Transformers play a vital role in industry today. In fact, they are important for control circuits and can serve many applications. Transformer overload protection is essential for protecting equipment and limiting your downtime. Here are some important things to know on the subject.


When installing autotransformers, you must pay attention to the full-load rating of the transformer input side. Make sure your transformer overload protection (breaker) does not exceed the transformer rating. For instance, you should not use breakers rated more than 50 amps for a 50 amp transformer.

Make sure the shunt winding is not in series with the overcurrent device. Instead, you need to wire your protection device in series with the input conductor(s). This is important to remember.

You May Not Need to Protect the Secondary Windings

As long as the breaker rating for the primary side is not rated more than one hundred and twenty five percent, you do not have to protect the secondary. If protection is needed, you can use as many as six breakers (as long as they are not over 125% of the capacity).

Current Transformers

CTs (Current transformers) can aid in transformer overload protection in some cases. They can monitor current and reduce the current to a circuit. You may put current transformers on both sides of a breaker if you wish. You can even install two CTs for each bushing. This is often used when you have both primary and secondary relay systems.

Protecting Current Transformers

If a circuit breaker gets tripped, large voltage surges can occur and not just on the shorted side of the breaker. Make sure the breaker is installed on the side which is likely to experience current overload (and low voltage). This protects the CT from the electrostatic discharge which can happen.