Ssr control relays proportional controller and burst fire controller panel mount crydom mcpc4825c this 25a 480v ac microprocessor based load relay allows the partial control of the performance of an ac load functionally the relay works as a proportional controller that provides a portion of the ac sine wave in order to ease the load phase angle control control is via an 0 to 10v dc analogue signal and an optically isolated scr output enables high switching loads in industrial applications