Bus Iec 61439
In IEC 61439, a bus or busbar is a conductive bar within low-voltage switchgear and controlgear assemblies that distributes electrical power between incoming feeders and outgoing circuits. Busbars are bare or insulated live parts arranged to minimize internal short-circuits, and must be dimensioned and verified for short-circuit withstand, clearances, creepage distances, and thermal loading. This definition applies to busbar trunking systems (busways) under IEC 61439-6 and general assemblies under IEC 61439-1/-2.
On a manufacturing shop floor, IEC 61439-compliant busbars and busways safely distribute low-voltage power (e.g., 600 V) within switchgear, motor control centers (MCCs), and distribution panels. Busbars carry large currents from main breakers to feeders and loads, while busway trunking runs overhead to supply machines like CNCs, presses, and robotic cells via tap-off units. Design requirements include rated voltage and current, short-circuit withstand (thermal and peak), and minimum clearances (e.g., 10 mm phase-to-phase, 15 mm to structures up to 690 V). Enclosures must provide at least IP2X protection. Verification includes type tests and routine checks by the manufacturer. Compliance with WorkSafeBC Part 19 requires lockout/tagout, de-energized work, and qualified personnel access.
- Inadequate short-circuit and thermal withstand rating of busbars, leading to deformation, loosening joints, or arc-flash during faults.
- Insufficient clearances or creepage distances due to unauthorized modifications or contamination, increasing risk of phase-to-phase or phase-to-ground faults.
- Unauthorized modifications and lack of routine verification, such as adding non-approved tap-offs or skipping inspections, voiding ratings and violating safety regulations.
What IEC 61439 parts are directly relevant when specifying busbars or busways for a plant distribution system?
IEC 61439-1 provides general rules for LV switchgear and controlgear assemblies. IEC 61439-2 covers power switchgear and controlgear assemblies (e.g., main switchboards, MCCs). IEC 61439-6 specifically addresses busbar trunking systems (busways) for voltages up to 1,000 V AC or 1,500 V DC. IEC 61439-1 cannot be used alone to determine conformity; the assembly must comply with the relevant product standard (e.g., part 2 or 6).
How are busbars verified under IEC 61439 (type and routine verification)?
Design (type) verification includes temperature rise tests, short-circuit withstand tests (thermal and dynamic), dielectric tests, and checks of clearances and creepage distances. Routine verification is performed on every manufactured assembly and includes visual inspection of busbar arrangement, dielectric tests, and functional checks of interlocks. The assembly manufacturer is responsible for routine verification.
What specific geometric requirements apply to busbars to avoid internal short-circuits?
IEC 61439-1 recommends minimum clearances up to AC 690 V: bare live parts to each other (phase-to-phase) must be at least 10 mm, and bare live parts to bodies or constructional components (phase-to-metal) must be at least 15 mm. Busbars must be arranged so internal short-circuits are not expected in normal service. Enclosed assemblies require minimum IP2X protection overall and at least IPXXC during certain maintenance actions.