How to properly ground when installed on a metal roof.

chadhumm

I am new, doing some research and plan to do a solar install in the last quarter of 2013. Enough for 40% of my needs, if it works out then expand it in 2014. I'm trying to find out how to properly ground my system. I have not decided if I will use rails or not Possible S-5 clamps and if needed spacers to keep space between my panels and the metal roof. I plan to use the enphase microinverters. Grounding the microinverters is straight forward. But I am uncertain of how to properly ground the rest of the system. Or how to ground the rails if I use rails. Since it will all be in contact with the painted metal roof do I have to attach the ground to each rail? I would eventually have 2 rows in portrait. I think 2 rails is sufficient for mounting for each row. So 4 rails 60 feet across the metal roof. Also since the cable for the enphase contains a ground can that ground be wire nut tied to the array's ground wire and then to the grounding rod. Or should they run separately in parallel and each ground clamped to the grounding rod seperatly. If they can be tied together (in the junction box) can that ground wire be run through the same conduit as the other wiring to the main service panel?

Iv'e done enough reading that the whole process seems rather simple. Except for grounding. There does not seem to be many specifics out there in regards to proper grounding. Except for the microinverters themselves. Thanks for any knowledge you can share.

I will have it inspected, but wanted to perform the labor myself to save and get a faster payback. I want to do it right the first time.

Surfpath

Re: How to properly ground when installed on a metal roof.

chadhumm wrote: »

Iv'e done enough reading that the whole process seems rather simple. Except for grounding.

Amen brother. Grounding can be confusing at best.

I have a metal roof and, although, my system may be set up differently, this thread about my experience may be of limited help.

There are a lot of variables and NEC rules involved in grounding (note the NEC did not apply in my case). Here, though, seem to be a couple of principle tenets:

• Try to bring back all grounds to one single ground rod (properly grounded in conductive earth), or ground rods that are (ideally) close together and appropriately bonded.
• Avoid bringing the panel/mounting rail or combiner box grounds into your house. Bring those directly to your ground rod. Any metal structure/item on the roof should be grounded in this fashion.

There are other, sometimes controversial, topics related to grounding. However the above two points related to the equipment that you mount on your metal roof, seem to hold true.

I'm a newbie taking a stab, the real experts here will guide you well.
-SP

jaggedben

Re: How to properly ground when installed on a metal roof.

chadhumm wrote: »

I have not decided if I will use rails or not.

Meaning you are considering mid-clamps and end-claps directly to S-5 clamps? Or something like Zep, or Westinghouse?

Possible S-5 clamps and if needed spacers to keep space between my panels and the metal roof. I plan to use the enphase microinverters.

If you are using Enphase you will definitely benefit from some space between the roof and the panels to allow airflow to cool the inverters. I'd say 3" minimum. Probably worth the investment in rails, over the life of the system.

...I am uncertain of how to properly ground the rest of the system. Or how to ground the rails if I use rails.

Talk to the S-5 folks about which of their clamps are listed for grounding. If you use an S-5 clamp that bonds the roof to the rest of the equipment, then you don't need to do any additional bonding for the roof. (FWIW, I've never heard of an inspector requiring extensive metal roof bonding, but I haven't done that many metal roofs.)

Bonding the rails (and panels, unless you use WEEBS) can be done with tin plated lay-in lugs that are rated for use with both copper and aluminum, and have a stainless steel screw. (If they are rated for direct burial, they're good.) Use a stainless steel star-washer between the lug and the rail, and bolt to the rail with 10/32 or similar hardware. There are also lugs designed specifically for solar, such as by Wiley Electronics (WEEB system).

Since it will all be in contact with the painted metal roof do I have to attach the ground to each rail?

Yes. It is standard industry practice to bond every section of rail to meet NEC requirements. A metal roof doesn't change this.

Also since the cable for the enphase contains a ground can that ground be wire nut tied to the array's ground wire and then to the grounding rod. Or should they run separately in parallel and each ground clamped to the grounding rod seperatly. If they can be tied together (in the junction box) can that ground wire be run through the same conduit as the other wiring to the main service panel?

The green conductor inside the Enphase cable is an AC equipment ground that needs to be routed along with the AC wiring to the location of the circuit breaker. Typically it can be combined with the solar GEC (the array ground) into one #8 wire, and run back to the main panel if that's where the breaker is. There it is bonded to the existing premises GEC that goes to the ground-rod (or UFER, or other electrode). However if the circuit breaker is in a separate location (e.g. subpanel) from the existing grounding electrode, then you either need to run them separately, or find a way to continue the solar GEC to the existing premises GEC.

According to the NEC, you are supposed to use an irreversible splice (such as crimped C-tap) for any splices of the GEC. Not a wire nut. If this isn't your inspector's first solar system, he will expect this.

Iv'e done enough reading that the whole process seems rather simple. Except for grounding. There does not seem to be many specifics out there in regards to proper grounding. Except for the microinverters themselves. Thanks for any knowledge you can share.

I recommend reading section 690.47 of the 2011 NEC.

I will have it inspected, but wanted to perform the labor myself to save and get a faster payback. I want to do it right the first time.

Good luck.

solarix

Re: How to properly ground when installed on a metal roof.

It really doesn't matter what your roof is. Grounding per the code requires all the metallic stuff to be grounded and having a metal roof doesn't eliminate any grounding requirements for your PV system. Yes, in practice it is probably better grounded as far a lightning or faults are concerned, but the code doesn't care. Use the expensive type ground lugs on each panel and each rail all tied together with a continuous #8 bare copper wire run down to an irreversible splice onto the Grounding Conductor (GEC) going to the ground-rod.