Controlling two motors from one VFD (Allen Bradley 160) requires each motor to have its own overload protection. The application requires one that is capable of overlooking the startup inrush current, yet responsive enough to detect a product jam or locked up bearing. What type of overload protection is appropriate in this application? This is simple relay logic, no PLC available.

Thanks for you help.

 

Hi Doc

Use a combined thermal overload/circuit breaker for each motor, connected between the VFD and motor. The overload unit should be set to the motor rated current. A typical unit is the Integral range from Telemecanique.

Jamie Downs

 

Take a look at Allen-Bradley bulletin 809S motor protection relays or SSAC current relays. They do not replace overloads for each motor. Since the app. is relay logic I assume you want to stay away from A-B 193-E3 overload, which include a jam level and time delay, since they require a PC for programming.

 

You may, need two different types of devices.

Overload relays are designed to handle the inrush current of motors as well as momentary overloads. They are designed to operate at 6x current for 10sec (Class 10) or for 20sec (Class20). This time delay makes them impractical to use for detecting jams.

Overcurrent relays operate instantaneously at 1x current (although some have time delays available) which makes them ideal for detecting jams. These usually have a maximum current rating of 30A so a current transformer may be needed.

There are some solid state overload relays available that can perform both functions.

I would consider using a Telemecanique GV2 device for my overload and a RM4JA device for my overcurrent.