Short answer: a junction box you are likely to service energized owes the NEC 110.26(A) working space in front of it. That space is 30 in [762 mm] wide, 3 ft [900 mm] deep at 0-150 V to ground, and 6.5 ft [2.0 m] tall. A splice box you open with the circuit locked out owes none of that depth. It still owes access: above a lay-in ceiling, that means sitting under a removable tile or behind a panel that exposes the whole cover. The trap is calling every ceiling box exempt. The moment the box carries terminals a technician resets live, the depth rises to 3 ft 6 in [1.1 m] at 151-250 V to ground. A ceiling void cannot deliver it. Here is how the rule splits, with the numbers to put on the drawing.
What NEC 110.26(A) asks
The working-space rule attaches to equipment, not to boxes as a class. NEC 110.26(A), in the 2020 and 2023 editions, asks for clear space in front of equipment operating at 1000 V or less to ground when it is likely to require examination, adjustment, servicing or maintenance while energized. Older editions wrote the same scope at 600 V. The pivot is the word likely, and you judge it from the work the box actually sees.
Sort every box on your drawing into one of two labels before anything else:
- Dead-work box: splices, taps and spare capacity, opened behind a lockout. It claims no depth rectangle.
- Live-work box: disconnects, starters, live control terminals or diagnostic points a technician touches with the circuit on. The full dimensions apply.
A plain junction or pull box lands on the dead-work side in most panels: you open it to make or repair a splice, and that job starts with a lockout. Its remaining obligation is access, covered below. Equipment an operator resets under load, or that a tech troubleshoots with covers off, lands live-work, and the space becomes real geometry.
The label is also your safety story. Verify absence of voltage before opening any box you marked dead-work — the label holds only while the work behind it stays dead.
The three dimensions and their numbers
Live-work equipment claims a rectangle directly in front of its face. Table 110.26(A)(1) sets the depth by voltage to ground; the figures here are Condition 1, the column for exposed live parts on one side of the space and grounded parts on the other:
| Voltage to ground | Depth owed (Condition 1) |
|---|---|
| 0-150 V | 3 ft [900 mm] |
| 151-250 V | 3 ft 6 in [1.1 m] |
| 251-600 V | 4 ft [1.2 m] |
With exposed live parts facing you from both sides, the same table's deeper columns add 0.5 to 2 ft. Width is the greater of the equipment width or 30 in [762 mm], measured across the front; a 16 in wide enclosure still claims the full 30 in, centered on it. Height runs to 6.5 ft [2.0 m] above the floor or platform, or to the equipment top when that stands higher. NEC 110.26(A) adds one line for doors: equipment doors open at least 90 degrees inside the space.
Two habits keep the rectangle honest. Measure from the enclosure face, not from the wall behind it. And count every obstruction inside the strip: a pipe that sneaks in below the face fights the same math as working space with a pipe below the panel. The enclosure sizing guide walks these dimensions into a full panel layout.
What the rule leaves alone
A dead-work box owes no depth rectangle. It still owes access, and that comes from the code's box rules rather than from 110.26(A): a junction or pull box must be accessible — reachable, and openable without tearing out building structure or finish. Access has a shape you can check:
- Above a lay-in ceiling, the box sits inside a removable tile's opening, or within arm's reach of one.
- Behind drywall or plaster, a hinged or screw-fixed panel exposes the whole cover and its screws.
- The cover comes off with ordinary tools, and the splices stay visible for inspection.
The lay-in tile passes because the grid keeps the ceiling removable; sealed drywall fails until you cut the panel. Covers and access for concealed junction boxes sorts out each of these cases, and restoring access to a box sealed behind drywall shows the retrofit path. Watch the migration risk too: the day someone adds a contactor or test terminals to that ceiling box, the 110.26(A) rectangle arrives with them. A ceiling void cannot meet the 6.5 ft height leg, because there is no floor or platform in front of the box.
The ceiling decision, case by case
Run each ceiling box through three questions and the location answers itself.
- What work happens at this box? Splices opened behind a lockout stay dead-work. Terminals, disconnects or devices touched with power on go live-work.
- Can you reach it? Dedicate a lift-out tile, or cut an access panel at least as big as the cover plus working room — the access panel options for a recessed junction box cover the styles. A box you reach by cutting finish each time fails.
- If live-work, does the rectangle fit? Depth per the voltage column, 30 in wide, 6.5 ft tall measured from a floor or platform. A ceiling void supplies none of the height leg, so live-work equipment moves to a wall at standing height, or you build a platform with a permanent access opening and the full rectangle inside it.
A box recessed between joists fights the same depth math as a recessed cabinet between frame rails: the structure behind eats the space. Measure face-to-obstruction, never wall-to-wall.
Worked example: two boxes over one ceiling
Take one lay-in ceiling, structure at 9 ft [2.7 m], tiles 24 x 24 in [610 x 610 mm].
