Keep the ATX extension lead to ~30cm re remote sensing (but not on all pins)

Really, how does that work? Are some of the duplicated ATX connections
used for this or are they commoned together?

Typical desktop PC:
o Remote sensing is on the 3.3V rail
---- since 3.3V is quite a low voltage + power cables have length & voltage drop
---- and spec is +/- 5% which isn't a lot in voltage terms
o Implementation for desktop PCs is via pin 11
---- the power pins are commoned off the PSU PCB to distribute load per cable/pin
---- a few (Tyan dual CPU?) boards used to melt their ATX skts under high load
o Remote sensing is also required at the SATA 3.3V connector too IIRC
---- even the 2.5" SCSI 10k-rpm Savio is still 5V (I think)

Industrial PCs:
o Remote sensing can be on all of 3.3V, 5V & 12V rails
---- these still average across the ATX connector
o Remote sensing can get more sophisticated on mini-PCI multi-U arrays
---- these combine outputs from many std ATX PSUs re o/all current draw
---- they manage redundancy without expensive/unobtainable redundant PSUs

www.formfactors.org will have details for both ATX 2.1/2.2 & BTX.

Basically the spec just requires 3.3V remote-sensing.
I've never seen a cable length limit - but have seen 1.5m 1U PSU cables (oddly!).
If you take a standard ATX PSU, which has quite a long lead, some E-ATX super
server cases required a 30cm extension to be added to reach the power socket.

Never tried an 'overly-long' cable so can't comment on what happens, I suspect
the voltages would need careful monitoring during burn-in load testing. Would help
if the leads (wire) were a decent thickness - some are, and some are a bit skimpy.
--
Dorothy Bradbury
In RCD Nuisance Trip Hell.