Is this wiring OK?

[AntonLargiader]

I pulled 14-3 MC through a drilled hole in my soffit to fed the porch light; I used MC because of possible nails and so forth in the areas that I couldn't see. 3-wire because there's a 3-way inside the house and another 3-way outside.

Subsequently I decided that the outside switch box should be plastic so that a WiFi switch in it would get better signal. Even though the house end of the MC is bonded to a grounded metal box, I have read that I can't run the MC to a plastic box.

So, rather than run the 3-wire to the switch and then 2-wire back up to the fixture, I am hoping I can run the 3-wire to the fixture and then two 14-2 UF-b cables from there down some PVC conduit to the switch: one would be the travelers and one would be load and neutral.

Question: is it OK to repurpose the neutral conductor that way? I don't see any 4-wire at my Lowes.

 

[jeffmattero76]

Not an expert, but it is my understanding that the neutral must run in the same cable as the hot.

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[PCustoms]

If you are running conduit just get individual wires, thwn I believe.

 

[wyliesdiesels]

All conductors of a circuit must be together

 

[AntonLargiader]

Then it sounds like I should just go grab some 12-3 UF-b. That way I have travelers and their neutral in one cable going to the switch, and power and neutral in a separate cable going to the light.

If it was a "Sure, we double Romex up all the time that way" thing then that's one thing, but I don't want to generate any kind of sideways glance from the inspector.

I guess two Romex cables running together doesn't really count as together, right?

And it's not all conduit... just from the switch up through the ceiling. The trusses really clog up the space above that, and the switch is sort of in a wall between the main porch and the vestibule, which are each framed differently. I thought about conduit and gave up on that.

 

[wyliesdiesels]

How about some nm-b 12-2-2?

 

[AntonLargiader]

Doesn't have to be 12 since it's fed by 14. And where it comes down the post in conduit, I think it's a wet location. It will certainly get wet in some storms.

 

[teamextreme]

Wait a tic, back up to the original premise that you can't run MC to a plastic box. I've never heard of that. True, it's not something you normally see, but what code section would disallow it? As long as the metal jacket is grounded, which he says it is, what's the issue?

Edit: Nevermind, I think I just realized the issue... not being able to use a connector on the MC is probably the reason, Yes?

 

[Jkcolo22]

Wait a tic, back up to the original premise that you can't run MC to a plastic box. I've never heard of that. True, it's not something you normally see, but what code section would disallow it? As long as the metal jacket is grounded, which he says it is, what's the issue?

Edit: Nevermind, I think I just realized the issue... not being able to use a connector on the MC is probably the reason, Yes?

You could technically use the proper connector with a metal blank front plate with the 1/2” knockout... interested to see how this one comes out.


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[AntonLargiader]

My original plan (once I decided to use a plastic box) was to run the PVC conduit up into the ceiling and at that point I would use a double MC connector to join the original 3-wire NC and the 2-wire MC going to the fixture. The metal jackets would end at that connector (single strands going down the conduit is fine since they are identified as TWHN) and I'd have bonding all the way to the fixture. And I can still do that, but not if it raises any eyebrows.

Since the ceiling will be finished at some point, I am trying to avoid having exposed cover plates everywhere. If that wasn't an issue, I'd transition from one wire type to another to make this simpler.

 

[TRWham]

As long as everything is bonded, 314.3 has an exception that explicitly permits armored cable to be used with non-metallic boxes.

 

[mm08822]

As long as everything is bonded, 314.3 has an exception that explicitly permits armored cable to be used with non-metallic boxes.

Yes but AC cable is not MC cable, which is what the OP posted.

MC cable in between plastic boxes would not have the armor grounded. This could easily be a safety issue if a conductor becomes nicked and energized the jacket.

 

[TRWham]

Yes but AC cable is not MC cable, which is what the OP posted.

MC cable in between plastic boxes would not have the armor grounded. This could easily be a safety issue if a conductor becomes nicked and energized the jacket.

In this case, I interpret the code is using the term generically (referring to "metal-armored" (lower case) cable and not AC specifically), but I agree it could be interpreted differently. As long as there is a continuous ground path and each metal component is bonded, why would it not work? That MC has a separate ground conductor makes it even easier.

 

[alfredeneuman]

I As long as there is a continuous ground path and each metal component is bonded, why would it not work? That MC has a separate ground conductor makes it even easier.

Because plastic is non-conductive, and the armor must be grounded.

 

[alfredeneuman]

I pulled 14-3 MC through a drilled hole in my soffit to fed the porch light; I used MC because of possible nails and so forth in the areas that I couldn't see.

MC cable has the exact same rules as NM when it comes to protection from physical damage

 

[AntonLargiader]

In my case, the armor would be grounded. The originating box in the house is metal and grounded. The MC housing would be grounded all the way to the double MC connector, which would ground the housing from there to the fixture. But I don't know if that meets the letter of the law. I read some references to "internally bonded" which make me think of grounding bushings inside plastic boxes which would mean connections, which wouldn't work because I don't want another access cover.

If I can run the MC as described, bonding the two housings via the connector, then I'll just do that.

And if I can't, then I'll get some 14-3 UF-b and do it that way.

 

[AntonLargiader]

MC cable has the exact same rules as NM when it comes to protection from physical damage

I chose MC because it is better protected against the likely dangers when drilling and fishing through unseen areas in a 90 year old house. Rules had nothing to do with it.

 

[alfredeneuman]

I chose MC because it is better protected against the likely dangers when drilling and fishing through unseen areas in a 90 year old house.

