Fixture Wires

Article 402 covers fixture wires — the small-gauge, heat-rated conductors used within luminaires and to connect them to their branch circuit. It lists the types by insulation and temperature rating, sets minimum sizes, and specifies where each may be used.

Fixture wire isn't general branch-circuit wire: it's limited to the connection of fixtures and control gear, and it must be protected by an appropriately sized overcurrent device. The temperature rating matters most, because these conductors live in the hottest part of a lighting installation.

When it applies

Fixture wires are the small insulated conductors used inside luminaires and to connect them, types like TFN, TFFN, and RFH. Article 402 sets their permitted sizes, temperature ratings, and, importantly, the fact that they are not general branch-circuit wire, they connect fixtures and similar equipment, they do not replace building wire.

Common mistakes

• Using fixture wire as branch-circuit conductors in a raceway, it is not rated or sized for that role.
• Overlooking the temperature rating where the wire lands near a hot ballast or LED driver.
• Protecting small fixture wire at too high an overcurrent value instead of respecting its limited ampacity and the tap rules.

In the field

When I rework an old fixture I match the replacement lead to the original type and temperature rating. Grabbing whatever thin wire is in the truck is how insulation cooks against a warm driver and starts to crumble a few years down the road.