All About the Various PC Power Supply Cables and Connectors

All abou aboutt the var vario iou us PC PC pow power er supp supply ly cabl cables es and and con conn nect ectors

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Power supply information Compatibility issues for ATX power supplies and motherboards A short history of PC power supply voltage rails So what's all this rubbish about multiple 12 volt rails? All about the various va rious PC power supply cables and connectors Rail complications #1 - current limit problems: too much current Rail complications #2 - cross loading problems: unbalanced current Rail 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 powe p ower r supply cables and connectors The various power supply cables

Original PC main power cables

4 pin peripheral power cable

Floppy d


6 pin auxiliary power cable

20 pin ATX main power cable

4 pin ATX +12 volt power cable

6 pin PCI Express power cable


SATA power cable

24 pin ATX main power cable

8 pin EPS +12 volt power cable

8 pin P CI Express power cable

20+4 pin A

4+4 pin +12 vol

6+2 pin P CI Expre

General info If you'd like like more technical tec hnical data about ATX ATX power connectors then you can ca n find the current specifications and more at formfactors.org Wires and connectors are not perfect conductors. They have resistance. When current passes through wires and



connectors there is a voltage drop and that energy ene rgy is is lost as heat. As long as you don't don't overload them the voltage drop and extra heat don't matter. But the losses losses get worse as the current curre nt rises. That's why you see some some power cables with more that one wire for the same voltage. Having multipl multiplee wires reduce s the losses. losses. If you seriously seriously overload a line, the wire can get fairl fa irly y warm. The resistance of connectors t ends to increase as the y are plugged plugged and unplugged unplugged so after enough uses they can overheat and a nd even melt when passing a large current. So a lot of changes in connectors over time has to do with adding more more wires and connectors to make sure that none of these problems occur. Some Some of the t he tables below provide the maximum maximum wattage supported by a power cable and a nd its associated power connector. Some specifications clearly spell out the maximum allowed wattage. Other specifications just provide the suggested connector and wire gauge gauge and never specify a maximum maximum wattage. And there's never neve r reall rea lly y an absolute value to the maximum maximum wattage anyway. If you draw a little little more wattage watta ge then the maximum, maximum, the hardware doesn't immediately immediately burst into flames. The voltage drop and power dissipation dissipation increase as you increase the curre nt so there isn't isn't a clear maximum wattage wattage at which it stops working. working. Most of the specifications which spell out the maximum wattage provide a wide safety margin by defining a value which is far below the maximums maximums supported supported by the connector a nd wire. If the table be below low provides provides an "Official cable/connector maximum maximum wattage" then that specification has spelled out the maximum maximum wattage. In most cases that tha t wattage watta ge will will be significantly significantly below below what can actually a ctually be handled by the suggested suggested connector connec tor and wire. If the table provides an "Unofficial "Unofficial cable/connector maximum maximum wattage" then that specifi spec ification cation doesn't provide the maximum maximum and the value in the table t able is a practical prac tical maximum maximum wattage defined by the maximums maximums for the connector connec tor and the suggested suggested wire. An unofficial unofficial wattage doesn't have a wide safety margin margin built built in because beca use people differ on how much margin margin to provide. Some Some people happily use connector connect or and wire maximums maximums and other people like to have a wide safety margin. Power connectors included with various kinds of PCs Version

Introduction date

Included connectors

PC

1981

original PC main power cables original 4 pin peripheral cable

1995

20 pin main power cable ca ble 4 pin peripheral cable floppy cable

2000

20 pin main power cable ca ble 4 pin 12 volt cable 6 pin auxiliary cable 4 pin peripheral cable floppy cable

2003

20 pin main power cable ca ble 4 pin 12 volt cable 6 pin auxiliary cable SATA cable 4 pin peripheral cable floppy cable

2003

24 pin main power cable ca ble 4 pin 12 volt cable 6 Pin PCI Express power cable SATA cable 4 pin peripheral cable floppy cable

ATX

ATX12V 1.0

ATX12V 1.3

ATX12V 2.0

EPS12V

2003

24 pin main power cable ca ble 8 pin 12 volt cable 6 Pin PCI Express power cable SATA cable



4 pin peripheral cable floppy cable

P CI Express 2.0

24 pin main power cable ca ble 4 pin 12 volt cable 8 pin 12 volt cable 6 Pin PCI Express power cable 8 Pin PCI Express power cable SATA cable 4 pin peripheral cable floppy cable

