power connectors

8/10/2019 Power Connectors

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Power supply information

Compatibility issues for ATX power supplies and motherboardsA short history of PC power supply voltage rails

So what's all this rubbish about multiple 12 volt rails?All about the various PC power supply cables and connectorsRail complications #1 - current limit problems: too much current

Rail complications #2 - cross loading problems: unbalanced currentRail complications #3 - minimum loading problems: too little current

Using PC power supplies in things other than PCs

Last updated: July 15, 2008

All about the various PC power supply cables and connectors

The various power supply cables

Original PC main power cables 4 pin peripheral power cable Floppy

6 pin auxiliary power cable SATA power cable

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20 pin ATX main power cable 24 pin ATX main power cable 20+4 pin A

4 pin ATX +12 volt powercable

8 pin EPS +12 volt power cable 4+4 pin +12 v

6 pin PCI Express power cable 8 pin PCI Express power cable 6+2 pin PCI Exp

General info

If you'd like more technical data about ATX power connectors then you can find the

current specifications and more at formfactors.org

Wires and connectors are not perfect conductors. They have resistance. When currentpasses through wires and connectors there is a voltage drop and that energy is lost as

heat. As long as you don't overload them the voltage drop and extra heat don't matter.But the losses get worse as the current rises. That's why you see some power cables

with more that one wire for the same voltage. Having multiple wires reduces thelosses. If you seriously overload a line, the wire can get fairly warm. The resistance of

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connectors tends to increase as they are plugged and unplugged so after enough usesthey can overheat and even melt when passing a large current. So a lot of changes in

connectors over time has to do with adding more wires and connectors to make surethat none of these problems occur.

Some of the tables below provide the maximum wattage supported by a power cable

and its associated power connector. Some specifications clearly spell out the maximum

allowed wattage. Other specifications just provide the suggested connector and wiregauge and never specify a maximum wattage. And there's never really an absolutevalue to the maximum wattage anyway. If you draw a little more wattage then themaximum, the hardware doesn't immediately burst into flames. The voltage drop and

power dissipation increase as you increase the current so there isn't a clear maximumwattage at which it stops working. Most of the specifications which spell out the

maximum wattage provide a wide safety margin by defining a value which is far belowthe maximums supported by the connector and wire. If the table below provides an

"Official cable/connector maximum wattage" then that specification has spelled out themaximum wattage. In most cases that wattage will be significantly below what can

actually be handled by the suggested connector and wire. If the table provides an"Unofficial cable/connector maximum wattage" then that specification doesn't provide

the maximum and the value in the table is a practical maximum wattage defined by themaximums for the connector and the suggested wire. An unofficial wattage doesn'thave a wide safety margin built in because people differ on how much margin to

provide. Some people happily use connector and wire maximums and other people liketo have a wide safety margin.

Power connectors included with various kinds of PCs

Version Introduction date Included connectors

PC 1981original PC main power cables4 pin peripheral cable

ATX 1995

20 pin main power cable

4 pin peripheral cablefloppy cable

ATX12V 1.0 2000

20 pin main power cable4 pin 12 volt cable

6 pin auxiliary cable4 pin peripheral cable

floppy cable

ATX12V 1.3 2003


4 pin 12 volt cable6 pin auxiliary cableSATA cable


ATX12V 2.0 2003

24 pin main power cable4 pin 12 volt cable

6 Pin PCI Express power cableSATA cable


EPS12V 2003


8 pin 12 volt cable6 Pin PCI Express power cable

SATA cable

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4 pin peripheral cable

floppy cable

PCI Express 2.0 2007


4 pin 12 volt cable8 pin 12 volt cable6 Pin PCI Express power cable

8 Pin PCI Express power cableSATA cable


Original PC main power cables

The original PC debuted in 1981 and used two cables to connect the PSU (powersupply) to the motherboard. The two cables plug side by side into the motherboardconnectors. Sometimes they are keyed so they only plug in one way and sometimes

they aren't. Even if they're keyed you can insert them the wrong way if you put a littleeffort into it. You always have to remember to plug them in so the black wires are next

to each other. It's either "black to black" or smoke and a shower of sparks.

Pinout

Pin number Wire color Description

1 orange power good

2 red +5 volts or connector key

3 yellow +12 volts

4 blue -12 volts

5 black ground

6 black ground

1 black ground

2 black ground

3 white -5 volts

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4 red +5 volts

5 red +5 volts

6 red +5 volts

Connector part numbers

Motherboard

connector

Cable

connector Terminals

Maximum current per

circuit

Molex 15-48-0106 Molex 90331Molex

08-50-02765 amps

Unofficial cable/connector maximum wattage delivery for main rails

Voltage rail Number of lines Maximum current Maximum wattage

+5 volts 3 or 4 15 or 20 amps 75 or 100 watts

+12 volts 1 5 amps 60 watts

In old PCs, almost all of the chips ran directly off of the 5 volt rail. As a result the PSU

delivers most of its wattage at 5 volts. There are three or four lines dedicated to the 5volt rail. The other main rail is 12 volts. That was used primarily to run disk drives,

motors, and fans. The two negative rails are "bias" supplies which only have to providesmall amounts of current. Just for interest's sake, here's the specification for the PSU

which came with the original IBM PC. It provides a maximum of 63.5 watts. Boy, thosewere the days.

