Read the Size Before You Read the Spec Sheet
A tinned copper cable lug is defined by two numbers: the conductor cross-section it accepts (mm²) and the stud diameter it bolts onto (M4, M5, M6, and so on). Pick the wrong pairing and the lug either will not seat on the conductor or will not fit the busbar bolt. The chart below covers the common SC series so you can size a joint quickly, then we explain how to choose when your cable sits between sizes and how to validate the finished crimp.
How to Read the Size Chart
Before using the table, know what each column means:
- Cross-section (mm²) — the conductor area the barrel is designed to accept. This is the cable’s rated area, not its outer diameter.
- Stud (M) — the metric thread of the bolt the palm hole fits. Match this to the busbar or breaker terminal.
- Barrel Ø (mm) — the inner diameter of the tube that receives the conductor; it sets the crimp die you load.
- Palm width (mm) — the flat landing area; relevant when lugs sit side by side on a bar.
- Length (mm) — overall length, important in tight enclosures.
Typical SC Tinned Copper Lug Size Chart
Figures are a representative SC series; always confirm against the specific datasheet, as palm width and length vary slightly by manufacturer.
| Cross-section (mm²) | Stud (M) | Barrel Ø (mm) | Palm width (mm) | Length (mm) |
|---|---|---|---|---|
| 1.5 | M4 | 2.4 | 10 | 22 |
| 2.5 | M4 | 2.8 | 10 | 22 |
| 4 | M4 | 3.4 | 12 | 26 |
| 6 | M5 | 4.0 | 14 | 30 |
| 10 | M6 | 4.8 | 15 | 32 |
| 16 | M6 | 5.8 | 18 | 36 |
| 25 | M8 | 7.2 | 20 | 40 |
| 35 | M8 | 8.5 | 22 | 44 |
| 50 | M8 | 9.8 | 26 | 50 |
| 70 | M10 | 11.5 | 30 | 56 |
| 95 | M10 | 13.5 | 34 | 62 |
| 120 | M12 | 15.5 | 38 | 70 |
| 150 | M12 | 17.0 | 42 | 76 |
| 185 | M12 | 19.0 | 46 | 82 |
| 240 | M12 | 21.5 | 50 | 90 |
| 300 | M14 | 24.0 | 56 | 100 |
| 400 | M16 | 27.0 | 60 | 110 |
| 500 | M16 | 30.0 | 66 | 120 |
| 630 | M20 | 34.0 | 74 | 135 |
| 800–1200 | M20 | 38–46 | 80–92 | 150–170 |
How to Choose the Right Tinned Copper Cable Lug Size
Step 1: Match the Conductor Cross-Section
Start from the cable’s rated mm², not its diameter. The lug barrel is sized to the stranded conductor, so a 35 mm² cable takes a 35 mm² lug regardless of its outer jacket. Stranded and fine-stranded cables have slightly different packing, but standard SC barrels accept both; for very fine-stranded (class 5/6) conductors, confirm the barrel is rated for flexible wire or use a ferruled entry. If your cable is between standard sizes (for example a non-standard 28 mm²), choose the next size up only if the conductor fills most of the barrel; otherwise a proper ferrule or a custom lug is safer than a loose fit.
Step 2: Match the Stud Size
The stud hole must match the bolt on the busbar, breaker, or cable gland land. A lug with too large a hole lets the joint rock and loosen; too small and it will not mount. Common practice: 6 mm² and below use M4–M6, 10–50 mm² use M6–M8, 70–150 mm² use M10–M12, and 185 mm² upward use M12–M20. Metric (M) is standard; if your equipment uses imperial studs, select the nearest metric equivalent or a transition lug.
Step 3: Confirm the Crimp Die
The barrel diameter in the chart tells you which die to load in your crimping tool. A hex die that is even one step off leaves a void in the barrel and a joint that fails pull-out testing. Keep a printed chart at the bench so every installer uses the same reference, and label the die nest by lug size to avoid mix-ups on a busy line.
Step 4: Check the Installation Space
Palm width and length decide whether the lug fits in a crowded panel. In tight enclosures, a longer 240 mm² lug may collide with the next termination, forcing a bent conductor or a de-rated layout. When space is limited, confirm the physical envelope before ordering, not after wiring — and consider right-angle or compact-palm variants if your supplier offers them.