2007

Original PC main power power cables

The original original PC debuted in 1981 and used two t wo cables to connect the PSU (power supply) supply) to the motherboard. The two cables plug side by side into the motherboard connec tors. Sometimes Sometimes they are keyed so they the y only plug in one way and sometimes they aren't. Even if they're ke yed you can insert them the wrong way if you put a little little effort into it. You 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 co color

Description

1

orange

power good

2

re d

+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



4

re d

+5 volts

5

re d

+5 volts

6

re d

+5 volts

Connector part numbers Moth Mother erb board oard con connecto ectorr Cable able con connecto ectorr Molex 15-48-0106

Molex 90331

Term ermina inals

Maxim aximu um curr curren entt per per cir circuit cuit

Molex 08-50-0276

5 amps

Unofficial cable/connector maximum wattage delivery for main rails Voltage rail Numb Number er of lines Maximum Maximum current current Maximum Maximum wattage wattage +5 volts

3 or 4

15 or 20 amps

75 or 100 watts

+12 volts

1

5 amps

60 watts

In old PCs, alm a lmost ost all of the c hips ran directly off of the 5 volt rail. As a result the PSU delivers delivers most most of its wattage at 5 volts. There are three or four lines dedicated to the 5 volt rail. The The other main rail is 12 volts. volts. That was used primarily to run disk drives, motors, and fans. The two negative rails are "bias" supplies which only have to provide small small amounts of current. Just for interest's sake, here's the specification for the P SU which came with the original original IBM PC. It provides a maximum maximum of 63.5 watts. Boy, those were the days. Original IBM PC power supply Voltage oltage Maxim Maximum um curre current nt Maxim Maximum um watta wattage ge

4 pin peripheral power cable

+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



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 of things 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. The connector 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 te rm "4 pin Molex Molex power cable" ca ble" or "4 pin Molex" to refer to a four pin peripheral power cable. It's not a technically useful term because the 4 pin 12 volt cable is also a 4 pin Molex cable (Molex makes connect ors) but "4 pin Molex" is commonly commonly used to refer to t o peripheral cables anyway. lots of connectors) Pinout Pin num number ber Wire color color Descr Descrip iption tion 1

yellow

+12 volts

2

black

ground

3

black

ground

4

red

+5 volts

Connector part numbers Socket housing

Socket

Pin housing

Pin

Maximum current per circuit

AMP 1-480424-0 AMP 60619-1 AMP 1-480426-0 AMP 60620-1

13 amps

I don't know of any a ny official definition definition of the maximum maximum current allowed in a peripheral ca ble. The connector can handle 13 amps according to the manufacturer. But you normally find 18 awg wire wire in the peripheral cables. If you have an 18 inch cable (about a half a meter) and a re running 13 amps through 18 gauge gauge wire then you get a voltage drop of about 0.25 volts counting both the power wire and the ground (it's (it's got to go both ways) and the dissipation dissipation is about 3.3 watts. That's not good. I've just played it safe and listed the maximum current as 5 amps. Unofficial cable/connector maximum wattage delivery Voltage oltage rail Number Number of lines Maximum Maximum current current Maximum Maximum wattage wattage +5 volts

1

5 amps

25 watts

+12 volts

1

5 amps

60 watts

Current power supplies usually usually have at least two t wo separate peripheral pe ripheral 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 bet ween all of your cables. c ables. Don't just plug all your devices into one cable unless they're relatively low load devices. Spreading the current between the cables reduces the voltage drops and power loss. loss. If they're relatively low current devices like fans or it's just a disk drive or two the n it doesn't reall rea lly y 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) or connecting a video card's auxiliary auxiliary power, then spread the loads between the pe ripheral power cables. It's also helpful if you use a c onnector as a s close to the PSU as possible possible rather than sticking things things at the t he end of the t he cable. ca ble. Extra wire just means more voltage drop. And if you're using a peripheral connector to PCI Express adapter then be sure to plug each of the adapter's peripheral connectors into a separate PSU cable. They gave you two peripheral connectors connec tors for a reason. Plugging Plugging them both into the same P SU cable forces force s your video card to t o draw its 12 volt power through t hrough one 18 gauge wire. wire. That increases your voltage drop and power dissipation dissipation in the cable. Some current high-end high-end video cards can suck up more than 10 amps at 12 volts with most of it coming through through the PCI Express E xpress connector so it pays to be careful. It will will probably work if you don't spread the load but there's no excuse for not doing it properly. They gave you multiple cables. You might as well use them. Plus there 's just something something creepy a bout having warm wires even if the y're not melting. 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 Some of the two-wire peripheral connectors are for speed-controlled fans. That means that the voltage changes depending on the desired fan speed. The connec tor will only only provide 12 volts when the fan is going going full full