Original IBM PC power supply

Voltage Maximum current Maximum wattage

+5 volts 7.0 amps 35 watts

-5 volts 0.3 amps 1.5 watts

+12 volts 2.0 amps 24 watts

-12 volts 0.25 amps 3 watts

4 pin peripheral power cable

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The four pin peripheral power cable dates back to the original PC. It was used for

floppy drives and hard disks. It's still around and is now also used for all kinds ofthings including add-on fans, extra video card power, supplemental motherboard

power, and case lighting. It's as old as the hills but is still very widely used. Theconnector is shaped so that it only fits in one way. You don't have to worry about

inserting it the wrong way. People often use the term "4 pin Molex power cable" or "4pin Molex" to refer to a four pin peripheral power cable. It's not a technically useful

term because the 4 pin 12 volt cableis also a 4 pin Molex cable (Molex makes lotsofconnectors) but "4 pin Molex" is commonly used to refer to peripheral cables anyway.

Pinout


1 yellow +12 volts

2 black ground

3 black ground

4 red +5 volts


Socket

housingSocket Pin housing Pin

Maximum current per

circuit

AMP

1-480424-0

AMP

60619-1

AMP

1-480426-0

AMP

60620-113 amps

I don't know of any official definition of the maximum current allowed in a peripheral

cable. The connector can handle 13 amps according to the manufacturer. But younormally find 18 awg wire in the peripheral cables. If you have an 18 inch cable

(about a half a meter) and are running 13 amps through 18 gauge wire then you get avoltage drop of about 0.25 volts counting both the power wire and the ground (it's got

to go both ways) and the dissipation is about 3.3 watts. That's not good. I've justplayed it safe and listed the maximum current as 5 amps.

Unofficial cable/connector maximum wattage delivery

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Current power supplies usually have at least two separate peripheral power cables,each of which has two or more peripheral connectors. When you're plugging in

multiple high powered devices it's a good idea to spread the load between all of yourcables. Don't just plug all your devices into one cable unless they're relatively low loaddevices. Spreading the current between the cables reduces the voltage drops and

power loss. If they're relatively low current devices like fans or it's just a disk drive ortwo then it doesn't really matter. But if you're putting lots of hard disks into a

computer (some can draw almost 3 amps at 12 volts when doing some operations) orconnecting a video card's auxiliary power, then spread the loads between the

peripheral power cables. It's also helpful if you use a connector as close to the PSU aspossible rather than sticking things at the end of the cable. Extra wire just means

more voltage drop. And if you're using a peripheral connector to PCI Express adapterthen be sure to plug each of the adapter's peripheral connectors into a separate PSUcable. They gave you two peripheral connectors for a reason. Plugging them both into

the same PSU cable forces your video card to draw its 12 volt power through one 18gauge wire. That increases your voltage drop and power dissipation in the cable. Some

current high-end video cards can suck up more than 10 amps at 12 volts with most ofit coming through the PCI Express connector so it pays to be careful. It will probably

work if you don't spread the load but there's no excuse for not doing it properly. Theygave you multiple cables. You might as well use them. Plus there's just something

creepy about having warm wires even if they're not melting.

You will occasionally run into peripheral connectors which don't have all four wires.They are usually 12 volt only cables intended for fans. Never plug one of those into a

disk drive. Drives expect both 5 and 12 volts to be provided. Some of the two-wireperipheral connectors are for speed-controlled fans. That means that the voltage

changes depending on the desired fan speed. The connector will only provide 12 voltswhen the fan is going full speed and the voltage decreases to slow the fan down.Definitely don't plug that one into anything but a fan! Normally this kind of peripheral

connector has "fan" printed on it to warn you. As long as a peripheral connector hasfour wires: one yellow, two black, and one red and it doesn't have some kind of printed

warning attached then it's a standard peripheral cable and you can plug it intoanything.

Floppy drive power cable

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The four pin floppy drive cable showed up when PCs started including 3.5 inch floppy

drives. This kind of cable is also sometimes used as an auxiliary power cable for AGPvideo cards which use more power than can be drawn from the motherboard slot. The

connector is shaped so that it only fits in one way so you don't have to worry aboutinserting it the wrong way. Floppy cables are built with small connectors and 20 awg

wire so they are limited to relatively low current uses.

