National Electrical Code Top Ten Tips: Article 604, Manufactured Wiring Systems
- Though Article 604 has been around for many Code cycles (going back at least to the 2011 NEC) , you don't read much about it. One reason for that is this article occupies slightly less than one whole page in the NEC. Yet, it covers a type of wiring that is becoming increasingly common due to advantages in cost, speed, and quality.
- In essence, manufactured wiring systems are shop-built instead of field-built. But they are installed in the field [604.1].
- Because these systems cannot be inspected at the building site without damage to or destruction of the assembly [604.2], the NEC provides requirements for them [604.100] and for their installation [604.7].
- When installing these, be sure to secure and support them with the applicable Chapter 3 article for the cable or conduit type being used [604.7]. For example, if you connect these with FMC then you will need to treat the manufactured wiring systems as if they are part of an FMC wiring system; in that case, secure and support them per Article 348.
- Following on the same concept illustrated by 604.7, you must also follow the "Uses Not Permitted" of the applicable article [604.12].
- But you don't necessarily follow the "Uses Permited" of the applicable article. These can go in dry and accessible locations, but wet locations are excluded from the short list of permitted uses in 604.10.
- Cable types can be only listed Type AC cable or Type MC cable containing 600V, 8AWG to 12AWG insulated copper conductors [604.11(A)]. Other cables listed in 725.154, 800.113, and 830.179 can be used within the permissions of their respective articles.
- You cannot use FMT or any other kind of tubing with these systems. You can use only flexible metal conduit or liquidtight flexible conduit [604.11(A)(2)].
- You cannot use flexible cord for field installation. But it can be used as part of a listed factory-made assembly if it's suitable for hard usage and has 12AWG or larger conductors and isn't more than 6ft long and meets a few other requirements [604.100(A)(3)].
- Receptacles and connectors must be of the locking type. They must also be uniquely polarized, identified for the purpose, and part of a listed assembly for the appropriate system [604.100 (C)].