Data Centers

Power switch/supply connection calls for color consciousness

When attaching your computer's power supply to its power switch, be careful not to make the wrong connections. As long as you keep your colors straight, powering up should be no problem.


Connecting a power supply and the switch that regulates it is a fairly straightforward procedure. The process isn't complex—that is, as long as you know which wire goes to which terminal. Care must be taken to connect each wire (denoted by color) coming out of the power supply to the proper terminal on the power switch. No biggie, right? Well, don't tell that to TechRepublic member grosero who recently turned to the TechRepublic community for assistance with making just such a connection. In a turn of good fortune, grosero's query received a quick response by two TechRepublic members eager to help.

In his Technical Q&A posting, grosero wrote, "I have five cables coming out of the power supply that belong to the power switch. But, I do not know the right color order to hook them up into the switch." In seeking advice, grosero is kind enough to even provide a picture of both his power supply and the switch (see Figure A and Figure B).

Figure A
The power switch: (Notice the four terminals: two vertical prongs above and two slanted prongs below.)


Figure B
The five wires coming out of the power supply: (Notice the five different colors: black, white, brown, blue, and green.)


Keep those colors straight
TechRepublic members TheChas and RCOM are quick to point out that the switch and cables are for an AT-style power supply. The switch uses only four of the available wires: the black, white, brown, and blue. Looking at Figure A, the two prongs on top, nearest to the push button should be considered as pairing one. The two slanted prongs below should be considered as pairing two. For more information regarding power supplies and switches click here.

The important thing is to keep the pairings correct. As RCOM puts it, "As you look vertically [at Figure A], just make sure white and black are not on the same side (right or left). If you connect them on the same side, it will let the smoke out of the power supply (i.e., blow it). Since it's just an in/out switch, it doesn't really matter which side white or black goes on. Also don't turn it on without a load; that may also damage it. So if you want to test, connect a drive or something first."

TheChas concurs and tells grosero to connect the brown wire to the upper left prong and the blue wire to the upper right prong, completing pairing one. The black wire can be connected to the lower left prong and the white wire to the lower right prong, completing pairing two. Furthermore, "The black and white should be hot and neutral from the AC line in jack on the back of the power supply. Brown and blue should be hot and neutral on the AC out receptacle on the back of the power supply."

After making the connection, TheChas recommends checking the switch. With the switch pushed in (power on), "brown and black should be shorted together (0 ohms) and blue and white should be shorted together. You should verify the wires with an ohm-meter."

Five wires, four terminals?
Yes, the math doesn't add up—or does it? There is still one wire remaining: the green one. But don't worry, the green wire is for electrical grounding and can be connected to the computer's chassis. Now, the necessary circuits are completed and the power supply and switch are properly wired together. Following these directions, grosero will be powering his computer off and on in no time.

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