Pinout


1 red +5 volts

2 black ground

3 black ground

4 yellow +12 volts


Socket housing Socket Maximum current per circuit

AMP 171822-4 AMP 170262-1 3 amps





6 pin auxiliary power cable

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The aux power cable was added to provide extra wattage to motherboards for 3.3 and

5 volts. This connector is rarely used anymore. It's most commonly found on older dualCPU AMD motherboards. You're more likely to sight Bigfootthan a motherboard which

uses this connector. It plugs into the 6 pin version of the motherboard connector usedby the original PC main power cables.

Pinout


1 black ground

2 black ground

3 black ground

4 orange +3.3 volts

5 orange +3.3 volts

6 red +5 volts


Motherboard

connector

Cable

connectorTerminals

Maximum current per

circuit

Molex 15-48-0106 Molex90331-0010 Molex08-50-0276 5 amps



+3.3 volts 2 10 amps 33 watts


SATA power cable

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SATA was introduced to upgrade the ATA interface (also called IDE) to a more

advanced design. SATA includes both a data cable and a power cable. The powercable replaces the old 4 pin peripheral cableand adds support for 3.3 volts (if fully

implemented). The connector is shaped so it can only be plugged in the correct way.

Pinout

Pin number Wire number Wire color Description

1 5 orange +3.3 volts



4 4 black ground5 4 black ground

6 4 black ground

7 3 red +5 volts

8 3 red +5 volts

9 3 red +5 volts

10 2 black ground

11 2 black ground

12 2 black ground

13 1 yellow +12 volts




Cable connector Terminals Maximum current per circuit

Molex 67582-0000 Molex 67581-0000 1.5 amps

Official cable/connector maximum wattage delivery


+3.3 volts 3 4.5 amps 14.85 watts

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+5 volts 3 4.5 amps 22.5 watts

+12 volts 3 4.5 amps 54 watts

You have to be careful about SATA power cables. Some of them are missing the 3.3volt wire. People with older power supplies often use adapters which convert from 4

pin peripheral cablesto SATA power cables. But since 4 pin peripheral connectorsonly supply 5 and 12 volts, the SATA connector is missing 3.3 volts (there's no orange

wire). There are also a few older power supplies which inexplicably have SATA powercables which are missing the 3.3 volt wire. Currently, SATA drives rarely use 3.3volts. That may be because there are too many people using adapters so the drive

makers don't want the headaches which come with using 3.3 volts. But in the future,3.3 volt drives may become common so you need to be careful when using SATA power

cables which don't implement 3.3 volts.

ATX 20 pin main power cable

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In 1996 PC makers started switching to the ATX standard which defined a new 20 pinmotherboard power connector. It includes a 3.3 volt rail which is used to power newer

chips which require a lower voltage than 5 volts. It also has a standby 5 volt rail whichis always on even when the power supply is turned off to provide standby power to the

motherboard when the machine is sleeping. The new connector also allows themotherboard to turn the power supply on and off rather than depend on the user to

flip a power switch. This connector is polarized so it can only be plugged in pointing

in the correct direction.

Pinout

Pins 1 through 10 Pins 11 through 20

Description Wire color Pin number Pin number Wire color Description

+3.3 volts orange 1 11 orange +3.3 volts

+3.3 volts orange 2 12 blue -12 volts

ground black 3 13 black ground

+5 volts red 4 14 green PS_ON#


+5 volts red 6 16 black ground


PWR_OK gray 8 18 white -5 volts (optional)

VSB +5 volts purple 9 19 red +5 volts

+12 volts yellow 10 20 red +5 volts

Some of the voltage lines on the connector may have smaller sense wires which allowthe power supply to sense what voltage is actually seen by the motherboard. These are

pretty common on the 3.3 volt line in pin 11 but are sometimes used for other voltagestoo. The -5 volt line on pin 18 was made optional in ATX12V 1.3 (introduced in 2003)

because -5 had been rarely used for years. Newer motherboards virtually neverrequire -5 volts but many older motherboards do. Most newer power supplies don'tprovide -5 volts in which case the white wire is missing.


Motherboard

connector

Cable

connectorTerminals

Maximum current per

circuit

Molex 39-28-1203Molex

39-01-2200

Molex

39-00-0168,

Molex44476-1111

6 amps



+3.3 volts 3 18 amps 59 watts



Dell used to ship many computers which used motherboards and power supplies which

looked like plain old ATX but were not really ATX at all. If you plugged a real ATX

power supply into the motherboard then things went kaboom (or frzzzzzap or ...).Sadly, some large computer vendors like to lock customers into buying upgrades from

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them rather from a third party. That's nasty enough but Dell built their non-standardcomputers and motherboards with what looked like standard ATX components. You

only found out otherwise once sparks started flying. The Dell PCs which were carryingthis ticking time-bomb were made between 1996 and 2000. If you're replacing a Dell

power supply from this era then you should call Dell and make sure it's not aproprietary design. And if they say yes then be sure to voice your displeasure. This is

an evil business practice which should stop.

