Martindale cm55 400a ac clamp multimeter martindale cm55 p the model cm55 from martindale is a pocket sized high performance ac clamp meter that has ranges for ac current ac voltage dc voltage and resistance with continuity test the cm55 has a catiii 600v safety rating and is the ideal tool for residential and commercial electricians p p its compact yet rugged design enables accurate and reliable current measurement down to 10ma resolution without the need to break into the circuit f