A dilettante's question about NEC-approved wiring methods

[tfinks]

I observe many municipal and industrial structures made with square or rectangular steel tubing, welded on site. Inside the tubing sometimes is found wiring for lighting or other purposes. Since these purpose-built steel structures are not listed as an approved wireway, how does the NEC justify this wiring method? And how are approved fitting found to provide entrance and exit of the conductors? Should the wiring be done in approved conduit or wireway on the outside of the tubing?

 

[petersonra]

Governments in general are not subject to the NEC, unless they decide they want to be.

Some kinds of wire and cable do not require a wireway at all.

 

[GoldDigger]

One way around this would be to pull flexible metallic conduit inside the structural member. Or BX/MC/AC.
Some wires that do not require conduit (like PV wire and Tray Cable) would still be vulnerable to welding slag on inside of member during pulling or from vibration after pulling.

 

[Coppersmith]

Most lighting fixtures have wiring in some kind of tubing that is not an approved general purpose conduit. The wiring terminates either in a socket or in a base pan of some sort. The light fixtures are submitted for listing with a national testing agency. All the approved ones I have seen look safe. There are a bunch of unapproved (usually Chinese made) that look really dangerous.

 

[tfinks]

I was thinking especially about the SmartTrain terminals nearby and the lighting fixtures attached to the steel structures. There is no wiring seen external to the welded steel tubing, so the wiring must be inside. These folks never call me to show me what they are doing.

Many thanks for the replies.