Why would you think that, and why would the age of the house matter?
EDIT: I was replying to TRWham when I made the previous comment on the plastic

 

[AntonLargiader]

We can take it to an MC cable discussion thread if you're really interested.

 

[mm08822]

In this case, I interpret the code is using the term generically (referring to "metal-armored" (lower case) cable and not AC specifically), but I agree it could be interpreted differently. As long as there is a continuous ground path and each metal component is bonded, why would it not work? That MC has a separate ground conductor makes it even easier.

Because plastic is non-conductive, and the armor must be grounded.

That's the problem....the mc cable jacket used between two plastic boxes would be left ungrounded. Ac has a bare conductor in coontact with the armor and mc has an insulated grd.

 

[AntonLargiader]

That's the problem....the mc cable jacket used between two plastic boxes would be left ungrounded...

And I suspect much of what is written on forums may not distinguish between "between plastic boxes" and "to a plastic box."

 

[wyliesdiesels]

how would you bond the jacket of MC when youre using a plastic box?

 

[mm08822]

how would you bond the jacket of MC when youre using a plastic box?

Only way is from an upstream metal box.

One plastic box (downstream) of the mc cable could be considered ok. Too risky for my liking.

 

[mm08822]

And I suspect much of what is written on forums may not distinguish between "between plastic boxes" and "to a plastic box."

Probably not. It's kind of hack to mix hardware intended for different wiring methods.

 

[TRWham]

And I suspect much of what is written on forums may not distinguish between "between plastic boxes" and "to a plastic box."

I understood that you were running MC from the panel to a plastic box, then transitioning to UF and/or PVC conduit. There would only be one run of MC that is bonded at the panel and no need for further bonding as there is no more metal.

 

[AntonLargiader]

I understood that you were running MC from the panel to a plastic box, then transitioning to UF and/or PVC conduit. There would only be one run of MC that is bonded at the panel and no need for further bonding as there is no more metal.

Sorry the side of my diagram got cut off, but it's either:

1) MC to metal box and UF to plastic box, or
2) MC to plastic and bonding to another MC via a double connector.

I think I have my answer. Reading the responses here, option 2 may be OK but its legality is unclear or confusing to people who work with this stuff all day. No reason to go there.

 

[TRWham]

Sorry the side of my diagram got cut off, but it's either:

1) MC to metal box and UF to plastic box, or
2) MC to plastic and bonding to another MC via a double connector.

I think I have my answer. Reading the responses here, option 2 may be OK but its legality is unclear or confusing to people who work with this stuff all day. No reason to go there.

I had not seen the diagrams when I first responded so I was interpreting the original description. Option 1 seems clearly permitted and perfectly safe. Metal conduit to metal box, all bonded, then transition to UF and run to the plastic box.

I have seen option 2 described elsewhere as a work around but 1 seems more straightforward.

 

[TRWham]

Looking at your diagram again, I am prompted to ask why you need 5 wires at the switch? Which wires are already run? Is it still possible to run power straight to the light and 3 wires to each switch?

 

[alfredeneuman]

how would you bond the jacket of MC when youre using a plastic box?

With a connector that has threads and a grounding bushing?

 

[AntonLargiader]

Looking at your diagram again, I am prompted to ask why you need 5 wires at the switch? Which wires are already run? Is it still possible to run power straight to the light and 3 wires to each switch?

Three to carry the travelers and their neutral current, and two for the fixture. Keeps the neutrals with their associated conductors. Merely running three wires for a switch loop does not provide a neutral, which is required now.

 

[TRWham]

Three to carry the travelers and their neutral current, and two for the fixture. Keeps the neutrals with their associated conductors. Merely running three wires for a switch loop does not provide a neutral, which is required now.

Got it.

 

[mm08822]

With a connector that has threads and a grounding bushing?

very good!

 

[AntonLargiader]

In this case, I interpret the code is using the term generically (referring to "metal-armored" (lower case) cable and not AC specifically), but I agree it could be interpreted differently.

Looks like you're probably right. I found this quote here: "For the purposes of this exception, the term metal-armored cable includes cables with a metal covering such as mineral-insulated, metal-sheathed cable (Type MI), metal-clad cable (Type MC), and armored cable (Type AC)."

 

[mm08822]

Looks like you're probably right. I found this quote here: "For the purposes of this exception, the term metal-armored cable includes cables with a metal covering such as mineral-insulated, metal-sheathed cable (Type MI), metal-clad cable (Type MC), and armored cable (Type AC)."

You should go back and read the sentance before the one you take out of context. You'll find your plastic box alone doesnt meet the requirement.

Look at the pic i posted of the difference between ac and mc cable. Without special provisions within the plastic box, mc fails. (The sentance b4 the 1 u quoted.)

 

[AntonLargiader]

Not sure what you're getting at. There are two exceptions to 314.3 and both have the explanatory wording I cited that supports TRWam's opinion that MC cable was included in the exception. That's all. I was replying to his post saying he thought MC was included but he could be wrong.

Whether or not either of the exceptions apply to my situation is different, but it doesn't matter at this point.

You should go back and read the sentance before the one you take out of context. You'll find your plastic box alone doesnt meet the requirement.

Look at the pic i posted of the difference between ac and mc cable. Without special provisions within the plastic box, mc fails. (The sentance b4 the 1 u quoted.)

 

[AntonLargiader]

Done and working. The only hitch I ran into is that the waterproof Taymac enclosure (at the other end of that UF-b) was designed to use a switch with a metal frame, and the plastic frame of the Wemo switch is thicker and therefore makes the cover gap away from the box. I’ll get some thicker gasket for that.