You can plug a 20 pin ATX power cable into a motherboard with a 24 pin ATXconnector. The image above shows the 20 pin power cable plugged into a 24 pin

motherboard. A 20 pin power cable only fits into one end of a 24 pin motherboardconnector so you can't insert it incorrectly. The 24 pin motherboard connector is

actually just the 20 pin connector with 4 extra pins added on the end. The original 20pins were unchanged. The extra 4 pins are not separate rails. They're just extra linesto provide more current to the same rails. On every 24 pin motherboard I've seen, the

extra lines for ground, 3.3, 5, and 12 are just connected to the other lines on the samerail from the 20 pin connector. I've never heard of exceptions and it doesn't make

sense for motherboard makers to create any. As a result, you can plug a 20 pin cableinto a 24 pin motherboard and it will work just fine. At least, it will for a while. They

added those extra 4 pins for a reason. When you plug a 20 pin cable into a 24 pinconnector you're not providing the extra current carrying capacity which may be

needed by the motherboard. If your motherboard's current requirements are lowenough then it will work properly with only a 20 pin power cabled plugged in. But if

the motherboard draws enough current, then you can overheat the 20 pins you'reusing on the 24 pin connector. I've seen enough pictures of burned ATX mainconnectors to assure you that this happens. In adding the extra four pins, 3.3 volts

went from 3 to 4 lines. 5 volts when from 4 to 5 lines. 12 volts went from 1 to 2 lines soits capacity doubled. Connectors really do get hot if you overload them so the safest

thing to do is use a real 24 pin power supply on a motherboard with a 24 pinconnector. Note that your 24 pin machine may work fine with a 20 pin power supply

until you add a PCI Express card later on down the road. PCI Express cards can drawup to 75 watts through the motherboard connector so adding an expansion card can

substantially increase power draw through the main power cable. Many PCI Expressvideo cards which have the 6 pinor 8 pin PCI Express power cablestill draw a

substantial portionof their 12 volt load through the PCI Express slot. The extra 4 pins

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doubled the current capacity of the 12 volt rail so that one is easy to overload whenonly using a 20 pin main power cable.

The picture above shows an adapter which allows you to plug a 20 pin power supply

into a 24 pin motherboard. These do not solve the problems mentioned above. In fact,they usually make things worse. You still have only the same old 20 wires and

pin&socket connectors that you would have if you plugged it directly into themotherboard. But with the adapter you also have longer wires and another set of

pins&sockets so you have a higher voltage drop and more things which can go wrong.All the adapter does is remove the problem from the 24 pin motherboard connector

and move it to the 20 pin connector on the adapter. About the only good thing it doesis to make sure the 20 pin connector on the adapter melts rather than the 24 pinconnector on the motherboard. You shouldn't underestimate the potential problems

which come from adding another connector between the power supply and themotherboard. The resistance of connectors can increase due to being plugged and

unplugged. Increasing the resistance makes the connector drop more voltage anddissipate more heat. Any number of physical changes can also cause higher connector

resistance which causes more problems. You shouldn't put an extra connector in ahigh current path unless you've got a good reason. That's a good rule for power cables

in general but it goes doubly for the high current draws you sometimes find throughmotherboard main power cables. The best practice is to avoid these 20 to 24 pinadapters and get a real 24 pin power supply.

ATX 24 pin main power cable

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The 24 pin main power connector was added in ATX12V 2.0 to provide extra power

needed by PCI Express slots. The older 20 pin main power cableonly has one 12 voltline. The new 24 pin connector added one line apiece for ground, 3.3, 5, and 12 volts.

The extra pins made the auxiliary power cableunnecessary so most ATX12V 2.x powersupplies don't have them. The 24 pin connector is polarized so it can only be plugged

in pointing in the correct direction.

Pinout


Description Wire color Pin number Pin number Wire color Description+3.3 volts orange 1 13 orange +3.3 volts

+3.3 volts orange 2 14 blue -12 volts


+5 volts red 4 16 green PS_ON#


+5 volts red 6 18 black ground


PWR_OK gray 8 20 white -5 volts (optional)

VSB +5 volts purple 9 21 red +5 volts



+3.3 volts orange 12 24 black ground

Some of the voltage lines on the connector may have smaller sense wires which allow

the power supply to sense what voltage is actually seen by the motherboard. These arepretty common on the 3.3 volt line in pin 13 but are sometimes used for other voltages

too. The -5 volt line on pin 20 was made optional in ATX12V 1.3 (introduced in 2003)because -5 had been rarely used for years. Newer motherboards virtually never

require -5 volts but many older motherboards do. Most newer power supplies don't

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provide -5 volts in which case the white wire is missing.


