What this relay actually does on the bench
The Omron MJN2CE-DC12 sits in the MJN Series as an enclosed general-purpose power relay with a DPDT (2-pole, double-throw) contact set, so one coil throws both poles at once — useful where two circuits need to switch together from a single 12V DC command. The 20 A contact rating carries the load decision: 20 A at 277V AC and 20 A at 28V DC on the contacts, and it is flagged motor-rated with 3/4 hp at 120V AC and 1-1/2 hp at 240V AC — meaning a small motor or heater load is what the relay is sized for, not a contactor-class motor starter. Coil is the 12V DC nominal spec, called out directly on the part code as the -DC12 suffix, which matters when the control rail is a 12V battery, a 12V supply on a mobile platform, or a 12V tap off a DIN power supply rather than the usual 24V.
Mounting, wiring, and where it lands in the panel
Mounting style is surface with a side flange, so the relay fastens through the panel face or a bracket rather than sliding onto a DIN rail or socket — eight tab terminals bring the coil and contacts out for quick-connect. The enclosed case keeps the mechanism covered, so no exposed live contacts to worry about in a shop-floor enclosure.