are pigtail PSU cables really bad?

Posted by Shaqo_Wyn@reddit | buildapc | View on Reddit | 8 comments

I see a lot of content creators and people on this sub advice that you want to avoid using pigtail PCIe cables? are they really that bad? what are the reasons?

I ask because I've been hard pressed to find a good Gold 80+ that isn't 200> euros that has more than 2 PCIe ports that doesn't use pigtail cables to be compatible with 3x to 4x 8 pin GPUs. Most recent example I saw is the Pure Power 12M from BeQuiet where the 1000W supports 12VHPWR and only has 2 normal PCIe ports and comes two pigtail PCIe cables. It's a great PSU, good warranty, quiet, good components but does that mean you shouldn't buy it if you have 3x 8 pin GPU?

curious what you guys think.

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JTG-92@reddit

This is the simplest way to put it, pigtails are not “bad” they are just limited.

Il just explain where you can and where you shouldn’t use pigtails.

GPU with 2x 8 pin - only acceptable if you have no other option and your card usually never exceeds around the 160w range under load.

GPU with 3x 8 pin - if you cannot provide 3 separate 8 pins, it’s acceptable to use 1x pigtail and 1x 8 pin to populate all 3.

GPU with 4x 8 pin - do not use pigtails, if you can afford a 4090, use 4x separate 8 pins to that adapter if need be.

In your trying to use a 3x 8 pin GPU and it’s something like a 3080 which is like 400 max, then this is the break down of it all.

Each 8 pin connector is “rated” up to 150w, but the cable itself that goes to the PSU, is rated to supply up to 225w. So when you take a pigtail, your still limited by the cable of 225w, you don’t get 300w because it has 2 connectors.

So if you were to use a pigtail and another 8 pin or a pigtail but only use one connector, your looking at a supply of 225 + 150 = 375w and then the x16 pci slot itself supplies 75w which brings that total to 450w.

So at this point you just have enough headroom above it’s max usage to be considered acceptable, you would have 525w which is optimal headroom if you use 3x 8 pins.

However, it’s a very very acceptable use of pigtails for something like a 3080 in stock form. If it was something like a 3090/3090ti, or a heavily overclocked 3080, I’d probably say use separate cables for all 3.

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ensignlee@reddit

This was really helpful, ty

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IBananaShake@reddit

Hey, so I know this comment is like nearly half a year old, but I'm running two 8pins, one having a pigtail, on my 3070TI, it's working fine.

But I'm afraid that I've left some performance on the table considering it's an ROG Strix OC edition, should I rewire the rig to use 3x 8pins?

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JTG-92@reddit

Does your card need 450+ watts? Highly unlikely, so there’s no performance being wasted.

If my Strix 3080 OC can run flat out, your 3070ti definitely can, plus when my card is undervolted, it draws less than 300w most of the time without any performance loss.

As long as the card is reaching its clock speeds and is sufficiently cooled, you will be getting max performance with headroom even with the pigtails.

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