Box A — 277 V lighting splices. A 12 x 12 x 6 in steel box on a strut frame holds splice-only connections for a 277 V lighting circuit. The 277 V to ground would put live work in the 251-600 V column at 4 ft [1.2 m]. Splice work starts with a lockout, so the box is dead-work and claims no rectangle. Access check: the 24 in tile over the box is wider than the 12 in cover on every side, so the cover lifts out through the opening with room for a hand. Passes.
Box B — 240 V heater contactor. A 16 x 16 x 8 in terminal enclosure feeds a 240 V single-phase heater contactor that operators reset while energized. This is a live-work box at 151-250 V to ground:
- Depth owed: 3 ft 6 in = 42 in
- Width owed: the greater of 30 in or the 16 in box width = 30 in
- Height owed: 6.5 ft = 78 in above the working surface
Above the ceiling, the box face stands 26 in from the joist behind it: 42 - 26 = 16 in short, and there is no floor or platform to hang the 78 in height from. The ceiling location fails. Move the enclosure to the corridor wall below, where the opposite wall sits 48 in away: 48 - 42 = 6 in of spare depth. That passes. Center the 30 in strip on the box, keep the duct and the riser out of it, and the drawing holds.
Same building, two outcomes, decided by the dead-work and live-work labels alone.
What goes on the drawing and the order
Finish with these lines and the clearance question closes itself:
- Label every box dead-work or live-work on the panel schedule.
- Draw the working-space rectangle for live-work equipment: depth per the voltage column, 30 in wide, centered on the enclosure face.
- Give each above-ceiling box a dedicated lift-out tile, or an access panel at least the cover size plus working room — 16 x 16 in for a 12 x 12 in cover leaves 2 in per side.
- Keep the access opening wide enough for a hinged enclosure door to swing 90 degrees; NEC 110.26(A) counts the door swing.
- Mount live-work enclosures at standing height, with the highest operating handle no more than 2.0 m [6 ft 7 in] above the floor under NEC 240.24(A); the enclosure mounting guide carries the heights.
Choose the box for the environment, not the clearance. A stainless wall-mount enclosure rated NEMA 4X / IP66 by the manufacturer; not UL listed, seals water and dust, while the NEC sizes the space in front of it. Custom stainless enclosures build to your dimensions and cutouts from one piece, delivered in 10 business days from drawing approval, and the enclosure selector shortlists catalog sizes and carries the odd duty to a custom quote.
The decisions, one line each:
- Splice box under a lay-in ceiling: keep it inside a removable tile; no depth rectangle.
- Splice box behind drywall: cut an access panel that exposes the whole cover.
- Live-work box at 151-250 V to ground: 3 ft 6 in deep, 30 in wide, 6.5 ft high at standing height.
- Live-work box at 251-600 V to ground: 4 ft [1.2 m] deep.
- Live-work box offered a ceiling void: relocate it, or build the platform and the full rectangle into the access design.
Catalog dimensions to compare
Compare these catalog dimensions with your component layout. Open each enclosure for its rating, material and usable space, then check those specifications against your application.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 12 × 12 × 6 in | 304 stainless | 12 x 12 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 16 × 16 × 8 in | 304 stainless | 16 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 6 × 6 × 4 in | 304 stainless | 6 x 6 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 8 × 6 × 4 in | 304 stainless | 8 x 6 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Does a junction box above a suspended ceiling need 3 ft of working space?
Only when you are likely to service it energized. A splice box opened behind a lockout skips the NEC 110.26(A) dimensions, but it must stay accessible under a lift-out tile or behind a panel that exposes the whole cover. A box with 151-250 V terminals worked live owes 3 ft 6 in of depth, 30 in of width and 6.5 ft of height, which a ceiling void cannot supply.
How wide must the working space in front of a junction box be?
The greater of the equipment width or 30 in (762 mm), measured across the front of the box. A 16 in wide enclosure still claims the full 30 in, so center the strip on the box and keep conduit, ductwork and stored boxes out of it.
Does the enclosure's ingress rating change the clearance I need?
No. A rating such as NEMA 4X / IP66 - ours is rated by the manufacturer and not UL listed - seals water and dust at the door and gasket; it says nothing about the space in front. NEC 110.26(A) sizes that space by voltage to ground and by whether the equipment is likely to be serviced energized, whatever the enclosure is rated.
Can I keep a splice box behind drywall if I cut an access panel?
Yes, when the panel exposes the whole cover so you can remove it without cutting structure or finish. For a 12 x 12 in cover, a 16 x 16 in hinged panel leaves 2 in of working room per side; a screw-fixed panel works when its screws stay reachable. A panel smaller than the cover leaves the box sealed behind the wall, and the installation fails the access rule.
How high must the working space extend above the floor?
From the floor or platform to 6.5 ft (2.0 m) above the equipment, or to the equipment top when it stands taller. An above-ceiling box has no floor or platform in front of it, so live-work equipment belongs at standing height, with the highest operating handle no more than 6 ft 7 in (2.0 m) above the floor under NEC 240.24(A).
