Connector for romex to PVC box

Discussion in 'Electrical Forum discussion & Blog' started by mincam, Aug 25, 2020.

  1. mincam

    mincam New Member

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    I want to mount this box on the outside of the house and come into it through the back hole with romex from inside the house, and then change to stranded THHN to be run in PVC conduit outdoors.

    I am under the impression that I need a connector on the romex to secure it to the back of the box in the hole where it enters the box. My question is what type of connector do I use for this purpose?

    According to the code, any connector that has metal in it must be grounded. So I am looking for a non-metallic connector for romex that will fit/work with a PVC box. If I screw in a metal connector, it must be grounded and I am not sure how to ground it within the rules of the code, so I would prefer no metal in the connector.

    250.4(A)(2) Grounding of Electrical Equipment. Normally non-current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials.

    It would seem to me that there ought to be many non-metallic romex connectors for going into a PVC box, but I can't find any for that purpose. I feel I must be missing the obvious, but can't find it.

    Basically my question is very simple: How do you properly connect romex to a PVC box? (The key word is "connect.")

    [​IMG]
     
    Last edited by a moderator: Aug 25, 2020
  2. Reach4

    Reach4 Well-Known Member

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    I think a connector would be like an outlet. To ground the box, get a metal box. Those come in metal too. I think aluminum, but I am not sure what the common metal is. That box you pictured is not conductive.

    The threads match rigid conduit, which is threaded the same as NPT water pipe.
     
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  4. mincam

    mincam New Member

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    Basically my question is very simple: How do you properly connect romex to a PVC box?
     
  5. Reach4

    Reach4 Well-Known Member

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    A PVC box is not conductive materials.
     
  6. mincam

    mincam New Member

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    250.4(A)(2) Grounding of Electrical Equipment. Normally non-current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials.

    Any metal in the connector is conductive and it encloses the conductors.

    In any case it is irrelevant to my question which is how do you connect romex to a weatherproof PVC box?

    Any relevant reply will be only about connectors.
     
  7. ShadowAviator

    ShadowAviator Member

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    I am not a licensed electrician, but maybe I could help point you in the right direction.

    First, you may need THWN instead of THHN for a wet location. Maybe thats what you meant.

    Second, I am not sure if you can run romex into a w/p box outdoors even if it comes in from the back. I think if the box is mounted outdoors it may be considered a wet area. You may want to check your local codes. Maybe you could use UF instead of romex.

    As far as a connector, the only thing that comes to mind is a non-metallic UF connector. I am not sure if that would work for your application or not.

    Sorry I can't be of more help. It's difficult to know whats code for a specific area, especially in California.
     
  8. rman

    rman Master mechanic

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    In nj the wall that the Romex is fed from the back is not considered wet area. The connector is a standard 1/2 inch romex connector with two screws to secure the wire from being pulled out. The grounding of the connector only applies in 1-1/2 connector or larger. The Thhn wire in the pvc conduit is for wet locations. You’ll need a weather proof cover on the box.
     
  9. wwhitney

    wwhitney Well-Known Member

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    The isolated metal NM connector on a PVC box is definitely a corner case as far as 250.4(A) goes. It is arguably small enough to be ignored. If you used a metal cable tie to secure NM cable, or use a two hole metal strap on a metal surface, I don't think anyone would expect those to be bonded. Likewise for a PVC male adapter or liquidtight connection to a plastic enclosure hole, using a metal locknut to secure the male adapter. These otherwise all plastic connector often come with a metal locknut.

    But if you absolutely want to avoid metal for some reason, it looks like you could use an all plastic strain relief cable connector, with an oval hole for NM or UF cable. Something like this, although I don't know if the size is right:

    https://www.amazon.com/Liquid-Tight-Strain-Relief-Cord/dp/B06Y2J7N6K

    Cheers, Wayne
     
  10. WorthFlorida

    WorthFlorida The wife is still training me.

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    What I have done is use a short piece of conduit glued to a male nipple and thread it into the PVC box. Then use a weatherproof gasket between the house wall and PVC box and slip the romex through. Use some caulking on both sides of the gasket with it and seal it all up as you mount the PVC box to the wall. The romex feed from the back just needs to be secured 12" from the box. No anchors are needed inside the box. If you have a very smooth exterior wall, only caulking would be needed. Use siliconized caulking is best.

    https://www.homedepot.com/p/1-Gang-Weatherproof-Box-Gasket-10-Pack-of-2-GS100/204396180

    5A53591D-9925-4292-979D-B5C0525E6918_1_105_c.jpeg
     
    Last edited: Aug 27, 2020
  11. mincam

    mincam New Member

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    Very interesting, and I am not doubting you. However, please cite the section of the code that specifies 1-1/2 or larger. I need to be able to back your claim up. Thanks.
     
