300.22B Limitations

[DPW]

Question 1: From this code reference, Can multiple sections of Flexible Metal Conduit (<4' each) be installed?
Question 2: From this code reference, Is there a length limitation for MC cable?
Question 3: Is there any exceptions where liquidtight (LFMC) can be installed in a plenum per UL (#1995) or NFPA 90A?

300.22-
(B) Ducts or Plenums Used for Environmental Air Only wiring methods consisting of Type
MI cable, Type MC cable employing a smooth or corrugated impervious metal sheath without
an overall nonmetallic covering, electrical metallic tubing, flexible metallic tubing, intermediate
metal conduit, or rigid metal conduit without an overall nonmetallic covering shall be installed in
ducts or plenums specifically fabricated to transport environmental air. Flexible metal conduit
shall be permitted, in lengths not to exceed 1.2 m (4 ft), to connect physically adjustable
equipment and devices.................................

 

[iwire]

Not really.

Are you sure you are in a true 'duct' and not 'other space for environmental air'?

 

[Gregg Harris]

Question 1: From this code reference, Can multiple sections of Flexible Metal Conduit (<4' each) be installed?
Question 2: From this code reference, Is there a length limitation for MC cable?
Question 3: Is there any exceptions where liquidtight (LFMC) can be installed in a plenum per UL (#1995) or NFPA 90A?

300.22-
(B) Ducts or Plenums Used for Environmental Air Only wiring methods consisting of Type
MI cable, Type MC cable employing a smooth or corrugated impervious metal sheath without
an overall nonmetallic covering, electrical metallic tubing, flexible metallic tubing, intermediate
metal conduit, or rigid metal conduit without an overall nonmetallic covering shall be installed in
ducts or plenums specifically fabricated to transport environmental air. Flexible metal conduit
shall be permitted, in lengths not to exceed 1.2 m (4 ft), to connect physically adjustable
equipment and devices.................................

350.2 Definition.
Liquidtight Flexible Metal Conduit (LFMC). A raceway of circular cross section having an outer liquidtight, non-metallic, sunlight-resistant jacket over an inner flexible metal core with associated couplings, connectors, and fittings for the installation of electric conductors.

 

[DPW]

300.22B Limitations

This plenum space is actually inside an air handling unit. It is large enough to walk into. Imagine the size of an office cubicle to a small house. The entire interior is usually considered a plenum space. Ductwork is usually connected in various places to the air handler. It is usually located either on a roof or in a very large mechanical room.

 

[iwire]

This plenum space is actually inside an air handling unit. It is large enough to walk into. Imagine the size of an office cubicle to a small house. The entire interior is usually considered a plenum space. Ductwork is usually connected in various places to the air handler. It is usually located either on a roof or in a very large mechanical room.

Understood, if it is prefabed the NEC may not apply to it.

Beyond that you might have to stay outside of it and only penetrate it as close to the equipment as you can get.

 

[Smart $]

Question 1: From this code reference, Can multiple sections of Flexible Metal Conduit (<4' each) be installed?

If each has one end not in ductwork, yes. Otherwise, no.

Question 2: From this code reference, Is there a length limitation for MC cable?

No. But just to make sure you understand, the requirement isn't for your typical MC... it's referring to the kind that has a vapor impervious jacket (think corrugated tubing like used for gas range hookups)... not the typical spiral-wrapped metal ribbon.

Question 3: Is there any exceptions where liquidtight (LFMC) can be installed in a plenum per UL (#1995) or NFPA 90A?

If UL does except, you would have to get them to certify any customization (read, likely not going to happen). Not familiar with NFPA 90A.