Edited by Leland Teschler
The rails typically reside in enclosures and hold controls for managing factories, buildings, and machines.
As the space inside controls cabinets has become more dear, manufacturers have found ways to gang up multiple relays in a single package. are the result. They are widely applied in industries such as material handling and packaging. These devices may combine up to about eight relays in a housing that takes up an inch of rail space. Typical features include visual indication of relay status via LEDs, and connections to relays through pluggable connectors. Some models also incorporate a fuse in series with the relay contacts.
The relays housed in these devices typically are electro-mechanical rather than solid state. One reason is that an electromechanical switch takes up less space than a solid-state device rated for the same capacity. For example, an 8-A electromechanical relay occupies about the same space as a solid-state relay able to handle just 3 A.
In high-density relay modules, an 8-A capacity is standard. Modules containing a single relay in a so-called ice cube package style generally handle 10 A but are physically larger. The most widely used relay coil voltage is 24 Vdc. However, automotive plants still tend to use relays with 120-V coils.
Finally, module makers differentiate themselves with different features and form factors. For example, one style of module physically separates connections for the coil and contacts. This tends to minimize problems on 24-V coil lines from induced electromagnetic noise caused by 120-V contacts.
Automation Systems Interconnect Inc.(asi-ez.com) provided information for this article.