What's the difference between splitting 8-pin power inside vs outside the PSU?

[marcosscriven]

Long story short, I was using an 8-pin splitter for my 3080FE and seeing shutdowns. Moved to two separate cables, and all is now fine.

What I'm struggling to find now is a really good explanation as to why - there's a lot of posts out there taking it as common knowledge.

It *sounds* to me like the PSU is cutting out (presumably to protect itself) - but protect against what?

• The gauge of the wires is ample for a single cable, so I don't think it's temp
• The SF750 has a single 12V rail, so I don't think it's over power (especially as fine with two cable)
• I don't think there's per-plug monitoring on the PSU

All I can think is that, purely electrically, there's a slightly greater voltage drop when using one 8-pin with a splitter, vs two. But I'm not really sure why? The power has to split from a single rail either inside the PSU or outside via the y-cable. I don't know enough to know why that's different (and clearly enough to go from assured shutdowns to completely stable).

 

[marcosscriven]

Transfer losses:
Because no real world conductor is super conductor it has some resistance.
And when you double the current wire is carrying, you double the voltage loss.

Great explanation, thank you.

While I'm familiar with the essential school-level physics here, I hadn't thought the resistance of using one cable would be anywhere near *double* the resistance of two when considering the rest of the circuit in the PSU itself. That last point being the confusion here for me. If the PSU is itself one rail for 12V, isn't itself splitting that 12V across multiple sockets?

It seems to be it's the PSU that shuts off, presumably due to over-current protection.