Motherboard

connector

Cable

connectorTerminals

Maximum current per

circuit

Molex 39-28-1243 Molex39-01-2240

Molex

39-00-0168,Molex

44476-1111

6 amps



+3.3 volts 4 24 amps 79.2 watts



If you have an ATX power supply with a 24 pin main cable, it's okay to plug it into amotherboard with a 20 pin connector. It was designed to work that way. You can seean example in the picture above. The extra 4 pins on the cable just hang over the end

of the motherboard connector. The 24 pin cable only fits into a 20 pin socket at oneend so you can't plug it in incorrectly. The extra 4 pins were added to the 24 pin

version of the cable to provide one extra wire for ground, 3.3, 5, and 12 volts. But it'sokay to leave those 4 pins disconnected because a motherboard with a 20 pin

connector doesn't need them. The only problem you can bump into (literally) is if thereis something blocking the spot where the 24 pin cable hangs over the end. Or

sometimes the end of the 20 pin motherboard connector is too thick to fit between thepins of the 24 pin cable. You can solve that problem by carefully shaving down one

end of the 20 pin motherboard connector. It's just plastic. You won't miss it. If youcan't get them to fit together then you can get an adapter cable which will make it

work. The 24 pin cable plugs into one end of the adapter and then the adapter plugsinto the 20 pin motherboard. But you should avoid using that kind of adapter if youcan because the extra wire and connector are just more things which can go wrong.

Adapters also slightly increase the voltage drop which is something worth avoiding.

It's better to first see if you can get a 24 pin cable to fit into a 20 pin motherboardbefore resorting to an adapter.

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ATX 20+4 pin main power cable

Motherboards can come with either a 20 pin main power connectoror a 24 pin mainpower connector. Many power supplies come with a 20+4 cable which is compatiblewith both 20 and 24 pin motherboards. A 20+4 power cable has two pieces: a 20 pin

piece, and a 4 pin piece. If you leave the two pieces separate then you can plug the 20pin piece into a 20 pin motherboard and leave the 4 pin piece unplugged. Be sure to

leave the 4 pin piece unplugged even if it fits into another connector. The 4 pin piece

is not compatible with any other connectors. If you plug the two pieces of a 20+4power cable together then you have a 24 pin power cable which can be plugged into a24 pin motherboard.

4 pin ATX +12 volt power cable

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Older computers put most of their load on 3.3 and 5 volts. As time passed, computersdrew more and more of their load from 12 volts (see here). Before this power cable was

introduced there was just one 12 volt line provided to the motherboard. This cableadded two more 12 volt lines so more of the load could be shifted to 12 volts. Thepower coming from this connector is usually used to power the CPU but some

motherboards use it for other things as well. The presense of this connector on amotherboard means it's an ATX12V motherboard. For dual 12 volt rail power supplies,

this connector provides the voltage refered to as 12V2. The power cable which plugsinto the 4 pin connector has two black wires and two yellow wires. This cable is

sometimes called an "ATX12V" cable or "P4" cable although neither of those aretechnically accurate descriptions.

If you have one of these connectors on a motherboard then you must plug a power

cable into it or your CPU won't get any power. The one exception is that when thisconnector was new, some motherboards shipped with a socket into which you could

plug a 4 pin peripheral power cableas an alternative. That helped people who hadolder power supplies which didn't have the 4 pin 12 volt cable.

The 4 pin 12 volt cable is polarized so it can only be plugged into the 4 pin

motherboard connector correctly. If you look carefully at the picture above you can

see that two of the pins are square and the other two have rounded corners. Themotherboard connectors also have the same square and rounded arrangement so the

power cable only fits in one way. At least that's true unless you try really hard to forceit into the connector. With enough force you can sometimes get a cable with a small

number of pins into a connector which doesn't match. If you look carefully you can alsosee that the square and rounded pattern matches various positions on other

motherboard connectors like the 20 pin main power connectorand 24 pin main powerconnector. Do yourself a favor and only plug the 4 pin 12 volt cable into the

motherboard connector where it belongs (unless you enjoy smoke and friedcomponents).

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If your power supply doesn't have a 4 pin 12 V cable then you can provide one withthe adapter shown above. It converts a 4 pin peripheral cableinto a 4 pin 12 V cable.

Pinout

Pins 1, 2 Pins 3, 4


ground black 1 3 yellow +12 volts

ground black 2 4 yellow +12 volts


Motherboardconnector

Cableconnector

Terminals Maximum current percircuit


39-01-2040

Molex

39-00-0168,Molex

44476-1111

8 amps




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You can plug a 4 pin 12 volt power cableinto an 8 pin EPS motherboard connectorbut there's no guarantee that it will work. If the motherboard expects only one 12 volt

rail then a 4 pin 12 volt cablemay work. If the motherboard expects two 12 volt rails(many dual CPU motherboards require one 12 volt rail per CPU) then it won't work.

Even if the motherboard works with a 4 pin 12 volt cable, you are still only providinghalf of the current carrying capacity which would be provided by an 8 pin EPS cable.

