6/3 NM-B on conduit

[jansant]

I'm trying to prep our garage for the MY which will arrive in 2 months. I'm getting conflicting info from Home Depot and Lowes regarding running a 50 amp wire on a conduit from the main breaker. The run from the main to the garage is ~20 feet. I will be running a Tesla wall connector and a 14-50 from the same run BUT I will be using a double-throw safety switch (so, one method of charging can be used and not both) and another inline 50 amp breaker. I bought a 6/3 NM-B and thinking about using a conduit.

1. Home Depot said I cannot use a conduit on this wire (6/3 NM-B) because it will generate heat that could potentially become a fire hazard. HD said I need to run 4 separate wires if I want to use a conduit. Is this accurate? Also, if true, I guess I can remove the outside sheath of the 6/3 and use all the 4 wires to run in a conduit, correct?
2. If using a conduit is allowed, what is the recommended size, 3/4" or 1"? I'm planning on using EMT.

Thanks for any feedback!

 

[gfunkdave]

There is no rule against using romex in conduit (contrary to popular belief) but if you are using conduit you should use individual wires. Running 6/3 romex through conduit will be more trouble than you may realize. It's incredibly stiff and difficult to maneuver. If you use wires in conduit instead of romex you can downsize to 8 AWG wire for a 50A circuit, which will make things even easier.

Also it is forbidden to remove the romex sheath and use the individual wires, though it's not dangerous. The reason it's forbidden is that the entire cable assembly is what's inspected and certified, not the individual wires. But it's funny - those individual wires are the same wires made in the same factory that makes THHN/THWN wire. The only difference is that they aren't stamped THHN/THWN.

Also unless you are putting the conduit in the wall, romex can't be used in a garage because it's not allowed for wet locations, and a garage (even a finished garage, even conduit in a finished garage) is considered a wet location.

So, if you're looking to do it the right way (and easiest) use THWN wire in conduit.

As for what size conduit to use, google "conduit fill calculator" and it will tell you the minimum required for what you're planning.

edit to add: there's nothing in the NEC about romex in conduit, but local jurisdictions may differ blah blah consult a qualified professional. If you want to DIY and don't know what local code requires just call your local building inspector and ask.

 

[ATPMSD]

Curious, why a Wall Connector and a second 14-50? Also, if you are using seperate breakers you can run a 60-amp circuit to the wall connector (which gives you 48-amp charging rate instead of 40), but you will need 4-gauge wire for that run.

 

[jansant]

The 14-50 will serve as a backup in case the wall connector breaks, you just flip the switch then the 14-50 will be online cutting power to the wall connector. The 14-50's recommended max amp is 50 which I'm planning to use -- this way I utilize the same run w/o running a secondary line. Also, I don't mind running a 40amp charging rate (vs the 48amp). Thanks

 

[jansant]

There is no rule against using romex in conduit (contrary to popular belief) but if you are using conduit you should use individual wires. Running 6/3 romex through conduit will be more trouble than you may realize. It's incredibly stiff and difficult to maneuver. If you use wires in conduit instead of romex you can downsize to 8 AWG wire for a 50A circuit, which will make things even easier.

Also it is forbidden to remove the romex sheath and use the individual wires, though it's not dangerous. The reason it's forbidden is that the entire cable assembly is what's inspected and certified, not the individual wires. But it's funny - those individual wires are the same wires made in the same factory that makes THHN/THWN wire. The only difference is that they aren't stamped THHN/THWN.

Also unless you are putting the conduit in the wall, romex can't be used in a garage because it's not allowed for wet locations, and a garage (even a finished garage, even conduit in a finished garage) is considered a wet location.

So, if you're looking to do it the right way (and easiest) use THWN wire in conduit.

As for what size conduit to use, google "conduit fill calculator" and it will tell you the minimum required for what you're planning.

edit to add: there's nothing in the NEC about romex in conduit, but local jurisdictions may differ blah blah consult a qualified professional. If you want to DIY and don't know what local code requires just call your local building inspector and ask.I'll reconsider and use the THWN wire instead. I appreciate your feedback.

 

[jansant]

@gfunkdave

I'll reconsider and use the THWN wire instead. Thanks and I appreciate your feedback.

