“Draw a 400 V, three-phase 50 Hz supply through a 200 A isolator, 200 A main breaker, and busbar to a 160 A VFD feeder and 160 A VFD driving a 75 kW induction motor, with 70 mm² copper input and motor cables.”
Read the decisions behind it.
A 200 A main isolator precedes the main breaker for a visible upstream isolation point.
A dedicated 160 A breaker protects the VFD branch from the 400 V main busbar.
The VFD is rated 160 A, appropriate for the approximate full-load current range of a 75 kW, 400 V motor.
Both VFD input and motor output are shown as 70 mm² copper conductors, subject to installation derating.
Use this as a concept one-line for a 75 kW VFD motor branch. Final equipment ratings, cable sizes, protection settings, and harmonic measures require project-specific calculations.
Other examples in this family.
Common questions
Why is the VFD feeder rated 160 A?
A 75 kW motor at 400 V typically draws well above 100 A. The final rating must follow the motor and VFD manufacturer data.
Can 70 mm² copper always be used for this motor?
No. Ampacity and voltage drop depend on installation conditions, cable construction, ambient temperature, grouping, and local code.
Why is there an isolator ahead of the breaker?
It provides a local means of isolation for maintenance, subject to the selected device’s load-break and safety requirements.
Does this diagram show VFD control wiring?
No. It shows the power path only; start/stop, speed reference, interlocks, and safety wiring need a separate control schematic.