speed and the voltage decreases to slow the fan down. Definitely don't plug plug that one into anything but a fan! Normally Normally this kind kind of peripheral per ipheral connector has "fan" printed on it to warn you. As long as a peripheral connector has four wires: one yellow, yellow, two black, a nd one red and it doesn't have some kind of printed warning attached then it's a standard standa rd peripheral cable a nd you can ca n plug it it into anything. Floppy drive power cable

The four pin floppy drive cable showed up when PCs started including 3.5 inch floppy drives. This kind of cable is also sometimes sometimes used as an a uxiliary uxiliary power cable for AGP video cards which use more power tha n 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 about inserting it the wrong way. Floppy cables are built with small connectors and 20 awg wire so they are limited limited to relatively low current uses. Pinout Pin num number ber Wire color color Descr Descrip iption tion 1

red

+5 volts

2

black

ground

3

black

ground

4

yellow

+12 volts

Connector part numbers Socket housing

Socket

Maximum current per circuit

AMP 171822-4 AMP 170262-1

3 amps

Unofficial cable/connector maximum wattage delivery Voltage oltage rail Number Number of lines Maximum Maximum current current Maximum Maximum wattage wattage +5 volts

1

3 amps

15 watts

+12 volts

1

3 amps

36 watts

6 pin auxiliary power cable



The aux power cable was added adde d to provide extra wattage to motherboards for 3.3 and 5 volts. This This connector is rarely used anymore. It's most commonly found on older dual CPU AMD motherboards. You're more likely to sight Bigfoot than a motherboard which uses this connector. It plugs into into the 6 pin version of the motherboard connector used by the original PC main power cables. cables . Pinout Pin num number ber Wire color color Descr Descrip iption tion 1

black

ground

2

black

ground

3

black

ground

4

orange

+3.3 volts

5

orange

+3.3 volts

6

red

+5 volts

Connector part numbers Motherbo rboard co connecto ctor Cable con connector Molex 15-48-0106

Termin rmina als

Maximu imum current pe per cir circu cuiit

Molex 90331-0010 Molex 08-50-0276

5 amps

Unofficial cable/connector maximum wattage delivery Voltage oltage rail Number Number of lines Maximum Maximum current current Maximum Maximum wattage wattage

SATA power cable

+3.3 volts

2

10 amps

33 watts

+5 volts

1

5 amps

25 watts



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 power cable replaces the old 4 pin peripheral cable and adds support for 3.3 volts (if fully implemented). implemented). The connector is shaped so it can only be plugged plugged in the correct correc t way. Pinout Pin num number Wire num number Wire colo colorr Descrip Descriptio tion n 1

5

orange

+3.3 volts

2

5

orange

+3.3 volts

3

5

orange

+3.3 volts

4

4

black

ground

5

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

14

1

yellow

+12 volts

15

1

yellow

+12 volts

Connector part numbers Cable connector

Terminals

Molex 67582-0000 Molex 67581-0000

Maximum current per circuit 1.5 amps

Official cable/connector maximum wattage delivery Voltage oltage rail Number Number of lines Maximum Maximum current current Maximum Maximum wattage wattage



+3.3 volts

3

4.5 amps

14.85 watts

+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 3.3 volt wire. People with older power supplies supplies often use adapters a dapters which convert from 4 pin peripheral cables to SATA power cables. But since 4 pin peripheral connectors only 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 power cables which are missing the 3.3 volt wire. Currently, Currently, SAT SATA drives rarely use 3.3 volts. That may be because there are a re too many people using adapters so the drive makers don't want the headaches headache s which come with using using 3.3 volts. But in the future, fut ure, 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



