Power Supply Installation
You’re getting close! With all of the above components installed, the power supply unit (PSU) should come next. You could install the graphics card prior to the power supply, but they tend to get in the way for managing power cables
and their connectors usually face outward, so hooking them up last is easier. If you haven’t unboxed your PSU yet, do so now and keep all included cables handy for the coming steps.
An important note about voltage
Many modern PSUs automatically detect the voltage that they’re being fed from the wall socket (either 115V or 230V), but lower-cost PSUs may have a manual selector near the on-off switch. This will be a recessed
red switch that can be set to either 115 or 230. If your PSU has one, make sure it is set to the correct voltage now as using the wrong voltage setting can destroy your PSU and any connected components, and in extreme cases can cause a fire. If you aren’t completely sure which setting to use, we highly recommend exchanging the power supply for a higher-quality unit that can automatically detect.
If you have a modular PSU, you can insert the cables you’ll need into it now if you prefer. This guide will assume the power supply will be installed into the case first with the cables attached and routed second. If your case
has cable routing options you may want to attach cables later since it’ll be easier to route them one-by-one as they’re added into the system.
PSUs will typically mount either above or below the motherboard at the rear of the case. It will fit into a rectangular cavity with four mounting points on the rear panel to hold it in place once installed. The fan on the PSU is
an intake that vents to the rear, so if your case is designed to top-mount the PSU, you’ll want that fan facing downward towards the motherboard. If your case uses a bottom-mount PSU, you may have the option to mount it with
the fan facing either up or down. If the bottom of the case is vented where the power supply would sit (with mesh or holes and ideally an air filter), you’ll be running your system on a hard flat surface, and the feet on the
case give the bottom panel some clearance, you can mount the PSU with the fan facing downwards. This will keep the PSU fed with cool air from outside the case and will lower temperatures inside the case a small amount.
Your case should have a tab or bracket that the PSU will slide into. Noting the orientation that the PSU will be installed, and keeping any attached power supply cables clear of the case and other components, position your PSU
several inches forward from its final position and slide it into place. It should rest upon the aforementioned bracket, or the bottom of the case, as appropriate. Press it into the rear shroud then insert the four screws that
will hold it in place (these power supply screws will usually be the same size or slightly larger than your motherboard screws). Tighten until firm, but don’t over tighten as you can strip the threads on the PSU itself.
If your PSU is non-modular (all cables are attached directly), take a moment to find where the bundle of disconnected, unused power cables may sit within your case. They can be zip-tied or velcro-tied together and secured in
a safe location where they don’t block fans nor significantly impede airflow. Case bottoms, unused drive bays, and behind the motherboard tray in cases with a lot of space are good candidates. When you’re done routing the
cables you’ll need, route and secure the unused ones wherever they make the most sense.
As you progress through each cable in the build, pay attention to where the cables are going to rest. You don’t want any cables interfering with fans or blocking airflow. Good cases will have various holes, gaps, grommets,
channels, and metal loops strewn about that allow you to run cables cleanly from one location to another, oftentimes out of sight for all but endpoint connections. If you have an opportunity to run a cable behind the motherboard
tray or near a point you can zip-tie or velcro-tie them to hold them in place, do so.
At this point, look through your case and components and determine which and how many power cables you’ll need to connect. At minimum, you’ll need:
- An ATX 24-pin power cable, which powers the motherboard.
- Either a 4 or 8-pin EPS 12V power cable, which powers the CPU. Some motherboards may need more than one.
- A SATA power cable if any 2.5”, 3.5”, or 5.25” drives are installed (most of these have multiple heads and can connect to three drives simultaneously).
- Any number of 6 or 8-pin PCIe power cables for the graphics card, if you have one in your build.
The ATX power cable is thick and cumbersome, so we’ll start there to get it out of the way. The 24-pin connector on the motherboard is the most difficult to insert from the sheer resistance of plastic on plastic. Each power
cable will have a tab that secures the cable in place when connected, and a matching ridge on each receptacle will hold the tab. On nearly all motherboards the ridge for the ATX power connector will face towards the center
of the board. Verify this then press the cable in (it will only fit one way) as far as it will go without excessive force. If the tab isn’t hooking over the ridge, rock the cable end back and forth lengthwise along the
ATX power connector until the cable clips into place.
The EPS 12V power cables usually come as an 8-pin cable that can be split in half at the end that connects to the motherboard. If yours only needs a 4-pin connection, you can tie the unused 4-pin back onto the cable itself
to keep it clear of the motherboard. Again, these cables will only mount one way and will have a tab that slides over an accompanying notch on the motherboard. Press them in until they click into place.
SATA power cables are next, and more care should be taken with these than other cables. The male connectors on the drives themselves are only held in place using a thin piece of plastic that can be broken off without too much
force, rendering the drive unusable. This is not a major concern if you only have one device on a single SATA cable, but if you’re running several devices off a cable, make sure you’re not excessively bending or twisting
a cable to get it into place. It’s best to use a second cable at that point so you don’t damage any drives. SATA power cables should connect fairly easily to their L-shaped receptacle; a gentle lengthwise rocking should
be all you need to press them into place. These have no tabs and will instead press into place.
On the off chance your computer build uses a molex (LP4) power connector for any device, these will press into their female receptacle only one way but will generally have pretty loose pins on the male side of the port. The
cables are not defective! You will need to use additional care to make sure you’re not trying to force the pins into a piece of plastic but are instead guiding them into their opposite plugs.
PCI Express power cables work very much like the EPS 12V plugs above in that they’ll usually have an 8-pin head with a 6-pin base plus 2-pin breakout. These will have a tiny notch on the 2-pin breakout that helps keep the 6+2
together as if they were a single 8. Much like the EPS cables, they’ll press into your graphics card and will have a tab and notch to click into place.