Step 5: Copper, Tinned, and the Aluminum Question
These sizes assume a copper conductor. For aluminum cable, use a bi-metallic (copper-aluminum) lug or a proper transition, because direct copper-aluminum contact causes galvanic corrosion. Tin plating on the lug protects the copper surface during storage and in humid service, but it does not bridge a copper-aluminum mismatch. Equally, do not tin the aluminum conductor itself before a copper lug — that traps the joint and accelerates failure.
Step 6: Validate With a Sample Crimp
Before a full run, crimp one lug, section it, and check the strands are fully compressed with no voids. That single check prevents an entire batch of bad terminations. Pair lugs with non-insulated terminals for control wiring to keep the whole assembly consistent, and torque the finished stud to the panel manufacturer’s specification.
| Sizing mistake | Result |
|---|---|
| Lug too large for conductor | Void in barrel, weak crimp |
| Stud hole too large | Joint rocks, loosens under load |
| Wrong die for barrel | Incomplete compression |
| Aluminum in copper lug | Galvanic corrosion |
Reading the Chart for Real Installations
The table is a starting point, not the whole answer. In practice the lug you choose is constrained by three things at once: the conductor, the stud, and the space. A 70 mm² cable on an M10 bolt is straightforward, but a 70 mm² cable that must land on an M8 terminal forces a compromise — either a reducing washer (where the standard allows) or stepping the design. Build the habit of checking all three columns together rather than sizing from the cross-section alone.
Industry Examples
| Application | Typical lug |
|---|---|
| Solar PV string to combiner | 6–16 mm², M6–M8 |
| Battery storage bank | 70–240 mm², M10–M12 |
| EV charging cabinet | 35–120 mm², M8–M12 |
| Switchgear busbar | 185–630 mm², M12–M20 |
Storage and Handling of Lugs
Tinned copper lugs arrive with a protective plate that slows tarnish, but they still want dry storage. Keep them in the original sealed bag until use, and if a lug shows green or black surface oxidation, clean it with the degreaser before crimping — a contaminated surface undermines the cold weld. Sort by size in labeled bins at the bench so the right lug is in hand before the cable is stripped; that single habit prevents the most common field error of forcing the wrong size.
Why a Calculator Helps
Even with the chart, busy installers make size mistakes. A simple lookup that takes conductor mm² and stud size and returns the exact SC model removes the guesswork and the returned-material cost. It also lets a procurement team standardize every order on one part number per joint, which simplifies inventory and quality control across sites. For panels that mix sizes, lay out the lugs on the physical bar before crimping any of them. This “dry fit” catches stud mismatches and space conflicts while they are still free to fix, and it is the cheapest insurance against a re-worked enclosure. Pair it with a printed size chart taped inside the panel door and even new installers will land the right lug first time.
One Overlooked Step: The Dry Fit
Even with the chart in hand, the cheapest mistake to avoid is crimping before the lug has been placed on the actual bar. Lay out every lug on the physical busbar or terminal land before you strip a single cable. This dry fit catches a mismatched stud, a too-long palm that collides with the neighbor, or a barrel that will not clear the enclosure wall — all of which are free to fix at this stage and expensive after crimping. It also lets you confirm the stud bolt is actually present and the right thread, which sounds obvious until a panel arrives with the wrong hardware.
Pair the dry fit with a one-line note on the drawing: lug model, die number, and torque. That note turns a skilled-artisan task into a repeatable process any competent installer can match, and it gives the final inspector a checklist instead of a guess. For multi-site rollouts, standardize the note across every drawing so training and audit stay simple.
Frequently Asked Questions
Are SC lugs the same as DIN 46235?
SC is a common tubular lug profile; DIN 46235 is a specific standard with its own dimension set. Confirm which your project references.
Can one lug size fit two stud sizes?
No — the palm hole is fixed. Use the correct stud size or a washer/spacer only where the standard allows.
How do I size for a future upgrade?
Size the lug to the conductor you are terminating now; do not oversize the barrel hoping to reuse it later.
Need the full lug size chart and samples?
Niuli Electric supplies tinned copper SC lugs from 1.5 mm² to 1200 mm² with M4–M20 studs, plus matched crimping tools and a datasheet for every size. Request a sample kit for your panel build.
