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This is not about EPS 8 pin look carefully before flagging for that.

Let's look at a 8 pin PCI Express cable plug. One row has three notched connectors and one square. The problematic pin is on the other row, furthest from this square. It's notched usually. The diagram below calls this pin 8 -- I am not sure who made this diagram but it's quoted very often, including this site. I also attached a noname plug (I marked the pin with a blue stripe) and a Corsair plug showing this is notched. However, the PCI Express CEM 3.0 clearly prescribes a squared pin here, a screenshot is also attached (it's not a change in the standard, the earlier PCI Express 225 W/300 W High Power Card Electromechanical Specification was the same). It calls this "position 8". Receptacles as found on video cards do have a squared hole here as the standard prescribes.

As this comment notes, these sort of cable plugs allow a PCIe pinout plug to be inserted the EPS 12V socket which never works and can be catastrophic. That's clearly not what the standard maker wanted. Also, this comment from four years ago treats this pin to be notched self evident. Yet another answer shows this plug notched on an FSP PSU and again notes this is catastrophic for EPS 12V mismatch. (Edit: curiously they note Corsair doesn't notch it -- and looking for this indeed their basic Type 3 and Type 4 cables don't but the premium version does as attached.)

It's not about 2x3 compatibility: this is the two extra pins so in a normal configuration it won't participate when plugging the plug into a 2x3 receptacle. Even if you tried to plug it wrong, it's pin 7 which stops you from that.

So this pin being notched a) is a deviation from the standard b) doesn't matter in PCIe situations c) makes the EPS-PCIe situation much worse. Then why does this pin gets notched commonly?

Commonly, but not always as already noted above for Corsair. I also attached a plug photo from the Seasonic: Power supply cables and their uses page and it does use the correct square as well.

diagram

noname plug

Corsair Plug

standard

2x4 pin receptacle

enter image description here

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  • 2
    It's not an EPS connector. You can see it matches the diagram. Check more carefully, please. EPS connector doesn't have three notched pins in a row but it does have two squares next to each other which this doesn't. This is an EPS connector: i.imgur.com/AGPH3kp.jpeg I flagged every comment stating so as unnecessary.
    – chx
    Commented Jun 20 at 19:50
  • I see. Yea, got that wrong. Another reason I can see is that it is a matter of simplified manufacturing.
    – music2myear
    Commented Jun 20 at 19:54
  • If you make a google image search for "8 pin pcie connector", you will see that the vast majority of vendors implement for pin n° 8 either a square shape, or a P shape (as in your third image), and will not fit into an EPS socket. The few connectors I've seen with a simply notched pin n° 8 (and which will fit into an EPS socket) are from dubious vendors who will just try to have a low price, so they do not care too much about the specs. So I'd argue: buy your materials from reputable vendors, and return any items that do not meet the specs.
    – 1NN
    Commented Jun 27 at 8:19
  • Given the above, please specify what you'd expect from an answer. Thank you.
    – 1NN
    Commented Jun 27 at 8:20
  • Corsair is very far from a dubious vendor and yet sometimes they do it. That diagram also shows it. There must be some reason, some source, I do not know, a misunderstood presentation something at the root of this. It likely has happened so long ago it's now near impossible to find it.
    – chx
    Commented Jun 28 at 9:53

1 Answer 1

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A general answer; pinning and keying of cables in general is a mess - unless you have a "well described standard" for a single use cable/connector.

Plugged and notched positions is in most cases meant to be a help, to use the cable in the correct position(s), often also for a specific device.

As pinning many times differ vastly, a general (not plugged nor keyed) cable opens up for mishaps (especially if power feed is available on any pins).

Mishaps: that is when you break something and wish to send it back for either free replacement or warranty repair.
Which is costly for the claim recipient, and time consuming for you...

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4
  • > unless you have a "well described standard" for a single use cable/connector. Which is exactly what we have here!
    – chx
    Commented 2 days ago
  • Well, "standard" in my context/meaning is an ISO-standard, hardly present here.
    – Hannu
    Commented yesterday
  • I mean, that's the standard that defined this connector...
    – chx
    Commented yesterday
  • A standard defines something that is the same in all uses. Not seen here.
    – Hannu
    Commented yesterday

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