In 1996 PC makers started switching to the ATX ATX standard which defined a new ne w 20 pin motherboard power connector. It includes a 3.3 volt rail which which is used to power newer chips which require a lower voltage voltage than tha n 5 volts. It also has a standby 5 volt rail which is always on even when the power supply is turned off to provide standby power to the motherboard when the machine is sleeping. sleeping. The new connector c onnector also a lso allows allows the motherboard to turn the power supply on and off rather than de pend on the user to flip a power switch. This This connector is polarized polarized so it can c an only be plugged plugged in pointing in in the correct direction. Pinout Pins 1 through 10

Pins 11 through 20

Descr escrip ipti tion on Wire ire colo colorr Pin Pin number Pin Pin number ber Wire ire colo colorr

Descr escrip ipti tion on

+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

re d

4

14

green

P S_ON#

ground

black

5

15

black

ground

+5 volts

re d

6

16

black

ground

ground

black

7

17

black

ground

PWR_OK

gray

8

18

white

-5 volts (optional)

VSB +5 volts

purple

9

19

re d

+5 volts

+12 volts

yellow

10

20

re d

+5 volts

Some Some of the t he voltage lines on the connector connec tor may have smaller smaller sense wires which allow the power supply to sense what voltage is actually seen by the motherboard. These are pre tty common on the 3.3 volt line in pin pin 11 but are sometimes used for other voltages too. The -5 volt line on pin 18 was made optional in ATX12V 1.3 (introduced in 2003) because -5 had been rarely rare ly used for years. Newer motherboards virtually never require -5 volts but many older motherboards do. Most newer power supplies supplies don't provide -5 volts in which case the white wire is missing.



Connector part numbers Motherboard con connecto ctor Cable connector Mol Molex 39-28 9-28-1 -120 203 3

Molex olex 39-0 39-011-22 2200 00

Terminals

Maximu imum current pe per ci circuit

Molex 39-00-0168, Molex 44476-1111

6 amps

Unofficial cable/connector maximum wattage delivery for main rails Voltage rail Numb Number er of lines Maximum Maximum current current Maximum Maximum wattage wattage +3.3 volts

3

18 amps

59 watts

+5 volts

4

24 amps

120 watts

+12 volts

1

6 amps

72 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 them rather from a third party. That's nasty enough but Dell built built their non-standard computers and motherboards with what looked like standard ATX components. You only found out otherwise once sparks started flying. The Dell PCs which which were carrying this ticking ticking time-bomb time-bomb were made be tween 1996 and a nd 2000. If you're replacing a Dell power supply from this this era then t hen you should call Dell and make sure it's not a proprietary design. design. And if they say yes then be sure to t o voice your displeasure. This is is an evil e vil business business practice which should stop.

You can plug a 20 pin ATX power cable into a motherboard with a 24 pin ATX connector. connector. The image above shows the 20 pin power cable ca ble plugged plugged into a 24 pin motherboard. A 20 pin power cable only fits into into one e nd of a 24 pin motherboard connector so you can't insert it incorrectly. incorrectly. The 24 pin motherboard connector is actually just the 20 pin connector with 4 extra pins added on the end. The original original 20 pins were unchanged. The extra 4 pins are not separate rails. They're They're just extra lines to provide more current to the same rails. rails. On every 24 pin motherboard I've seen, the extra lines for ground, 3.3, 5, and 12 are just connected to t he other lines on the same rail from the 20 pin connector. I've never heard of exceptions and it doesn't make sense for motherboard makers to create cre ate any a ny.. As a re sult, you can plug a 20 pin cable ca ble into a 24 pin motherboard and a nd it will work work just fine. At least, it will will for a while. They added those extra 4 pins for a reason. When you plug a 20 pin cable into a 24 pin



connector you're not providing the extra current carrying capacity which may be needed by the motherboard. If your motherboard's current requirements re quirements are low enough then it will work work properly with only a 20 pin power cabled plugged plugged in. But if the motherboard draws enough current, then you can overheat the t he 20 pins you're using using on the 24 pin connector. I've seen enough pictures of burned ATX ATX main connectors to assure you that this happens. In adding a dding the extra four pins, 3.3 volts went from 3 to 4 lines. lines. 5 volts when from 4 to t o 5 lines. 12 volts went from 1 to 2 lines so its capacity doubled. Connectors really do get hot if you overload them so the safest thing to do is use a rea reall 24 pin power supply on a motherboard with a 24 pin connector. Note that tha t your 24 pin machine may work fine with with a 20 pin power supply until you you add a PCI Express card ca rd later on down the road. roa d. PCI Express cards can draw up to 75 watts through the motherboard connector so adding an expansion card can substantially substantially increase power draw through the main power cable. Many P CI Express video cards which have the 6 pin or 8 pin PCI Express power cable still draw a substantial portion of their 12 volt load through the PCI Express slot. The extra 4 pins doubled the current c apacity of the 12 volt rail so that one is easy to overload when only using a 20 pin main power cable.

