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  • Writer's pictureCraig Drabyk

Electrical Sags & Undervoltage

There are a number of power quality issues that can cause problems in a building or facility. These include voltage sags, undervoltage, overvoltage, surges, interruptions, and several others. Voltage sags and undervoltage are the most common, accounting for about 92% of commercial and industrial power quality problems.

A voltage sag or dip is a brief reduction in voltage (below 90% of its nominal value) that lasts between 0.5 cycle to one minute. Undervoltage is when a power sag exceeds one minute. While undervoltage is usually a chronic problem due to conditions beyond the user’s control (weather, high demand, or distribution system design) sags can be caused by both internal and external factors. Sags that originate in a user’s facility typically occur due to a sudden increase in loads, such as when motors or magnets are started, short circuits or faults, or when there is an abrupt increase in source impedance, often due to a loose connection. If chronic undervoltage is an issue, even small sags can exacerbate the problem.

For critical light loads, a local or central UPS should be installed to guard against power quality issues and provide clean, constant power when needed. For larger loads such as motors, HVAC, and heaters, sags and undervoltage can be more challenging. Monitoring equipment can be used to determine how, when and where issues are occurring, and identify whether the issue is internal or external. Some equipment, such as VFDs, can be programmed with catch-on-the-fly and auto restart. If it is determined that your power issues are external, contact your utility company.

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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