  12. mincam

    mincam New Member

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    "It is arguably small enough to be ignored" does not satisfy prohibiting ungrounded "conductive materials enclosing electrical conductors ," although I agree that it is being incredibly picky in this case.

    But,

    BINGO!!!!

    You win the prize with the plastic lock nut, thank you so much.

    [​IMG]
     
  13. wwhitney

    wwhitney Well-Known Member

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    FWIW, that's not correct. You always need to secure the cable to the box [314.17(C)] and secure the cable within 12" of the box [334.30]. The two exceptions I'm aware of for securing to the box:

    1) For flush mount single gang boxes, you can instead secure the cable within 8" of the box and skip the attachment to the box. Would not apply in this discussion, as the box is surface mounted. 314.17(C) exception
    2) For exposed work in crawl spaces and basements, 334.15(C) allows you to sleeve the NM in a short run of conduit leading to a box where it is needed for protection, and it requires you to secure the cable within 12" of entry to the sleeve. I believe it is implicit that 334.15(C) relieves you of the requirement to secure the cable to the box.

    Cheers, Wayne
     
  14. wwhitney

    wwhitney Well-Known Member

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    Actually, I think the prize goes to the practitioner who realizes this is not the place to be "incredibly picky." : - ) But I agree, if you came up on an incredibly picky inspector you couldn't budge, go for the plastic cable gland.

    Cheers, Wayne
     
  15. mincam

    mincam New Member

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    Changing the subject, just a little, with three questions:

    1) Although I don't have the code in front of me, so I can't really search it, this is what I can Google:

    370-17c says: All cable SHALL BE secured to the box, except for single gang non-metallic boxes, if stapled within 8 inches of the box.

    In all my searches, I don't see flush mount mentioned. That does not mean it's not there, but can you confirm it? Citation?

    2) Does this mean that in a home with flush mounted single gang boxes, you do not need connectors on your romex as long as it is stapled properly?

    3) As I understand it, you can run UF through a PVC riser when bring it above ground from its 24" deep trench. Do you need a connector when you bring it into a box on top of the riser? I kind of doubt it, but would like to know what the code says. Cite the section if you can, please.

    Thanks
     
  16. mincam

    mincam New Member

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  17. wwhitney

    wwhitney Well-Known Member

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    You can read the NEC at nfpa.org/70, you just need to make a free account. It's not very searchable, though.

    The 2020 citation is 314.17(B)(2), and the exception uses the phrase "mounted in walls or ceilings" which I took to mean flush mount rather than surface mounted.

    Yes, in fact you will find that standard non-metallic single gang boxes don't have cable clamps at all.

    I'm going to go with no, as well, but don't have a cite for you. If you want a searchable PDF of the NEC, you can find the 2016 CEC "born digital" at archive.org. It does have the California amendments, and it's one code cycle behind the current version.

    Cheers, Wayne
     
  18. mincam

    mincam New Member

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    This is an interpretation of the code, which presumably is correct.

    From: https://www.ecmag.com/section/codes...ies-and-fittingsgeneral-installation-sections

    All permitted wiring methods must be secured to nonmetallic boxes, unless the Section 370-17(c) exception is met. If three conditions are satisfied, nonmetallic-sheathed cable and/or underground feeder and branch-circuit cable may enter a nonmetallic box without being secured to the box. These conditions include: 1) the box must be a single-gang box no larger than a nominal size 21/4 by 4 inches, 2) the cable must be fastened within 8 inches of the box measured along the sheath, and 3) the sheath must extend through a cable knockout at least 1/4 inch. Of course, the third condition is required regardless of the exception.

    Question: What do they mean by "branch-circuit cable?" Could a romex coming through an exterior wall into the back of a PVC box be one? Or is it part of the underground feeder?
     
  19. wwhitney

    wwhitney Well-Known Member

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    Look at the definitions in Article 100. However, in this case, you might as well read the sentence as ". . . satisfied, NM and/or UF cable may . . ."

    Cheers, Wayne
     
  20. Reach4

    Reach4 Well-Known Member

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    What do you mean by "connectors"?
     
  21. wwhitney

    wwhitney Well-Known Member

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    In this context it means a fitting for connecting a wiring method to an enclosure.

    So a clamp that goes into a knockout for a cable wiring method, or a fitting to provide a threaded end for a locknut for a non-threaded conduit type wiring method. Rigid conduit doesn't have to use connectors, you can just thread the conduit and use two locknuts. Or if threading is too much trouble these days, there are compression-type rigid connectors, so you can just cut the pipe to length.

    Cheers, Wayne
     
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