Question Can I use a single dual output 8 (6+2) pin cable to power graphics card that needs two 8-pin power connectors?

[zzzhhh]

Some graphics card requires two 8-pin power connectors to power it. At the same time, some PCIe power cable contains dual output 8 (6+2) pin connectors like this: https://www.ebay.com/itm/124575794621. Can I use a single such dual output cable to connect to both 8-pin power connectors on the graphics card to power it? That is, I buy exactly one such cable, the input end plugs to the 8-pin PCIe power output of PSU, and the two output 8-pin connectors of the same cable plug to two 8-pin power connectors on the graphics card, respectively. Can I do that (I mean safely and correctly)?

 

[boju]

Good power supplies are able to but generally is best to use separate cabling to reduce heat, especially for power hungry cards.

Another issue here also is you can't just buy random pcie cables, even if they look and fit the same. There isn't a universal pinout diagram psu companies follow so using the wrong cable will lead to electrical short, as in the wires in the cable terminate to different pins in the plug. That pcie cable you linked is for Corsair AX, depending what your psu is, you'd buy a cable meant for your unit, if you misplaced or weren't given leftover cables if it was prebuilt.

What is your power supply?

 

[Misgar]

According to this web site, a single 8-pin PCIe GPU connector is designed to deliver up to 150W. At, 12V, that's 150/12=12.5A, split over 3 yellow wires = 4.16A per wire.
https://graphicscardhub.com/graphics-card-pcie-power-connectors/

If the wire gauge is 18AWG and it's rated at 9.5A (free air) you can connect the second 8-pin connector and provide up to 300W and 8.32A per wire. That might be considered "pushing it" because the bunched rating for 18AWG is only 7A for 3 wires close together.
https://www.engineeringtoolbox.com/wire-gauges-d_419.html

If you're connecting the lead in your link to a Corsair PSU, then yes you can use both connectors on one lead, but I'd be happier using separate leads when pushing a GPU up to 375W (additional 75W from the PCIe slot).

 

[geofelt]

It is not recommended to power two 8 pin connections with just one lead.
Yes, it will work, but the current draw on the one cable may be too high for the cable to support.

 

[Misgar]

Yes, it will work, but the current draw on the one cable may be too high for the cable to support.

I have to ask, why would a reputable company like Corsair fit two 8-way plugs to some of their PCIe cables if they weren't confident they were capable of supplying up to 300W? Better to play safe and fit one 8-way (150W) and one 6-way (75W) plug on the lead for 225W rating instead of 300W.

As I mentioned before, if the gauge of wire used is 18AWG and the "free air" rating of 18AWG is taken as 9.5A per wire, the power rating is 9.5A x 12V = 114W per wire, or 3 x 114W = 342W (nominal) for all 3 wires. GPUs are only specified to draw up to 300W total from two 8-way connectors, so that leaves a notional reserve of 42W.

But if we take the "bunched" 3-wire de-rated maximum current per wire of 7A on 18AWG, then the maximum power that can be sustained by the PCIe lead is 3 x 7A x 12V = 252W. In that case, I would be reluctant to use both 8-way plugs on a single lead, if the GPU card requires more than 252W from the PCIe lead (not including an additional 75W max from the motherboard).

In any event, some high power GPUs using "old style" connectors are fitted with three 8-way power inputs for up to 450W (+75W from PCIe motherboard socket). For these GPUs, you'd have to use more than one double-headed PCIe power lead, i.e. at least two separate PCIe leads, or even three for peace of mind.

Perhaps double ended 8-way PCIe power leads could fail in the same manner as early 12VHPWR cables on power hungry RTX4090 cards, but I think some of those melted connectors were attributed to failing to fully mate the cable end with the GPU card. At least that's what the manufacturers claimed initially.

To answer the original question again, I personally would be happy using both 8-way plugs on a single PCIe lead, provided I had installed a "quality" PSU from a reputable manufacturer. I would not feel confident using both plugs on a cheap and nasty PSU, purchased for less than $30. Does that help?

 

[geofelt]

As to why, ask Corsair.
They are the experts on their products.

Modern graphics cards can have some unusually high power draws that have damaged cables.
Hence the recommendation to use two cables to power graphics cards with two 8 pin ports.

 

[Zerk2012]

It all depends on the design.
My Seasonic said 225 watts or less on a single cable.

 

[Misgar]

Hence the recommendation to use two cables to power graphics cards with two 8 pin ports.

This is borne out by Seasonic's recommendation to use only one 8-way connector on each PCIe lead.
https://knowledge.seasonic.com/arti...ark-for-high-power-consumption-graphics-cards

I like they way they describe the option to use both 8-way connectors as "Standard". It's as if they're secretly admitting the design of such cables (which presumably conform to one of the ATX standards) is not quite "up to the job", which is in line with my remark about bunched 18AWG de-rated to 7A per wire, or 252W max.

A quick look at a few Seasonic PSU ads appears to show their PCIe leads have only one 8-way connector at the GPU end. If so, well done Seasonic. i guess they get fewer RMAs that way.
https://www.overclockers.co.uk/seas...-gold-modular-power-supply-pow-ssc-03150.html

I'm more familiar with Corsair PSUs which often come with double-headed 8-way connectors, making it more likely people will use both of them and not 2 or 3 separate leads, which would be preferable.

I suppose we could place the onus on the people writing the ATX PSU cable standards. They're probably trying to keep manufacturers' costs down to a few dollars per connector pair, so something has to suffer. Witness the debacle with early 12VHPWR connectors on RTX4090s.

https://www.corsair.com/us/en/explo...units/evolving-standards-12vhpwr-and-12v-2x6/

I'm used to specifying connector pairs costing hundreds of dollars each for use on Aerospace/MIL projects, where quality, de-rating and durability are the norm. By comparison ATX PSU connectors are barely adequate.

I think I'll change my recommendation to that of Seasonic and say you should only use both 8-way connectors on a double-headed PCIe cable if you have no other option (apart from buying another PSU). I have only one GPU which requires two 8-way connectors and I use two separate cables.

 

[BFG-9000]

I have to ask, why would a reputable company like Corsair fit two 8-way plugs to some of their PCIe cables

It appears Corsair did use both 18AWG for their older dual-6+2 ribbon cable (which that generic eBay cable is a copy of) as well as a more sensible 16AWG to the first plug, then 18AWG to the 2nd on their later sleeved cable. Maybe they smartened up.

 

[Misgar]

as well as a more sensible 16AWG to the first plug

Thank's for heads up. I'm much happier with 16AWG with its 15A (single) and 10A per wire (3-cores) rating. Less likely to cause a conflagration at 300W.