Measure wire bending space from the end of the lug, in a straight line, perpendicular to the wall the conductor crosses — not to the nearest hole. For one 750 kcmil conductor per terminal in a power junction box, NEC 312.6, Table 312.6(B) gives 19 in [483 mm]. Two 750 kcmil on one lug raise that by 25 percent, to 23.75 in [603 mm]. The dimension decides the box before anything else does: it sets how high the lugs sit above a bottom gland plate, or how far front to back the body runs when cables enter the rear wall. Work it out at the drawing stage, because a stiff 750 kcmil tail gives you no second chance on installation day.
What wire bending space is
Bending space is the clear room a conductor needs for its final bend into the terminal. A shortfall buys you scored insulation, kinked strands and a lug levered sideways. NEC Article 312 covers cabinets and cutout boxes, and 312.6 sets the minimum at terminals from the conductor size and the number of conductors per terminal. The table value is a clearance you keep empty: it is measured to the first obstruction, so a duct corner, a spare tail or a clamp inside it shrinks the number to that obstruction.
Keep the rectangle around each lug empty on the drawing, and position bus, duct and terminals so the space survives fabrication; the backplate and DIN rail layout guide walks that arrangement. Bending space also sits apart from box fill. NEC 312.8 limits how much of a cabinet goes to conductors, splices and taps, and the two checks never share a dimension.
Where you measure from
Start at the end of the lug or wire connector, where the conductor leaves the barrel, and run a straight line perpendicular to the wall the conductor crosses. In a power junction box with bottom entry, that wall is the bottom gland plate, so the bending space is the vertical gap from each lug tip down to the plate. The wall your lugs are bolted to does not set the direction; the entry wall does.
The termination-point-to-box-entrance shortcut only works when the gland sits directly opposite the lug. A gland 8 in [203 mm] to the side changes nothing, because the dimension ignores the cable's route and takes the perpendicular distance instead. Measuring along the cable path is the mistake that turns a compliant clearance into a box that fails inspection.
Which table applies, and what it asks
NEC 312.6 splits into two tables. Table 312.6(A) applies when the conductor does not enter or leave the wall opposite its terminal, the layout of gutters and splice cabinets; the same table gives the minimum width for wiring gutters. Table 312.6(B) applies when the conductor crosses the box and enters or leaves the wall opposite its terminal, which is the power-junction-box case. Table 312.6(B) carries the larger dimensions, and it sizes heavy feeders.
| Layout | Conductor, one per terminal | Table | Minimum space |
|---|---|---|---|
| Same wall or gutter | 1 AWG | 312.6(A) | 2 in [51 mm] |
| Same wall or gutter | 4/0 AWG | 312.6(A) | 4 in [102 mm] |
| Opposite wall, power box | 750 kcmil [380 mm²] | 312.6(B) | 19 in [483 mm] |
A lug that holds two or more conductors grows the dimension 25 percent per conductor beyond the first. Two 750 kcmil on one lug take 23.75 in [603 mm]; three take 28.5 in [724 mm]. The adder is the parallel-set case, where two conductors per phase is a normal feeder layout.
Sizing a power box for two 750 kcmil on one lug
Inputs. Two 750 kcmil [380 mm²] copper conductors terminate on each lug, a parallel feeder set. MCM and kcmil name the same conductor, and the 500 MCM and kcmil conversion page untangles the naming. The lugs stand off the backplate on stands, the conductors rise through the bottom gland plate and cross to them, so Table 312.6(B) governs and the entry wall is the bottom plate.
Rule. One 750 kcmil per terminal needs the 19 in base from the table. Each conductor beyond the first on the same lug adds 25 percent of that base.
Arithmetic. 19 in × 1.25 = 23.75 in [603 mm] of clear space from every lug tip.
Result. Each lug tip needs that 23.75 in of straight-line clearance to the bottom plate, measured perpendicular to it. In this layout that is the vertical gap from lug tip to gland plate.
