CUPAL Washers
Copper-aluminium bimetal washers M6 to M20 — 11 sizes in stock, from HUF 412 net. Galvanic-corrosion protection for bolted joints.
CUPAL Washers (net, HUF)
| Bolt size | Outer dia. | Max. lug | SKU | Net list price | Quantity (pcs) |
|---|---|---|---|---|---|
| M6 | 16 mm | 120 mm² | ICALCU6CS | 437 Ft~ €1.20 | |
| M8 | 18 mm | 120 mm² | ICALCU8CS | 412 Ft~ €1.14 | |
| M10 | 23 mm | 240 mm² | ICALCU10CS | 677 Ft~ €1.87 | |
| M10 (large) | 26 mm | 300 mm² | ICALCU10CS2 | 759 Ft~ €2.09 | |
| M12 | 26 mm | 240 mm² | ICALCU12CS2 | 801 Ft~ €2.21 | |
| M12 (large) | 30 mm | 400 mm² | ICALCU12CS | 1,131 Ft~ €3.12 | |
| M12 (extra) | 46 mm | 500 mm² | ICALCU12CS3 | 2,357 Ft~ €6.49 | |
| M16 | 35 mm | 500 mm² | ICALCU16CS | 1,234 Ft~ €3.40 | |
| M16 (large) | 46 mm | 630 mm² | ICALCU16CS2 | 2,357 Ft~ €6.49 | |
| M20 | 37 mm | 500 mm² | ICALCU20CS | 1,768 Ft~ €4.87 | |
| M20 (large) | 46 mm | 630 mm² | ICALCU20CS2 | 2,357 Ft~ €6.49 |
Available with short lead time: 2–10 business days.
Cross-reference — distributor designations
| Distributor designation | Bore / outer / thickness | Our size | Our SKU |
|---|---|---|---|
| NEXANS Cupal M 8 Al-Cu | 8 / 18 / 1 mm | M8 | ICALCU8CS |
| NEXANS Cupal M 10 Al-Cu | 11 / 23 / 2 mm | M10 | ICALCU10CS |
| NEXANS Cupal M 12 Al-Cu | 13 / 28 / 2 mm | M12 or M12 (large) | ICALCU12CS2 / ICALCU12CS |
Which of our CUPAL washers matches the designation used by other distributors.
Mapped by bolt size and nearest outer diameter — check the outer diameter against your lug footprint before ordering. For sizes not listed here (M16, M20 and the large variants) request a quote; the full stock range is in the table above.
Also sold as a transition washer or bimetallic washer
If a specification, an earthing drawing or a bill of materials calls for a transition washer between an aluminium conductor and a copper lug or busbar, these are the parts that meet it. Earthing and substation suppliers usually call this part a transition washer or a bimetallic washer; cable-lug catalogues list it as an Al/Cu washer or a copper-aluminium transition washer. Those names all describe the same thing — a roll-bonded copper-aluminium disc that goes into a bolted joint so each conductor only ever touches its own metal. The name transition washer is also used for a different part: profiled copper-alloy washers, whose raised pattern bites through the aluminium oxide film when the bolt is tightened. Those are copper alloy throughout, not a bimetal, and the transition is made as the joint is tightened; ours is roll-bonded across the whole disc, so the transition is built into the part. Bimetallic connector is a looser term still: where that line on a drawing means a disc, this is the part; where it means a crimpable transition piece with an aluminium barrel and a copper palm, that is our CUPAL cable-lug range. Requirements for joints between dissimilar metals are set by IEC 61238 for cable connectors and IEC 61439 for low-voltage switchgear. Both apply to the installation the washer is fitted into, not to the CUPAL material itself.
If the specification only says "transition washer", first check which of the two parts it means: bimetallic or toothed transition washer — how to tell them apart.
The cladding ratio, and why it is worth checking
Not every copper-aluminium washer on the market is the same material. Ours is 70 % aluminium / 30 % copper by layer thickness, density 4.6 g/cm³, conductivity about 41.9 m/Ω·mm² — which is the mainstream European specification. Others differ substantially: some washers are as lean as 15 % copper, and some sheet is supplied at a 1:1 ratio, which is roughly 5.8 g/cm³ and carries around two-thirds more copper. More copper means more conductivity per unit area and more weight and cost; less copper means the opposite. Neither is better in the abstract — it depends on whether the joint is carrying working current or is an earthing and bonding path where the bolt size sets the contact area. What matters is that you can tell. Many suppliers publish no ratio at all, which makes it impossible to specify against a drawing. If your specification calls for a particular ratio or a minimum copper thickness, tell us and we will confirm before you order.
Our list prices are published, net of VAT. An EN 10204 material certificate accompanies every shipment — 2.2 as standard, 3.1 on request — and we cut to size from your drawing.
Prices are net list prices. Gross = net × 1.27 (27 % Hungarian VAT applies to HU-issued invoices).Volume discounts apply (200+ pcs) — request a tailored quote.
Effective: 2026-07-20
In short
The CUPAL washer is a copper-aluminium bimetal transition washer, M6 to M20, that eliminates galvanic corrosion in bolted copper-aluminium joints. Its copper face meets the copper cable lug, its aluminium face the aluminium busbar — like metal to like metal, no anti-corrosion paste, with EN 10204 certification.
- M6–M20
- 11 stocked sizes
- 2mm
- Material thickness
- 412Ft
- From net list price
- 70/30
- Al / Cu ratio
Why use a CUPAL washer?
When you bolt a copper cable lug onto an aluminium busbar, the two dissimilar metals come into direct contact. The result: galvanic corrosion that gradually loosens the joint and increases contact resistance. The joint heats and eventually fails; on a high-current joint the temperature rise can reach fire-hazard levels. The CUPAL washer solves this: copper side to copper, aluminium side to aluminium — no corrosion.
A CUPAL washer is needed because direct contact between a copper cable lug and an aluminium busbar causes galvanic corrosion. The washer has a different metal on each side: copper towards the lug, aluminium towards the busbar. No contact corrosion, the joint doesn't loosen, resistance doesn't increase.
Which size do you need?
Two things decide it: the bolt sets the bore, and the lug cross-section sets the outer diameter — the palm has to sit fully on the washer face. For lugs up to 120 mm² that is M6 at 16 mm outer diameter or M8 at 18 mm. For 240 mm², M10 at 23 mm or M12 at 26 mm; for 300 mm², the large M10 at 26 mm; for 400 mm², the large M12 at 30 mm. For 500 mm² there is M16 at 35 mm, M20 at 37 mm or the extra M12 at 46 mm, and for 630 mm² the 46 mm versions of M16 and M20. All 11 sizes are 2 mm thick, so a larger diameter does not change the bolt length.
Custom geometry? Send us the DXF →Frequently asked questions about the CUPAL washer
Custom-cut to any shape — no one else offers this
Circles, strips, rectangles or fully bespoke contours — we cut any shape from CUPAL sheet. Send your drawing or describe the dimensions, and we respond within 1 business day.
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