Joint and splice plates
Straight plates bolted across the butt joint of two collinear bars, often on both faces for higher current.
Power distribution guide
Busbar Connector Components
A busbar connector is the part that joins one busbar to another, or a busbar to a device terminal, while carrying the full circuit current. Connectors come in three broad types: rigid link plates, flexible connectors that absorb movement, and laminated connectors for compact, low-inductance layouts, together with the bolts, washers and spacers that hold every joint tight. A well-made joint should run no hotter than the bar on either side of it.
- Types
- Rigid, flexible, laminated
- Materials
- Copper, aluminium, Cu-Al bimetal
- Finishes
- Bare, tin, silver, nickel
- Key standard
- IEC 61439 temperature rise
What a busbar connector has to achieve
Busbars themselves rarely fail; joints do. Every bolted or clamped interface adds contact resistance, and resistance turns current into heat. If a joint loosens, oxidises or is too small, it heats, expands, loosens further and can eventually fail. A good connector therefore combines enough contact area, sufficient and lasting clamping pressure, compatible materials and a surface finish suited to the environment.
- Carry rated current with a temperature rise within the limits of the switchgear standard
- Maintain contact pressure through thermal cycling, vibration and creep
- Accommodate thermal expansion, vibration and installation misalignment where needed
- Avoid galvanic corrosion where copper and aluminium meet
- Fit the available space and insulation clearances
Rigid busbar connectors and link plates
Rigid connectors are flat plates or formed straps cut from busbar stock and drilled to match the bars they join. They are the simplest and lowest-resistance option where both ends are fixed and expansion is small, such as splices within a switchboard section or links between parallel bars.
Bolt-on link plates
Offset or angled plates that connect bars at different levels or directions, or connect a bar to a breaker or transformer terminal.
Copper and aluminium links
Copper for compact high-current joints; aluminium for lighter, lower-cost links where space allows a larger section.
Rigid links are specified by material and temper, thickness and width, hole pattern and spacing, bend geometry and contact finish. For aluminium links, electrical alloys such as 1350, 6101 or 6063 are typical; harder 6xxx tempers resist creep under bolts better than soft pure aluminium.
Flexible busbar connectors
Where bars move relative to one another, a rigid link would transmit force to the terminals and loosen the joint. Flexible connectors absorb this movement.
| Type | Construction | Typical use |
|---|---|---|
| Laminated foil connector | Stack of thin copper or aluminium foils, pressure welded into solid contact pads at each end | Transformer and generator terminals, expansion joints in busbar runs |
| Braided connector | Flat braid with crimped or welded terminals | Vibration isolation, earthing, moving contacts |
| Insulated flexible busbar | Thin laminated strip in a PVC or silicone sleeve, bendable by hand | Panel wiring between devices, battery modules |
Flexibles are sized on the same current-carrying principles as solid bars, with derating for the sleeve and for the reduced cooling of tightly packed laminations.
Laminated busbar connectors
Laminated connectors stack flat conductors, usually positive and negative, separated by thin insulation films and bonded into one assembly. Keeping the conductors close together cuts loop inductance, which reduces voltage overshoot when power semiconductors switch. They are standard in inverters, converters, UPS systems, traction drives and EV power electronics, and are built to the customer's layout with terminals and insulation sized for the working voltage.
Connector hardware and matching components
Bolts and nuts
Steel or stainless fasteners in a property class able to hold the specified torque, sized to the joint and hole pattern.
Flat washers
Wide washers spread clamping force over the soft conductor and protect the surface from the bolt head and nut.
Spring and conical washers
Disc (Belleville) or spring washers keep tension when the joint expands, contracts or creeps, which is especially important on aluminium.
Bimetallic washers and plates
Copper-aluminium transition washers or plates put copper against copper and aluminium against aluminium, keeping the dissimilar-metal interface sealed inside a bonded part.
Spacers and shims
Set gaps between parallel bars and compensate for thickness differences at joints.
Contact compound
Grease or paste that excludes air and moisture from aluminium contact surfaces after the oxide has been abraded.
