Lug Torque Chart: UL 486A/B Tightening Torque for Mechanical Lugs, Set Screws, Breaker Terminals and Bolted Connections by Conductor Size
Sep 10, 2026
Summary: NEC 110.14(D) requires every terminal to be tightened to the torque marked on the equipment or in its instructions, using a calibrated torque tool. Where no value is marked, UL 486A/B Table 10 applies to slotted and hex set-screw connectors by conductor size: 14 to 10 AWG 35 lb-in; 8 AWG 40 lb-in; 6 to 4 AWG 45 lb-in; 3 to 1 AWG 50 lb-in; 1/0 to 2/0 AWG 50 lb-in with a slotted screw or 120 lb-in with a 3/8 in hex; 3/0 to 4/0 AWG 250 lb-in; 250 to 350 kcmil 325 lb-in; 400 to 500 kcmil 375 lb-in; 600 to 750 kcmil 375 lb-in; 800 to 1000 kcmil 500 lb-in. Bolted lug-to-bus connections use the bolt grade and size, not the conductor: 1/4-20 60 to 80 lb-in, 5/16-18 15 ft-lb, 3/8-16 20 ft-lb, 1/2-13 50 ft-lb for grade 5 steel or silicon bronze.
The code requirement
NEC 110.14(D), added in the 2017 cycle and unchanged since, says a tightening torque indicated on the equipment or in its installation instructions shall be achieved with a calibrated torque tool, or an approved means. The manufacturer's marking governs. UL 486A/B provides the default values used when a connector is unmarked, and those are the values manufacturers list for standard set-screw lugs. Inspectors in most jurisdictions now ask to see the torque tool on service and panel inspections.
Set-screw mechanical lugs, UL 486A/B Table 10
| Conductor size | Slotted screw, lb-in | Hex socket screw, lb-in | Hex key |
|---|---|---|---|
| 18 to 10 AWG | 35 | 45 | 1/8 in |
| 8 AWG | 40 | 45 | 5/32 in |
| 6 to 4 AWG | 45 | 110 | 3/16 in |
| 3 to 1 AWG | 50 | 150 | 1/4 in |
| 1/0 to 2/0 AWG | 50 (slotted) / 120 (3/8 hex) | 180 | 5/16 in |
| 3/0 to 4/0 AWG | 250 | 250 | 3/8 in |
| 250 to 350 kcmil | 325 | 325 | 3/8 in |
| 400 to 500 kcmil | 375 | 375 | 1/2 in |
| 600 to 750 kcmil | 375 | 375 | 1/2 in |
| 800 to 1000 kcmil | 500 | 500 | 1/2 in |
Slotted-screw values assume the screw slot width and depth in UL 486A/B; a screw with a smaller slot has a lower value stamped on the lug. Conversions Tech mechanical lugs from 14 AWG to 1000 kcmil carry the value for their screw on the product page and the carton.
Breaker and panelboard terminals
Circuit breaker terminals are marked individually and vary by manufacturer; typical values are 20 to 25 lb-in for 15 and 20 A breakers with 14 to 10 AWG, 35 to 50 lb-in for 30 to 60 A breakers with 8 to 4 AWG, and 120 to 275 lb-in for 100 to 225 A frames with 1 to 250 kcmil. Use the breaker label, not this table. Main lugs and neutral bars in load centers are marked on the panel label; when a replacement lug is installed on a neutral or ground bar, the UL 486 value for the lug applies.
Bolted connections: lug to bus, lug to lug
| Bolt | Grade 5 steel or silicon bronze, dry | Stainless 18-8 | Notes |
|---|---|---|---|
| #10-24 | 25 lb-in | 22 lb-in | Belleville washer on aluminum bus |
| 1/4-20 | 60 to 80 lb-in | 70 lb-in | Two-hole lug NEMA spacing 1 in |
| 5/16-18 | 15 ft-lb (180 lb-in) | 11 ft-lb | |
| 3/8-16 | 20 ft-lb (240 lb-in) | 20 ft-lb | Most 250 to 500 kcmil lugs |
| 1/2-13 | 50 ft-lb | 45 ft-lb | 600 kcmil and up, 1-3/4 in NEMA spacing |
| 5/8-11 | 95 ft-lb | 90 ft-lb | Utility and transformer bushings |
Bolt torque is a function of the hardware, not the conductor. Use a flat washer under the head and nut, a Belleville (conical spring) washer against aluminum bus or an aluminum lug to hold clamping force through thermal cycling, and never a lock washer alone on aluminum. Silicon bronze hardware is preferred on copper bus; stainless is acceptable and required in corrosive locations.
Torque procedure
- Strip to the lug's marked depth; brush aluminum and apply oxide inhibitor.
- Seat the conductor fully; no insulation under the screw, no strands outside the barrel.
- Tighten to the marked value with a calibrated tool in one continuous motion; do not back off and re-tighten.
- Mark the screw head with torque seal or a paint stripe, and record the value on the panel schedule or job file. Many AHJs accept a photo of the tool reading as documentation.
- Do not re-torque at a later inspection unless the manufacturer instructs it. Re-torquing a set-screw lug on aluminum crushes strands that have already cold-flowed and reduces contact pressure.
What under- and over-torque do
Under-torque leaves the conductor free to move under load cycling; contact area shrinks, resistance rises, and the termination heats. Thermal imaging of panels finds under-torqued lugs as the majority of hot spots. Over-torque strips the screw, cracks the lug body, or cuts strands at the screw tip, which reads fine on the day and fails months later. Both are invisible without a torque tool, which is the reason 110.14(D) exists.
Quick answers
What torque for a 2/0 aluminum lug? 50 lb-in with a slotted set screw, 120 lb-in with a 3/8 in hex set screw, per UL 486B, unless the lug is marked otherwise.
Do I torque a compression lug? The crimp is not torqued; the bolt holding the lug to the bus is, per the bolt table above.
Is a torque screwdriver required by code? NEC 110.14(D) requires the marked torque to be achieved with a calibrated tool or an approved means; in practice that is a torque screwdriver or wrench.
Should I re-torque lugs annually? No, unless the manufacturer's instructions say so. Inspect with thermal imaging instead.
Conversions Tech mechanical lugs, neutral and ground bars and insulated multi-taps list the UL 486A/B torque on every product page. Related: how to choose a mechanical lug, compression lug die chart.
