Grounding question

Re: Grounding question

pogonip wrote: »

I am installing a two strings of eleven 225 watt panels for a grid tie system.

Does each string have to have a separate ground or can I run one ground wire for both strings?

What size grounding wire would be recommended?

Thanks

Dan

You can run a single equipment grounding conductor serpentine through lugs on all the modules and rails. #8 bare copper is commonly used.

Re: Grounding question

niel wrote: »

each string should have its own ground lead going to a single common ground rod even if code would otherwise allow. if separate rods are used due to distances between the strings being too great then bury a bare copper wire of at least #6 and tie the rods together and thus making them appear as one larger ground point. i would not recommend zig-zagging a single continuous ground lead between separate strings as ground leads should not have many bends in them and zig-zagging would not only add many bends, but would also add more distance and resistance to reaching the ground rod.
as was said, #8 is fine to use to ground the pv strings with, but it can be a larger sized wire if you would like. be sure the rod is at least an 8ft copper ground rod. it's usually copper plated steel so the rod has some strength to it to drive through some hard grounds or rocks that would easily bend a straight copper pipe being driven. i'm not sure how well that works with permafrost though.

YMMV, but every rooftop multistring system I have worked on has used a single continuous bare copper EGC connecting all module frames and racking components. Ground mounted units usually have a separate ground rod for each subarray. String architecture and frame grounding have no electrical relationship to each other.

Re: Grounding question

pogonip,
essentially you are running 2 ground wire runs, but the connection from the top string to the bottom is not needed. it is sufficient to have the continuous ground wire go from each string to ground as if the other did not exist making the interconnection between them to make a loop unnecessary and i strongly advise against a loop arrangement as it can create a problem.

mr.radon,
that is fine that you did that as it is not against the law to zig-zag the wire, but i am telling you from a lightning and emp standpoint that zig-zagging is a very bad thing to do and will negate some of the protections a ground wire outside is supposed to accomplish. very high voltages with harmonic content act very differently on the ground wire than inner household grounds and most inspectors haven't much of a clue of lightning or emp grounding techniques. why do you think it is against the rules to connect one wire to another and to another to continue to ground for pvs rather than the continuous rule and they don't require the continuous run inside a home? connections can be made, but given the numbers of problems that has arisen from those unfamiliar with the problems that a bad ground connection has when employed outside to ground large areas of metal and not small electrical boxes. zig-zagging between 2 or more strings just to still use 1 wire was not the intention of the nec as this negates a low resistance path that is as short as possible to ground. even i see the difficulty they have in legislating some things, but i don't think they foresaw the results of taking their rules literally in all cases and is one of the reasons they have to keep modifying or adding to their own rules.

let's start this understanding of some of what i am conveying here with an example install. let's say it has 3 pvs in a series arrangement on the left side of a 45ft ranch home's roof and for simplicity it is an off grid battery to inverter setup, but due to shading they needed to put an expansion to the system with 3 series pvs on the right side of the home's roof. how would you ground it?