How to Choose a Mechanical Lug: Conductors, Holes, Dual-Rated AL9CU, Stud Size and Torque
Sep 09, 2026
Mechanical lugs get chosen by eye more than any other termination, and the failures show up two years later as a warm breaker or a loose neutral. The selection is four questions and a torque wrench.
1. How many conductors land here?
One conductor per barrel. A single-barrel lug takes one wire; a two-barrel takes two; three- and four-barrel lugs land a three-phase pigtail or several small feeders on one point. Never double up in a barrel unless the lug is marked for it; UL 486A/B listing is per conductor per barrel. Stacked designs (CT-SL series) put two barrels one above the other on a single tongue for tight gutters.
2. What conductor range?
The marking gives a minimum and maximum, e.g. 14 AWG to 1/0. Both ends matter: a 14 AWG in a lug rated 6 AWG to 250 kcmil will not clamp properly no matter how hard the screw is driven. Choose the smallest lug whose range covers your largest and smallest conductor.
| Your conductor | Single-barrel part | Two-barrel part |
|---|---|---|
| 14 to 6 AWG | CT-T1H1-6A | CT-T2H1-1/0A |
| 14 to 4 AWG | CT-T1H1-4A | CT-T2H1-1/0A |
| 14 AWG to 1/0 | CT-T1H1-1/0A | CT-T2H1-1/0A |
| 14 AWG to 2/0 | CT-T1H1-250 | CT-T2H1-2/0A |
| 6 AWG to 250 kcmil | CT-T1H1-250 | CT-T2H1-350 |
| 6 AWG to 350 kcmil | CT-T1H1-350 | CT-T2H1-350 |
| 4 AWG to 500 kcmil | CT-T1H1-500 | CT-T2H1-600 |
| 2 AWG to 600 kcmil | CT-T1H1-600 | CT-T2H1-600 / CT-T3H1-600 |
| 300 to 800 kcmil | CT-T1H1-800 | CT-T2H1-800 |
| 500 to 1000 kcmil | CT-T1H1-1000 | CT-T2H1-1000 |
3. Copper, aluminum or both?
AL9CU (or AL7CU) means the lug is listed for aluminum and copper, at 90 C or 75 C. A copper-only lug on aluminum wire is a code violation and a fire risk; the dissimilar metals corrode and the joint loosens. All CT tin-plated aluminum lugs are AL9CU. The copper offset lugs (210-21001 series) are copper-conductor only. On aluminum conductors, wire-brush the strands and apply oxide inhibitor before landing.
4. One hole or two, and what stud?
One hole is fine for panel neutrals, ground bars and anything under 250 kcmil. Two holes are specified for switchgear and busbar above 250 kcmil and wherever fault current could rotate the lug; most gear calls out NEMA 1 in spacing for 1/4 to 3/8 in studs and 1-3/4 in for 1/2 in and up. Match the hole to the stud or bolt, not the other way: a 1/4 in hole on a 3/8 in stud means drilling the lug, which voids the listing. The CT-T3H2-1/0A is the three-conductor two-hole answer for subpanel neutrals and transfer switches; the CT-SL42-600 covers four feeders on a two-hole pad.
5. Torque
NEC 110.14(D) requires a calibrated torque tool to the marked value. UL 486B values for set-screw lugs with slotted or hex screws:
| Conductor | Torque |
|---|---|
| 14 to 10 AWG | 35 lb-in |
| 8 AWG | 40 lb-in |
| 6 to 4 AWG | 45 lb-in |
| 3 to 1/0 AWG | 50 lb-in |
| 2/0 to 4/0 AWG | 100 lb-in (3/8 in hex) |
| 250 to 350 kcmil | 250 lb-in |
| 400 to 600 kcmil | 275 lb-in |
| 700 to 1000 kcmil | 375 lb-in |
Check the lug marking; a manufacturer's marked value overrides the table. Re-torque is not required after the initial connection on a properly installed mechanical lug, and repeated re-tightening over-compresses aluminum strands.
Mechanical or compression?
Mechanical when the connection may need to come apart, on Class B stranded THHN, and in gear that ships with mechanical lugs. Compression for fine-strand cable, vibration, buried grounding and anything nobody will touch again; see Compression vs Mechanical Lugs.
Cross-reference
CT-T1H1 and T2H1 series cross to Burndy KA series, Ilsco TA and PB, and Panduit CL by wire range and stud; the mechanical lug cross-reference lists them by part number. Every lug on the mechanical lug page is in stock and ships same day; contractor pricing at 25 pieces.
