At that point, it assumes it can safely draw all the power that the ATX spec says it can: 450W (ignoring the PCI slot itself). Assuming it is responsible (I have not tested it), it will only function if it it senses three 8 pin connectors plugged into it. This brings us to our hypothetical GPU - it asks for three 8 pin connectors. It does nothing to stop anything from drawing more. At the end of the day, the only real difference between the 6 and 8 pin cables in general is to inform whatever is using them of how much current is intended to be provided. This is why a 6+2 pin is effectively equivalent to an 8 pin cable - there's no increased electrical risk. While there's some debate as to the purposes of the extra pins, the 3 hot wires within both cables indicate that both can carry the same amount of current. But to further confound the issue, both 6 pin and 8 pin connectors have the same number of current-carrying wires in them: 3. Accordingly, the ATX standards set the safety margins (6 pins for 75W, 8 pins for 150W) far below the point where this will occur. If the wires get too much power, they will melt - or worse, catch fire. If the GPU can't get enough power, it will shut itself off. If the PSU can't supply enough power, it will shut itself off*. The power must still be carried from the PSU to the GPU, and it's here where the ATX standards are the most restrictive, and for good reason: the PSU supplies power and the GPU will take as much power as it needs, but neither does so with much regard to what's between them. This tells us that the 12V rail - where the 8 pin connectors on the PSU connect to - can supply plenty of power, far more than the GPU in question needs. Basic electrical formulas indicate this makes sense: Watts = Volts x Amps. PSUs differ in their specifications, but in my example 850W PSU the 12V rail can output the full 850W**, further limited by a max amperage of ~70A. The relevant rail for this question is the 12V rail, where by far most of the power is drawn from in a modern desktop. Each of these rails is limited to a certain share of the total power. Broadly speaking, these voltages are divided into "rails" - so everything of a single voltage (12V, 5V, 3.3V, etc.) comes out of the same power source*. All power in the computer comes filtered through the PSU, subdivided into different voltages for various pieces of hardware. However, they are only standards, and electricity listens to physics, not standards. These standards are reasonable, safe, and followed by virtually all consumer desktop hardware. The ATX standard determines a lot of the numbers thrown around here: 6 pins being restricted to 75W, and 8 pins being restricted to 150W. This question can be broadly broken down into 3 parts: the power source (PSU), the power transfer (the wires connecting the PSU and the GPU), and the GPU itself.įirst, the PSU. First off, I am not an electrician and my answer here certainly doesn't meet any professional or legal standards. I did a significant amount of research on my own, as well as learning a lot about basic electrical concepts to figure out the answer to my question. I've been trying to understand PSU cable specifications but have been unable to find a definitive source. On the surface, it certainly appears as though it would only provide 300W of power, but I can't understand why PSU makers would give you an 8-pin to 2x 6+2-pin connector if it meant that each of the 6+2 pins could only provide half of the power as a normal 8-pin (because, again, they're supposed to be functionally equivalent). Ignoring the power from the PCI slot itself, this would either provide 300W of power (for the 2 8-pin connectors facing the PSU) or 450W of power (for the 3 6+2-pin connectors plugged into the card). In that scenario, can you safely use two 8-pin to 2x 6+2 pin cables to connect the GPU (note: this would leave one of the 6+2 pins unplugged). One rumor has it that the upcoming 3000-series cards from Nvidia might utilize 3x 8-pin connectors. My research so far has informed me that an 8 pin provides about 150W of power. If that's the case, then how can one 8-pin connector effectively supply two 6+2 pin connectors? However, based on reading (such as PCI-e Power - Does 6 + 2 Equal 8?) an 8-pin is effectively the same as a 6+2 pin. A common cable included in modern modular PSU's is the 8-pin to 2x 6+2 pin.
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