In relay or contactor: The bobbin latching current is same holding current and is less than bobbin inrush current because of difference between circuit reluctance in two various conditions. As you know in relay holding position the air gap of moving magnetizing part is minimum. In SCR: – Holding current is the minimum forward current required for the thyristor to maintain forward conduction. – Latching current is the minimum forward current that causes the thyristor to initially latch. This is usually higher than the holding current because of inherent inductive/resistive characteristics of circuit and transient response of circuit to initial pulse. It is important because the gate pulse may be relatively short.