How to Wire Junction Box for PV in Series and Roof Penetration

[Kuma]

Installing 2 string arrays to grid tied SMA inverter and want to confirm how ground wire from PV rails to inverter is wired. Going to use EMT J boxes at each string and join them with a J box, roof penetration, then to SMA Inverter. Is a bus bar added to the J box, ground wire from rail to bus bar, then another ground wire from bus bar to inverter ground connection? Also an instructional video showed a 6awg ground wire from rail to bus bar then 12awg to inverter.

Its a little confusing because a neighbor had a professionally installed PV and they used a PVC J box then EMT conduit to the inverter. I realize PVC can be used but I prefer EMT.

 

[timselectric]

Inside the house, the solar circuits must be in metal.
On the roof, PVC is fine.
Ground conductor size is based on the circuit it is protecting. But if the ground conductor is exposed to physical damage (not in conduit) the minimum allowed size is #6.

 

[Kuma]

Inside the house, the solar circuits must be in metal.
On the roof, PVC is fine.
Ground conductor size is based on the circuit it is protecting. But if the ground conductor is exposed to physical damage (not in conduit) the minimum allowed size is #6.

Roof penetration is through roof eave. No attic or house wall electrical.

Rail to J box 6awg, bus bar in J box and ground emt J box and emt conduit, then appropriate ground wire size to inverter. PVC is very tempting given no electrical in attic or house wall. And no need to ground conduit or box. It can get hot here a few days a year though with temps 110.

 

[zanydroid]

Metal NEMA3 (or whatever the rating that’s appropriate) will require more pain to do knockouts for than using a step bit on PVC NEMA3. As well as harder to source the boxes in the first place, those PVC boxes are in every big box store.

EDIT: I mean metal NEMA boxes you are meant to customize knockouts for. Bell boxes are widely available but then you are stuck with exactly where the pre drilled and tapped conduit holes are.

PVC conduit will need a lot more thinking about expansion couplings than EMT. You already need to think about bonding for the rails, adding bonding bushings in the ends of the EMT is no big deal compared to everything else’s. PVC is also harder to bend than EMT (required heating), while simple EMT bends just need a $40 conduit benders. Doing simple 45 and 90 doesn’t require you to have a lot of expertise.

EDIT: IMO once you mess up with PVC it probably involves cutting and tossing some fittings. EMT mistakes are reversible apart from bending. You would probably use a bandsaw or skilsaw to blast through either conduit type so I don’t think cutting is a big difference either. Maybe reaming

 

[zanydroid]

Not sure what you mean by EMT JB

 

[timselectric]

Roof penetration is through roof eave. No attic or house wall electrical.

As soon as you transfer from outside to inside, it must be in metal. Doesn't matter if in attic, crawl space, or living space.

 

[timselectric]

Rail to J box 6awg, bus bar in J box and ground emt J box and emt conduit, then appropriate ground wire size to inverter.

 

[Kuma]

Metal NEMA3 (or whatever the rating that’s appropriate) will require more pain to do knockouts for than using a step bit on PVC NEMA3. As well as harder to source the boxes in the first place, those PVC boxes are in every big box store.

EDIT: I mean metal NEMA boxes you are meant to customize knockouts for. Bell boxes are widely available but then you are stuck with exactly where the pre drilled and tapped conduit holes are.

PVC conduit will need a lot more thinking about expansion couplings than EMT. You already need to think about bonding for the rails, adding bonding bushings in the ends of the EMT is no big deal compared to everything else’s. PVC is also harder to bend than EMT (required heating), while simple EMT bends just need a $40 conduit venders. Doing simple 45 and 90 doesn’t require you to have a lot of expertise.

EDIT: IMO once you mess up with PVC it probably involves cutting and tossing some fittings. EMT mistakes are reversible apart from bending. You would probably use a bandsaw or skilsaw to blast through either conduit type so I don’t think cutting is a big difference either. Maybe reaming

Rail bonding is easy with IronRidge. IronRidge may not be the cheapest but its easy for permitted diy'ers given calcs are included and an easy design tool that kicks out the parts list. I did a preliminary plan review with the County and mentioned IronRidge and the guy smiled and said "good choice".

Bell has aluminum J box's that would work great since the IronRidge rails are aluminum, if I decide to mount them directly to the rail. And the typical knockout locations should work just fine. Some conduit bending perhaps, but nothing ridiculous. The hardest part will be bending the conduit over the hips that are tile and trying to make it look nice but with the required clearances. Their could be some conduit wasted because esthetic's matter to me even though no one else can see it or care.

