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Electricalaka: J-boxaka: splice boxaka: pull box

Junction Box

In Plain English

A metal or plastic box where electrical wires are joined together, kept accessible behind a removable cover.

Definition

An enclosed protective container where electrical wires are connected together, providing a safe and accessible location for wire splices. Junction boxes must remain accessible and cannot be buried inside walls or ceilings without a cover. They are sized based on the number and gauge of conductors they contain.

Why It Matters in Bidding

Junction boxes are a high-count, easily missed item in electrical takeoffs, and because each one carries box, cover, mounting, conductors, and termination labor, undercounting them quietly erodes a bid's accuracy. Code-required accessibility also affects scope, since boxes concealed above hard ceilings or behind finishes may need access panels or relocation, all of which an estimator should catch before pricing rough-in.

Example

Doing rough-in takeoff for a tenant fit-out, the estimator counts every junction box at lighting whips, equipment connections, and home runs, then verifies none fall above the new gypsum hard ceiling where they would be inaccessible and require relocation.

Related Terms

ConduitConductorRacewayCircuit

Frequently Asked Questions

Code requires that wire splices stay reachable for inspection and future maintenance, so junction boxes cannot be permanently buried inside walls or above hard ceilings without an accessible cover or access panel. In estimating, this drives extra cost when boxes land behind finishes, since the team must add panels or reroute to keep them serviceable.
Estimators tally each box on the drawings at splice points, equipment terminations, lighting whips, and home runs, then attach material and labor units per box. Box size depends on conductor count and gauge under fill rules, so larger boxes carry more cost. Missing boxes is a common source of rough-in underestimates.
Box size is governed by the number, gauge, and arrangement of conductors and devices inside it, under code fill calculations that ensure wires are not crowded. More or larger conductors require a bigger box. Estimators match box sizes to the conductor schedule so the priced box actually accommodates the splices it will hold.

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