Metal Wireways

A metal wireway is essentially a long rectangular sheet-metal trough with a hinged or removable cover. Because you can open the whole length, it's ideal where many conductors run in parallel and need frequent additions or changes — around control panels, machine lineups and equipment rooms.

The article caps how many current-carrying conductors can fill it before derating, limits the cross-sectional fill to 20 percent, and requires supports and, in wet locations, a raintight design. Splices are allowed inside as long as they don't exceed 75 percent of the wireway's area at that point.

When it applies

Metal wireways are sheet-metal troughs with removable covers that let you route and splice many conductors with easy access. They shine in equipment rooms and control areas where circuits get added and changed often.

Common mistakes

• Overfilling past the twenty percent conductor fill limit because the cover still latches.
• Ignoring derating once a large number of current-carrying conductors ride together in the trough.
• Splicing without keeping the taps and splices within the allowed percentage of the wireway's cross-section.

In the field

In a motor control room I used a wireway as the backbone so future circuits could be dropped in without ripping open conduit. The removable cover makes additions clean. The discipline is fill and heat: I keep the conductor area under twenty percent and apply derating when the bundle count climbs. Treated with respect, a wireway is the most maintainable raceway in the building.