That can overheat both the motherboard connector and 4 pin cable. Scorched ormelted connectors can be a result. A motherboard which has the 8 pin EPS connector

expects a lot of current and you are taking a serious risk by plugging in a 4 pin cable.

The 4 pin cable only fits at one end of the 8 pin EPS motherboard connector so youcan't plug it in improperly. That is, it only fits into one end of the motherboard

connector unless you force it. If the cable doesn't go into the socket easily then you'reprobably trying to plug it into the wrong end. But then again, it's not a good idea to

try to run with a 4 pin cable in an 8 pin motherboard anyway.

8 pin EPS +12 volt power cable

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This cable was originally created for workstations to provide 12 volts to power

multiple CPUs. But as time has passed many CPUs require more 12 volt power and the8 pin 12 volt cableis often used instead of a 4 pin 12 volt cable. Depending on the

power supply, the connector may contain one 12 volt rail in all 8 pins or two 12 voltrails taking up 4 pins apiece. It is often refered to as an "EPS12V" cable.

The 8 pin 12 volt cable is polarized so it can only be plugged into the 8 pin

motherboard connector correctly. If you look carefully at the picture above you cansee that four of the pins are square and the other four have rounded corners. The

motherboard connectors also have the same square and rounded arrangement so thepower cable only fits in one way. At least that's true unless you try really hard to forceit into the connector. With enough force you can sometimes get a cable with a small

number of pins into a connector which doesn't match. The 8 pin cable has enough pinsthat it's pretty hard to insert it in the wrong direction but determined people might be

able to do it. If you look carefully you can also see that the square and roundedpattern matches various positions on other motherboard connectors like the 20 pin

main power connectorand 24 pin main power connector. You should only plug the 8pin 12 volt cable into the motherboard connector where it belongs unless you enjoy

the smell of fried electronics.

You can also plug an 8 pin 12 volt cableinto a 4 pin 12 volt motherboard connector. I

don't have a picture of this one but it looks similar to this. Four of the pins on the 8 pincable fit into the motherboard connector and the other four pins hang off the end. The

8 pin cable only fits into one end of the 4 pin motherboard connector unless you tryhard to force it into the wrong position. The 8 pin cable is electrically compatible but

it may not fit into a 4 pin motherboard. There is often a component which blocks thearea where the 4 pins would hang off the end. And sometimes the plastic end of the 4

pin connector is too thick to fit between the pins of the 8 pin cable.

Make sure that you don't try to plug an 8 pin 12 volt cableinto the 8 Pin PCI Expresspower connectoron a video card. The two cables look very similar so it's easy to get

the two confused. 8 Pin PCI Express power cablesare usually labeled to distinguishthem from 8 pin 12 volt cables. The PCI Express cable usually has "PCI-E" printed on

the connector. If there are no labels then you can usually use wire colors to tell thetwo kinds of cables apart. An 8 pin 12 volt cablehas yellow wires on the same side as

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the connector clip. An 8 Pin PCI Express cablehas black wires on the clip side. Thetwo power cables are also keyed differently so you can't plug one kind of power cable

into the other kind of connector. But as with this kind of connector, you can sometimesforce the wrong kind of cable into a connector if you push hard enough. Make sure you

have the right kind of cable before plugging it in. The two are definitely notcompatible with each other.

Pinout


DescriptionWire

color

Pin

number

Pin

number

Wire

colorDescription

ground black 1 5 yellow +12 volts (12V1)

ground black 2 6 yellow +12 volts (12V1)

ground black 3 7 yellow+12 volts (12V1 or

12V2)

ground black 4 8 yellow+12 volts (12V1 or

12V2)


Motherboard

connector

Cable

connectorTerminals

Maximum current per

circuit


39-01-2080

Molex39-00-0168,

Molex44476-1111

7 amps




If you don't have an 8 pin 12 volt cable then you can use the adapter shown above. Itconverts a couple of 4 pin peripheral power cablesinto an 8 pin 12 volt cable. If you

use one of these adapters then be sure to plug the 4 pin peripheral connectors intoseparate cables coming from the power supply. If you plug them both into the same

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power supply cable then you are drawing all the power of the 8 pin 12 volt connectorthrough a single 18 gauge wire. You can often get away with that but there's no

reason to do it.

4+4 pin +12 volt power cable

Motherboards can come with either a 4 pin 12 volt connectoror an 8 pin 12 voltconnector. Many power supplies come with a 4+4 pin 12 volt cable which is

compatible with both 4 and 8 pin motherboards. A 4+4 power cable has two separate4 pin pieces. If you plug the two pieces of a 4+4 power cable together then you have a

8 pin power cable which can be plugged into an 8 pin 12 volt connector. If you leavethe two pieces separate then you can plug one of the 4 pin pieces into a 4 pin 12 volt

connectorand leave the other 4 pin piece unplugged.

