Switchgear & Distribution Panels
Where aluminium feeders meet copper busbar — a bolted joint that stays stable without paste, with EN 10204 2.2 on every shipment and 3.1 on request.
You are the one signing the routine verification
The IEC 61439 series splits the work in two. The original manufacturer brings the design verification with a certified system; the assembly manufacturer — the panel builder — puts the cabinet together, carries out the routine verification and signs it. The moment you depart from the certified configuration, the burden of proof moves with you.
There is one joint in that cabinet you cannot verify your way around: the incoming aluminium feeder cable landing on the copper busbar through a bolted joint. IEC 61439-1 allows a 70 K temperature rise at terminals at rated current. A direct Al/Cu contact builds an oxide film and starts galvanic corrosion; within a few years the junction shows up as a hotspot on a thermal survey and drifts out of the temperature budget under summer peak load. Antioxidant paste can be re-applied every few years — but that means booking a maintenance window, documenting the work and signing for it, which is not something anyone running a hospital, a data centre or a process plant wants on a recurring basis.
The trouble does not appear at handover. It appears two or three years later, on a thermographic survey, as a hot spot — on a document with your name on it.
In short
In a switchgear cabinet or distribution panel, the incoming aluminium feeder meets the copper busbar; a CUPAL transition plate or M6–M20 washer solves this bolted joint with no galvanic corrosion and no paste, staying within the 70 K temperature-rise limit of IEC 61439-1.
- 70K
- IEC 61439-1 temperature-rise limit
- 1.2A/mm²
- Cu current density (DIN 43671)
- M6–M20
- 11 CUPAL washer sizes
- 5–10working days
- Custom-cut production (quote within 24 h)
Which washer goes into the joint
Two numbers decide it: the bolt in the joint gives the thread size, and the conductor cross-section of the lug gives the outer diameter you need. Check the palm width separately — if it is wider than the outer diameter of the row you picked, step up to the next outer diameter. Net list prices are published per size on the CUPAL washer product page.
| Bolt size | Outer Ø | Max. lug cross-section | SKU |
|---|---|---|---|
| M6 | 16 mm | 120 mm² | ICALCU6CS |
| M8 | 18 mm | 120 mm² | ICALCU8CS |
| M10 | 23 mm | 240 mm² | ICALCU10CS |
| M10 (large) | 26 mm | 300 mm² | ICALCU10CS2 |
| M12 | 26 mm | 240 mm² | ICALCU12CS2 |
| M12 (large) | 30 mm | 400 mm² | ICALCU12CS |
| M12 (extra) | 46 mm | 500 mm² | ICALCU12CS3 |
| M16 | 35 mm | 500 mm² | ICALCU16CS |
| M16 (large) | 46 mm | 630 mm² | ICALCU16CS2 |
| M20 | 37 mm | 500 mm² | ICALCU20CS |
| M20 (large) | 46 mm | 630 mm² | ICALCU20CS2 |
What CUPAL does in the joint
CUPAL puts the whole transition into a single diffusion-bonded plate or washer, and the rule is the same everywhere: each face meets its own metal. In this cabinet the aluminium side faces the cable lug or terminal and the copper side faces the busbar; where the lug is the copper part and the bar is aluminium, the same washer goes in the other way up. Either way the electrochemical driver of galvanic corrosion — two dissimilar metals sharing an electrolyte at the joint — is removed at the contact itself. No paste, no annual re-torque, no oxide surprises on the thermographic survey. Tightening torque remains whatever the busbar and bolt manufacturers specify; CUPAL has no torque table of its own, and the rest of the fitting sequence is in the CUPAL installation guide.
Order without a minimum quantity, with net list prices per size and the distributor cross-reference (NEXANS, Mentavill), on the CUPAL washer product page.
The base material carries DIN 17007 / DIN 1787 designations (aluminium AL 99.5 / 3.0255, copper E1-Cu58 / 2.0065); EN 10204 2.2 with every shipment, EN 10204 3.1 on request. The material comes from an ISO 9001:2015 certified supply chain, and HIDRA-MIX Kft. has been supplying the Hungarian electrical industry since 1991.
What this looks like in numbers
Where it fits in the cabinet
Four places in the cabinet where you will hit an Al/Cu joint — and the table above gives the SKU for the one you land on.
Incoming feeder → main busbar
The problem you need to solve. A three-phase aluminium feeder (e.g. 3×240 mm² Al) lands on the main copper busbar through a bolted lug. Thermally it is one of the hardest-worked joints in the cabinet under IEC 61439-1.
How CUPAL solves it. A CUPAL transition plate between the lug and the bar, cut to the existing bolt pattern. Al face to the lug, Cu face to the bar, standard M10/M12 hardware. Torque is set by the busbar and bolt manufacturers' specification — CUPAL has no torque table of its own.
