Short answer: with no conduit, you size the junction box from three numbers — NEC conductor volume fill, 6x the largest cable's jacket OD from gland to terminal, and one gland diameter of metal between hole edges. For a washdown splice with one 0.75 in [19 mm] power cable and three 0.45 in [11 mm] control drops, those checks land on a 10 in wide x 10 in high x 6 in deep stainless box. The same cables in an 8 x 8 x 4 in box miss the gland row by about 1 in [25 mm] and the depth by 0.5 in [13 mm]. Below is the tape-and-pencil work, from conductor count to the layout you send with the order.
Why conduit trade size does not apply
The NEC writes box sizing in two registers, and both lean on raceways. For conductors 4 AWG and larger, the NEC sizes pull and junction boxes from the raceway's trade size: 8 times trade size for a straight-through pull, 6 times for a pull that turns. You measure from the entry to the opposite wall. For smaller boxes, the NEC's volume table counts cubic inches per conductor. Nothing there hands you a trade size when the cable arrives through a gland — and you don't need one. The gland takes the raceway's place, so you run the same multiples on the cable jacket: 8 x OD for a straight pull, 6 x OD for a pull that bends to the terminals. Add the volume count and the gland row, and the box is fully determined.
The enclosure sizing guide runs the same checks for a panel with DIN rail; this piece stays cables-only.
The volume check: what the copper needs
The NEC's per-conductor volume allowances set the floor: 2.00 in³ for each 14 AWG conductor, 2.25 in³ for 12 AWG, 2.50 in³ for 10 AWG, 3.00 in³ for 8 AWG and 5.00 in³ for 6 AWG. Count every conductor that terminates in the box, including splices, pigtails and the cable's own ground. Multiply each size by its allowance and add; a terminal block changes nothing. In a gland box this check rarely wins, because the geometry you mark next wants far more room than the copper does. For 8 AWG landed as bare splices with no glands, the 8 AWG splice box sizing works the volume the classic way.
The pull check: 6 x the jacket OD
Mark the pull with the jacket OD, not the conductor size: the gland seals and the cable bends on the jacket. The NEC's 6-times multiple, transposed from trade size to jacket OD, gives the working number — 6 x OD of straight jacket from the gland's cable exit to the first terminal or bend, in every pull direction. A straight-through pull needs 8 x OD between the two gland faces instead. Most flexible power and control cables list a minimum bend radius of 6-8 x OD, so the mark matches the datasheet. Where the datasheet is stricter, it wins. Single-conductor power cable wants more, and armored cable most of all (the armored gland article takes that case).
| Pull | Multiple of jacket OD | Where you measure |
|---|---|---|
| Straight through | 8 x OD | between the two gland faces |
| Turn to terminals | 6 x OD | gland exit to first terminal |
For the 0.75 in cable in the worked example, the mark is 6 x 0.75 = 4.5 in [114 mm]; for a 0.45 in control drop, 2.7 in [69 mm]. Terminals add their own bending space for the conductor at the lug; measuring wire bending space covers that end of the box.
The gland-row check: holes and spacing
Gland makers put one fact plainly for certified Ex gear: minimum hole spacing comes from the enclosure's certificate rather than the gland. A non-classified stainless box leaves the spacing to you, and three clearances set it: one diameter of the larger gland between hole edges, room to swing the locknut wrench, and 0.6 in [15 mm] of metal from every hole edge to a bend or the gasket face. Clearance holes run about 0.04 in [1 mm] over the thread, so an M32 hole drills at 1.30 in [33 mm] and an M20 at 0.83 in [21 mm].
Pick each gland by clamp range rather than thread alone — a typical M32 clamp spans 14-24 mm [0.55-0.94 in] and an M20 spans 6-12 mm [0.24-0.47 in], and the clamp must land on the jacket. Two cables of different OD through one gland loses the seal, so give each cable its own gland sized to its jacket. Past ten or so glands, the row becomes a gland plate. In classified areas, gland selection and spacing both follow the certificate; selecting Ex cable glands for stainless junction boxes walks that side, and our stainless boxes serve non-classified areas.
Size the box in six steps
You need a tape, calipers for the jacket ODs, the gland datasheets, your conductor count and the terminal rail's depth. Then:
- Write the cable schedule. One line per cable: conductors and AWG, measured jacket OD, gland size and clamp range.
- Run the volume fill. Conductors times allowance, in cubic inches.
- Mark the pulls. 6 x the largest OD from each gland exit to the terminal rail; 8 x for any straight-through run.
- Stack the height. Gland body inside the box, plus the pull mark, plus the terminal rail height, plus 1 in [25 mm] of spare.
- Draw the gland row. Clearance holes, one larger-diameter gap between edges, 0.6 in [15 mm] margins; the row sets minimum inside width.
- Convert and order. Add about 0.5 in [13 mm] per face for walls, gasket flange and mounting panel; step up a size on any dimension that misses; send the schedule and the hole layout with the quote.
Lock out and tag the supply before the first conductor lands in the box — a splice point is not work-live territory.
Worked example: one 8 AWG feed, three control drops
Label these as example inputs, because the cables are what you replace with your own schedule: a 3-conductor 8 AWG flexible power cable with ground, jacket OD 0.75 in [19 mm]; three 4-conductor 14 AWG control cables, OD 0.45 in [11 mm]; a terminal rail 2.0 in [50 mm] tall; washdown duty, so 304 stainless with factory cutouts.
| Cable | Conductors | Jacket OD | Gland (clamp range) |
|---|---|---|---|
| Power feed | 3 x 8 AWG + ground | 0.75 in [19 mm] | M32 (14-24 mm) |
| Control drop, x3 | 4 x 14 AWG | 0.45 in [11 mm] | M20 (6-12 mm) |
Fill: 4 x 3.00 in³ (8 AWG) + 12 x 2.00 in³ (14 AWG) = 12.0 + 24.0 = 36.0 in³.
