bob16314
Don't forget the card can get up to 75W from the PCIe slot itself, above and beyond the rated 150W from an 8-pin and 75W from a 6-pin PCIe connector.

Your unit also uses HCS terminals (High-Current System for the MB, CPU and PCIe connectors) and related components..Each HCS terminal is rated to carry up to 11 Amps of current (132 Watts for the 3x 12V wires) for a total of 396 Watts on the 12V in an 8-pin connector.

Very nice box there, by the way 

2080ti's can have sudden spikes of up to 380w+, you need high precision equipment to capture this but it has
 
> blown up power supplies
> tripped OCP in otherwise fine UPS setups.

kevinc313
This is generally correct.  There are very real electrical engineering specs rating cables for current because of heating and voltage drop.  This is a pretty big concern for low voltage DC / high current power supply in many applications.  The common solution to for this in the PC space is multiple smaller wires, it is a good scaled solution and is actually the less bulkly solution due to how derating works.   USE THE TWO CABLES.
 
Even if you could get a special single cable made that used correctly rated thicker wire and split into two 8 pin connectors, you would still have the single connector at the PSU that would be overwhelmed.

Cool story, bro..But here are some 'Fun Facts.'

8-pin/6-pin Y cables and their connectors are rated for more than the allowed load..Miners/Folders commonly use them in buku GPU setups.

8-pin PCIe Supplemantal Power Connectors (also referred to as PEG connectors, or PCI Express Graphics connectors) have three +12V terminals..Each single terminal is rated to carry up to 8 Amps of current (96 Watts @ 12V) using 'Standard' terminals for a total of 288-watts per connector.

Each 'HCS' (High-Current System) terminal is rated to carry up to 11 Amps of current (132 Watts @ 12V) for a total of 396 Watts, per connector.

Each 'Plus HCS' terminal is rated to carry up to 12 Amps of current (144 Watts @ 12V) for a total of 432 Watts, per connector.

HCS and Plus HCS terminals are sometimes advertised as 'gold plated terminals' or 'high current' connectors.

The terminals/connectors on the PSU and GPU should be rated similarly.

Another 'Fun Fact' is that electric/current flows on the surface of wires..The size/number of strands in a braided wire determines the current handling rating/capability, and braided wires have a higher current handling rating/capability than a solid wire due to the increased surface area.

It's also a common misconception/misstatement that a PSU can 'provide' up to 75W (6.25A @ 12V) and 150W (12.5A @ 12V) total to the 6-pin and 8-pin PCIe Supplemantal Power Connectors..The PSU can 'provide' what the rail is rated at and is way more than enough to overheat/melt/catch things on fire, it's the graphics card's VBIOS and voltage regulation/monitoring circuitry that determines how much the card is 'allowed' to 'draw' from the PCIe slot/6-pin/8-pin within the PCI-SIG spec of 75W/75W/150W and is often programmed to 'draw' less.

PCI-SIG is the group that writes the industry-standard specifications for all things PCI/PCIe that manufacturers 'should' adhere to, just like Intel writes the industry-standard Power Supply Design Guide specifications for PSUs that manufacturers 'should' adhere to..There are parts of the PCI-SIG and Power Supply Design Guide specs that say manufacturers 'must' adhere to these certain things and parts saying they 'should' adhere to these other things.

It used to be an issue when Intel specified that PSUs have mandatory multiple +12V rails for safety reasons..Then, graphics card manufacturers complained that Intel's +12V multi-rail spec didn't meet the needs of their more powerful graphics cards and would sometimes trip the OCP (Over Current Protection) on multi-rail PSUs..So then, single-rail +12V units were born due to backlash from graphics card manufacturers that demanded that Intel's multi-rail specs be voluntarily abandoned to meet their power needs.
 
 

squall-leonhart
Prior issues with HXi power supplies and 2080ti indicate that it is best to either use the HXi configured to single rail, or run two cables from PSU to card and use multi rail.
 
History has demonstrated a 2080ti can overload the unit in Multirail mode.

I didn't know there were issues with HXi psu's, I have my HX1000i powering an oc 9900k and 2080ti XC Ultra set to multi-rail(with separate pcie cables), guess to be on the safe side I'm going to stop procrastinating installing icue and configure it to single rail.   

bob16314

kevinc313
This is generally correct.  There are very real electrical engineering specs rating cables for current because of heating and voltage drop.  This is a pretty big concern for low voltage DC / high current power supply in many applications.  The common solution to for this in the PC space is multiple smaller wires, it is a good scaled solution and is actually the less bulkly solution due to how derating works.   USE THE TWO CABLES.

Even if you could get a special single cable made that used correctly rated thicker wire and split into two 8 pin connectors, you would still have the single connector at the PSU that would be overwhelmed.

Cool story, bro..But here are some 'Fun Facts.'

8-pin/6-pin Y cables and their connectors are rated for more than the allowed load..Miners/Folders commonly use them in buku GPU setups.

8-pin PCIe Supplemantal Power Connectors (also referred to as PEG connectors, or PCI Express Graphics connectors) have three +12V terminals..Each single terminal is rated to carry up to 8 Amps of current (96 Watts @ 12V) using 'Standard' terminals for a total of 288-watts per connector.

Each 'HCS' (High-Current System) terminal is rated to carry up to 11 Amps of current (132 Watts @ 12V) for a total of 396 Watts, per connector.

Each 'Plus HCS' terminal is rated to carry up to 12 Amps of current (144 Watts @ 12V) for a total of 432 Watts, per connector.

HCS and Plus HCS terminals are sometimes advertised as 'gold plated terminals' or 'high current' connectors.

The terminals/connectors on the PSU and GPU should be rated similarly.

