okay, Working on some custom wiring I ran into a problem. The connector indeed has 4 seperated wires, and the cable indeed has 4 insulated cables. But for what ever reason the wires are seperated into 2 pairs which are shorted together. There appears to be no easy solution for making it into 4 or even 3 seperate wires. So here's my question: Is it possible for me to use the 2 wires as the -12V and -5v rails. And then the metal case as a common ground? The case has a few external connections including a radiator. So I was thinking I could ground it to that plus the case. do you think this would work or am I overlooking something? I'm not really worried about the -12v or -5v rails shorting to the ground either as everything would be properly insulated
It will work, but make sure you have good conductivity between the PSU and the case sides. Paint and other impurities can make for bad contact, and under high current, this will "arc out" or Heat up, and could be damaging.
It isn't really a good idea. the 'ground' the case is at is not really the 'ground' all the electronics is at. There are 2 problems I can see with it, firstly the case is connected to the mains ground which in the event of any problems with the psu will take the mains current safely to earth and trips your circuit breaker. Connecting other things to this could lead to damage to these things or even worse comprimise the low resistance path to earth and your circuit breaker wouldn't trip if there were any problems. secondly, because the case does not have to be the ground that electronics is at it means that it does not have to be at 0V (although generally it is) and could cause over or under volting in whatever you connect to it. If you look carefully at your motherboard you'll see that none of the metal contacts around the screw holes have any connection to the ground plane on the motherboard. There is, I presume, a reason for that. If any one knows better than that then I'd like to hear. acrim?
I think I'm going to go for it, The case specifically had 2 of the pins on the head connector already grounded to it ( incase your wondering its the am 598 in my radio mod) So I figure it should be okay, After I finish I'll monitor the V making sure its within acceptable limits. IF you still have more to add, go ahead and butt in. This is my most graceful option though
While building my current computer, I took apart the psu to put a plexi case on it. From looking inside it, both the mains ground and the case ground are connected together and to the case of the psu. because the case of the psu is metal, It connects to the rest of the computer. the reason that the mobo doesn't appear to connect to the case might be one of two things. one reason might be that the mobo manufacturer didn't want to rely on the quality of the case ground and just didn't use it. the other reason that it might appear that the metal around the screw terminals is not hooked up to ground is that the motherboard is made up of many layers of substrate and copper traces. just because there is no trace on the top or bottom, doesn't mean that it is not connected. To see if there is a ground connection, turn the comp off and use an ohm meter to measure the resistance between a ground wire off of a molex plug and the case. if there is little or no resistance, then they are connected. in the unlikely scenario that there is too much resistance or no contact at all, make sure that the psu has metal on metal contact with the case (no paint in-between) and if that still doesn't help, screw a ground wire to the case wherever convenient then pull the ground off the case at the other end with another screw.
All grounding taps for almost all components in the PSU lead to the standoffs which are connected directly to the chasis. The chasis is essentially one big extension for the ground tap... what the above poster said.
