New Concept in Motor and Motor Circuit Protection

Common motor circuit protection has consisted of thermal overload to sense motor overcurrent and a short circuit protective device which acts after a catastrophic condition has occurred. While this combination has provided adequate protection for the most common motor and motor circuit problems, it has not provided good protection against many of the problem conditions that can occur in the motor circuit. Common motor and motor circuit problems, the circuit variances that occur and the use of common devices under these conditions are discussed. It is shown how a solid-state logic approach can sense these circuit variances and result in an economical package providing improved protection, coordinated and easily applied, which can help eliminate or minimize loss due to many of these common problems.