If you look carefully at the image above then you can see the polarization of the pinswhich prevents you from plugging the cable in improperly. Some of the pins are

square and some of them have rounded off corners. The motherboard connectors havematching square and rounded off corners to prevent the cable from being plugged in

the wrong way. But if you look reallycarefully at the right half of this particular cableand then look at the 8 pin 12 volt cablepictured above you'll notice that they don't

match. A regular 8 pin cable has four square pins and four rounded ones but the 4+4cable shown above has two square pins and 6 rounded ones. The left half of the 4+4matches the left half of an 8 pin cable but the right half is different. Hmmmm... And

this isn't some bizarre cable either. I've seen plenty of 4+4s which look like this one.And then there are other 4+4 cables which look just like an 8 pin cable split in two

(which makes sense). Since rounded pins fit into square holes in motherboardconnectors, this particular cable will fit just fine into an 8 pin 12 volt motherboard

connector. But both halves of this 4+4 will fit into a 4 pin 12 volt motherboardconnector. You're supposed to use the left half of the cable shown above when

plugging it into a 4 pin motherboard connector but the right half will also fit. As ithappens, either half will work fine in a 4 pin motherboard because both halves of the

4+4 just provide 12 volts. The pinouts are the same for both halves so either one willwork. I'm not sure why they make cables like this one because you'd figure a 4+4cable would just be an 8 pin cable which splits in two. And you only need one half of a

4+4 cable to plug into a 4 pin motherboard. The other half is unused. But the kind of4+4 cable shown above is pretty common so don't let it throw you.

6 pin PCI Express power cable

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This cable is used to provide extra 12 volt power to PCI Express expansion cards. PCIExpress motherboard slots can provide a maximum of 75 watts. Many video cards

draw significantly more than 75 watts so the 6 pin PCI Express power cable wascreated. These high-power cards draw most of their power from the 12 volt rail so this

cable provides only 12 volts. These are sometimes called "PCI Express cables". Theyare also occasionally called "PEG cables" where "PEG" stands for PCI ExpressGraphics. If your power supply doesn't have a 6 pin PCI Express cable then you can

use the adapter shown above on the right to convert two 4 pin peripheral cablesinto aPCI Express cable. If you use an adapter then be sure to plug the 4 pin peripheral

connectors into separate cables coming from the power supply. If you plug them bothinto the same power supply cable then you are drawing all the power of the PCI

Express connector through a single 18 gauge wire. You can usually get away with thatbut there's no reason to do it. The PCI Express 6 pin connector is polarized so it can

only be plugged in pointing in the correct direction. But as with connectors of thistype, you can sometimes force them into the wrong kind of socket if you try hard

enough. If it doesn't slide in easily then you're probably plugging it into the wrongplace.

Some video cards come with the 8 pin PCI Express power connectorto support higher

wattage than the 6 pin PCI Express connectors. It's okay to plug a 6 pin PCI Expresspower cable into an 8 pin PCI Express connector. It's designed to work that way butwill be limited to the lower wattage provided by the 6 pin version of the cable. The 6

pin cable only fits into one end of the 8 pin connector so you can't insert it incorrectlybut you can sometimes force the 6 pin cable in the wrong way if you try hard enough.

Video cards can sense whether you have plugged a 6 pin or 8 pin cable into an 8 pinconnector so the video card can impose some kind of restriction when running with

only a 6 pin power cable. Some cards will refuse to run with only a 6 pin cable in an 8pin socket. Others will work with a 6 pin cable at normal speeds but will not allow

overclocking. Check the video card documentation to get the rules. But if you don'thave any other information then just assume that if your video card has an 8 pin

connector then you must plug in an 8 pin cable.

Pinout


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Description Wire color Pin

number

Pin

number

Wire

colorDescription

+12 volts yellow 1 4 black ground

+12 volts or not

connected

yellow or not

connected2 5 black ground

+12 volts yellow 3 6 black groundConnector part numbers

Video card

connector

Cable

connectorTerminals

Maximum current per

circuit

Molex 45558-0002Molex

45559-0002

Molex39-00-0168,

Molex44476-1111

8 amps



+12 volts 3 2.083 amps 75 watts

The PCI Express specification is, unfortunately, not a free, public specification. So

most people have never seen it. Including me. ATX specification: freely available to all.PCI Express specification: expensive so hardly anyone has seen it. ATX: good. PCIExpress: bad. It's a shame when a widely used standard isn't freely available to the

public. Nonetheless, information leaks out from the specification and the 6 pin PCIExpress power cable is actually rated at an extremely conservative 75 watts. I have no

idea why the wattage is rated so low because the specifications from Molex clearlyallow substantially more power. Part of the reason may be that pin 2 (listed above as a

12 volt line) may be listed as not connected in the specification. I've never seen a 6

pin PCI Express power cable with pin 2 not connected. They've all had a 12 volt lineconnected to pin 2. I've also seen claims that there may be unimplemented sense linesin the specification. Welcome to the uncertainty which happens when you don't have

freely available specifications. Even with only two 12 volt lines the standardimplementation of PCI Express power cables use large enough gauge wire and a good

enough connector to provide much more than the three amps per wire required toprovide 75 watts. Nonetheless, the 6 pin PCI Express power cable officially providesonly 75 watts. In all likelihood, however, real implementations of this power cable can

provide far more than 75 watts.

