Short answer: leave 1 in [25 mm] of clear finger space between the terminal blocks and the wiring duct on each side of a row, and 2 in [50 mm] per side when wires land on the top and bottom faces instead of the front. The bay is blocks plus space: 2.75 in [70 mm] blocks in a 5 in [127 mm] bay leave 1.125 in [28.6 mm] per side, which passes for front-entry wiring. Voltage does not set the pitch, because the block holds its clearance to the DIN rail inside its own footprint. What follows is the rule, the bending-space logic behind it, the layout steps, and the enclosure depth you order once the backplane stands off for drive cables.
How much space do you leave between terminal blocks and finger duct?
Leave the front-entry gap above the row and the same below it when every wire lands on the front face, and the wider gap per side when wires enter an end face or field cable runs straight from the duct to the block. That space is where your fingers strip, dress and torque the wire, and where the ferrule turns out of the duct into the screw. Front-entry blocks spend the least bay because the wire arrives on the face you work on. Blocks that plug in top and bottom, safety relays being the usual case, need the wire to rise off an end face and turn, so they get the wider space.
| How the wires land | Space each side of the row | Clear bay for 2.75 in [70 mm] blocks |
|---|---|---|
| Front face only | 1 in [25 mm] | 4.75 in [121 mm] |
| One end face plus the front | 2 in [50 mm] on the end side, 1 in [25 mm] on the other | 5.75 in [146 mm] |
| Top and bottom faces | 2 in [50 mm] both sides | 6.75 in [171 mm] |
The number moves with the conductor. At 6 mm² [10 AWG] control wire the narrow gap holds; lug-ended power wire wants the wider treatment and its own bay at the top of the cabinet, where control cabinet power wiring belongs.
Does electrical clearance set the row spacing?
No. A rail-mount terminal block keeps its clearance and creepage distances to the DIN rail inside its own body, and its maker's application notes rate those distances for 1000 V service, so the gap between rows is for wire and hands, not for voltage. That frees you to set pitch by wiring alone.
A screw-clamp block datasheet lists fine-stranded conductors from 0.14 mm² (about 26 AWG) up to 6 mm² (about 10 AWG); the top of that range sets your bending habit, and the finger rules above already cover it. For rail cutting, mounting and how rows share a plate, the backplate and DIN rail layout guide carries the fundamentals this page builds on.
What does the code say about bending space at terminals?
NEC 312.6 sets minimum wire bending space at terminals of cabinets and cutout boxes, in Table 312.6(A) where the conductor stays on its own side and Table 312.6(B) where it passes through toward the wall opposite its terminal, and panel builders carry the same idea onto terminal rows. Those tables size the bend by conductor size, and they govern the big landings such as breaker lugs and disconnect terminals. For block-level wiring at 0.14 to 6 mm², the front-entry gap holds a dressed bend, and any conductor crossing toward the far wall takes its value from Table 312.6(B). NEC 312.8 separately caps how full an enclosure for switches or overcurrent devices may be, which is one more reason the duct, not the bay, carries the wire count.
On the duct side, a wiring-duct maker's fill tables cap fill at 50% of the duct's interior cross-section, citing NFPA 79-2012 section 13.5.2: round cables leave air gaps, and half is what a duct realistically holds. Arithmetic for a 2 x 2 in duct: 2 x 2 = 4 in² of interior, 50% of that is 2 in² usable, and at 0.022 in² per wire (10 AWG THHN at about 0.168 in OD) you get 2 / 0.022 = about 90 wires. Size the duct from that count, then confirm the bay still fits the duct you chose; wiring duct and DIN rail layout in a CNC cabinet shows the same count on a real panel.
How do you lay out a terminal bay step by step?
Work from the blocks outward, row pitch first, then finger space, then duct, and the bay height falls out of the arithmetic; six steps turn that into a drawing a builder can cut to.
- List each row: block height (2.75 in [70 mm] in this example), which faces the wires land on, and the largest conductor, say 6 mm² [10 AWG].
- Set the pitch from the table above: the front-entry gap for front faces, the wider value wherever a wire rises off an end face.
- Size each duct from the wire count at 50% fill; put the field-wiring duct at the bottom of the panel and power wiring at the top.
- Reserve the side gap from the enclosure wall with the same logic; the article on terminal clearance from an enclosure wall gives that gap its own number.
- Mark behind-the-plate cable routes, standoff positions and grommet holes while the plate is on the bench, and lay pull strings before it goes in.
- Send row pitch, duct sizes and hole coordinates on the drawing you approve, so the plate arrives cut to them.
Does a 5 inch bay work with 2.75 inch terminal blocks?
