Melting 12VHPWR Cables
PCI-SIG, the group that governs PCIe standards, has issued an email to all of its members and their suppliers regarding melting 12VHPWR cables. That email was technically private, but so many groups were on the email that it inevitably got passed around and ended up in our hands too.
As a reminder, 12VHPWR is the official name for the new PCIe 5.0 12+4-pin cable used on some current and upcoming high-power graphics cards and is capable of handling 600W sustained on a single cable.
You may have already seen this story covered on some rumor sites citing that the problem is with adapters converting to 8-pin PCIe connectors, but that’s incorrect and may have been based on incomplete information. Here’s what the email had to say:
“Please be advised that PCI-SIG has become aware that some implementations of the 12VHPWR connectors and assemblies have demonstrated thermal variance, which could result in safety issues under certain conditions. Although PCI-SIG specifications provide necessary information for interoperability, they do not attempt to encompass all aspects of proper design, relying on numerous industry best-known methods and standard design practices. As the PCI-SIG workgroups include many knowledgeable experts in the field of connector and system design, they will be looking at the information available about this industry issue and assisting in any resolution to whatever extent is appropriate.”
“As more details emerge, PCI-SIG may provide further updates. In the meantime, we recommend members work closely with their connector vendors and exercise due diligence in using high-power connections, particularly where safety concerns may exist.”
The PDF explains that Nvidia has been testing 12VHPWR connectors to validate that prototype power supplies and cables can meet the specification of 55A continuous. During this testing, Nvidia found certain cable routing conditions led to excess heat and, in some cases, melting.
The conditions required for the excess heat were either subjecting the cables to severe bending or a high number of mating cycles (about 40). Cables tested in these scenarios exhibited hot spots at roughly 2 and a half hours, and melting at 10 to 30 hours. Connectors from multiple suppliers have failed.
This is with a continuous 55A of current (or 660W at 12V), which would not be a typical load condition, especially not in gaming. Nvidia did not observe any failures on connectors with low mating cycles and without any bend.
Photos provided in the PDF show some pretty gruesome melting, and it’s not in the same area each time. The failures occurred on different pins depending on the direction the cable was bent. This could be seriously dangerous.
The document includes per-pin measurements taken during the testing. As the cable was bent in various directions, severe current imbalance resulted from huge swings in resistance. We’ll use the last set of data as an example as it’s the most severe. The resistance in pins 3 and 4 measured high, especially pin 3, resulting in a measured 36.4A on a single pin, or 436W on a single pin, leading to a hotspot temperature of 180 degrees celsius. By the way, the current rating of stranded 16AWG is only between 5A to 7A, so we’re talking about 5 to 7 times the rated current.
The PDF goes on to hypothesize that the bending and side-loading cause the plug to improperly seat in the receptacle, perhaps deforming it. The testing conditions might seem extreme, with the cable being bent around at full load for hours on end, but this kind of thing is done to ensure a margin of safety as products get used and age in various circumstances.
Group members are encouraged to do independent testing and share the results with Nvidia, who also has volunteered to work with the manufacturers of the connectors to fix this issue. Nvidia and the PCI-SIG are trying to get ahead of a potential problem before it is allowed to become widespread.
Our opinion is that while the situation is serious and should be taken seriously, this isn’t likely to be a problem that you’ll encounter in your gaming PCs. The test conditions are intentionally extreme in a way that you likely won’t have in your own system, especially if you take care not to put too much strain on any of your cables and connectors. It’s never a good practice to shove, bend, or cram any cables.
Source: GamersNexus
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