I need guidance on some conduit rules

[donb108]

I have an existing solar system with panels on a shed roof and back wall. It produces way more power than I can use at the shed, so I'm going to rewire the panels to a new system that will be in the garage (EG4 12000XP, 20KWH battery). The DC run from the shed-to-inverter is about 210 feet. I got this guidance from the author of a YouTube channel I follow:

"Metal Conduit is required on DC power from Solar panels when it is on or inside a building until it gets to the first disconnecting means. (which is usually the disconnect on the inverter). DC power when not on or in a building can be run in PCV. AC power is run the same as any other residential installation." I really like this guys videos.

Wires from the panels go through the shed roof, enter a short run of PVC conduit (in the shed), then to a DC breaker that I use as a disconnect for the panels. From the DC breaker, the wires, still in PVC conduit, go to a wiring trough, and then to the 3K inverter.

The DC breaker is the first disconnect. As I read it, I can use PVC from the DC breaker to the garage inverter. The run will go underground, then up to an attic, then over to the connected garage, and then down to the inverter; all using PVC. Sound OK, or does metal conduit have to be used somewhere?

 

[fatjay]

I think that guy is mistaken. PVC is fine. I actually prefer pvc because it's insulating and not conducting. I have all mine in pvc.

 

[robbob2112]

Actually - metal conduit is required for PV wires in or on a dwelling, any other type building can be whatever you like so long as nobody sleeps/lives there... the best practice is EMT or FMC in/on the building. When outside use rain-tight connectors for the EMT.

The reason is the PV panels are an infinite source of current and if there is a short they will keep supplying their max power. This is also why the PV wire size is 156% of the Isc of the panels... so it won't melt if there is an issue and a short. Since PV panels can only supply a max current you can't just fuse them and call it good or the fuse will blow in normal use.

So you can use whatever type conduit you want on the shed-- I would use EMT where it is exposed and convert to PVC when it goes into the ground. Once you come up out of the ground you converter back to EMT at the house and keep using metal until you hit the MPPT/AIO.

Inside all this conduit - you can use THHN instead of PV wire, it is cheaper and easier to pull. This includes the EGC that runs from the AOI/MPPT and connects to the panel frames, racking, and metal roof --- everything at the same potential so no shocks possible.

Make sure to put a SPD at the disconnect just before the conduit enters the house... This should attach to both PV wires and the EGC --- it will kill any nearby lightning strike without damaging things.

Also use a SPD at the shed so it prevents a nearby strike from blowing all the bypass diodes in the panels

 

[captcarib]

Your source is correct. Metallic conduit is code for DC conductors both on roof mounted and when penetrating inside a structure. If the PV wires are intended for burial, then PVC conduit is fine. Another option to not have to run metal conduit inside is to use a combiner box on the roof and switch to regular AC conductors running inside to your inverter or charge controller via PVC conduit. PVC conduit on rooftops is ill advised due to the increased heat being on a exposed roof plus the heat generated by the PV conductors themselves. If you look at the temperature rating of the typical PVC electrical conduit its 140F max. Thus, if you add the heat already generated by the energized conductors in the conduit plus the external heat of being exposed on the rooftop in full sun it quickly adds up and can lead to problems. Also, make sure your conduit fill rules are adhered to closely to avoid overheating and conductor damage, reduced efficiency of the pv array, conduit damage etc.

690.31​

"(D)Direct-Current Circuits on or in Buildings. Where inside buildings, PV system dc circuits that exceed 30 volts or 8 amperes shall be contained in metal raceways, in Type MC metal-clad cable that complies with 250.118(10), or in metal enclosures.

Exception: PV hazard control systems installed in accordance with 690.12(B)(2)(1) shall be permitted to be provided with or listed for use with nonmetallic enclosure(s), nonmetallic raceway(s), and cables other than Type MC metal-clad cable(s), at the point of penetration of the surface of the building to the PV hazard control actuator."

 

[fatjay]

Actually - metal conduit is required for PV wires in or on a dwelling, any other type building can be whatever you like so long as nobody sleeps/lives there... the best practice is EMT or FMC in/on the building. When outside use rain-tight connectors for the EMT.

The reason is the PV panels are an infinite source of current and if there is a short they will keep supplying their max power. This is also why the PV wire size is 156% of the Isc of the panels... so it won't melt if there is an issue and a short. Since PV panels can only supply a max current you can't just fuse them and call it good or the fuse will blow in normal use.

