A variety of control voltages are used throughout the world for industrial process control. The most common control voltage in North America was 120VAC. Over the past decade, 24 VDC has gained in popularity. 120VAC has its advantages if the controls are to be mounted in a dirty environment, if the control wiring it going to be very long or the area is inherently electrically noisy. 24VDC control is a safer system over 120VAC for shock hazards, etc... With the acceptance of IEC standards for electrical control in North America, 24VDC controls are becoming more cost effective than their 120VAC counterparts.