Busway Resistance, Reactance & Impedance Explained

Understanding R, X & Z for Better System Design and Performance

When engineers evaluate a busway system, rated current and short-circuit performance are not the only important parameters. Resistance (R), reactance (X) and impedance (Z) also affect voltage drop, power loss, fault current and overall electrical performance. These values become especially important in long feeder routes, rising mains and high-current applications.

Resistance (R) represents the opposition of the conductor to current flow. Higher resistance increases power loss and voltage drop. It is influenced by conductor material, cross-sectional area, busway construction, temperature and route length.

Reactance (X) is caused by the electromagnetic characteristics of an AC system. It depends on conductor spacing, phase arrangement, geometry and frequency. Reactance also contributes to voltage drop and overall system impedance.

Impedance (Z) is the combined electrical effect of resistance and reactance:

Z = √(R² + X²)

It influences voltage drop, losses, prospective fault current and long-distance power distribution performance.

For three-phase systems, voltage drop is affected by current, route length, R, X and power factor. Therefore, two busway systems with the same rated current can still have different voltage-drop performance.

For proper evaluation, customers should provide the SLD, rated current, voltage, frequency, route length, power factor, conductor preference, layout and project specification.