Another 'Fun Fact' is that electric/current flows on the surface of wires..The size/number of strands in a braided wire determines the current handling rating/capability, and braided wires have a higher current handling rating/capability than a solid wire due to the increased surface area.

It's also a common misconception/misstatement that a PSU can 'provide' up to 75W (6.25A @ 12V) and 150W (12.5A @ 12V) total to the 6-pin and 8-pin PCIe Supplemantal Power Connectors..The PSU can 'provide' what the rail is rated at and is way more than enough to overheat/melt/catch things on fire, it's the graphics card's VBIOS and voltage regulation/monitoring circuitry that determines how much the card is 'allowed' to 'draw' from the PCIe slot/6-pin/8-pin within the PCI-SIG spec of 75W/75W/150W and is often programmed to 'draw' less.

PCI-SIG is the group that writes the industry-standard specifications for all things PCI/PCIe that manufacturers 'should' adhere to, just like Intel writes the industry-standard Power Supply Design Guide specifications for PSUs that manufacturers 'should' adhere to..There are parts of the PCI-SIG and Power Supply Design Guide specs that say manufacturers 'must' adhere to these certain things and parts saying they 'should' adhere to these other things.

It used to be an issue when Intel specified that PSUs have mandatory multiple +12V rails for safety reasons..Then, graphics card manufacturers complained that Intel's +12V multi-rail spec didn't meet the needs of their more powerful graphics cards and would sometimes trip the OCP (Over Current Protection) on multi-rail PSUs..So then, single-rail +12V units were born due to backlash from graphics card manufacturers that demanded that Intel's multi-rail specs be voluntarily abandoned to meet their power needs.

Great facts.  Still sounds like running one cable is a bad idea.

bob16314
Guys, keep in mind that I'm just talking about the current-handling capability for those who think "Oh, it will get hot and melt", or something..That was demonstrated to be somewhat true in ye olde days of yore and on Low-Tier/El Cheapo units, which most of them don't even come with a Y splitter cable anyway, and especially when using junk adapters.

I wasn't saying it would melt.  I was saying there would be heating and voltage drop to the point that the card wouldn't operate well under load, even if everything was within spec.  Common issue in high power low voltage DC electronics.

bob16314

kevinc313

bob16314
Guys, keep in mind that I'm just talking about the current-handling capability for those who think "Oh, it will get hot and melt", or something..That was demonstrated to be somewhat true in ye olde days of yore and on Low-Tier/El Cheapo units, which most of them don't even come with a Y splitter cable anyway, and especially when using junk adapters.

I wasn't saying it would melt.  I was saying there would be heating and voltage drop to the point that the card wouldn't operate well under load, even if everything was within spec.  Common issue in high power low voltage DC electronics.

Mmmk..And the Voltage Drop in 1 foot of AWG 18 copper wire passing 12VDC in a solid wire using Standard 8A (max) rated terminals is approx. 0.849% or 0.102V..Braided wire used in PSU cables would be slightly more..Not enough to matter, especially when considering that the voltage tolerance on the nominal +12VDC line is +/- 5%, or a Min/Max of 11.4VDC to 12.6VDC as stated in the Intel Power Supply Design Guide.

One has to figure that PSU and GPU manufacturers have tested the real voltage drop and heating that a single cable encounters feeding a high power GPU mounted in a PC case, thus recommending dual power cables, while not even providing dual 8-pin cables with their modular power supplies.  Clearly a simple voltage drop calculation doesn't capture the nuances of the real application.

HeavyHemi

bob16314

kevinc313

bob16314
Guys, keep in mind that I'm just talking about the current-handling capability for those who think "Oh, it will get hot and melt", or something..That was demonstrated to be somewhat true in ye olde days of yore and on Low-Tier/El Cheapo units, which most of them don't even come with a Y splitter cable anyway, and especially when using junk adapters.

I wasn't saying it would melt.  I was saying there would be heating and voltage drop to the point that the card wouldn't operate well under load, even if everything was within spec.  Common issue in high power low voltage DC electronics.

Mmmk..And the Voltage Drop in 1 foot of AWG 18 copper wire passing 12VDC in a solid wire using Standard 8A (max) rated terminals is approx. 0.849% or 0.102V..Braided wire used in PSU cables would be slightly more..Not enough to matter, especially when considering that the voltage tolerance on the nominal +12VDC line is +/- 5%, or a Min/Max of 11.4VDC to 12.6VDC as stated in the Intel Power Supply Design Guide.

Have you considered the issue could be more related to supplying the entire current via one connector on the PSU? Back in the day, it was rather trivial to trip a HX1000 if you were running SLI and did not spread your load correctly.
It was internally two separate 500 watt power supplies one for each rail.  While these are 'virtual rails' or single rails, you're still again, using one molex style connector on a PSU. You're running upwards of 20+ amps on the connector. That all being said, generally speaking you will be okay using a single dual head cable. Especially if you're running stock. However, if you're overclocking or having stability issues, using two or using two for troubling shooting is just common sense. There's too many cases of just using two, solving a stability issue for it to be a myth.
 

Heating and voltage drop through any connector pin and mating pair is a common concern.  Not to mention safety factor of the system when combined.

I'm going to replace all my house wiring with 18G, it's rated for over 15 amps.

Cool GTX
 
Yes if it Works

Until it doesn't and things start going kablooey.

Seriously. I don't know why so many people are blowing thousands of dollars on GPUs and building these incredible rigs only to cheap out on something as easy as just running separate, dedicated, power cables to the PSU.

DeadlyMercury
I think that is not about "cheap" - but about good looking and less cables.
But still there is not much difference about running single or two pci-e wires for gpu.

If only EVGA sold something to help out with that...