Tunnels - Indoor vs Outdoor?

[NEC User]

Are tunnels considered indoors or outdoors?

NEC 225.7 Lighting Equipment Installed Outdoors => NEC 225.7(B) Common Neutral. The ampacity of the neutral conductor shall not be less than the maximum net calculated load current between the neutral conductor and all ungrounded conductors connected to any one phase of the circuit.

Is this required for tunnels?

 

[texie]

Are tunnels considered indoors or outdoors?

NEC 225.7 Lighting Equipment Installed Outdoors => NEC 225.7(B) Common Neutral. The ampacity of the neutral conductor shall not be less than the maximum net calculated load current between the neutral conductor and all ungrounded conductors connected to any one phase of the circuit.

Is this required for tunnels?

A common neutral is not required for any outdoor feeder or branch circuit, rather just an option. It is the only place left (almost) in the code where you can do this. This relates to using 1 neutral for 2 or more ungrounded conductors on the same phase. Not to be confused with a MWBC.

As for the question of if a tunnel is outdoors or not, I'm not sure. I'd be inclined to say no.

 

[Smart $]

FWIW and JMO, indoors typically refers to the inside of a building or any substantially enclosed portion of a structure removed from exposure to weather elements. Anything not indoors is considered outdoors or an indoor-outdoor barrier.

A tunnel, or portion thereof, can be either an indoor or outdoor location, IMO. I would use the "exposure to weather elements" as the main determining factor.