Yes, for front-entry blocks: 5.00 in - 2.75 in = 2.25 in, so 1.125 in [28.6 mm] per side, which clears the front-entry rule by 0.125 in [3 mm]. The same bay fails the other two cases. Top-and-bottom landing needs 2.75 + 2 + 2 = 6.75 in [171 mm], so the 5 in bay runs 1.75 in short. One end face plus the front needs 2.75 + 2 + 1 = 5.75 in [146 mm], still 0.75 in more than the bay gives you.
Decision: keep the 5 in bay while every wire screws in from the front, and re-pitch the row the moment a pluggable block or safety relay lands on an end face. With only 0.125 in [3 mm] of margin, land and torque one ferrule in the gap before you mount the duct above it, so you feel the clearance you actually have.
Where do thick drive cables go when the bay is tight?
Behind the mounting plate: stand it off the enclosure back wall with 3 in [76 mm] standoffs, pass each cable through a grommeted hole in the plate, and land it straight into a wireway at the drive, so the terminal bays never see it. Use stainless hex standoffs threaded both ends, with studs fixed into the plate holes. In a food plant the hardware is stainless and the body is too, rated NEMA 4X / IP66 by the manufacturer and not UL listed, with a sloped top and entries kept low.
Clamp each cable shield on an EMC clamp on a short DIN rail just below the plate holes, and bond that rail to the panel ground bus with a conductor sized from the overcurrent device ahead of it under NEC Table 250.122; the grounding and bonding guide works that sizing through. The bend decides the wireway. A servo cable of 0.6 in [15 mm] OD with a 3.6 in [91 mm] minimum bend radius turns 90° inside a duct whose inside height is at least radius plus OD: 3.6 + 0.6 = 4.2 in [107 mm]. A 6 x 6 in wireway clears that with room to spare, and a barrier kit inside it keeps drive power away from control wiring, the same separation shown in servo drive and computer wiring separation.
Anything that must pierce the enclosure wall itself goes through a gland at the bottom; the article on bottom conduit entry into a NEMA 4 floor-mounted enclosure keeps that seal honest.
What enclosure depth do you order after the standoffs?
Depth is standoff plus plate plus tallest device plus the door clearance: with a 3 in [76 mm] standoff, an 8 in [203 mm] deep body leaves about 5 in [127 mm] in front of the plate for rows, ducts and compact drives. Measure the drive's depth on its datasheet before you commit; if it stands deeper than the space left, order the next depth up rather than spending the finger space.
We cut the material, width, height, depth and every hole from one piece, delivered in 10 business days counted from your approval of the drawing; the custom stainless enclosures page shows what belongs on that drawing. Still counting DIN modules rather than rows? The enclosure selector sizes the body from the module count.
How do you check the layout before the first wire lands?
Dry-run it: one block, one stripped 6 mm² [10 AWG] wire and the closed door, and the wire bends duct-to-screw without rubbing the duct lip while the door clears the tallest device by the door-clearance gap.
- Finger gap: the ferrule turns into the screw inside the front-entry or end-face space, untouched.
- Bay pitch: blocks plus gaps equals the measured bay; 2.75 + 1 + 1 = 4.75 in [121 mm] is the floor for a front-entry row.
- Duct fill: half the interior still shows air at the final wire count, per the 50% fill tables.
- Behind-the-plate run: a pull string slides plate-to-gland without snagging, and the shield rail is bonded to the ground bus.
- Door clearance: room to close over the tallest device, with the 3 in [76 mm] standoffs fitted.
Do all of this dead: lock out and prove the absence of voltage before your hands go into a wired bay. A row that passes those five checks wires quickly and troubleshoots faster, which is the whole point of the pitch.
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 |
|---|---|---|---|
| 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 |
| 60 × 36 × 16 in | 304 stainless | 60 x 36 x 16 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
How tall a bay do two rows of 2.75 inch blocks need?
Add blocks, finger space and the shared duct: 2.75 + 1 + 2 + 1 + 2.75 = 9.5 in [241 mm] for two front-entry rows, and 2.75 + 2 + 2 + 2 + 2.75 = 11.5 in [292 mm] when both rows land on end faces. A 12 in bay carries the second case with 0.5 in to spare.
What wireway size does a servo cable with a 3.6 inch bend radius need?
Size the inside height at the bend radius plus the cable OD: 3.6 + 0.6 = 4.2 in [107 mm]. A 6 x 6 in wireway clears that with room to spare; anything much under 4.2 in of inside height makes the cable kink at the corner.
Do backplate standoffs change the enclosure's rating?
The holes go through the mounting plate, not the enclosure wall, so the wall keeps its glands and its seal. A 3 in [76 mm] standoff only moves the plate forward; confirm the closed door still clears your tallest device by the door-clearance gap.
Is 1 inch of finger space enough for a screwdriver?
Yes: terminal screwdriver shafts run about 6 to 8 mm [0.24 to 0.31 in] across, so that much gap clears the shaft, the ferrule and two fingers. Move to the wider end-face gap when the wire rises off a top or bottom face instead of the front.