 

[ATPMSD]

The 14-50 will serve as a backup

This seems like overkill for a lot of reasons

1. The failure rate of Wall Connectors is very low
2. You can use a SuperCharger or public L2 chargers (such as ChargePoint) as a backup
3. The 14-50 outlet is going to cost you at least $80 for a high quality outlet (don’t get a cheap one), at least $100 for a GFIC breaker (required by code) and $45 for an adapter - plus wiring
4. You cannot use a GFIC breaker with the wall connector, you will need two paths instead of a switch
5. If you go with the single wall connector you can run a 60-amp line and get maximum charging out of the wall connector

 

[ATPMSD]

4. You cannot use a GFIC breaker with the wall connector, you will need two paths instead of a switch

Or: you run a line from the main breaker to a sub-panel, then a line with a standard breaker from the sub-panel to the wall connector, and a 2nd line from a GFIC breaker from the sub-panel to the 14-50. Additional cost for the sub-panel of course.

 

[rwiegand]

There is no rule against using romex in conduit (contrary to popular belief) but if you are using conduit you should use individual wires. Running 6/3 romex through conduit will be more trouble than you may realize. It's incredibly stiff and difficult to maneuver. If you use wires in conduit instead of romex you can downsize to 8 AWG wire for a 50A circuit, which will make things even easier.

The NEC (2014) in 312.5(c) says: "(C) Cables. Where cable is used, each cable shall be secured to the cabinet, cutout box, or meter socket enclosure. Exception: Cables with entirely nonmetallic sheaths shall be permitted to enter the top of a surface-mounted enclosure through one or more nonflexible raceways not less than 450 mm (18 in.) and not more than 3.0 m (10 ft) in length, provided all of the following conditions are met:...)"

So yes, unless it has changed in your jurisdiction there is a rule against NM cable in conduit, at least for distances >10 ft. I'm assuming the IRC says the same thing, but I haven't checked.

 

[Rocky_H]

@jansant There are generally just the two methods of doing the wire run: Either NM-B cable or individual wires in conduit. And the types of locations it is going through generally determine which one of those two you would choose. If it's going inside walls, or under floors or above ceilings, then that's what NM-B is for. If it's going to be out in exposed areas, like along the surface of walls, then you would use wires in conduit.

There is no rule against using romex in conduit (contrary to popular belief)

Yes, that's correct. It's not forbidden, but as you mentioned, it's cumbersome, so you shouldn't just plan on doing it unless needed for a short part of the run.

edit to add: there's nothing in the NEC about romex in conduit,

That is mentioned, but it's a little vague on the wording. It's in a section about how and where to use NM-B. It says that if the NM-B goes into an area where it is being exposed and could be subject to harm or damage, then it needs to be protected with conduit. An example use case might be where you would normally be running the NM-B in a standard NM-B kind of place, like through an attic or through wall, but then you get to a place where it has to transition outside, along the surface to go the last few feet. Instead of splices and junctions and stuff like that, you can just put conduit over that last few feet of the NM-B to meet that "protect from damage" requirement.

*Edit* Ah, I see @rwiegand 's comment about a length limitation. I could see that then, where it's needed in some limited cases, but they don't want people intentionally doing really long runs with it.

 

[gfunkdave]

The NEC (2014) in 312.5(c) says: "(C) Cables. Where cable is used, each cable shall be secured to the cabinet, cutout box, or meter socket enclosure. Exception: Cables with entirely nonmetallic sheaths shall be permitted to enter the top of a surface-mounted enclosure through one or more nonflexible raceways not less than 450 mm (18 in.) and not more than 3.0 m (10 ft) in length, provided all of the following conditions are met:...)"

So yes, unless it has changed in your jurisdiction there is a rule against NM cable in conduit, at least for distances >10 ft. I'm assuming the IRC says the same thing, but I haven't checked.

I don't want this thread to become a "romex in conduit" thread but this isn't really relevant. 312.1 (2020 edition, free access at nfpa.org) states the scope of section 312 is to cover "cabinets, cutout boxes, and meter socket enclosures" below 1kV and not branch circuits.

Section 334 covers NM cable and specifies the following uses not permitted (I'm not going to type all this hehe):

https://imgur.com/z1mPxuv

, but note that it never specifies "in conduit". In fact, 334.15(B) specifically says NM should be installed in EMT or PVC conduit to protect it from physical damage, and 334.15(C) says that NM can be installed in conduit in unfinished basements or crawlspaces, connected directly to an outlet box.

In fact, the only place that it can't be installed in conduit is a wet location, which a garage is considered.