Outgoing feeder: Cu busbar → Al cable to MCC
The problem you need to solve. The outgoing direction lands copper busbar on aluminium cable feeding a motor control centre or sub-distribution. Same Al/Cu bolted joint, often with stricter handover documentation.
How CUPAL solves it. A CUPAL washer between busbar and lug. One part, no extra tools, no paste — and the material ships with an EN 10204 certificate you can drop into the panel dossier.
N / PE equipotential bar
The problem you need to solve. In a multi-storey riser, aluminium neutral and PE conductors terminate onto the cabinet's copper bonding bar. Thermal cycling relaxes the bolted joint, oxide adds resistance.
How CUPAL solves it. A CUPAL transition plate between bonding bar and riser. Both bolted faces put like metal against like metal, so the joint no longer depends on the aluminium oxide film — there is no interface left to clean and re-paste on a cycle.
Brownfield retrofit
The problem you need to solve. A 10–20-year-old cabinet gets an Al feeder upgrade on capacity, but the original copper busbar stays. Catalogue parts do not always fit the old bolt pattern or the stack-up height.
How CUPAL solves it. A CUPAL plate cut to the existing pattern from a DXF, PDF or JPG drawing — quote within 24 hours, 5–10 working days in production. It installs without structural modification.
Compared to the usual alternatives
Four familiar approaches to the same bolted joint — what happens to it over time, and how much freedom you have on geometry.
| Approach | Initial joint behaviour | Maintenance | Geometry |
|---|---|---|---|
| Cu lug + antioxidant paste | Acceptable, drifts over time | New paste + re-torque every 2–3 yrs | Standard lug footprints |
| Specialty compression bimetal lug (imported) | Stable | None | Fixed, catalogue geometry |
| Over-sized pure copper conductor | Excellent | None | Removes the joint, but the conductor run is re-specified |
| CUPAL washer or custom-cut plate | Stable | None | 11 stocked washer sizes, or any contour from DXF, PDF or JPG |
Washer, lug or cut plate
The same material in four forms — the geometry of the joint decides which one belongs in it.
| Form | When this is the one | Geometry | Availability |
|---|---|---|---|
| CUPAL washer (M6–M20) | A finished lug bolts onto the bar and the bolt pattern is fixed | 11 stocked sizes, all 2 mm thick | From stock, 2–10 working days to delivery |
| CUPAL bimetal cable lug (ICALCU) | The cable end itself has to change metal | 109 SKUs — eye-lugs, butt-splices, pin lugs | From stock |
| CUPAL sheet, 500 × 500 mm | Bar-to-bar transition, larger contact area | 0.5 / 1.0 / 1.5 / 2.0 mm | 0.5 and 1.0 mm from stock; 1.5 and 2.0 mm 5–10 working days |
| Custom cutting | The existing bolt pattern takes no catalogue part | Any contour from a DXF, PDF or JPG drawing | Quote within 24 h, 5–10 working days in production |
What we supply, and what we don't
We have been supplying tooling and material to switchgear, busbar and cable-lug manufacturers and to lightning-protection contractors since 1991 — we supply into your bill of materials, we do not bid for your work. We do not build cabinets, and we do not sell enclosures, busbar systems, terminal blocks, circuit breakers or installation labour. One line item goes into your BOM: the copper-aluminium transition — as an M6–M20 washer, as an ICALCU bimetal cable lug, 109 SKUs from stock, as CUPAL sheet, 500 × 500 mm, or as a contour cut to size from your DXF, PDF or JPG drawing.
We do not sign the declaration of conformity for the cabinet either. EN 10204 2.2 — 3.1 on request — certifies the material; IEC 61238 and IEC 61439 apply to the assembly the part is fitted into, not to CUPAL itself. Under MSZ EN 61439 the routine verification belongs to the assembly manufacturer, and it stays there. What we add is the EN 10204 material certificate for your handover file and a summary of how the standards relate to one another.
One route falls outside ours: if the specification calls for a Cuponal busbar profile, that is a different supply chain — Cuponal is made by hydrostatic extrusion and exists only as long product (busbar, rod, profile, wire). If what you need is a Cu-Al transition as a sheet, a disc, a strip or a washer, that is CUPAL, and that is us.
If the retrofit bolt pattern takes no catalogue part, send us the drawing — DXF, PDF or JPG all work, and we quote within 24 hours. And if it is not cable onto bar but bar onto bar, the Al/Cu busbar transition is the closer page.
FAQs from panel builders
Recommended CUPAL products
Applicable standards for this field
Knowledge Base — CUPAL Technical Resources
3/1/2026
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Read the full article →2/15/2026
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CUPAL is a cold-roll-bonded, diffusion-welded copper-aluminum bimetal composite. Learn its composition, manufacturing process and properties.
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