Short answer: NEC 110.26(A) applies to equipment likely to be examined or serviced while energized, and it asks for the working space in the table below - a minimum width, a depth that grows with voltage, and a door that opens 90 degrees. A 20 in cabinet recessed between frame rails misses that width wherever the rails stand proud of the face. You make the layout legal one of three ways. Interlock the door to the machine disconnect so the panel is dead before it opens; split the line voltage into a separate enclosure that keeps its own clearance; or bring the cabinet face out flush with the rails. The rule keys on the words 'while energized', not on the box size - that phrase is the whole escape hatch.
What NEC 110.26(A) asks for
NEC 110.26(A) covers equipment at 600 V or less that is likely to require examination, adjustment, servicing or maintenance while energized. Those last two words decide the question. A cabinet you open only after lockout sits outside the working-space rule; a cabinet you troubleshoot live owes the dimensions in the table, measured from its face. The 2020 and 2023 editions carry the same numbers.
| Dimension | What 110.26(A) asks | Note |
|---|---|---|
| Width | 30 in [762 mm] or the equipment width, whichever is greater | A 20 in cabinet still gets the full minimum, not its own width |
| Depth | 3 ft [900 mm] minimum for 0-150 V to ground in Condition 1 | Table 110.26(A)(1) grows the depth at higher voltages or when live parts face you from both sides |
| Height | 6.5 ft [2.0 m] or the equipment height, whichever is greater | Measured from the floor or platform |
| Door swing | At least 90 degrees | Set by the hinges, not the rails |
The space must stay clear: the zone runs from the face outward to the stated depth, and anything standing inside it counts as an obstruction. A frame rail flush beside the cabinet is scenery; a rail proud of the face is standing in the room you work in. The sizing guide applies the same numbers to a freestanding cabinet - how to size an electrical enclosure walks them in full.
Where the protruding rails break it
Work a 20 in cabinet recessed 2 in [50 mm] between frame rails, and the geometry fails before any argument starts:
- Space owed, panel serviced energized: 30 in wide x 36 in deep x 78 in high [762 x 914 x 1981 mm].
- Width past the cabinet edges: 30 - 20 = 10 in [254 mm], so 5 in [127 mm] of the required zone lies beyond each side.
- Rail intrusion: each proud rail occupies the first 2 in of the 36 in depth, right where the zone must be clear.
- Verdict: the full working-space rectangle is obstructed at both ends, so the recess fails for equipment you work on live.
The 90 degree door test usually passes - a door on the recessed face clears a 2 in rail within the first few degrees of swing. Width and clear depth are what fail. Clearance lives at the face you service from: rails behind the cabinet, or flush beside it, are irrelevant; proud of the face, they are inside the working space.
What the rule does not reach
The rule's own trigger is 'while energized'. A panel that goes dead before the door opens is not equipment likely to be examined or serviced energized, so the working space does not apply to it. Machine-build practice matches: NFPA 79, the standard for machine control panels, expects a supply disconnect on every machine and treats doors that expose live parts with interlocks or securing means.
Three clarifications settle most of the argument:
- Low voltage is no discount by itself. The depth table starts at the 0-150 V row, so a 48 V panel you probe live owes the same rectangle as a line-voltage one. The escape is dead-before-entry, not the voltage number.
- A panel listed to UL 508A changes nothing here. The listing covers the build; the room in front is an installation question under 110.26(A).
- Junction boxes ride on frames for the same reason. You open them with the circuit locked out, so they are not energized-service equipment either. Where a 120 V control circuit needs its own disconnect, when a 120 V enclosure needs a disconnect walks that call.
Three ways to make the recess pass
(a) Interlock the door to the machine disconnect. A lockable hinged door that cannot unlatch until the disconnect opens makes the whole panel dead-before-entry, and the recess stands as built. Keep the interlock in the circuit and the disconnect handle within NEC 240.24(A)'s 2.0 m [6 ft 7 in] reach rule; the mounting heights sit in the enclosure mounting guide, and the per-door interlock checks in electrical enclosure door interlock requirements.