 

[rwiegand]

OK, I guess as long as you don't run the NM in conduit back to your breaker cabinet you're OK. Sorry for the interruption. Learned something new.

 

[jansant]

Thanks for all the feedback. All great information

 

[DaMC]

I just bought Romex 6/3 type NM-b cable, a 14-50 outlet and 50 breaker from Home Depot. I plan to run the cable up the wall(inside the wall) across the unfinished attic to the back of the house (approx 55-60ft) to the Breaker box. Will I need to use conduit or can I run the bare wire across this distance? Do I really need a $100 14-50 outlet? Thanks

 

[jcanoe]

I just bought Romex 6/3 type NM-b cable, a 14-50 outlet and 50 breaker from Home Depot. I plan to run the cable up the wall(inside the wall) across the unfinished attic to the back of the house (approx 55-60ft) to the Breaker box. Will I need to use conduit or can I run the bare wire across this distance? Do I really need a $100 14-50 outlet? Thanks

Should not require conduit unless the NM-B wire run is exposed inside the garage at height less than (I believe 7 ft.) Will require 50A GFCI circuit breaker (about $100) to be code compliant. Either the Hubbell, Bryant or Cooper receptacle should be fine, well under $100. (Hubbell and Bryant merged into a single company.)

Hubbell 9450a: $85
Bryant 9450fr: $40
Cooper 5754n: $50

For Hubbell or Bryant use the Hubbell cover plate part no. SS701 (~$9.) The Leviton cover plate does not fit.

* Prices for these receptacles may have changed

 

[DaMC]

Thank you!!!! I had to buy the Bryant from Granger bc inflation has hit the other two.

 

[SpaceshipNels]

There is no rule against using romex in conduit (contrary to popular belief) but if you are using conduit you should use individual wires. Running 6/3 romex through conduit will be more trouble than you may realize. It's incredibly stiff and difficult to maneuver. If you use wires in conduit instead of romex you can downsize to 8 AWG wire for a 50A circuit, which will make things even easier.

Also it is forbidden to remove the romex sheath and use the individual wires, though it's not dangerous. The reason it's forbidden is that the entire cable assembly is what's inspected and certified, not the individual wires. But it's funny - those individual wires are the same wires made in the same factory that makes THHN/THWN wire. The only difference is that they aren't stamped THHN/THWN.

Also unless you are putting the conduit in the wall, romex can't be used in a garage because it's not allowed for wet locations, and a garage (even a finished garage, even conduit in a finished garage) is considered a wet location.

So, if you're looking to do it the right way (and easiest) use THWN wire in conduit.

As for what size conduit to use, google "conduit fill calculator" and it will tell you the minimum required for what you're planning.

edit to add: there's nothing in the NEC about romex in conduit, but local jurisdictions may differ blah blah consult a qualified professional. If you want to DIY and don't know what local code requires just call your local building inspector and ask.

Hello, looking for some clarification on where you concluded a "finished garage" is a WET and/or Damp location? . . I can find no such definition or clarification in the NEC. And everyone I have asked states the contrary to your assertion.

 

[ATPMSD]

Hello, looking for some clarification on where you concluded a "finished garage" is a WET and/or Damp location? . . I can find no such definition or clarification in the NEC. And everyone I have asked states the contrary to your assertion.

210.8(A) GFCI Protection for Personnel: … require GFCI protection for commonly used receptacle outlets in the specified areas of 210.8(A)(1) through (A)(11):

Bathrooms, Garages and Accessory Buildings, Outdoors, Crawl Spaces, Basements, Kitchens, Sinks, Boathouses, Bathtubs and Shower Stalls, Laundry Areas, Indoor Damp and Wet Locations.

 

[davewill]

Another reason for using THHN (not that it appears you needed one) is that 6ga THHN in conduit is good for 60a, but 6/3 Romex is only good for 50a. It gives you an upgrade path if you ever wanted to use 48a charging.

 

[ATPMSD]

Another reason for using THHN (not that it appears you needed one) is that 6ga THHN in conduit is good for 60a, but 6/3 Romex is only good for 50a. It gives you an upgrade path if you ever wanted to use 48a charging.

To be clear #6 Romex wire is rated at 55a and THHN at 75a. Since Romex is limited to 44a continuous the wall connector has to be limited to 50a, which I am pretty sure is your actual point.

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