The correct screw-terminal capacitor torque is the value published for the exact capacitor series, terminal size, and accessory stack—not a universal plant setting. TDK and Nippon Chemi-Con examples show why: their published limits differ by thread size and construction. A reliable OEM process therefore identifies the part, verifies the current datasheet, controls screw engagement, uses a calibrated tool, restrains cable loads, and inspects the joint after assembly.
Key Takeaways
The six decisions that prevent avoidable joint damage
Use the exact series datasheet; thread size alone does not define the limit.
Confirm screw length and engagement before setting the torque tool.
Keep cable and busbar loads from acting on the terminals.
Control mounting-band torque separately from electrical-terminal torque.
Record the tool, setting, operator, and inspection result for traceability.
Stop if the assembly stack differs from the validated drawing.
Why one torque value cannot cover every screw-terminal capacitor
Published limits change with thread size, series, and accessory
A torque instruction such as “tighten all capacitor terminals to the same value” is too broad for production. In TDK’s general aluminum-electrolytic guidance, the listed maximum is 2.5 N·m for M5, 4.0 N·m for M6, and 10.0 N·m for M12. The same document also warns that a supplied accessory may carry a lower limit. Nippon Chemi-Con publishes different examples: up to 89 mm case diameter, an M5 × 0.8 × 10 mm terminal screw is limited to 3.23 N·m; for a 100 mm case, an M8 × 1.25 × 16 mm screw is limited to 6.31 N·m. These are manufacturer examples, not interchangeable specifications.
The practical conclusion is simple: the bill of materials must resolve to a manufacturer, series, case code, terminal option, and approved hardware stack. Purchasing substitutes and alternate lugs should trigger engineering review instead of inheriting the old work instruction.
| Source example | Thread / hardware | Published value | OEM action |
|---|---|---|---|
| TDK general guidance | M5 | 2.5 N·m max; engagement ≥8 mm | Verify series and accessory limit |
| TDK general guidance | M6 | 4.0 N·m max; engagement ≥9.5 mm | Control screw length and stack |
| TDK general guidance | M12 | 10.0 N·m max | Use a suitable calibrated tool |
| Chemi-Con FAQ | M5 × 0.8 × 10 mm | 3.23 N·m max | Apply only to the stated case group |
| Chemi-Con FAQ | M8 × 1.25 × 16 mm | 6.31 N·m max | Apply only to the stated 100 mm case |
| Chemi-Con FAQ | Metal mounting band | 0.78 ± 0.05 N·m | Keep mounting and terminal settings separate |
How to build a repeatable torque-controlled assembly
Start with screw engagement and the complete connection stack
Before tightening, compare the released mechanical drawing with the actual screw, washer, lug, busbar, and terminal stack. TDK’s general guidance lists minimum engagement of 8 mm for M5 and 9.5 mm for M6. A separate TDK B43745/B43765 series datasheet lists minimum reaches of 7.5 mm for M5 and 10.0 mm for M6, illustrating again that the exact series drawing governs. A screw that bottoms before clamping can give a torque reading without creating the intended joint pressure; an overlong screw may also damage the terminal structure.
Then set a calibrated torque tool to the approved value. Use a socket or bit that fully fits the fastener, apply force in line with the screw axis, and avoid using the capacitor terminal as a lever while routing cables. If a busbar or cable naturally pulls the terminal sideways, correct the routing or add strain relief before final tightening.
Separate electrical-terminal control from mechanical mounting
The terminal joint and the case mounting system perform different jobs and can have different torque limits. Chemi-Con’s example of 0.78 ± 0.05 N·m for a metal mounting band is far below its terminal-screw examples. Production travelers should therefore show two distinct controls: one for the electrical connection and one for the mounting clamp, bracket, or band. This prevents a technician from copying a terminal value into a mounting operation.
Orientation also belongs in the work instruction. Chemi-Con advises against installing an aluminum electrolytic capacitor with the seal or pressure-relief vent facing downward. For horizontal mounting, it recommends positioning the vent upward or placing the anode terminal upward so the vent faces horizontally. Torque cannot compensate for poor orientation, inadequate clearance, or obstructed venting.
What OEM buyers should include in an RFQ and drawing review
Request the data that connects the capacitor to the assembly process
An RFQ should do more than state capacitance and voltage. Ask for the exact terminal option, supplied screw specification, permissible torque, minimum and maximum engagement, approved washer or lug arrangement, and mounting-hardware limit. Include the busbar thickness, cable-lug thickness, expected vibration, service temperature, installation orientation, and available vent clearance. These details help suppliers identify mechanical mismatches before samples reach the line.
For broader selection work, review LORIDA’s aluminum electrolytic capacitor range, the vent-clearance checklist, and the engineering inquiry page. Send the application, electrical target, mechanical drawing, terminal stack, and expected production method together.
Frequently Asked Questions
Can I use one torque setting for every M5 capacitor terminal?
No, M5 identifies the thread size but not the complete permissible torque. The limit can vary with manufacturer, series, terminal insert, screw, washer, and accessory. TDK’s general guidance lists 2.5 N·m maximum for M5, while the cited Chemi-Con example lists 3.23 N·m for a defined M5 screw and case group. Treat those as manufacturer-specific examples. Your work instruction should reference the exact approved part number and current datasheet. If a replacement part, lug, or screw changes, engineering should review and revalidate the setting before production resumes.
Why does screw engagement matter if the torque wrench clicks?
A click confirms applied torque, not that the joint achieved the intended clamp condition. If the screw bottoms in the terminal before the lug and washer are clamped, the tool can reach its setting while the electrical connection remains loose. If engagement is too short, threads may be overstressed; if the screw is too long, it may damage internal structure. Verify the series drawing, stack height, and engagement before tightening. TDK examples show that even M5 and M6 minimum reaches can differ between general guidance and a specific series.
Should the mounting band use the same torque as the terminals?
No, mounting-band torque must be controlled separately from electrical-terminal torque. In the cited Chemi-Con guidance, the metal mounting band is specified at 0.78 ± 0.05 N·m, much lower than its terminal-screw examples. The band secures the case, while terminal torque controls an electrical joint; copying one value to the other can deform the case or leave the assembly insecure. Put both operations on the drawing or traveler as separate steps, with different tool settings and inspection points.
What should I send a capacitor supplier for torque review?
Send the exact capacitor part number, terminal option, screw and washer details, lug or busbar stack, drawing, and proposed torque. Add cable size and routing, vibration environment, installation orientation, case mounting method, vent clearance, temperature range, and expected service conditions. A photo or section drawing of the joint is useful when the hardware stack is unusual. This package allows the supplier to distinguish terminal torque from mounting torque, check engagement, and flag side-load risks before the assembly is released.
Need a torque-ready screw-terminal capacitor review?
Send the drawing, electrical target, and complete hardware stack
LORIDA can review your application inputs and help organize the electrical and mechanical questions for supplier confirmation.
Sources
Manufacturer documents used for the numeric examples
Last Updated: September 29, 2026
