In the Home Owner's electrical test, the term "environmental air" is used. What does this term mean, and where is it defined? and can you use a non-metallic box?

Also when reading the question do you read that the box is installed inside the duct or in the framing that the duct is in?



Physically Constructed Ducts or Plenums

This would be the actual tube where HVAC air is moved through.

In a physically constructed duct or plenum, there is no wiring allowed unless it is necessary for the direct action upon, or sensing of, the contained air. Even then, nonmetallic boxes are not allowed.

Spaces Used for Environmental Air, Other Than Ducts and Plenums

This might be the area above a drop ceiling, or under a raised floor.

In this case, only specific things are allowed.

  • Type MI cable.
  • Type MC cable without an overall nonmetallic covering.
  • Type AC cable.
  • Factory assembled multiconductor control or power cable that is specifically listed for the use.
  • Listed prefabricated cable assemblies of metallic manufactured wiring systems without nonmetallic sheath.
  • Electrical Metallic Tubing (EMT).
  • Flexible Metallic Conduit (FMC).
  • Intermediate Metal Conduit (IMC).
  • Rigid Metal Conduit (RMC) without an overall nonmetallic covering.
  • Surface metal raceway, or metal wireway with metal covers, or solid bottom metal cable tray with solid metal covers.

Again, no nonmetallic boxes.

300.22(C)(2) Equipment

This section does not apply, since a junction box is likely not considered "Electrical Equipment" as far as this code section is concerned.

If you'd like to read the actual code verbiage, it can be found in my answer to this question.

This YouTube Video from Mike Holt on the subject, might also be worth watching.

  • The verbage still is confusing after the video. This is the only question I missed on the exam. However I did not write the codes used on at least 2 other answers and instructions said I was supposed to... Did you understand the sentence first hand? I asked an electrician I know and he was confused and that I was talking about in between walls or ceilings where ducts were ran. – DMoore Aug 6 '13 at 21:23
  • @DMoore Is the title of this question the exact wording from the test? – Tester101 Aug 7 '13 at 12:58
  • Yes, except for "according to the NEC 2008" which is assumed for every question. – DMoore Aug 7 '13 at 14:48
  • Then the answer is no, according to 300.22(B) and 300.22(C). Nonmetallic boxes are not mentioned in the acceptable materials listed within these code sections. Therefore, they are not allowed. – Tester101 Aug 7 '13 at 15:46

"Environmental Air" seems to mean ducting/plenums for air conditioning/etc. 300.22(B) relates specifically to the ducts/plenums, while 300.22(C) is specific to the spaces around the ducts/plenums (ie ceiling spaces, wall cavities, etc).

I think you're looking for:

*300.22(C) Other Spaces Used for Environmental Air (2) Equipment. Electrical equipment with a metal enclosure, or with a nonmetallic enclosure listed for the use and having adequate fire-resistant and low-smoke-producing characteristics [...]

Also, this Q&A states in the last paragraph that:

Electrical equipment with metal enclosures is permitted to be installed in a cavity plenum space [300.22(C)(3)]. Examples of electrical equipment permitted in a cavity plenum space would be air-handlers, junction boxes, [...]

So, I revise my answer to, "Yes, provided that they have adequate fire-resistant and low-smoke-producing characteristics."

  • I saw that but didn't see if it referred to the boxes having to be metallic or not. – DMoore Aug 2 '13 at 19:26
  • Fair enough -- I didn't see anything specifically call out boxes. Guess it was a sort of assumption given that every other provision requires uncovered metallic <pieces>. – Jacob S Aug 2 '13 at 19:30
  • So the way the question is phrased seems bad or wrong to me. Maybe I am wrong though? I take it to mean that you have ductwork in a joist. What kind of box do you need to use in that same joist (framing)? I mean there are plastic gang boxes meant for this right? Really confused on the terminology. – DMoore Aug 2 '13 at 19:36
  • Maybe they fall under "Electrical Equipment" enclosures of 300.22(C)(3), Electrical equipment with a metal enclosure, or with a nonmetallic enclosure listed for the use and having adequate fire-resistant and low-smoke-producing characteristics. – Jacob S Aug 2 '13 at 19:36
  • Specifics on conduit "Electrical nonmetallic tubing and rigid nonmetallic conduit are not recognized for use in other space used for environmental air in accordance with 300.22(C)." 518.4 (C)(2) note – Jason Aug 2 '13 at 19:36

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