Why are ferroresonant transformers oversized when protecting computers, PLCs or CNCs?
Inherent in the design of ferroresonant transformers is a current limiting characteristic. Current limiting means that the output current will be limited to a predetermined value regardless of the load demands. This predetermined value is typically 150% of the full rated running current. Often the power supplies of the computers, PLC’s and CNC’s will demand a high current surge. This current surge (often termed inrush VA or inrush Amps) will typically be 200% of the continuous running current. Obviously, if the Ferroresonant Transformer has a current limiting value of 150% of its rated output current, it will not be able to deliver a 200% current surge if sized right at the continuous power level rating. Therefore, ferroresonant transformers typically are sized with a VA rating 50% greater than the loads continuous VA rating. Marelco’s PLC Protector ferroresonant transformers are designed to be able to deliver the high current demands mentioned above so that no VA oversizing needs to b