So you can use whatever type conduit you want on the shed-- I would use EMT where it is exposed and convert to PVC when it goes into the ground. Once you come up out of the ground you converter back to EMT at the house and keep using metal until you hit the MPPT/AIO.

Inside all this conduit - you can use THHN instead of PV wire, it is cheaper and easier to pull. This includes the EGC that runs from the AOI/MPPT and connects to the panel frames, racking, and metal roof --- everything at the same potential so no shocks possible.

Make sure to put a SPD at the disconnect just before the conduit enters the house... This should attach to both PV wires and the EGC --- it will kill any nearby lightning strike without damaging things.

Also use a SPD at the shed so it prevents a nearby strike from blowing all the bypass diodes in the panels

Since PV is an infinite power source, if there's a short and the metal conduit becomes electrically charged, how is that better than pvc? Theres no fuses or breakers to trip, so there's literally no way to have the metal conduit become safe until nightfall.

Am I misundersatnding something here?

 

[robbob2112]

Since PV is an infinite power source, if there's a short and the metal conduit becomes electrically charged, how is that better than pvc? Theres no fuses or breakers to trip, so there's literally no way to have the metal conduit become safe until nightfall.

Am I misundersatnding something here?

The EMT conduit must be bonded to the grounding system using a bonding ring..... so if the PV wires short together, you just get a hot spot... if one wire shorts to the EMT you get nothing... if both get cut and short to it you get a hot spot..... but the PV wires should be floating and the negative of the battery not tied to the ground system... so the metal is the same potential as all of the other pieces of metal you could touch to get a shock...

And there should be an IMO disconnect just before entering the building ... and I would put one at the array as well.

Turn either or both off and the conduit is safe...

Note the bonding ring needs to exist at the shed to the EGC and at the house to the EGC which is tied to the grounding system.

 

[ricardocello]

Since PV is an infinite power source, if there's a short and the metal conduit becomes electrically charged, how is that better than pvc? Theres no fuses or breakers to trip, so there's literally no way to have the metal conduit become safe until nightfall.

Am I misundersatnding something here?

The idea is that the wires in the conduit could short together, causing an arc that will melt PVC.
Whereas with EMT, the arc will not penetrate the metal and burn down the house.

 

[robbob2112]

The idea is that the wires in the conduit could short together, causing an arc that will melt PVC.
Whereas with ENT, the arc will not penetrate the metal and burn down the house.

The only other thing - I am not sure how wires inside EMT would short unless damaged when originally pulled ... I suppose you could put a megger on each wire to the conduit and see if there is leakage current and detect silent damage -- of course before hooking up any electronics or the EGC to the house ground system but to the conduit ... so it is an isolated system

 

[ricardocello]

The only other thing - I am not sure how wires inside EMT would short unless damaged when originally pulled ...

It happens, sadly. There shouldn’t be any sharp edges to do that.

 

[fatjay]

The EMT conduit must be bonded to the grounding system using a bonding ring..... so if the PV wires short together, you just get a hot spot... if one wire shorts to the EMT you get nothing... if both get cut and short to it you get a hot spot..... but the PV wires should be floating and the negative of the battery not tied to the ground system... so the metal is the same potential as all of the other pieces of metal you could touch to get a shock...

And there should be an IMO disconnect just before entering the building ... and I would put one at the array as well.

Turn either or both off and the conduit is safe...

Note the bonding ring needs to exist at the shed to the EGC and at the house to the EGC which is tied to the grounding system.

Thank you for the explanation, learn something new every day.

 

[donb108]

Actually - metal conduit is required for PV wires in or on a dwelling, any other type building can be whatever you like so long as nobody sleeps/lives there.

It seems like I'm splitting hairs on some of this. I've seen YouTubes where the owner ran Romex through studs, all over his garage. It wasn't covered by drywall, and exposed, and you could walk up and touch it. But, the garage was an unoccupied structure and nobody was going to live in it. The AHJ made the owner replace all exposed Romex and replace it with MC. Was the AHJ correct?

My attic has Romex strung across the attic floor. I assumed it was OK because the attic isn't an occupied structure, but it's above the entire house (bedrooms, kitchens, etc.), which is occupied. Is a that guys garage different than my attic?

So you can use whatever type conduit you want on the shed

Thanks you, I really didn't want to rework the shed wiring.

