• Craig Drabyk

Managing Inrush Current During Building and Process Equipment Startup


Inrush current is the maximum instantaneous input current drawn by an electrical device when first turned on. Managing inrush current during building and process equipment startup is extremely important, particularly when power is restored after an outage.

When starting a motor, inrush current is necessary to overcome the inertia of a dead stop. Depending on the motor sizes, quantities, and load, startup of too many air handlers, pumps, fans, compressors, and other pieces of equipment at once can cause breakers to trip, fuses to blow, or generators to shut down. Many facilities are unaware of the problem until there is a loss of power and equipment is restarted on generator or restored utility power.

Inrush current can be managed by starting equipment according to a timed sequence at specific ramp speeds. This can usually be programmed through the building management system or process control system. Equipment must be started up at intervals and in the right order. For example, process chilled water should be flowing before chillers are started. Timing and sequence should be tested to ensure that a facility won’t fail to run when needed and to uncover important equipment that was mistakenly omitted from the sequence. An accurate and up-to-date electrical coordination study and taking steps to ensure that breakers are set properly also help to eliminate nuisance trips on upstream breakers.


About Omni

Omni Instrumentation & Electrical Services, Inc., located in New Jersey and Maryland, is a premier instrumentation and electrical contractor, providing superior total care solutions since 1986. Services include instrument installation, tubing installation, instrument calibration, control loop testing, startup and commissioning, power and lighting, process control wiring, BMS wiring, telecommunications and data wiring, fire alarm wiring, security wiring, process network wiring, and control panel fabrication. Omni Instrumentation & Electrical Services, Inc., is certified in Foundation Fieldbus, Profibus, DeviceNet and ASI-Bus installation.

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