Busbars carry the full current of a switchboard or panel section, and undersizing them creates a hidden risk that doesn't show up until a sustained high load or a fault event — by which point it's a safety incident, not a paperwork issue. Here's what to check.
1. Continuous Current Rating
The busbar's cross-sectional area must safely carry the maximum expected continuous current with an appropriate temperature rise margin — manufacturers publish current-carrying capacity tables per busbar size (width x thickness) for both copper and aluminium, typically referenced to a specific ambient temperature and temperature rise limit (commonly 30-35°C rise above a 35-40°C ambient for indoor panels).
2. Copper vs Aluminium
Copper has roughly 60% higher conductivity than aluminium for the same cross-section, meaning a smaller copper busbar can carry the same current as a larger aluminium one — useful where panel space is limited. Aluminium is lighter and cheaper for large current ratings but needs larger cross-sections and careful joint treatment (proper compound/plating) to prevent oxidation at connections, which can cause high-resistance joints and localized heating over time.
3. Short-Circuit Withstand (Mechanical)
During a fault, busbars experience strong electromagnetic forces between conductors proportional to the square of the fault current — the busbar and its support insulators must be mechanically rated (and properly spaced/braced) to withstand these forces without deforming or the supports failing, for the duration until upstream protection clears the fault.
4. Short-Circuit Withstand (Thermal)
Separately from the mechanical force, the busbar must not overheat during the fault's duration — manufacturers specify a short-time withstand current rating (kA for a specified duration, commonly 1s) that the busbar cross-section must meet or exceed for your system's actual fault level.
5. Spacing and Clearance
Phase-to-phase and phase-to-earth clearances must meet the panel's rated insulation voltage and altitude/pollution degree — busbar supports (insulators) are rated for specific voltage classes and must be spaced according to the panel manufacturer's type-tested design, not arbitrarily.
6. Temperature Rise at Joints
Bolted busbar joints are a common weak point — correct torque, contact surface preparation (cleaning, appropriate plating), and using the specified number/size of bolts all affect joint resistance and long-term reliability. A poorly made joint can run significantly hotter than the busbar itself under full load.
Practical Guidance
For a new panel design, always work from the switchboard manufacturer's type-tested busbar configuration (rated current, short-circuit rating, and physical layout as a matched set) rather than mixing components from different sources — type-testing verifies the whole assembly meets its rating, not just individual components in isolation.
TEKTOW supplies busbars, insulators, and panel components. Get in touch with your panel's current and fault level requirements.