Matching low quality riser with high-power GPU is not a good idea
A Redditor has reported damage to a PCIe riser cable used with an ASUS TUF GeForce RTX 5090 in a vertical GPU mount. The card itself did not appear to suffer electrical damage, but the riser cable insulation reportedly melted where it was touching the GPU backplate.
The user later clarified that only the insulation was damaged. The cable had been routed in direct contact with the backplate, which left melted plastic on the GPU. The owner also said the cable had to be peeled away from the card after the system was opened for cleaning.
A PCIe x16 slot can provide up to 75W of power, while the rest of the graphics card power is supplied through the external connector. In this case, users in the thread pointed out that the damaged wires were not the main power pins and they are correct, only first few pins transfer 12V power.
Source: Wikipedia
Backplates can still get hot
GPU backplates usually do not reach temperatures high enough to melt proper cable insulation during normal use. They can still become hot to the touch on high-power cards, depending on cooler design, board layout (like dual-sided memory) and thermal pad placement.
NVIDIA GeForce RTX 5090 is a 575W card, so sustained load can put a lot of heat into the card and surrounding area. That does not mean a backplate should damage a riser cable by itself, but direct contact removes airflow and exposes the cable jacket to constant heat.
I collected some examples from AORUS, Lian Li, Corsair and Thermaltake. As you can see, the riser should not touch the card, and ideally the card is pushed back as far from the riser as possible. Unfortunately, this is much easier said than done with quad-slot GPUs in closed cases, but I’m quite sure they are not supposed to melt even when they touch the card. I have used risers for over 10 years now, and I have never seen them melt.
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