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The 8 + 6 pin PCIe cable (EVGA)


#1

With my supernova 850W G2 I got 2 x 8(6+2) pin PCIE and 2 x 8(6+2) + 6 pin PCIE cables.

I’m wondering if the combo 8 + 6 pin connectors are meant to be used either-or or both? I did put both in a Sapphire card that takes 8 + 6 pin where the 6 pin is described as optional and the card will work with just the 8 pin so I’m not sure if this has any benefit.

I guess the question boils down to if the PSU can provide enough amperage through one cable to accommodate for whatever the standard specifies for 8 and 6 pin connectors but I’m not managing to find this info in the documentation from EVGA. It does state that the total 12 V wattage can be ~850 W.


#2

The instructions on my 770 said to plug in both the 8 pin and the 6 pin into the card.

My dau’s 1060 just had the 6 pin and her 380 Antec PSU just had one plug also


#3

Right, but this is a RX 570 where the 6 pin is optional and I have both plugged in. What I’m wondering is if I should have used separate cables or if the 8 + 6 pin cable is a solid option.


#4

I tend to run 2 8+6 pin cables and use only the 8-pin on both for power hungry GPUs like the GTX 770 Classified in OC mode, because the 6pin is wired parallel to the 8pin at the end of those cables and the draw from both is going down 8 wires. If it goes down 16 wires, the “hot” 12V cables have less amps going down to the PSU than only one set of wires.

Of course, if you custom make sleeved PSU cables, you could forgo all the issues with 8+6pin.


#5

If a pcie power plug is on a graphics card, it’s not optional. Only in very, very rare cases such as old EVGA KingPin cards has that ever been a thing; and it was only a thing on those cards because they were specialized extreme overclocking cards that had excess plugs in case a user was going to pull massive power under liquid nitrogen. So, in short, no its not optional.

As for the use of a daisy-chained power connector instead of two separate connectors, no, it doesn’t matter. On Nvidia cards it has been shown that there can be a minuscule difference when using separate cables over a daisy-chained cable, but on AMD this difference is non-existent. Nvidia has much, much more accurate power monitoring hardware on their graphics cards and thus the difference between a daisy-chained cable and two separate cables can be exposed, but not on AMD. The power monitoring hardware on AMD gpu’s is far less sophisticated and doesn’t even monitor some areas of the card, whereas Nvidia’s is basically all-encompassing.


#6

My power supply (Seasonic 860 Platinum) recommends no more that 200 watts per PCIe cable coming from the PSU. And since I’d rather be safe than sorry, I follow that rule. Since you have a decent PSU as well you could probably follow that as well. So if your card’s power draw is 200 watts or less I’d say go for one cable. If it’s over 200 watts I’d personally go with two.

But that’s just my opinion.


It says it’s optional on Sapphire’s website.

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#7

Hi @caprica I’ve seen on a post you got a rx570 working on a XPS 420, I’m trying to do the exact same but when I plug in and boot the pc it just turns on and blows fans at max rpm constantly and nothing shows on the screen. Any help?


#8

I’m not sure if I can be of much help. What model is the card? The one I have (the one from Asus, not the Sapphire discussed here) has a modified mining bios but for that to improve compatibility with older systems would be a bit odd to me. Check out https://anorak.tech/ for bios and flashing of RX series cards if you want to test that route and you would have to flash it on another PC and it’s risky if you don’t know what you’re doing.


#9

The PCI-e power cable specification includes the following:
PCI-e x16 ports can carry up to 75W
PCI-e 6-pin cables can carry up to 75W
PCI-e 8-pin cables can carry up to 150W

AMD claim that the “typical board power” for an RX 570 is 150W, however in testing Tom’s Hardware found that Asus’ Strix card draws up to 225W:
http://www.tomshardware.com/reviews/amd-radeon-rx-570-4gb,5028-15.

This is below the combined limit of the PCI-e slot and the single 8-pin on the card (just).

Given that the RX 570 has some over clocking headroom it would be possible for it to exceed this power draw in some cases.

Bottom line is that if a graphics card has PCI-e power ports, you need to plug them in. Very rarely will one work without all ports plugged in, and even if it does running it like that is likely to cause you problems.