Run MC cable inside the ENT (Smurf Tube)

Z

zemingduan

Senior Member
Location
Philadelphia,PA
Occupation
Electrical Designer
In a prefabricated manufacture home, the ENT(Electrical Nonmetallic Tubing) is factory installed and is attached to the junction boxes through the connector. The ENT is concealed in wall/ceiling and the junction box is flushed mounted in the wall/ceiling. Only the junction boxes opening are accessible. However, the local fire alarm code amendment requires metal raceway or MC cable for fire alarm wiring. But obvious, only factory installed ENT conduit is provided.

I am thinking to pull MC cable inside the ENT conduit and make sure the conduit fill is met. After all, I think the ENT provide additional protection to the MC cable. I am not sure if local AHJ will allow this. I will verify with the township.

Before verify with local AHJ I want to know if the NEC allow you to pull MC cable inside the ENT if the conduit fill is met? I know this sounds silly because typically you strip off the MC cable metal armor and only pull the conductors inside the raceway when switch from MC cable to conduit. If its' allowed, can I pull the MC cable into the box, strip off the metal armor inside the box, install red head bushing and connect the conductors to the terminals? Or what else do I need?

Thanks!
 
Yes, the NEC allows cable assemblies to be installed in smurf but the manufactured home wiring is part of listed unit so the NFPA is probably not applicable for inside wiring.
 
roger said:
In the case of metallic cable sheaths in NM raceways you probably would.
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The ENT smurf tube is attached to the box with a listed connector. The MC cable is like the conductors pulled inside the ENT conduit. Do you still need attach the MC cable to the box in this case?

How and what type of connector do you use to attach the MC cable to the box if it is pulled in the ENT that is already attached to the box through a connector? And please note the box is installed in the finished wall/ceiling. I am an engineer and not very familiar with the installation. I want your advices of the connector and how the installation would look like :D
 
There really is no way to do this installation correctly. The MC cable sheathing needs to be bonded and the conductors need to be protected from the cut ends of the sheathing.

Is this a very large home? Curious why fire alarm wiring is even required.
 
I presume that you have NM tube to NM boxes.

I think that to do this installation you would need to replace the NM box with a metallic box, use the existing NM tube as a sheath to enable fishing the MC, and attach the MC cable to the metallic box. If the MC tube is considered a sleeve rather than a conduit assembly, then fill rules don't apply (but you have practical limits of what you can get through the sleeve).

You can get MC connectors for fished MC cables that you insert from _inside_ the box.
 
You may also double check that the locals actually do have jurisdiction, a in lot of places HUD or state requirements preempt local jurisdictions for manufactured homes.

I think the only way to do it is to cut out the boxes and whatever ENT you can reach from the existing hole in the wall, fish the MC through the ENT, and connect to a new metallic box as suggested above. You could probably use standard MC connectors and connect to the box before you shove the box into the wall also, dealer's choice.
 
curt swartz said:
There really is no way to do this installation correctly. The MC cable sheathing needs to be bonded and the conductors need to be protected from the cut ends of the sheathing.

Is this a very large home? Curious why fire alarm wiring is even required.
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I agree with you. Even though the MC cable has insulated ground wire that will serve as the EGC, the NEC requires the non-current carrying metal parts that is likely to be energized to be bonded. The metallic sheath can bot float electrically inside the box.
 
NEC Inspector said:
You may also double check that the locals actually do have jurisdiction, a in lot of places HUD or state requirements preempt local jurisdictions for manufactured homes.

I think the only way to do it is to cut out the boxes and whatever ENT you can reach from the existing hole in the wall, fish the MC through the ENT, and connect to a new metallic box as suggested above. You could probably use standard MC connectors and connect to the box before you shove the box into the wall also, dealer's choice.
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Yes. This is the only way I can think of too. We need to cut the box in the finish ceiling/wall, attached the MC cable to the junction box through connector. And use the ENT as sleeve only not the raceway.
 
winnie said:
I presume that you have NM tube to NM boxes.

I think that to do this installation you would need to replace the NM box with a metallic box, use the existing NM tube as a sheath to enable fishing the MC, and attach the MC cable to the metallic box. If the MC tube is considered a sleeve rather than a conduit assembly, then fill rules don't apply (but you have practical limits of what you can get through the sleeve).