(b) Split the line voltage out. Put the incoming supply, breakers and drive inputs in a separate enclosure mounted where the full working-space rectangle exists, and keep the recessed bay to the PLC and 24/48 V DC, fed through the supply switch that lives in the line-voltage box. The recessed door then only opens on a dead panel, which is stronger than an interlock - why the line side stays live in a separate disconnect enclosure covers the part an interlock leaves hot.
(c) Bring the face flush, or widen past the minimum. Move the cabinet forward the 2 in the rails steal, and the zone starts clean at the face, with the table's clear depth doing the rest. Widening the cabinet to the minimum width works the same way: the working space then equals the cabinet width and the proud rails stand outside it. This is the route that never needs an argument - the panel stays serviceable energized and the numbers simply pass.
Decide by what the machine gives you. A proper supply disconnect and a lockout routine make (a) the least work. Spare space elsewhere on the frame makes (b) the cleanest for maintenance. Two inches of envelope or a wider door make (c) unconditional.
What to put on the drawing
- The recessed cabinet at your width, with hinge side, interlock cutout and gland plate decided at order time; we build each box from one piece and deliver in 10 business days from drawing approval - start at custom enclosures.
- The separate line-voltage enclosure, sized with the enclosure selector by inside width, height and module count, mounted where the clear working-space zone exists.
- Adjustable mounting brackets behind the recessed cabinet, so you can pull the face flush with the rails later without rework.
- The disconnect handle within NEC 240.24(A)'s 2.0 m [6 ft 7 in] reach, on the side of the machine the operator actually uses.
Recess the cabinet, make it go dead first, and you keep both the machine footprint and the code.
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 |
|---|---|---|---|
| 60 × 36 × 16 in | 304 stainless | 60 x 36 x 16 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 48 × 36 × 16 in | 304 stainless | 48 x 36 x 16 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 60 × 36 × 12 in | 304 stainless | 60 x 36 x 12 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Does NEC 110.26 apply to a 48 V DC control panel?
The depth table in 110.26(A) starts at the 0-150 V-to-ground row, so 48 V DC sits inside it: a panel you probe live owes the full working-space dimensions from the table. The depth follows the highest voltage inside the panel, so 24 V I/O circuits in a 480 V cabinet change nothing either. The honest escape is dead-before-entry - one lockable supply switch - which makes it equipment you only open de-energized.
How wide must the clear space in front of a 20 in cabinet be?
The table's minimum width, because NEC 110.26(A) sets it at the equipment width or that minimum, whichever is greater, and the 20 in cabinet loses the comparison. Frame rails standing 2 in proud of the face sit inside the zone. Bring the cabinet face flush with the rails and keep the full clear rectangle, door opening 90 degrees.
Does a door interlock remove the working-space requirement?
Yes, on the rule's own words: 110.26(A) reaches equipment likely to be examined or serviced while energized, and a lockable door interlocked to the machine disconnect makes the panel dead before the door unlatches. Build the interlock into the door latch rather than a separate switch a hand can bypass - a defeatable interlock puts the panel back in energized-work territory and the working-space rule applies again.
How deep does the space in front of a 480 V machine panel have to be?
A 480 V three-phase feed is 277 V to ground, in the 151-250 V row of Table 110.26(A)(1): the table's depth in Condition 1, where live parts are guarded or sit on one side only. Where live parts face you from both sides it rises to 4 ft [1.2 m]. The 0-150 V row starts at the same depth, so a low-voltage panel owes the same room - the split buys width and a dead-before-entry design, not a smaller number.
Does listing the panel to UL 508A change the clearance answer?
The listing covers the build, the clearance covers the room. UL 508A lists the panel; NEC 409.2 defines an industrial control panel, and 409.110 asks for the enclosure type number on it. NEC 110.26(A) still governs the space in front at the machine: the working-space width and depth for a panel you service energized, whatever the label says.
