Sags - Effect on Data Flow

Sags are short duration changes in the RMS level of the voltage. They typically last for less than a few seconds. They occur whenever there is a sudden change in the load current. Ohm's Law tells us that changes in the voltage occur when a changing current interacts with system impedance. If there is a sudden increase in current due to a load turning on, then a sag will result. On single phase circuits, a corresponding neutral-ground swell also occurs.

When a sag occurs, the power supply inside electronic devices 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 may lose its ability to maintain an exact DC voltage to all of the integrated circuits inside the device - even for a few milliseconds. This is enough time for a the 1's and 0's inside the computer to get confused, and data to be lost or corrupted.

When voltage sags are a problem, the first step in solving it is to identify what is being disrupted and why. Where is the load causing the changing current? If that load or group of loads can be located, then a solution may be as simple as relocating either the victim or the culprit.

Since sags are closely dependent on wiring impedance, another possible solution is to increase the wire size in the distribution path for the sensitive load. This decreases the impedance, ultimately reducing the magnitude of the sag.

Should these steps not be possible, then voltage regulation must be introduced to maintain voltage stability and keep data integrity.

Voltage regulators may be stand-alone devices, or used with other technologies such as transformers to add to their capabilities.