Connectors and Terminals on Power Supplies

The output connector rarely decides which supply you buy, and then it decides how long installation takes and how often you are called back. It is worth a minute’s thought at the selection stage.

The common types

• Screw terminals. The default on enclosed and DIN rail supplies. Cheap, tolerant of a range of conductor sizes, and field-serviceable with a screwdriver. They need periodic checking, because thermal cycling can loosen a screw over years.
• Plug-in (pluggable) blocks. The wiring stays in the connector, so a supply can be swapped without disturbing the loom. Worth the small premium anywhere downtime matters or the unit may be changed in the field.
• Flying leads. Common on open-frame and external supplies. Nothing to tighten and nothing to work loose, but the termination is then someone else’s problem further down the harness.
• PCB pins. On open-frame and DC/DC modules, where the supply is soldered into the board and the connection is designed once.

What actually causes trouble

Two things, more than the connector style itself. The first is conductor size: a terminal rated for a maximum cross-section will not accept a cable sized generously for volt-drop, which is discovered at the worst moment. The second is ferrules — stranded cable into a screw terminal without a ferrule spreads, and a spread strand is a future short.

Check the terminal’s accepted range against the cable you have actually specified, not the minimum the current demands.

Tell us the enclosure and the cable size and we will point you at supplies whose terminations suit the build.