The picture above shows an adapter which allows allows you to plug a 20 pin power supply into 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 tha t you would have if you plugged plugged it directly into the motherboard. But with the adapter adapte r 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 t he 20 pin connector on the adapter. adapte r. About the only good good thing it it does is to make sure the 20 pin connector on the adapter melts rather than the 24 pin connector on the motherboard. You You shouldn't underestimate underestimate the potential pote ntial problems which which come from adding another connector connec tor between the power supply and the motherboard. The resistance of connec tors can increase due to being plugg plugged ed and unplugged. unplugged. Incre asing the resistance resistance makes the connec tor drop more voltage and dissipate more heat. Any number of physical changes can also cause higher connector connect or resistance which causes more problems. You You shouldn't shouldn't put an a n extra connector in a high high current path unless you've got a good reason. That's a good rule rule for power cables in general but it goes doubly for the high current draws you sometimes find through through motherboard main power cables. The best practice is to avoid these 20 to 24 pin adapters and get a real 24 pin power supply. supply. ATX 24 pin main power cable



The 24 pin main power connector was added in ATX12V ATX12V 2.0 to provide ext ra power needed ne eded by P CI Express slots. The older 20 pin main power cable only has one 12 volt line. The new 24 pin connector added adde d one line apiece for ground, 3.3, 5, and 12 volts. The extra pins made the auxili auxiliary ary power cable unnecessary so most ATX12V 2.x power supplies don't have them. The 24 pin connector is polarized so it can only be plugged in pointing in the correc t direction. Pinout Pins 1 through 12

Pins 13 through 24

Descr escrip ipti tion on Wire ire colo colorr Pin Pin number Pin Pin number ber Wire ire colo colorr

Descr escrip ipti tion on

+3.3 volts

orange

1

13

orange

+3.3 volts

+3.3 volts

orange

2

14

blue

-12 volts

ground

black

3

15

black

ground

+5 volts

re d

4

16

green

P S_ON#

ground

black

5

17

black

ground

+5 volts

re d

6

18

black

ground

ground

black

7

19

black

ground

PWR_OK

gray

8

20

white

-5 volts (optional)

VSB +5 volts

purple

9

21

re d

+5 volts

+12 volts

yellow

10

22

re d

+5 volts

+12 volts

yellow

11

23

re d

+5 volts

+3.3 volts

orange

12

24

black

ground

Some Some of the t he voltage lines on the connector connec tor may have smaller smaller sense wires which allow the power supply to sense what voltage is actually seen by the motherboard. These are pre tty common on the 3.3 volt line in pin 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 rare ly used for years. Newer motherboards virtually never require -5 volts but many older motherboards do. Most newer power supplies supplies don't provide -5 volts in which case the white wire is



missing. Connector part numbers Motherboard con connecto ctor Cable connector Mol Molex 39-28 9-28-1 -124 243 3

Molex olex 39-0 39-011-22 2240 40

Terminals


Molex 39-00-0168, Molex 44476-1111

6 amps

Unofficial cable/connector maximum wattage delivery for main rails Voltage rail Numb Number er of lines Maximum Maximum current current Maximum Maximum wattage wattage +3.3 volts

4

24 amps

79.2 watts

+5 volts

5

30 amps

150 watts

+12 volts

2

12 amps

144 watts

If you have an ATX power supply with a 24 pin main cable, it's okay to plug it into a motherboard with a 20 pin connector. It was designed to work that way. You You can see an example in the picture above. The extra 4 pins on the cable ca ble just hang over over the e nd of the motherboard connector. c onnector. The 24 pin cable only fits fits into a 20 pin socket at one end so you ca n't plug it it in incorrectly. 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's okay to leave those 4 pins disconnected because a motherboard with a 20 pin connector doesn't need them. the m. The only problem you can bump into (literally) (literally) is if there is something something blocking 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 the pins of the 24 pin cable. You 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 you can't get them to fit together the n you can get an a n adapter cable which will will make it work. The 24 pin cable plugs plugs into one end of the adapter and a nd then the adapter plugs plugs into the 20 pin motherboard. But you should avoid using that kind of adapte r if you can because bec ause the extra e xtra wire and connec tor are just more more things which 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 motherboard before resorting to an adapte r. ATX 20+4 pin main power cable c able