You can get MC connectors for fished MC cables that you insert from _inside_ the box.
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Thanks all your input and I learn a lot! This is a multi-family building with each apt unit that is prefabricated module and delivered to the site. The apt module is still in manufacturing. The junction boxes will be metal.

I will ask them to change the preinstalled conduits for fire alarm wiring to metal conduits like EMT or FMC. In this case we can strip off the metal sheath of MC cable and only run conductors in the preinstalled conduits.
 
Primarily as a thought exercise, it seems to me that if forced to run MC cable through ENT between metal boxes, you could do it by creating a sort of locally double walled box, where the ENT is terminated to the outer wall, and the MC cable is terminated to the inner wall with an "install from inside the box" type MC connector. And the inner wall is just an appropriately sized L-shaped piece of steel, with one leg screwed to the back of the box (in a manner that qualifies as a bonding connection), and the other leg has the appropriately sized hole for the MC connector.

Cheers, Wayne
 
Your local fire alarm wiring amendments say to use MC or metal conduits because those cable "systems" are all that exist that will meet code. Fire alarm wires must hold a 2 hour fire rating and hold an active UL FHIT. That FHIT documnet is what NEC Article 728 will require you to follow to the letter and will supersede the rest of the NEC in case of conflict. Basically you must follow the FHIT's rules which will mandate certain brand conduits, connectors/couplers, different wire fill and special wire. Not to mention more supports, etc. Essentially, local restrictions are in line with the UL FHIT documents that are required by the NEC. What you are proposing will violate all FHIT's available and won't be code complaint. There are EMT and IMC systems that use FPLR wire which would probably be your best bet. Also the physical protection rule goes out the window since that is a conflict between the FHIT and the NEC, whereas the FHIT wins (Article 728).
 
NEC Inspector said:
You may also double check that the locals actually do have jurisdiction, a in lot of places HUD or state requirements preempt local jurisdictions for manufactured homes.
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THIS ☝️

Are you sure you even need to follow this local fire alarm code? It is really not practical for a manufactured home.
 
To clarify: only manufactured homes that you would see in a typical trailer park would fall under HUD regs and could be exempt from local jurisdiction in some areas. They are different from all other pre-manufactured structures because of Clinton era federal regulations and the resulting state regulations.

Just because something was built in a factory or off site does not give exemption to local requirements. The only way something built elsewhere and shipped in can be exempt from local codes is if the local building official decides to trust whoever is inspecting them at the factory. The building official would vet them the same way he would vet any other third-party inspector, and they would be submitting inspection reports to the building official for review.

An apartment building with premanufactured units like this one is absolutely subject to whatever the local guys want.

Interestingly, HUD regulations actually say that anything not covered by their handful of special rules falls under the 2008 NEC, so their requirements should line up with NFPA pretty well.
 
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Boingo1972 said:
Your local fire alarm wiring amendments say to use MC or metal conduits because those cable "systems" are all that exist that will meet code. Fire alarm wires must hold a 2 hour fire rating and hold an active UL FHIT. That FHIT documnet is what NEC Article 728 will require you to follow to the letter and will supersede the rest of the NEC in case of conflict. Basically you must follow the FHIT's rules which will mandate certain brand conduits, connectors/couplers, different wire fill and special wire. Not to mention more supports, etc. Essentially, local restrictions are in line with the UL FHIT documents that are required by the NEC. What you are proposing will violate all FHIT's available and won't be code complaint. There are EMT and IMC systems that use FPLR wire which would probably be your best bet. Also the physical protection rule goes out the window since that is a conflict between the FHIT and the NEC, whereas the FHIT wins (Article 728).
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NEC 728 is the requirements for fire resistive cable system. It applies to cable that is required to be fire resistive by other parts of the code. I don't think fire alarm wire is generally required to be fire resistive or 2 hr fire rating. Where do you get this requirement?

I think fire resistive or 2hr fire rating fire cable is required for Circuit Integrity (CI) Cable or some other specific applications.
 
760.176 Listing and Marking of NPLFA Cables.
Non-power limited fire alarm cables installed as wiring within buildings shall be listed in accordance with 760.176(A) and (B) and as being
resistant to the spread of fire in accordance with 760.176(C) through (F), and shall be marked in accordance with 760.176(G).

760.176(F)(1) and (2) require CI cables.
 
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