PVC conduit on rooftops is ill advised due to the increased heat being on a exposed roof plus the heat generated by the PV conductors themselves.

I'm in south Louisiana. When I moved here, the cable installer warned me not to spend much time in the attic during the summer; risk of heat stroke. Like....no more than 10-15 minutes.

The idea is that the wires in the conduit could short together, causing an arc that will melt PVC.
Whereas with EMT, the arc will not penetrate the metal and burn down the house.

Burning down the house would ruin my whole day. That leads to the next question, below...

I would use EMT where it is exposed and convert to PVC when it goes into the ground. Once you come up out of the ground you converter back to EMT at the house and keep using metal until you hit the MPPT/AIO.

Again, splitting hairs. It will come out of the ground, up a brick wall, through the soffet, into the attic, turn 90 deg, and then run across the floor joists. Do I make the switch to EMT at the ground, or in the attic?

And there should be an IMO disconnect just before entering the building

I wondered about this. The breaker I mentioned is inside a locked shed. And, the inverters disconnect will be inside a locked garage. Seems like I may need an additional disconnect on that brick wall?

 

[sunshine_eggo]

It seems like I'm splitting hairs on some of this. I've seen YouTubes where the owner ran Romex through studs, all over his garage. It wasn't covered by drywall, and exposed, and you could walk up and touch it. But, the garage was an unoccupied structure and nobody was going to live in it. The AHJ made the owner replace all exposed Romex and replace it with MC. Was the AHJ correct?

Unfortunately, the AJH is the ultimate authority, and whatever they say goes.

 

[robbob2112]

Most of the time the AHJ want metal plates where the romex goes through the studs... then they don't worry about the exposed wire assuming you intend to put up sheetrock and finish it off. The metal plates prevent someone from putting a nail or screw through the wire. I can maybe see the MC if there was not a plan to finish it.

Switch to EMT about 6 inches to a foot above ground. There needs to be an anchor there and every 4ft technically. Then when you turn to go into the attic use a LB so you can pull the wires easy. About chest level put an IMO brand disconnect and SPD. This protects from nearby lightning strikes. Most AHJ want the disconnect near the service entrance or a sign at the service entrance to tell where the disconnect is.

In any case you have to do as the AHJ says or you can try to fight it and go over their heads but be prepared for a long fight.... mostly you can politely ask which section of the NEC covers what they are unhappy about and go study it.... they generally won't tell you more than something is wrong and what section it violates... so your neighbor was lucky enough to be told how to fix the problem.

If you have a complete plan that looks good you can meet with the inspector to talk about it and ask questions... they won't educate you, but simple questions where you ask if something will pass they will answer.

In any caseyou are stuck with what the AHJ says

The IMO disconnect comes is single string, 4 terminal switches inside enclosures and in multiple string versions that aren't in a case. You put those in a UL listed box rain tight box.... I use the Vevor brand, but there are many to choose from. For the SPD I prefer the midnite solar ones.

Make sure to use rain-tight connectors on the EMT.

 

[donb108]

Switch to EMT about 6 inches to a foot above ground. There needs to be an anchor there and every 4ft technically. Then when you turn to fo into the attic use a LB so you can pul the wires easy. About chest level put an IMO brand disconnect and SPD. This protects from nearbu lightning strikes. Most AHJ want the disconnect near the service entrance or a sign at the service entrance to tell where the disconnect is.

Sounds good, I'll try it this way.

 

[robbob2112]

Also note - The different AHJ might tweak the label requirements but read this

Post in thread 'Robbob2112 Answer thread'

Dec 2, 2024

Came up today - labeling requirements for NEC inspections - Original PDF attached

Building Inspector-s Guide - NEC 690 PV Labeling Requirements | HellermannTyton

www.hellermanntyton.us

• robbob2112

• 

 

[ksmithaz1]

The idea is that the wires in the conduit could short together, causing an arc that will melt PVC.
Whereas with EMT, the arc will not penetrate the metal and burn down the house.

Yea, I keep hearing this because nobody has ever cut thru metal with a DC arc thus you should be safe. . . No wait. . .

 

[ricardocello]

Yea, I keep hearing this because nobody has ever cut thru metal with a DC arc thus you should be safe. . . No wait. . .

I don’t write the codes

I would think a thin-walled EMT pipe would get hotter than hell if a DC arc was inside.
The PVC would just melt away. Not clear which case would be better, depends what is surrounding it.