8 pin PCI Express power cable

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The PCI Express 2.0 specification released in January 2007 added an 8 pin PCI

Express power cable. It's just an 8 pin version of the 6 Pin PCI Express power cable.Both are primarily used to provide supplemental power to video cards. The older 6 pin

version officially provides a maximum of 75 watts (although unofficially it can usuallyprovide much more) whereas the new 8 pin version provides a maximum of 150 watts.

It is very easy to confuse the 8 pin version with the very similar-looking EPS 8 pin 12volt cable.

The 8 pin PCI Express and the EPS 8 pin 12 voltconnectors are polarized differently

so you won't be able to plug one kind of cable into the other kind of connector. That is,

you won't be able to plug the wrong kind of cable in unless you try really hard.Unfortunately, the Molex Mini-fit Jr. connectors used by both kinds of power cablescan sometimes be forced into a differently-polarized connector if they only have a few

pins and you push hard enough. If the cable won't slide in easily then you're probablytrying to insert the wrong kind of cable. The 8 pin PCI Express connector does have asmall plastic bridge which prevents it from being plugged into an EPS 8 pin 12 volt

motherboard connector. You can see the bridge in the image above between therightmost two pins in the top row of the connector. But there's no such protection to

prevent EPS 8 pin 12 volt cablesfrom being plugged into an 8 pin PCI Expressconnector on a video card. That combination may fit if you shove hard enough. And if

you plug in the wrong kind of cable then expect fireworks. Some of the grounds and12 volts wires for an EPS 8 pin 12 voltare reversed compared to an 8 pin PCI Express.

Fortunately, most 8 pin PCI Express connectors are labeled "PCI-E" so people won'tconfuse them with EPS 8 pin 12 voltcables. If the connectors aren't labeled then you

can tell an 8 pin PCI Express power cable from an EPS 8 pin 12 volt cable by checkingthe color of the wires which plug into the clip side of the connector. On the EPS 8 pin

cable, the yellow wires (the 12 volt wires) go into the clip side of the connector. Onthe 8 pin PCI Express cable, the wires on the clip side are all black (grounds). That'sthe same as it is with the 6 Pin PCI Express power cable. Of course, none of this helps

you if your cable uses the trendy all-the-same-color-wires design which is popular withhigh-fashion power supplies. In that case you'll just have to be very careful or hope the

connectors are labeled.

Pinout


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Video card

connector

Cable

connectorTerminals

Maximum current per

circuit

? ? ? ?



+12 volts 3 4.167 150 watts

6+2 pin PCI Express power cable

Some video cards have 6 Pin PCI Express power connectorsand others have 8 Pin PCIExpress power connectors. Many power supplies come with a 6+2 PCI Express power

cable which is compatible with both kinds of video cards. The 6+2 PCI Express powercable is made up of two pieces: a 6 pin piece, and a 2 pin piece. If you put the two

pieces together then you have a full 8 pin PCI Express power cable. But if you split theconnector into two parts then you can plug the 6 pin part into the older 6 pin PCIExpress connector and leave the 2 pin part unplugged. That way, your power supply

only needs to have one 6+2 cable to be compatible with both 6 pin and 8 pin PCIExpress connectors.

Video card information

How to select a video card

How to install a video card

How to troubleshoot video card problems

The big fat table of video cards

AGP compatibility for sticklers

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DVI compatibility for sticklers

Troubleshooting AGPTroubleshoot your video card by underclocking

Diagnose your video card problems by comparing with example corrupted screensTroubleshooting DVI problems

The basics of 3D graphics without making your eyes glaze over - just enough to getyou started

How to uninstall your current display driversHow to install display drivers for your video cardUnderstanding video RAM memory bandwidth

What kind of expansion slot should you use for your video card?VGA video card outputs

Useful technical information

How to install your motherboard chipset driversTest your motherboard memory with Memtest86

Torture test your CPU with Prime95How to find specifications for your computer

Create a system restore point in case something goes wrongGetting administrator privilegesFiddling with your BIOS

How to boot into safe mode or VGA modeRate your CPU speed at games

Glossary of technical terms

Random stuff

My favorite RollerCoaster Tycoon 3 coasters

PeepFactory peep generator for RollerCoaster Tycoon 3The view from my old backyard

Copyright 2005 - 2008 by Mark Allen

power connectors

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