Current transformers are used in conjunction with a burden resistor that is placed across the secondary winding. The current flowing in the secondary winding passes through the burden resistor generating a signal voltage that can be monitored to evaluate system function. The burden resistor is selected based on the maximum voltage the winding can support and the range of currents to be measured. Foster’s Engineering staff can work with you to pick the correct resistor for your application.

Foster’s standard EI core current transformers are ideal for measuring the magnitude of current flowing through a conductor. Unlike a toroidal core transformer, the line or wire being measured does not have to pass through the center of the core. The wire can be broken and attached to either side of the current transformer’s primary winding. This simplifies installation, lowers costs, and makes field repairs simpler because a wire does not have to be cut to remove the transformer or the board to which its connected from the equipment. Our model 16051 goes one step further by providing standard 1/4" quick connect tabs for the high current connection. This keeps the high current off our your circuit board completely.

If current transformers utilizing an EI core are less costly and simpler to install, why not use them all of the time? The answer is phase shift. The coupling between windings on an EI core is generally not as good as it is with a toroidal current transformer. This results in a phase shift between the voltage and current being monitored. Often this phase shift is unimportant. For applications where it is important to monitor both the magnitude of the current flowing in a conductor and its phase relationship, a toroidal core transformer is often a better solution. If your application requires monitoring both the phase and magnitude of the current passing through a conductor, consult Foster for a custom solution.