Weg thermal overload relays are an inexpensive solution to protecting expensive electric motors from burn-up due to overload conditions, phase-loss or current unbalances.
Protected Conditions:
Overload can occur when the motor is asked to do more work than it was designed for, or from mechanical failures in the machinery. Attempting to run too much material too quickly through a machine is one common cause of failure. Pump motors can also be overloaded by attempting to pump more water over a given amount of time than the motor was designed for. Other mechanical faults can also cause overloading, including motor and machinery bearing failures.
Phase-Loss is a common cause of motor winding failures and occurs when one of the fuses in a three-phase circuit blows. Weg thermal overload relays detect phase-loss and shut down the motor by opening up the contactor.
Current Imbalance can occur when one there is a voltage drop or surge in one of the phases in incoming power. The higher or lower voltage causes more or less current on one of the power leads to the motor, which can eventually burn up the windings. The Weg thermal overload relays sense current imbalance and shut down the motor.
Standard Features
- Class 10 Trip characteristics (read more below about Class trip ratings)
- Selectable Auto/Man reset button (read more below)
- Settable current overload range
- Phase-loss and current imbalance protection
- Isolated 1 NO & 1NC contact
- 2 and 3-pole versions available (single and three-phase)
What is Trip Class?
Class 10, 20, and 30 ratings on overloads refer to how quickly the overload will respond to an overload event. Similar to a fuse, the larger the overload, the more quickly the relay will trip. The graphic below shows the response times vs overload for the 3 classes:
Multifunction Reset / Test Button
The button has four positions:
- A - Auto Reset Only: The test feature is disabled, and the relay will attempt to reset itself after the recovery time period.
- Auto = Auto Reset / Test: The test featuer is enabled, and the relay will attempt to reset itself after the recovery time period.
- Hand - Manual Reset / Test: The test feature is enabled and the relay will only reset after the button has been pressed and the recovery time period has elapsed.
- H - Manual Reset Only: The test feature is disabled and the relay will only reset after the button has been pressed and the recovery time period has elapsed.