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PSU Cabling Guidelines - If using splitters, how many and for what connections are recommended?

Last response: in Components
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May 14, 2014 10:47:57 PM

Hi Guys,

I've built a PC in the past that didn't have enough pins for all of the components and case features. It was for my partner so he told me he didn't need the top panel for SATA HDD's and such, so we worked with what we had an used one splitter that came with the PSU to make two of the fans run off of one pin.

But - Only recently i've discovered that i could have fixed this by either obtaining some more splitters or making my own...

What i'm curious about is - What would you guys recommend being a safe guideline to follow in regards to splitting off the power. I can imagine that it wouldn't be a huge deal for low power consuming connections such as fans and leds but in regards to everything else?

A little bit of insight would be greatly appreciated!
a b ) Power supply
May 15, 2014 5:39:10 PM

a typical max load would be no more then 10 amps on any one pin on the plug (standard atx max is 11amps but that wire will be hot). id recommend staying below 7amps personally. the best way is to keep each of the main cables equal power draw. usually if you have a graphics card don't use that cable to power anything else as most cards can draw that much power by themselfs. remember that 10 amps at 5 volts is 50 watts of power going though that wire and 10 amps at 12 volts is 120 watts(yes the wire should handle that to meet atx MAX LIMIT standards but I wouldn't recommend pushing it)
a c 288 ) Power supply
May 15, 2014 6:47:37 PM

For SATA, i would say running more than about 8 SATA devices split off of one connector might be pushing it since you'll be pushing almost 100W at that point, but 8 SATA devices is also a lot. If you were to throw a couple splitters on a SATA chain i'd say 12 is about the limit for how much power i'd push through those wires, though at that point you will likely need to look into staggered spinup to reduce startup load on the PSU.

For molex, chain as many normal fans as you want, a big fan might pull 0.4A@12V so ~5W, if we are sticking with ~100W as a fair limit for a peripheral connector to deal with then you can run 20 fans off of one molex, more than any practical limit.

PCI-e is a different beast though, here you are playing with power levels that matter. A 6 pin is rated to provide 75W@12V(6.25A), an 8 pin is rated to provide 150W@12V(12.5A), in both cases this power is provided over just 3 wires putting each wire feeding a PCI-e 8 pin at about 4.2A. Again the connector is going to be the limiting factor here, I'm always hesitant against PCI-e splitters because that lets you take a line with 2 PCI-e 6 pin cables on it, which may have originally been spec'd to carry only 4.2A per wire, and you can quadrouple that if you split each 6 pin into 2 8 pin connectors, that means that the 6 pin connector, intended for ~2A per pin, is now supplying 8A per pin, thats going to get hot fast. The wires feeding it are likely only rated for ~10A, if you now split a PCI-e into a pair of 8 pins you now have 8.3A per wire, if you split two PCI-e connectors into a pair of 8 pins, you now have 16.3A per wire! Thats more than you should be running through 14AWG wiring in a house let alone 18AWG wiring in a PC.


Splitting to feed low power devices is fine, but don't split high current connectors like PCI-e or ATX/EPS, the current increases quickly beyond design specs.
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