Hello,

This is a first timer attempting to install a AC/DC converter into a metal project box.

I purchased the following power supply.

http://www.digikey.ca/scripts/DkSearch/dksus.dll?Detail&itemSeq=177796837&uq=635749668715775879

The power supply only requires live and neutral. I plan to earth the metal casing. Please let me know if that is incorrect.

Additionally, the power supply has 2 of 4 exposed contacts at the corners of the board. Each of these exposed contacts are at the opposite ends of the board. Obviously these can be used to connect ground to the casing via metal screw. What I am confused about is that these 2 exposed contacts are not electrically connected.

The picture below show these contacts. I am afraid to connect them using a metal screw. If someone can clarify why this is designed like this and how it should be properly installed?

DC end (exposed contact)

Top view, AC end left, DC end right

AC end (exposed contact)

Thank you
Daniel

 

Nylon (plastic) screws and standoffs. In the US available from McMaster Carr Supply or just about any electronics supply house.

Ron

 

Yes, you're meant to use metal screws and yes, you're meant to earth everything. The contacts on the corners of the board are internally connected to the PSU's common/gnd and are supposed to have continuity to the case and earth wire on the infeed cable. This way, earth faults can be detected and the user is safe from electric shock.

 

What I am confused about is that these 2 exposed contacts are not electrically connected.

I doubt the truth of this statement. Not connected to each other or not connected to anything? Even if I am wrong, bolting a hole (with no electrical connection) to the chassis causes no connection. The absence of a circuit does not cause a circuit. Bolt that sucker down.

 

OK, allow me to add to what I wrote. In your images the screw holes are likely ground. That does not mean you can screw that board down on a metal chassis. Thus I suggested nylon. As long as the bottom of the board is elevated with standoffs you should be fine. If using nylon the board should be grounded where applicable.

Ron

 

As Ron indicated, the supply must be mounted on standoffs because there are many surface mount components on the bottom side that can not touch anything conductive.

Both of the holes in the 2nd photo *can* be connected to the metal case, with conditions. The one at the AC end is an earth ground connection to the noise filter components in the power supply front end. The intent is that a 3-wire power line cord is connected to the supply with a 2-wire connector for line and neutral and a ring terminal on the earth ground wire. The ring terminal goes to the mounting hole, and a metal screw and standoff complete the connection to the metal case.

The ground hole on the output end probably is another earth ground connection, this time to output filter components, and probably is not connected to the input side earth ground contact. This can be verified with an ohmmeter. The supply outputs are completely floating from earth ground.

ak

 

These PSU types often have optional earths on the mounting points, if you read the datasheet you will find that if you don't connect them to earth then the EMC performance of the PSU is compromised and the PSU will be outside of the specified EMC regulations quoted but the PSU will still work. Normally it's best just to connect the earth points if you can.

By the way your link doesn't work.