 

[zanydroid]

Bell has aluminum J box's that would work great since the IronRidge rails are aluminum, if I decide to mount them directly to the rail

What guarantees that the mount will penetrate anodization and oxide layer on the rail and on the jbox? (EDIT: maybe you referred to dissimilar metal corrosion) Are they listed for bonding this way? Screwing a metal conduit fitting in should be sufficient, but I haven't confirmed this (I always thought screwing into a hub makes a bond, and those threads on a bell box i thought was an integrated waterproof hub).

For going over a hip I think you want to do a shepherd's crook bend.

You can always trim the straight parts after getting the bend part right, depends on how ugly you find the extra watertight coupling that will add.

Note if you give up on hard conduit / conduit bodies and go to anything flexible outdoor rated you will have to mind the temperature derating, I don't think those are good to 75C/90C in wet conditions, though you could maybe appeal to the 10%/10ft rule. It'll look like ass though.

There's an approach where you just get it finaled and PTO, and then clean it up later

 

[Kuma]

What guarantees that the mount will penetrate anodization and oxide layer on the rail and on the jbox? (EDIT: maybe you referred to dissimilar metal corrosion) Are they listed for bonding this way? Screwing a metal conduit fitting in should be sufficient, but I haven't confirmed this (I always thought screwing into a hub makes a bond, and those threads on a bell box i thought was an integrated waterproof hub).

For going over a hip I think you want to do a shepherd's crook bend.

You can always trim the straight parts after getting the bend part right, depends on how ugly you find the extra watertight coupling that will add.

Note if you give up on hard conduit / conduit bodies and go to anything flexible outdoor rated you will have to mind the temperature derating, I don't think those are good to 75C/90C in wet conditions, though you could maybe appeal to the 10%/10ft rule. It'll look like ass though.

There's an approach where you just get it finaled and PTO, and then clean it up later

I may use the conduit tile mounts for the J box/conduit and not physically attach J box to rails. Creating a hole(s) in the rails(s) to use sheet metal screws or other fasteners voids IronRidge warranty. A lot of people do drill holes in the rails though without issue.

Another option are the IronRidge J Box but at a cost ~$50 each...


Yes, referring to dissimilar metals.

 

[zanydroid]

I got the unirac Eboss jbox hangers from I think platt on a deep discount. Less than a dollar each? Not sure I will end up using them. No holes but I’m not sure what keeps it from moving.

You can probably just use some kind of chemical adhesive, tape, or twist tie, + prayer, to get these kinds of hangars to stay put. Also sometimes standard hex nuts or other brand hardware will fit in the rail slots. It’s not something that requires mechanical strength so mixing and matching seems fine.

UniRac E-Boss Junction Box Mounting Bracket - Qnty. 1 - 00802JB

UniRac E-Boss Junction Box Mounting Bracket - Qnty. 1 - 00802JB Â EcoDirect.com sells UniRac Solar Mounts at the lowest cost. Order Online or Call Us! 888-899-3509

www.ecodirect.com

 

[Kuma]

I got the unirac Eboss jbox hangers from I think platt on a deep discount. Less than a dollar each? Not sure I will end up using them. No holes but I’m not sure what keeps it from moving.

You can probably just use some kind of chemical adhesive, tape, or twist tie, + prayer, to get these kinds of hangars to stay put. Also sometimes standard hex nuts or other brand hardware will fit in the rail slots. It’s not something that requires mechanical strength so mixing and matching seems fine.

UniRac E-Boss Junction Box Mounting Bracket - Qnty. 1 - 00802JB

UniRac E-Boss Junction Box Mounting Bracket - Qnty. 1 - 00802JB Â EcoDirect.com sells UniRac Solar Mounts at the lowest cost. Order Online or Call Us! 888-899-3509

www.ecodirect.com

Nice, will look into them. Possibly can use IronRidge fasteners. They are $2 from Platt now but not a problem))

 

[zanydroid]

Those tile conduit hangars look nice and easy to use. Depending on how you interpret support and secure, you could potentially just go with some kind of spacer that sticks solely on the conduit and somehow stays in place, but if you can get the hangars at a reasonable price I would get a few and see how they work.

I also got a couple of these (pretty cheap) https://unirac.com/product/conduit-mount/, if you can find a bolt+nut that can dock with the slots on the IronRidge you can attach conduit on the side of a rail, running conduit parallel to a rail. It will be plenty secure. You might be able to get away with avoiding one or two of the hangars.

I ended up overbuying these things a little bit, actually decided to just use a bunch of EZ Roof junction boxes to go through my composition shingles instead of dealing with bending conduit and planning conduit hangars. Only conduit now is in the attic. It's a lot more labor to get these on-roof junction boxes onto tile roof than a composition shingle roof, and the end product on tile is a lot uglier.