On Wed, 29 Sep 2004 00:29:05 GMT, "Dorothy Bradbury"
wrote:

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.

I see. If i was to extend an ATX power cable I'd use some chunky
speaker cable for the high power connections, looks nice and a few
mm2+ is easily available. The lower power and signal connections would
be handled with standard 4 way flat speaker cable.

All the plugs would be moved down to the far end, using some
heatshrink which would look neat. Might need multiple cores or very
thick cable for the high power connections, I wonder what sort of
cable a standard ATX supply uses...

--
Dorothy Bradbury
In RCD Nuisance Trip Hell.

May be worth measuring leakage currents to see if they are excessive
when combined. Also test the wiring or equipment with a Megger or
something similar.

If it's intermittent earth leakage, connecting different equipment or
circuits into an isolation transformer or maybe even a UPS would help
narrow down the cause.

Failing heater elements, damp and even spideys can be a cause of
tripped RCDs.

cheers,
Pete.