In, reality, how important are 5 grounds on an 8pin PCIe cable?

JonSimonzi · Mar 28, 2011

Sorry if this is a stupid "they're there for a reason" question.

Looking at an 8pin PCIe power cable pin out, it has 3x 12v and 5x grounds, vs. 3x 12v and 3x grounds on a 6 pin. Now, clearly they're for a reason like I said, but how important are they? I know the card (at least my GTX480 does) needs something plugged in there, you can't just use a 6 pin cable, but it will start even if it's just a dummy plug plugged in there.

Now, for the stupid question part. So, would it be ok to just take those two cables out of the 8 pin plug?

hUMANbEATbOX · Mar 28, 2011

Will it be OK? Who knows? And why would you want to or need to find out?? Just leave em be!

kommanderkodiak · Mar 29, 2011

Some are redundant, the last thing you want to figure out, though, is where redudant ends and essential begins

hokiealumnus · Mar 29, 2011

A dummy plug definitely won't work; there aren't pressure sensors inside the thing that would tell it "hey, some plastic is plugged in here". If they don't sense ground, the card won't funciton; period.

Now, the ground may not necessarily have to be a long wire to the PSU. The two PSUs I have that have 8-pin connections both have 2-pin + 6-pin connectors, meaning the extra two grounds are short wires jumped off of two of the 6-pin grounds.

I don't have access to the PCIe specification .pdf, so I can't say for sure what they are supposed to accomplish. A person from Tom's forums seems to think they are to help reduce resistance. Of course, they don't do much of that by just being jumped to the existing 6-pin connector.

Long story short - they don't have to be actual ground wires from the PSU itself, but they have to be connected to ground in some manner. A dummy plug won't cut it. If you have a 6-pin only PSU and need to power an 8-pin card, you can manually jump the ground from your 6-pin connector to the 8-pin one though (I've heard paper clips worked but did try them in a pinch once and it wasn't functionally sound enough for my tastes).

Heh, I too am curious why you wouldn't just leave them be if they're already there. :shrug:

JonSimonzi · Mar 29, 2011

hokiealumnus said:
A dummy plug definitely won't work; there aren't pressure sensors inside the thing that would tell it "hey, some plastic is plugged in here". If they don't sense ground, the card won't funciton; period.

Now, the ground may not necessarily have to be a long wire to the PSU. The two PSUs I have that have 8-pin connections both have 2-pin + 6-pin connectors, meaning the extra two grounds are short wires jumped off of two of the 6-pin grounds.

I don't have access to the PCIe specification .pdf, so I can't say for sure what they are supposed to accomplish. A person from Tom's forums seems to think they are to help reduce resistance. Of course, they don't do much of that by just being jumped to the existing 6-pin connector.

Long story short - they don't have to be actual ground wires from the PSU itself, but they have to be connected to ground in some manner. A dummy plug won't cut it. If you have a 6-pin only PSU and need to power an 8-pin card, you can manually jump the ground from your 6-pin connector to the 8-pin one though (I've heard paper clips worked but did try them in a pinch once and it wasn't functionally sound enough for my tastes).

Heh, I too am curious why you wouldn't just leave them be if they're already there.

It's an issue with sleeving my PSU. The PCIe cables on the Corsair AX series, they have 2x 6+2 on one cable. On the PSU end of that one cable, there are 12x pins that plug into the PSU, that branches out into 16x pins on the card end. So, 4 of the cables are doubled up, which make sleeving a little bit more difficult, when going for a full uni-sleeve job. 12x on the PSU end going into 12 on the card end would make it much easier, and more neat.

The reason I asked about the dummy plug, is because I plugged the 2x 6pins into my GTX480, an took the second PCIe cable, that wasn't plugged into the PSU, and used the 2pin part of that, so it really didn't ground anything, and still allowed the card to power on. Now, I didn't go past the BIOS since I wasn't sure of the security risk of it, but it did allow it to turn on with that spare cable plugged in, without being grounded into anything really. Sorry if I'm not making sense, it's a little hard to describe

hokiealumnus · Mar 29, 2011

I think I am having a bit of trouble understanding. Your card has one 6-pin and one 8-pin connector, yes? Why don't you just snip the two wires that aren't needed and plug the remaining 8-pin and the now-6-pin in as designed?

When you say uni-sleeved, do you mean one-sleeve for the entire bundle or individual wire sleeving as has been popular of late?

I also think it's an issue with the card that it will boot. If it has the plugs, you should probably use them to be safe. The card I tried to use two 6-pins on (6970 when away from home, with someone else's PSU that didn't have 8-pin plugs) would not even boot to BIOS without the two additional pins grounded.

JonSimonzi · Mar 29, 2011

hokiealumnus said:
I think I am having a bit of trouble understanding. Your card has one 6-pin and one 8-pin connector, yes? Why don't you just snip the two wires that aren't needed and plug the remaining 8-pin and the now-6-pin in as designed?

I'm sorry, I'm just really bad at explaining myself in situations like these

Yes, my card has one 6 pin, and one 8 pin.

Here's the entire cable from my AX850. One plug into the PSU, gives 2x 6+2 pin cables.

Here's the end that plugs into the PSU

Out of those 12 pins that go into the PSU, 6 go to each cable end, which is 8 pins (6+2). So that means, into that 12 pin end that goes into the PSU, 4 sets of those have 2 individual cables going into one pin, like below.

Now, having 2 individual cables going into one pin hole, adds a little complication to the sleeving, since I do plan on sleeving each one individually. As you said, for one half of the cable, I can easily remove the +2 pins, no problem at all, eliminating 2 sets of those "double cables" into one pin at the PSU side.

But, that'll still leave the other half, having 6 pins on the PSU side, going to 8 pins on the GPU side. That's where I'm trying to see if it's safe to remove that second set of the +2, and not cause any danger to my GPU.

Hopefully this better explains what I'm trying to get at

Bijiont · Apr 4, 2011

I am still a little confused. . . not sure about anyone else.

If you are going to individually sleeve the wires it won't matter if 1 pin has a dual wire as your sleeving will only go up to the connector not over it.

Unless I am still out in left field somewhere watching butterflys I am not seeing what the problem is.

Please don't take my post as rude, honestly want to help but just having a hard time putting 2 and 2 together. . .

For the grounds. . . really depends on if the card needs it which will be trial and error with no clue as to what you may do to your card in the process. Unless you can find a diagram or something which tells you which each pin does other than (hot, ground, ect, ect) I don't see what other options you have.

I guess the short version, just resleeve it and don't remove anything

hokiealumnus · Apr 4, 2011

I'm also having trouble figuring out the issue. Just sleeve as you normally would. They may be a bit close to each other at the PSU end, so just put the heat shrink on both of those wires and heat it up at the same time. Or put both of those into one sleeve, I doubt it will be that noticeable if you did that.

Or maybe I'm still confused too. :shrug:

Long story short - Do give your GPU the power it needs and figure out how to sleeve it. Don't focus more on sleeving and then keep your fingers crossed on your GPU maybe having the power it needs.

In, reality, how important are 5 grounds on an 8pin PCIe cable?

JonSimonzi

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hUMANbEATbOX

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hokiealumnus

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JonSimonzi

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hokiealumnus

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