Sags - Effect on Disrupted Equipment

Like all sags, externally-based sags result from load changes and system impedance. In this case, however, the customer has little or no control over the problem. As far as the customer is concerned, the source voltage at the service entrance dipped.

When a sag occurs, a device's power supply uses some of its stored energy to compensate for the loss of input voltage. If enough energy is lost due to the sag, the power supply can no longer keep the system operating, and it shuts down. Since the switch is still on, as soon as the sag is over, the system turns back on, or restarts.

While the lost energy may not be enough to shut down the device, it could still confuse the digital components. If this happens, a lock-up may result.

Some form of voltage regulator or energy storage device is needed to remedy these types of disturbances. Products that provide longer ride-through times such as enhanced power supplies, that regulate the voltage such as tap-switching conditioners, or that switch to temporary back-up power like an SPS, will suffice.