Control.com - Nerds in Control

We are improving the control of the fans on our chiller. We have one circuit breaker protecting 20 1 hp fans. I feel we need overloads on each fan, but our electrician claims the motors have internal thermal protection and that we do not need the overloads. The overloads will not protect the motor because if the overload heats up the motor already needs to be replaced. All comments will be appreciated.

Your electrician is probably correct. Most small motors do have internal overload protection. Ask him to show you or go look yourself and get the nameplate data and google the manufacturer's website if you haven't got the manual. There is often an external reset button on the overload built right in to the motor that should be obvious.

I would not add additional overload protection if it exists in each motor already because you're not gaining anything and will end up with an angry electrician if he's got to do the all the work. However, the I do wonder about having 20 motors on a single breaker, unless there is individual circuit overcurrent protection such as fuses feeding each motor.

Besides, if there were no means of individually isolating each motor, it would also be an awkward system to maintain, as you would have to shut down the chiller to work on individual motors. And with 20 motors, they're you're going to have problems.

If there is no over current protection ahead of each motor, a ground fault or short in the wires to one motor, or a major fault in one motor will trip the breaker taking out all the motors before an overload has a chance to trip. Then down goes the chiller and your electrician has to find the problem among 20 possibilities. This is probably not the case, but it should be looked into as a reliability/maintainability.

It is preferred to make individual protection circuit for each motor to improve the reliability of the system because any tripping for the protection circuit of any motor will lead to tripping in the main circuit breaker.
For the protection of any motor it must contain short circuit protection and over load protection.

No problems to use over load with motor with internal thermal protection, in the other hand it will consider as a backups for the protection.

For modern motor starter it contains short circuit protection and over load protection in the same module, for example Siemens motor starter