Motherboards can come c ome with either a 20 pin main power connector or a 24 pin main power connector. connector. Many power supplies supplies come with a 20+4 cable which is compatible with 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 20 pin piece into a 20 pin motherboard motherboard and leave the 4 pin piece unplugged. unplugged. Be sure to leave the 4 pin piece unplugged unplugged even if it fits into another connector. connec tor. The 4 pin piece is not compatible with any other connectors. If you plug the two pieces of a 20+4 power cable together then t hen you have a 24 pin power cable which can be plugged plugged into a 24 pin motherboard. 4 pin ATX +12 volt power cable



Older computers put most of their load on 3.3 and 5 volts. As time passed, computers drew more a nd more of their load from 12 volts (see here here). ). Before this power cable was introduced there was just one 12 volt line provided to the motherboard. This cable added two more 12 volt lines lines so more of the load could be shifted to 12 volts. The power 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 a motherboard means it's an ATX12V motherboard. For dual 12 volt rail power supplies, supplies, this connector provides the voltage refered to as 12V2. The power cable ca ble which plugs into the 4 pin connector has two black wires and two yellow wires. This cable is sometimes called an "ATX12V "ATX12V"" cable ca ble or "P4" "P 4" cable a lthough lthough neither of those are technically accurate descriptions. descriptions. If you have one of these connectors connec tors on a motherboard then the n you must plug a power cable ca ble into it or your CPU won't get any power. The one exception exc eption is that when this connector connec tor was new, some motherboards shipped shipped with a socket into which you could plug a 4 pin peripheral power cable as an alternative. alternat ive. That helped people who had older power supplies supplies which didn't have the 4 pin 12 volt cable. The 4 pin 12 volt ca ble is polarized polarized so it can only be plugged 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. The motherboard 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 force f orce it into the connector. With enough force you c an sometimes sometimes get a cable with a small small number of pins into a connector which doesn't match. If you look carefully you can also see that the square and a nd rounded pattern matches various positions positions on other motherboard connectors like the 20 pin main power connector and 24 pin main power connector. connector. 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 fried components). c omponents).



If your power supply doesn't have a 4 pin 12 V cable then you ca n provide one with the adapter shown above. It converts a 4 pin peripheral cable into a 4 pin 12 V cable. Pinout Pins 1, 2

Pins 3, 4

Desc Descrip riptio tion n Wire ire color color Pin num numbe berr Pin num numbe berr Wire ire color color Desc Descrip riptio tion n ground

black

1

3

yellow

+12 volts

ground

black

2

4

yellow

+12 volts


Molex olex 39-0 39-011-20 2040 40

Terminals


Molex 39-00-0168, Molex 44476-1111

8 amps


2

16 amps

192 watts



You can c an plug a 4 pin 12 volt power cable ca ble into an 8 pin EPS motherboard connector but there's no guarantee that it will will work. If the motherboard expects expect s only one 12 volt rail then a 4 pin 12 volt cable may work. If the motherboard expects t wo 12 volt rails (many dual CPU motherboards require one 12 volt ra il per CPU) then it won't work. Even if the motherboard works with a 4 pin 12 volt cable, cable , you are still only providing half of the current carrying c arrying capacity which would would be provided by an 8 pin EPS EP S cable. That can overhea t both the motherboard connector and a nd 4 pin cable. Scorched or melted connectors ca n be a result. A motherboard motherboard which has the 8 pin EPS connector expects a lot of current and you are taking a serious risk risk by plugging plugging in in a 4 pin cable. The 4 pin cable only fits at one e nd of the 8 pin EP S motherboard motherboard connector connec tor so you can't plug it in improperly improperly.. That is, it only fits into one end of the motherboard connector c onnector unless you force it. If the cable doesn't go into the socket easily then you're probably trying to plug it 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