Materials and contact finishes
| Option | Conductivity | Strengths | Watch points |
|---|---|---|---|
| Copper (C11000 / Cu-ETP) | About 100 % IACS | Compact, high current, easy to plate and solder | Heavy and costly |
| Aluminium 1350 / 1060 | About 61 – 62 % IACS | Light and economical | Soft; creep under bolts; needs surface preparation |
| Aluminium 6101 / 6063 (T6 tempers) | About 52 – 57 % IACS | Stronger, better creep resistance | Slightly lower conductivity |
| Copper-clad aluminium | Between the two | Copper surface for contacts with lighter core | Edges and holes expose aluminium |
| Tin plating | — | Stable contact resistance, good for Cu-Al joints and humid air | Softer surface wears under repeated make-break |
| Silver plating | — | Lowest contact resistance, high-temperature joints | Tarnishes in sulphur-bearing air; cost |
| Nickel plating | — | Hard, heat and corrosion resistant | Higher contact resistance than tin or silver |
Conductivity values are typical; minimums are set by the relevant material standard and temper.
Making reliable bolted joints
- Size the overlapGive the joint enough overlap and bolts that its resistance is no higher than an equal length of bar; joint design guides commonly relate overlap to bar width.
- Prepare surfacesClean plated surfaces with a solvent. On bare aluminium, wire-brush or abrade the contact area and apply contact compound immediately.
- Use the right hardwareFlat washers under head and nut, plus disc springs on aluminium joints to maintain pressure.
- Torque correctlyTighten to the value for the bolt size, material and lubrication, using a calibrated tool, and mark the bolts.
- Separate copper and aluminiumUse tin-plated aluminium or copper, or bimetallic washers, and keep the joint dry.
- VerifyMeasure joint resistance with a micro-ohmmeter and check temperature by thermography under load.
Relevant standards
| Standard | Scope |
|---|---|
| IEC 61439-1 / -2 | Low-voltage switchgear assemblies, including temperature-rise limits for busbars and terminals |
| ASTM B317/B317M | Aluminium alloy extruded bar and profiles for electrical purposes (bus conductor) |
| ASTM B187/B187M | Copper bus bar, rod and shapes |
| EN 13601 | Copper rod, bar and wire for general electrical purposes |
| UL 857 / IEC 61439-6 | Busway (busbar trunking) systems |
References and standards
- IEC 61439-1 – Low-voltage switchgear and controlgear assemblies: general rules
- ASTM B317/B317M – Aluminum-Alloy Extruded Bar, Rod, Tube, Pipe and Profiles for Electrical Purposes (Bus Conductor)
- ASTM B187/B187M – Copper, Bus Bar, Rod, and Shapes and General Purpose Rod, Bar, and Shapes
- Copper Development Association – Copper for Busbars (Publication 22)
- The Aluminum Association – Aluminum Electrical Conductor Handbook
Busbar connectors: frequently asked questions
When should I use a flexible rather than a rigid busbar connector?
Use a flexible connector wherever the bars or terminals can move relative to each other: at transformer and generator terminals, across expansion joints, on vibrating equipment, or where installation tolerances need to be absorbed.
Can I bolt copper directly to aluminum busbar?
It is not recommended in damp conditions because galvanic corrosion attacks the aluminium. Use tin-plated parts, bimetallic copper-aluminium washers or transition plates, contact compound and spring washers.
Why are spring or conical washers used on aluminium joints?
Aluminium slowly creeps under constant bolt pressure and expands more than steel bolts when hot. Disc springs keep the clamping force up as the joint cycles, which keeps contact resistance low.
Which plating is best for busbar connectors?
Tin is the general choice for stable contact resistance and copper-aluminium joints. Silver suits high-temperature or very low-resistance joints but tarnishes in sulphur-bearing air. Nickel is chosen for heat and corrosion resistance.
How do I check a busbar joint after installation?
Measure its resistance with a micro-ohmmeter and compare with an equal length of bar, confirm bolt torque, and inspect under load with an infrared camera for hot spots.
Need busbar stock or connector parts?
Send drawings, alloy, finish and quantities to sales@metline.in, and our team will reply with options for aluminium busbar and cut-to-drawing parts.
