24 V DC control-an emerging alternative to legacy 120 VAC control applications in North America

A variety of control voltages are used throughout the world for industrial process control. The most common control voltage in North America is 120 VAC. IEC standards that are widely accepted in other countries including Europe, have used 220 or 240 VAC. Over the past few years, 24 VDC is gaining acceptance. Products based on 24 VDC control are now becoming more available from major manufacturers. This paper reviews various issues associated with 24 VDC and 120 VAC control.