Power Cables in a Computer: Every Internal PSU Cable Explained
Quick answer / TL;DR: Power cables in a computer are the internal leads that carry power from the PSU to the motherboard, CPU, GPU, drives and front panel. The standard set is 24-pin ATX, EPS 4+4 for the CPU, PCIe 6+2 for graphics cards, SATA power for drives, and legacy 4-pin Molex for older fans.
Open a desktop case and you see a fan of cables: black, yellow, red, orange and blue leads, all of them power cables inside the computer, mixed in with data and front-panel headers. New builders get confused about which cable feeds which component, and why some connectors split into two smaller pieces.
This guide names every internal PSU cable, what it powers, the current it is rated for, and the common mistakes – forcing a 6-pin into a 6+2, mixing ATX 12V and PCIe cables – that can damage hardware. Keep it open when wiring a build.
The Main Internal PSU Cables
24-pin ATX: the motherboard main feed
The 24-pin ATX connector is the main power feed to the motherboard, delivering the 3.3 V, 5 V and 12 V rails. One cable per motherboard – never share it with another board or adapter. The keying slot in the connector stops it going in backwards.
EPS 4+4: CPU power
The EPS connector (often labeled ATX 12V) feeds the CPU voltage regulator. The 4+4 split lets modern PSUs support both old 4-pin and current 8-pin sockets – use the full 8-pin for current CPUs. Do not repurpose a PCIe 6+2 as CPU power: the 12 V wire colors differ and the amperage is not guaranteed.
PCIe 6+2: graphics card power
The PCIe 6+2 connector powers graphics cards and some high-end CPU coolers. The 6-pin and 8-pin variants come from one cable – a 2-pin tab snaps on to make it 8-pin. A 300 W or larger GPU usually needs two or three of these, each from its own PSU cable, not daisy-chained from a single lead.
SATA power and 4-pin Molex
SATA power feeds SSDs, 2.5-inch drives and many front-panel USB headers. The older 4-pin Molex still shows up on fans, optical drives and some controllers. Both are keyed, and SATA power is the modern default for anything added after about 2010.
Internal PSU Cable Ratings at a Glance
| Cable | Feeds | Typical colors | Practical rating |
|---|
| 24-pin ATX | Main board rails | Black, yellow, red, orange | Full PSU output |
| EPS 4+4 | CPU VRM | Black, yellow, red | 22-30 A on the 12 V rail |
| PCIe 6+2 | GPU | Black, yellow, red, orange | 150 W at 6-pin, 225 W+ at 8-pin |
| SATA power | Drives | Black, orange, red, yellow | 5 V and 12 V rails |
| 4-pin Molex | Old fans and drives | Yellow, red, black | 5 V and 12 V |
The ratings above are typical per-cable values from mainstream PSUs; check the label of your specific unit for the exact 12 V amperage before wiring a high-wattage GPU.
Common Wiring Mistakes
- Using one PCIe cable to feed two 8-pin GPU sockets – each socket needs its own cable
- Forcing a 6+2 tab that does not seat fully
- Routing internal cables across the CPU air cooler intake
- Using an aftermarket PSU extension cable with a different pinout from the original
Most internal cable problems are mechanical: a connector that clicks but does not sit square, or a lead kinked near the PSU. Before powering a build on, re-check that every header is fully seated and no pins are bent.
Real-World Applications
DIY build: a mid-range 750 W PSU ships with two 24-pin ATX leads (one spare), two EPS 4+4, four PCIe 6+2, six SATA power and two Molex – enough for one 8-pin GPU and four drives. Upgrade path: when adding a second GPU or an eGPU dock, budget for a PSU with dedicated PCIe cables rather than daisy chains. Cable management: bundle the unused internal cables with cable ties behind the motherboard tray to keep intake airflow clean.
Related reading: Does a gaming rig need a special power setup on the outside? — gaming-pc-power-cord
Related reading: The external side: which power computer cable feeds the PSU from the wall — power-computer-cable
Frequently Asked Questions
What are the different power cables inside a computer?
The core set is the 24-pin ATX main board feed, the EPS 4+4 CPU connector, PCIe 6+2 graphics card connectors, SATA power for drives, and legacy 4-pin Molex for older fans. Some PSUs also add front-panel USB power headers for the case connectors.
Can I use a PCIe cable for CPU power?
No. The 12 V wire colors differ and the amperage rating is not the same. The CPU socket needs the EPS 4+4 (8-pin) connector specifically; swapping in a PCIe cable can overload the connector and damage the motherboard or the PSU.
Why do some power cables split into two connectors?
The 4+4 and 6+2 splits exist for backward compatibility: one thicker cable can act as a smaller older connector (4-pin or 6-pin) or the full modern one (8-pin). The two halves of a split connector are not interchangeable with separate cables.
How do I know if my PSU has enough internal cables?
Count the connectors the board and GPU need: one 24-pin ATX, one 8-pin EPS, and as many PCIe 8-pin connectors as the card has. If the PSU lacks one, it is undersized for that build – a 300 W+ GPU typically needs a 750 W+ unit with multiple dedicated PCIe cables.
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