Conduit Questions

[pcarpe01]

Hi everyone - I decided to go a different direction with my shed electrical and use conduit from the sub panel inside my nearby garage. The garage is connected to my house and the panel is on the house side. I would need to run conduit up the wall, over the ceiling and down the opposite wall (and outside - underground to the shed). I am fine doing this, but I have the following questions maybe someone can assist with:

1- The garage walls are insulated - is there any restrictions on using PVC within insulated walls or do I need to use EMT?

2- Should I just use EMT inside the walls and transition to a PVC pull box for the transition outside of the garage and into the ground to the shed?

Please let me know your thoughts and thank you in advance!

 

[ImOld]

Growing up in the area and watching every type of metal rust/corrode outside, personally, I would use PVC throughout. There are no restrictions on its use in walls. Remember, the gray pipe, not white.

 

[Sponsor]

 

[pcarpe01]

Thank you, but correct me if I am wrong, isn't there a 122 degree max ambient temp. limitation with PVC conduit? I live in NY (Long Island) and the conduit will be run above the ceiling joists. There will be insulation between the joists. Not sure how hot it can get up there, but I imagine it can get hot. There is also some NM cables up there that was run by a reputable licensed electrician.

 

[Luke M]

Electrical PVC (as opposed to plumbing PVC) is 90C rated, same as the wires running in it.

 

[pcarpe01]

Yes, but the UL listing for schedule 40 states the following. It is possible I do not understand the listing.

1.2.3 The following restrictions apply to use of the Schedule 40 and Schedule 80 rigid PVC conduit and fittings mentioned in 1.1.1:

a) Use at 50°C (122°F) and lower ambient temperatures and

b) Use with 75°C (167°F) wiring, but the conduit and fittings may be used with 90°C (194°F) wiring if they comply with the construction (see Conduit for Use with 90°C Wire, 6.15) and marking (see 8.2.1, 8.2.4 and 8.2.5) requirements covering use with 90°C (194°F) wiring.

 

[Luke M]

Good catch. Yes, 122F ambient. I guess above that the PVC can soften and maybe sag if not well supported.

 

[ImOld]

NEC 353.12(D) Ambient Temperatures. Where subject to ambient tem-
peratures in excess of 50°C (122°F) unless listed otherwise.

The electrical conduit sold at the big box stores is listed for 90C ambient.

 

[pcarpe01]

Should I just forget PVC and go with EMT inside the walls for the garage and transition to PVC outside the garage and into the ground?

Would this be a better option?

 

[ImOld]

Nassau and Suffolk counties as well as many Long Island communities have their own NEC ammendments. Give the inspector a call. PVC outside gets tricky with cold and hot expansion as well as physical damage. You do know that the conduit system must be connected and complete before you pull in the wires. Did I mention the conduit wire capacity tables?

 

[Luke M]

The electrical conduit sold at the big box stores is listed for 90C ambient.

No, pcarpe01 is correct. The 90C rating means you can use 90C rated wire. There is separately a 50C ambient temperature limitation.

The other thing to worry about is thermal expansion. You definitely need to use expansion fittings with PVC when not in a stable temperature environment (e.g. buried). EMT also expands/contracts with temperature, but much less so.

 

[ImOld]

I will not debate the fact that millions of houses have PVC piped though attics.

Don't forget to call your utilities location service before you dig your 18" deep trench across your yard. Never know where the sewer, water, gas, cable, power, might be wandering around. Don't want to be on other forums here asking how to fix broken whatever.

 

[pcarpe01]

Yeah, I am aware of the ratings for the individual conductors and the fill table. My calculation yielded 3/4" for PVC or EMT (I am aware there are different values for conduit types). I agree that it's a great idea to call an inspector, I have a call out to him. Let's see what he says. Yes I am sure there are millions of homes with PVC in hot spaces, but I have the opportunity to do it right. The location of the trench doesn't have any lines nearby, so I should be good. We are cesspools, which are in the front, along w/plumbing and there is no gas in the area. Which stinks, because I hate oil.

Thanks again!

 

[WorthFlorida]

If your attic got that hot, you would have other problems including any existing wiring. LI does get some hot days but nothing compared to any southern states. As far as schedule type, any conduit that can be subject to impact by auto, lawn mowers, kids playing ball, etc., must be schedule 80. It usually where conduit come in and out from a bury line or low horizontal runs along a wall.

 

[pcarpe01]

I spoke with the inspector that handles local codes and he said, while there is no restriction for using conduit within walls or above joists, which may be hot, it is not "best practice". He went on to say that I should just run NM from the panel and stub out to a weather proof box on the outside, then underground conduit to the shed.

I do not know what the future holds, so my idea for running conduit was to future proof the garage for things like a mini-split for HVAC in the garage or additional wiring in shed.

Thoughts anyone? what would you guys do? EMT or PVC conduit in the walls? stub out with NM and possibly conduit over the drywall if needed in the future?

Thanks