Site Issue: Running Capacity Is Adequate, but Motor Starting Trips the System
Many factories add up equipment nameplate ratings and conclude that generator capacity is sufficient. During an actual outage recovery, however, compressors, pumps, fans or chillers may start together. The resulting current can far exceed running demand, causing frequency dips, breaker trips or generator shutdown.
Installing a larger generator alone does not solve this problem. Starting methods, load sequencing, control logic, paralleled capacity and low-voltage protection settings must be reviewed together.
Configuration Review: Starting Methods and the Largest Simultaneous Start Combination
Group motors by direct-on-line, star-delta, soft-start, VFD and process-interlock operation. Confirm which equipment restarts automatically after utility return or generator takeover and which loads can be delayed.
- Power list for compressors, fans, pumps, chillers and large motors.
- Starting method, current multiplier and permitted start delay for each item.
- Maximum simultaneous running load and largest simultaneous-start combination.
- Data for breakers, contactors, soft starters, VFDs and control logic.
Why This Design: Capacity, Controls and Distribution Must Be Engineered Together
If large motors must start together, generator capacity and transient response need adequate margin. If the process allows staged recovery, delayed loading, soft starters or VFDs can reduce the impact. The two approaches differ in cost and reliability and must be evaluated against the available process window.
For paralleled systems, load sharing, synchronization logic and automatic start/stop strategy also matter. Adding another generator does not by itself create redundancy; starting demand and load allocation must both remain controlled.
Review Documents: Motors and Starting Methods
- Nameplate photos for motors, compressors, pumps, fans and chillers.
- Starting methods, sequence, automatic-recovery logic and process constraints.
- Maximum simultaneous load, priority recovery loads and loads that can be delayed.
- Photos of low-voltage switchboards, breakers, soft starters and VFDs.
- Existing generator rating, controller model, alarm history and trip records.