What Is the Difference Between a Brownout and a Voltage Sag?
In some buildings, you may have noticed that the lights dim down for a few seconds when a large motor activates. For example, this may happen when starting a central air conditioner or a centrifugal pump. These quick voltage drops that only last for a few seconds are called sags.
When starting an electric motor, the inrush current can be 5 to 8 times higher than the normal current, and this will cause a voltage sag if the motor is large. Electrical engineers recommend inverter drives, which start motors by ramping up the voltage gradually, instead of applying the full voltage at once. This starting method reduces the inrush current, eliminating sags.
A brownout is an extended event, on the other hand, lasting for several minutes or even hours. When a building is affected by a brownout, the cause can be external or internal:
- When a brownout affects a large area, the most likely cause is a power grid overload. The voltage drops because electricity generation cannot keep up with consumption, and electric companies may also lower the voltage intentionally to reduce power demand.
- Brownouts that affect individual buildings are clear warning sign of electrical issues. For instance, if too many appliances share the same circuit, the resulting overload can cause a localized brownout.
When a brownout is due to external causes, you should focus on protecting your electrical devices. On the other hand, if the brownout cause is inside your property, you can get an electrical inspection to find a solution.