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 a nd the 8 pin 12 volt cable is often used instead of a 4 pin 12 volt cable. cable . Depending on the power supply, supply, the connector may c ontain one 12 volt ra il in in all 8 pins or two 12 volt rails taking taking up 4 pins apiece. apiece. It is often refered refere d to as an "EPS12V" "EPS12V" cable. The 8 pin 12 volt ca ble is polarized polarized so it can only be plugged plugged into the 8 pin motherboard connector correctly. If you look carefully at the picture above you can see 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 the power cable only fits in one way. At least that's true unless you try really hard to force f orce it into the connector. With enough force you c an sometimes sometimes get a cable with a small small number of pins into a connector which doesn't match. The 8 pin cable ha s enough pins that it's pretty hard to insert it in the wrong direction direction but determined det ermined people might might be able to do it. If you look carefully you can also see that the square and rounded pattern matches various positions positions on other motherboard connectors conne ctors like the 20 pin main power connector and 24 pin main power connector.. You connector You should only plug the 8 pin 12 volt cable into the t he motherboard connector where it belongs belongs unless you enjoy the smell of fried electronics. You can also plug an 8 pin 12 volt cable into a 4 pin 12 volt motherboard connector. connector. I don't have a picture of this one but it looks similar to this this.. Four of the pins on the 8 pin ca ble fit into the motherboard connector a nd 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 try hard to force it into the t he wrong position. 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 the area where the 4 pins would would hang off the end. And sometimes sometimes the plastic end of the 4 pin connector is too thick to fit betwee n the pins of the 8 pin cable. ca ble. Make sure that you don't try to plug an 8 pin 12 volt cable into the 8 Pin PCI Express power connector on a video card. The two cables look very similar similar so it's easy to get t he two confused. c onfused. 8 Pin PCI Express power cables are usually labeled to distinguish them from 8 pin 12 volt cables. cables . The PCI Express cable usually has "PCI-E" printed on the connec tor. If there are no labels then you can usually use wire wire colors to tell the two kinds of cables apart. An 8 pin 12 volt cable has yellow wires wires on the same side as the connector c onnector clip c lip.. An 8 Pin PCI Express cable has black wires on the clip side. side. The two power cables are also keyed differently so you can't plug one kind of power cable into the other ot her kind of connector. But as with this kind of connector, you can sometimes sometimes force the wrong kind kind of cable into a c onnector if you push hard enough. Make sure you have the right kind of cable before bef ore plugging plugging it it in. The two are definitely not compatible with each other.



Pinout Pins 1 through 4

Pins 5 through 8

Descrip cripttion ion Wire ire color lor Pin Pin number Pin number Wire ire color lor

Descript iption ion

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)


Molex olex 39-0 39-011-20 2080 80

Terminals


Molex 39-00-0168, Molex 44476-1111

7 amps


4

28 amps

336 watts

If you don't have an 8 pin 12 volt cable then you can use the adapter shown above. It converts a couple of 4 pin peripheral power cables into an 8 pin 12 volt cable. If you use one of these adapters ada pters then be sure to plug the 4 pin peripheral connectors into separate separat e cables ca bles coming coming from the power supply. supply. If you plug them both into the same power supply cable then you are drawing all all the power of the 8 pin 12 volt connector through t hrough a single single 18 gauge gauge wire. You 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 c ome with either a 4 pin 12 volt connector or an 8 pin 12 volt connector. connector. 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 separate separa te 4 pin pieces. If you plug the two pieces of a 4+4 power cable ca ble together then you have a 8 pin power cable which can be plugged plugged into an 8 pin 12 volt connector. connector. If you leave the two pieces separate then you can plug one of the 4 pin pieces into a 4 pin 12 volt connector and leave the other 4 pin piece unplugged. If you look carefully at the image above then you c an see the polarization polarization of the pins which 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 have matching square square and rounded off corners to prevent the cable from being plugged plugged in the wrong way. But if you look really carefully at the rig r ight ht half of this particular cable and then look at the 8 pin 12 volt cable pictured above you'll notice that they don't match. A regular regular 8 pin cable ha s four square pins and four rounded ones but the t he 4+4 cable c able shown above has two square pins and 6 rounded ones. The left half of the 4+4 matches the left half of an a n 8 pin cable ca ble but the right right half is different. Hmmmm... Hmmmm... And this isn't isn't some bizarre cable either. I've seen plenty of 4+4s which look like like this one. And then there the re are other 4+4 cables c ables which look just like an 8 pin cable split in two (which makes sense). Since rounded pins fit into square holes in motherboard connectors, this particular cable will fit fit just fine into an 8 pin 12 volt motherboard connector. connector. But both halves of this 4+4 will fit into a 4 pin 12 volt motherboard connector. connector. You're 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 it happens, either half ha lf will will work fine in a 4 pin motherboard be cause both halves of the 4+4 just provide 12 volts. The pinouts are the same for both halves so either e ither one will work. I'm not sure why they make c ables like this one because you'd figure a 4+ 4 cable would just be an 8 pin cable which splits in two. And you only need one ha lf of a 4+4 cable c able to plug into into a 4 pin motherboard. The other half is unused. unused. But the kind of 4+4 cable shown above is pretty comm c ommon on so don't let it throw you. 6 pin PCI Express power cable



