Martindale cp301 110v industrial socket tester martindale marcp301 p the martindale cp301 is designed for use on 110v centre tapped circuits it is fitted with a yellow 110v 16a ct plug to bs 4343 iec309 the cp301 shows similar fail safe indications to the classic martindale check plug p p using leds to highlight possible fault combinations the cp301 is invaluable for instantly checking sockets in factory or on site installations p martindale marcp301 110v industrial socket tester