Select the relay contact load type and capacity both at home and abroad have long proved that about 70% occur at the contact point, this serves to show the correct choice and use of relay contacts is very important. Contact form and contact number should be determined according to the control circuit to the actual situation. Works the same for relays and contactors. Main difference is that the main contact of contactor can be big ones, and relay contact only through small currents. Therefore, relay are generally not used for direct control of the main circuit (instead of through the control contactor and other indirect control of main circuit of switching equipment).