Decision. Mount the lug tips 25 in [635 mm] above the bottom plate and set the outside height at 30 in [762 mm]. The gap then clears the table figure with 1.25 in spare, even after wall thickness. Depth stays at the catalog 16 in [406 mm], because the clearance consumes height, not depth. Move the entry to the rear wall and the same clearance runs front to back, which no 16 in deep wall-mount body passes — keep heavy entries in the bottom plate, where wall-mount bodies run to 60 in of height. Lock out the feeder and verify absence of voltage before you drill that plate.
What it changes in a real panel
- Entry direction first. Decide the entry wall before the size. Bottom entry turns the clearance into height, the cheapest dimension to grow on a wall-mount stainless body. That line runs to 60 x 36 x 16 in [1524 x 914 x 406 mm] outside, and rear entry runs the same distance across the depth and fails it.
- Motor terminals. The NEC's motor rules send motor terminations to Table 312.6(B) as well, so a machine-mounted terminal box ending 750 kcmil carries the same per-terminal space, and the 25 percent adder for two on the lug. The motor lead splices outdoors article pairs the box, glands and terminations for runs like this.
- Parallel sets. Two conductors per phase is a parallel set: keep the tails equal in length and watch the steel wall between them, which heats by induction where the pair runs close and parallel. The article on running parallel conductors through a steel enclosure gives the layout fixes.
- Two tails, one lug. Landing two conductors in one barrel is a terminal choice, not a field improvisation; the two wires on one terminal article covers listed lugs and crimp practice.
- Glands carry the seal. Match each gland to the cable outside diameter and the hole it sits in. A drilled plate with the wrong gland drags the whole rating down with it: the cutouts and glands guide lists the drilling checks, and the gland too short for the box threads article shows the thread-engagement failure.
- Fill and clearance together. NEC 312.8 keeps conductor volume, splices and taps inside limits, and the lug clearance never shares that space, so run both checks on the same drawing. The enclosure sizing guide walks the full size-up.
What to put on the order
Write the clearance onto the drawing rather than into the conversation. Three lines do it: conductor size and count per lug (2 × 750 kcmil); the entry wall and gland positions, dimensioned; and the lug tip height above the entry plate (25 in, against the 23.75 in table minimum). Send those with the cutout drawing and the plate comes back drilled where the cables need it.
Pick the grade from the environment: 304 for a dry switch room, 316L for washdown or coastal air. The custom stainless cutouts page compares a standard body with new openings against a fully custom one, and the stainless size finder filters the wall-mount line by grade and outside size. Every box is rated NEMA 4X / IP66 by the manufacturer; not UL listed. Delivery is 10 business days worldwide, counted from your order or, on custom work, from your approval of the drawing.
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 |
| 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 |
| 10 × 8 × 4 in | 304 stainless | 10 x 8 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Does the 19 in apply when a VFD feeds the junction box?
Yes. Bending space follows the termination, not the supply: two 750 kcmil on one lug with entry opposite the terminals take 19 in × 1.25 = 23.75 in [603 mm] whatever feeds it. Size the vertical gap from each lug tip to the gland plate at that figure, and keep the gland position out of the measurement.
Is 750 MCM the same conductor as 750 kcmil?
Yes. MCM and kcmil both mean 1,000 circular mils, so 750 MCM equals 750 kcmil, about 380 mm² of copper. The NEC tables print kcmil, and the bending space is the same 19 in per terminal under either name.
Does aluminum change the dimension?
No. NEC 312.6 sizes the space by conductor size and count, not by metal, so 750 kcmil aluminum takes the same per-terminal figure as copper. A 1 AWG aluminum tail lands at 2 in under Table 312.6(A), the same row the copper value comes from.
How much room do three 750 kcmil on one lug need?
Each conductor beyond the first adds 25 percent of the base: 19 in × 1.5 = 28.5 in [724 mm]. Mount the lug tips at least 29 in above a bottom gland plate and dress the three tails with equal bends so none loses its share of the clearance.
Do bending space and box fill double-count the same wire?
They are separate checks. NEC 312.8 limits the volume of conductors, splices and taps in a cabinet, while bending space is clear distance at the lug. A box can pass fill on 2 × 750 kcmil and still fail the 23.75 in clearance, so both belong on the same drawing.
