Voltage Detector Unit, IEC compliant for MV cabinets Voltage Detecting Unit SCA/B indicates absence or presence voltage in MV distribution cabinets. You should use SCA/B in combination with appropriate MV capacitive isolator in the range 6kV-24kV. SCA/B has three lamps and three test points on front and one terminal block connector on the rear The current supplied should be in the range 2.5μA and 35μA.