 

[robbob2112]

Yea, I keep hearing this because nobody has ever cut thru metal with a DC arc thus you should be safe. . . No wait. . .

Always the negative nelly aren't you!

 

[robbob2112]

I don’t write the codes

I would think a thin-walled EMT pipe would get hotter than hell if a DC arc was inside.
The PVC would just melt away. Not clear which case would be better, depends what is surrounding it.

Interesting question - I wonder just how hot a 10ft piece of EMT would get with an arc in the midpoint from frayed wires... or a short from the same... The EMT would act like a heatsink and there would be a hot spot but a lot of the heat would be carried away... assuming the wires are 156% they wouldn't melt so only the point of contact would get hot

 

[rogerheflin]

I don’t write the codes

I would think a thin-walled EMT pipe would get hotter than hell if a DC arc was inside.
The PVC would just melt away. Not clear which case would be better, depends what is surrounding it.

I think they are less worried about the arc issue and more worried about someone damaging the conduit and hitting the 200-600v DC wires and getting a significant shock. At least with EMT/MC there is a decent chance if you penetrate the conduit and a wire that it will short to the ground and conduit and no one will get a significant shock.

 

[ksmithaz1]

Interesting question - I wonder just how hot a 10ft piece of EMT would get with an arc in the midpoint from frayed wires... or a short from the same... The EMT would act like a heatsink and there would be a hot spot but a lot of the heat would be carried away... assuming the wires are 156% they wouldn't melt so only the point of contact would get hot

EMT is not cast iron. An arc will burn thru it in less than a few seconds. I could argue PVC might melt around the wires and put the arc out, but I digress. At least they don't require +- in seperate conduits, of course if they were then metallic. . .

Two possibilities, an open within a wire creating an arc or a short between the wires creating an arc. The former is more likely with solid wire, the latter unlikely, and use stranded. Either way if it get's going for any length of time at all, you have a serious problem no matter the conduit. PVC can burn though not well. Hopefully you trip a fuse or breaker.

 

[ksmithaz1]

I think they are less worried about the arc issue and more worried about someone damaging the conduit and hitting the 200-600v DC wires and getting a significant shock. At least with EMT/MC there is a decent chance if you penetrate the conduit and a wire that it will short to the ground and conduit and no one will get a significant shock.

Well if you crack pvc, the pipe itself would not be energized, wires would likely just cut worst case, momentary arc across the shovel/tool. OTOH, if you crease the metal and bite into the wire, fun things could result. Sorry, I just don't see any diminished risk with steel vs pvc. Each have their pro's and cons, and each have different failure scenarios, none of which are all that great.

 

[robbob2112]

Well if you crack pvc, the pipe itself would not be energized, wires would likely just cut worst case, momentary arc across the shovel/tool. OTOH, if you crease the metal and bite into the wire, fun things could result. Sorry, I just don't see any diminished risk with steel vs pvc. Each have their pro's and cons, and each have different failure scenarios, none of which are all that great.

I wonder which factors the NEC folks considered before writing the rules around it.

 

[rogerheflin]

Well if you crack pvc, the pipe itself would not be energized, wires would likely just cut worst case, momentary arc across the shovel/tool. OTOH, if you crease the metal and bite into the wire, fun things could result. Sorry, I just don't see any diminished risk with steel vs pvc. Each have their pro's and cons, and each have different failure scenarios, none of which are all that great.

The metal conduit rule is for DC wires inside the house walls. Where screws, nails, sawzall's, drywall saws, and potentially fireman with axes are involved. And some of those tools may or may not cleanly cut some of the stranded wires cleanly every time.

 

[skyking1]

Well if you crack pvc, the pipe itself would not be energized, wires would likely just cut worst case, momentary arc across the shovel/tool. OTOH, if you crease the metal and bite into the wire, fun things could result. Sorry, I just don't see any diminished risk with steel vs pvc. Each have their pro's and cons, and each have different failure scenarios, none of which are all that great.

you're trying too hard there. nobody said bury EMT. If you did bury metal it woud be rigid. I have encountered PVC and rigid in the ground many times over the decades of excavating and hands down, rigid wins. PVC is OK if you are a skilled operator in the right conditions.
In a wall EMT will deflect all but a pefectly centered screw, and you'd be grinding there a while. PVC not so much.
If you hit an EMT with the sawzall expectig drywall and studs, you'd take notice and investigate. It is not that easy to just blunder into.