Can I use an ATX PCI plug as 4-PIN or 8-PIN EPS CPU power plug?

Date:

2013-12-16

“Can I use an ATX PCI plug as 4-PIN or 8-PIN EPS CPU power plug?”

I’ve seen this question asked often and without a good answer (except from the guy who just plugged it in and burnt the motherboard). The main reasons behind that questions are:

  • Oddly enough, you can in fact physically plug the PCI plug in the CPU power pins on the motherboard, it will insert just fine. However, if you boot, you’ll burn the motherboard.
  • Many motherboards with 8 PINs EPS CPU plugs don’t boot if no power is supplied to at least 4 of those PINs.
  • Not all power supplies have 4 or 8 PIN CPU plugs.
  • Everyone has spare PCI plugs (6 and 8 PINs) or at least a Molex to PCI plug (they always put those in graphic card packages)

So yes.. but... with modifications only

  • The PCI’s plugs 12v and ground are the reverse of the CPU plugs (4 and 8 PINs)
  • Since you need only 4 PINs most of the time, you can get away with cutting the PCI plug to 4 PINs if that’s easier (8 PINs work too). If you have a molex converter plug, it could be that it doesn’t provide enough power for 8 PINs, anyway.
  • You have to connect the PCI plug reverse so that 12v is properly connected.

For a clearer idea, check the pictures in the table below. In a nutshell, both PCI and CPU pins are 12v and it’s all about plugging the 12v in the right PIN.

Warning

Failure to do so = burnt motherboard. Properly done = it will just work.

../_images/pcie.jpg

Notice how black (ground) wires are tab-side and yellow (12v) cables are on the other side

../_images/eps.jpg

And that’s the reverse on the EPS 8 PIN CPU plug (and the 4 PIN one for that matter). 12v (yellow is tab side).

../_images/molex.jpg

The molex plug has 4 PINs: 12, ground, ground and 5v. PCI converters just use the 12v (yellow) and the 2 grounds (black).