Pull: 6 x 0.75 in = 4.5 in [114 mm] from the M32 exit to the lowest terminal; 6 x 0.45 in = 2.7 in [69 mm] for the M20s.
Height stack: 1.0 in (M32 gland body) + 4.5 in (pull) + 2.0 in (rail) + 1.0 in (spare) = 8.5 in [216 mm].
Gland row: 1.30 + 1.30 + 0.83 + 0.83 + 0.83 + 0.83 + 0.83 = 6.75 in [171 mm] of holes and gaps, plus 0.6 in margins each side = 7.95 in [202 mm] of inside width.
Depth: 0.5 in (back wall and panel) + 2.0 in (terminal blocks) + 1.0 in (door clearance) = 3.5 in [89 mm].
The marks want at least 8.0 in wide x 8.5 in high x 3.5 in deep inside. Take 0.5 in [13 mm] per face, and a 10 in wide x 10 in high x 6 in deep box gives 9.0 x 9.0 x 5.0 in inside — about 405 in³ against the 36 in³ fill — so every check clears with room to work. The 8 x 8 x 4 in candidate gives 7.0 x 7.0 x 3.0 in inside: 1.0 in short on the gland row, 1.5 in short on the stack, 0.5 in short on depth. Order the 10 x 10 x 6; custom stainless enclosures build it as one piece with the cutouts you drew, delivered in 10 business days from your approval of the drawing.
Checks when the box is built
Run five checks with the box on the wall and the door open:
- A tape shows 4.5 in [114 mm] of straight jacket between the M32 exit and the first terminal, and 2.7 in [69 mm] on the control drops.
- A hand pull on each cable moves nothing at the terminal, and the gland clamp grips the jacket.
- Each clamp seal visibly compresses on its jacket, and the wrench has stopped turning.
- The door closes without pinching a jacket, and the gasket seats all the way round.
- Bottom glands carry drip loops and every unused hole is plugged; drip loops, glands and drains for outdoor boxes shows the outside work.
Land the cable grounds on a ground terminal and bond the box itself; the grounding and bonding guide sizes that conductor from the overcurrent device ahead of it.
Mistakes that cost the rating
The rating dies at the holes and the glands long before it dies at the box:
- Filing a hole oversize or oval: hold the drill to the clearance size — 1.30 in [33 mm] for M32, 0.83 in [21 mm] for M20 — because an oversize hole leaks and rocks the gland.
- Clamping the conductors instead of the jacket: the seal leaks and the strands work-harden at the terminal.
- Trusting a gland stamped IP68 to lift the assembly: the assembly runs at the weakest part's rating, so every gland and plug must match the box. Ours is manufacturer-rated NEMA 4X / IP66; not UL listed.
- Forcing a straight pull through a shallow box: 8 x 0.75 in = 6.0 in [152 mm] between gland faces wants more than the 5.0 in inside a 6 in deep box, so stagger the entries or go longer.
- Cramming the row past one gland diameter between edges: the gasket face cracks and the wrench has nowhere to go.
What to send with the order
Four items get the quote right the first time: the cable schedule, the gland list with clamp ranges, the hole layout with edge distances, and the grade — 304 stainless for washdown and most outdoors, 316L where salt, brine or chlorine lives. Catalog stainless boxes run from 6 x 4 x 4 in to 60 x 36 x 16 in (H x W x D), and the stainless size finder filters them when one covers your marks. The cutouts and glands guide details the hole work, and the cutout designer turns your layout into a drawing that ships with the box.
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 |
|---|---|---|---|
| 8 × 8 × 4 in | 304 stainless | 8 x 8 x 4 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 conductor fill ever decide the box size?
Rarely. The worked example needs 36 cubic inches of conductor volume — four 8 AWG conductors at 3.00 in³ plus twelve 14 AWG at 2.00 in³ — while the 10 x 10 x 6 in box that clears the pull and gland marks holds about 405 in³. Fill is the floor; the 6 x OD pull mark and the gland row set the order. Fill decides only in small splice boxes packed tight with conductors.
How far apart should cable gland holes be?
Keep one diameter of the larger gland between hole edges: 1.30 in [33 mm] between an M32 clearance hole and an M20 hole, 0.83 in [21 mm] between two M20 holes, and 0.6 in [15 mm] from any hole edge to a bend or the gasket face. On Ex-certified gear the enclosure certificate sets spacing instead; our stainless boxes serve non-classified areas.
What size box for four 12 AWG cable splices through M20 glands?
An 8 in wide x 8 in high x 6 in deep box just clears all three checks: 18 in³ of fill for eight 12 AWG conductors, a 7.0 in gland row against 7.0 in of inside width, and a 6.5 in terminal stack against 7.0 in of height. When you want an inch of margin, order 10 in wide x 10 in high x 6 in deep instead.
Can I field-drill the gland holes instead of ordering cutouts?
Yes, and hold three numbers: drill the M32 hole at 1.30 in [33 mm] and the M20 at 0.83 in [21 mm], keep every hole edge 0.6 in [15 mm] from bends and the gasket face, and deburr inside and out before a chip rides the gasket. A hole saw on low speed keeps the stainless from tearing. Once the layout is settled, factory cutouts keep the gasket face true and put every hole on the drawing.
