Transitioning from Dry to Wet location

[marmathsen]

I just got called out by an inspector for using type NM in a wet location.

The installation has a 40 amp NM feeder running through the attic, then penetrates the exterior wall and is run in PVC conduit down about 4 feet to a small surface mounted breaker panel. That breaker panel serves as a disconnect for a heat pump as well as feeds a dedicated service receptacle for said heat pump

My question is regarding the use of NM cable where it transitions from dry location to wet. Where is an approved location to transition from dry rated wiring (NM) to wet rated wiring (THWN, UF, etc.)? I could clearly transition inside the house in the attic. But what about a surface mounted exterior junction box right where it penetrates the wall? If that's NOT approved, then am I to assume that any wiring that penetrates a wall from dry to wet/damp location should be damp/wet rated, even if it's going straight into a light box or receptacle box etc.?

Furthermore, if I AM allowed to use dry rated wiring to feed a receptacle/light box, at what point is dry wiring not allowed? If I run through a 6" conduit to feed a light/receptacle? 12" conduit? 24" conduit?

Does anyone out there use damp/wet rated wiring when feeding exterior outlets or lights? Even if feeding into the back of a surface mounted box or recessed box?

In another forum (http://forums.mikeholt.com/showthread.php?t=168212) it is implied that a recessed junction box would likely be considered dry location whereas a surface mounted maybe not.

 

[infinity]

You can enter an exterior box with the NM cable and then transition to THWN, UF or some other wet location conductors. The interior of the raceway is considered a wet location not the interior of the box.

 

[marmathsen]

You can enter an exterior box with the NM cable and then transition to THWN, UF or some other wet location conductors. The interior of the raceway is considered a wet location not the interior of the box.

Thanks Rob.

300.9 states that the interior of raceways installed in wet locations abovegrade (typo in my 2014 Handbook!) shall be considered to be wet location.

Is there by chance an article that you know of that explicitly states that the interior of a junction box installed in a wet location is considered dry?

-RobG

 

[ActionDave]

Is there by chance an article that you know of that explicitly states that the interior of a junction box installed in a wet location is considered dry?

-RobG

There is not. There is only the art. 100 definition of a wet location and a j box inside of a wall should not meet that criteria.

 

[GoldDigger]

There is not. There is only the art. 100 definition of a wet location and a j box inside of a wall should not meet that criteria.

But a surface mounted j-box (bell box?) with the NM coming in through the back would not be as clear cut.

 

[infinity]

But a surface mounted j-box (bell box?) with the NM coming in through the back would not be as clear cut.

How so?

 

[GoldDigger]

How so?

Just that a surface mounted box on an outside wall might be in a wet location. Whether or not that makes the inside of the box a wet location too is still in question.

ActionDave chose to refer to a box inside a wall.

 

[infinity]

Just that a surface mounted box on an outside wall might be in a wet location. Whether or not that makes the inside of the box a wet location too is still in question.

ActionDave chose to refer to a box inside a wall.

I noticed that about Dave's post.

I'll go out on a limb and say that the interior is considered a dry location which allows the dry location cable to enter the back of the box from the interior. There are probably ten million of those in existence.

 

[ActionDave]

Just that a surface mounted box on an outside wall might be in a wet location. Whether or not that makes the inside of the box a wet location too is still in question.

ActionDave chose to refer to a box inside a wall.

I see your point. I did say a box in the wall on purpose but I was not really thinking of a flush mounted bell box. In such a case I will repeat that only the inside of a raceway is called a wet location by code, so in my mind even the inside of a weather proof box is not a wet location.

I also agree with Rob that there is millions of these type installs in service with no problems.

 

[marmathsen]

Thanks for all the responses!

I heard back from the inspector today and he told me that as far as the city of Seattle is concerned, so long as the wiring goes directly into a box or enclosure from a dry location, the inside of that box is deemed dry. But the second the wiring enters a raceway that's located in a wet location, then that wiring needs to be wet rated.

He also made a point to address the fact that the NEC doesn't clearly detail whether wiring straight into a junction box (recessed or surface mount) without first entering a raceway is deemed dry. So Seattle and other AHJs are forced to make their own determinations.

Thanks again everyone!

- RobG