PCIe cables are used primary to provide power to the installed graphics cards and other large and power hungry expansion cards. PCIe cables connect directly from the Power Supply Unit to the installed PCIe Expansion Card; Graphics Card.
A typical PCIe x16 slot on which you install the graphics card supplies 75 watts of power. This, is not nearly sufficient for many mid to high-end graphics cards.
In order to cater to the power requirement of such large and demanding cards, PCIe cables are used. In the text below, we explore what are PCIe cables used for in detail, how they connect and what their uses are.
While most of the expansion cards like a network adapter, sound card, video capture card etc, do not require PCIe cables – as they get sufficient power from the slot itself – graphics cards, on the other hand, require extra power directly supplied from the PSU.
Depending upon the installed card you have, you may require a single, all the way to three or more PCIe power cables.
What Are PCIe Cables Used For?
So as mentioned earlier, PCIe cables are used to connect power hungry devices like a graphics card to a Power Supply Unit.
For most PCIe expansion cards, the power provided by the PCIe slot itself suffices. However, for demanding cards like graphics cards, the 75 watts provided by the PCIe x16 slot is not sufficient.
It is worth noting here that only the medium to high end graphics cards have a need for PCIe cables to provide them with extra power.
Some Graphics Cards Do Not Require Power Cables
Many low end dedicated cards do not need to be connected to a PCIe cable.
Image: Gigabyte NVIDIA GT 710. Source: Gigabyte
Take for instance the NVIDIA GT 710. This is a very basic card primarily procured to enable video output on systems as well as to add multiple monitor capability. This is far from being a gaming based graphics card and thus has a very low power demand.
As such, this graphics card does NOT require an external PCIe power cable. It can receive sufficient power from the X16 slot it goes into.
Also Read: Do Graphics Cards Come with Cables?
Some Require As Many 3 x 8 Pin Power Cables
Contrast this with a top of the line ASUS ROG Strix NVIDIA Geforce RTX 3090 below.
This graphics card requires a whopping 3 x 8 pin power cables.
Image: ASUS ROG Strix Spec Sheet showing requirements of 3×8 pin PCIe cables.
The bottom line is that whenever you’re buying a new PCIe device, particularly a graphics card, it is important to check its power requirements and confirm if your PSU can supply it.
Also Read: How to Add More PCIe Slots?
How to Connect PCIe Cables to an Expansion Card
We have already established that some PCIe devices may need more power, and this needs to come straight from the power supply.
You use a PCIe power cable for this by routing it from your PSU and plugging it into your PCIe card for it to work. Components that require this include high-performance Graphics cards.
Also Read: How Many PCIe Cables Do I Need?
Routing Power Through Power Supply Unit
Power Supply Units come with PCIe power cables. However, the amount of PCIe cables you get depend upon the model of the PSU.
The most recommended type of power supply unit for gamers and workstation systems are modular power supply units. These have extra connectors for installing more PCIe power cables if needed.
Let us look at an example. The following Power Supply Unit comes with two 6+2 pin power cables built-in and ready to use. So essentially, I can connect upto a graphics card that has a 2 x 8 pin power requirement.
In the following photo, I have connected the 6+2 pin power cables to a graphics card that has a 2 x 6 pin connector requirement:
Note that the +2 extra pin on both cables are now in spare. It is worth pointing out here that ALL OF THE POWER CONNECTORS ON YOUR GRAPHICS CARD NEED TO BE CONNECTED.
So given the spare +2 pins, I could have connected a larger graphics card with a 2×8 pin requirement as well.
Now if I wanted to connect an even larger card that has a connector requirement of MORE than 2 x 8 pins, I could use the modular capability of the power supply unit.
You can see above that this power supply has extra power sockets due to its modular nature. Hence, I could connect more PCIe cables to this if needed.
I would have to procure the extra power cables myself though. So in essence, your graphics card will determine whether or not you will need a PCIe power supply cable and how many of it.
The manufacturer will make this information available in the shape of how many POWER CONNECTORS the graphics card has.
Also make sure that along with sufficient PCIe connectors, your PSU also has a sufficient power rating. This is because some high-performance cards have high power demands and overloading your PSU can result in performance drops.
So even if you can meet the power connector number requirement, you need to have a the right size of the power supply unit.
PCIe Power Supply Cables and Basic Types
There are numerous PCIe Power Cables out there distinguished by their PIN configuration and their power supply capacity.
6-Pin Power Cable
These are the smallest available and can deliver a power of upto 75 watts.
8-Pin Power Cable
8 Pin PCIe cable has a power delivery capacity of upto 150 watts. You may be wondering how a 6 pin delivers 75 watts and an 8 pin doubles that capacity without doubling the pin count.
That has to do with the fact that not all pins in the cable deliver power. Some pins have a different role such grounding, sensing/signals etc.
The 6+2 Pin Cable
We saw this in our example above. A 6+2 pin connector is essentially an 8 pin cable that can deliver both lower and higher power depending upon the connector requirement of the graphics card. Hence, you get more flexibility here.
12 Pin Cables
These are the latest connectors developed by NVIDIA to cater to their RTX 3000 series graphics cards
Depending upon the gauge of the cable, a 12 pin cable can supply 500-600 watts of power.
These are fairly rare at the moment and only found in very high end systems.
PCIe Pigtail Cables
There are also the PCIe cables with pigtail connectors. These basically have one end connected to the power supply unit and then they split into two connectors on the other side.
So the cable above is an 8 pin pigtail cable. One end will go into the power supply unit. The other end has two separate 8 pin connectors that can be used on the graphics card.
There is generally a debate on whether you should go for pigtail cables or separate cables. Many hardcore enthusiast believe that separate cables should be the way to go. However, others have proven that pigtail cables do not result in a huge performance drops.
PCIe Cables and Graphics Card Maximum Power Consumption
Depending upon the type and amount of connectors on your GPU, the max power consumption can be summed up as follows:
|6 Pin Cable|
|8 Pin Cable|
|12 Pin Cable|
|75W||1 x 75W||0||0||150W|
|75W||0||1 x 150W||0||225W|
|75W||2 x 75W||0||0||225W|
|75W||1 x 75W||1 x 150W||0||300W|
|75W||0||2 x 150W||0||375W|
|75W||1 x 75||2 x 150W||0||450W|
|75W||0||3 x 150W||0||525W|
|75W||0||0||1 x 600W||600W|
You should now have a clear idea of what are PCIe cables used for and how to connect them. Essentially, they provide power to your graphics card from the PSU.
Not ALL expansion cards that go into PCIe slots require a PCIe power cable.
Understanding your power supply unit specs, the cables available to you and the connector requirement on your graphics card is key to good power management for your system.