavy gage wire is connecting them underground. you don't always have to dig the soil up as many places can use just a piece of wood like a small length of plywood hammered into the ground and pulled back out leaving a small width hole that could be done the entire length to bury the interconnecting wire in. this does become difficult where concrete is in the way, as in steps and driveways. that interconnecting wire is also like having a longer ground rod as it gives more metal to soil contact area
  • FrankFrank Solar Expert Posts: 54 ✭✭✭
  • System2System2 Posts: 6,290 admin
    Re: Ground wiring technique?

    As I understand it, the ground wire has to be attached to the panels so if one is removed, all the other's remain grounded. I typically run a #8 bare copper wire with lugs attached by a stainless steel self drilling screw, with a star washer to cut through the anodization. From the panels I go to a combiner box into an insulated lug as opposed to a wire nut or solder.
  • FrankFrank Solar Expert Posts: 54 ✭✭✭
    Re: Ground wiring technique?

    It sounds like you may be confusing Equipment Grounding and Bonding. If you bond your system (some are required by NEC to be bonded) you typically connect your DC negative to a grounding point at one place only. I believe that with a GFI-protected array that this bond occurs via the GFI breaker. (My system is pole-mounted so I don't have the GFI.)

    Grounding is different: I don't see why you can't use multiple grounding points ex. from the array directly to a ground rod. Why don't you email John Wiles, describe your situation and ask what he thinks? He published contact info on every article he writes.
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