This cable is used to provide extra 12 volt power t o PCI Express Expre ss expansion cards. PCI Express motherboard slots can provide a maximum of 75 watts. Many video ca rds draw significantly significantly more more than 75 watts so the 6 pin PCI Express Expre ss power cable was create d. These high-power 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 c ables". They are also occasionally occasionally called "PEG cables" ca bles" where "PEG" stands for PCI Express Expre ss Graphics. Graphics. 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 cables into a PCI 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. supply. If you plug them both into the same power supply cable the n you are drawing all all the power of the PCI P CI Express connector connec tor through a single single 18 gauge wire. You You can usually usually get away with that but there's no reason rea son to do it. The PCI Express E xpress 6 pin connector is polarized polarized so it can only be plugged plugged in pointing pointing in the correct direction. But as a s with connectors of this type, you can sometimes 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 wrong place. Some Some video cards c ards come with the 8 pin PCI Express power connector to support higher higher wattage than the 6 pin PCI Express Expre ss connectors. It's okay to plug a 6 pin PCI Express power ca ble into an 8 pin PCI Express connec tor. It's designed designed to work that way but will be limi limited ted to the lower wattage provided by the 6 pin version of the ca ble. The 6 pin cable only fits into into one end of the 8 pin connector so you can't insert it incorrectly but you can sometimes sometimes force the 6 pin cable c able in the wrong way if you try hard enough. Video Video cards can ca n sense whether you have plugged plugged a 6 pin or 8 pin cable into an 8 pin connector so the video card can c an impose some 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 8 pin socket. Others will work with with a 6 pin cable at a t normal speeds but will not allow allow overclocking. overclocking. Check the video card documentation to get the rules. But if you don't have any other information information then just assume that if your video card has an 8 pin connector then you must plug plug in an 8 pin cable. Pinout Pins 1 through 3 Description

Wire color

+12 volts

yellow

+12 volts or not connected yellow or not connected

Pins 4 through 6 Pin number Pin number Wire color Description 1

4

black

ground

2

5

black

ground


+12 volts


yellow

3

6

black

ground

Connector part numbers Vide ideo card connector Cable connector Mole Molex x 455 45558 58-0 -000 002 2

Mol Molex 455 45559 59-0 -000 002 2

Terminals

Maximu imum current per cir circuit

Molex 39-00-0168, Molex 44476-1111

8 amps

Official cable/connector maximum wattage delivery Voltage oltage rail Number Number of lines Maximum Maximum current current Maximum Maximum wattage wattage +12 volts

3

2.083 amps

75 watts

The PCI Express specification is, is, unfortunately, not a f ree, public specification. So most 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: ATX: good. good. PCI Express: bad. It's a shame when a widely used standard isn't freely ava ilable ilable to the public. public. Nonetheless, information leaks leaks out from the specification and the 6 pin PCI Express 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 Molex clearly allow substantially substantially more power. Part of the reason rea son may be that pin 2 (listed (listed above as a 12 volt line) line) may be listed as not connecte d 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 line line connected connect ed to pin 2. I've also seen claims that there t here may be unimplemented unimplemented sense lines in the specification. Welcome Welcome to the uncertainty which happens when you don't have freely available specifications. specifications. Even with only two 12 volt lines lines the standard implementation implementation of PCI E xpress power cables use large enough gauge gauge wire and a good enough connector to provide much more more than the t he three amps per wire required to provide 75 watts. Nonetheless, the 6 pin PCI Express power cable officially provides only 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

The PCI Express 2.0 specification released in January 2007 added a n 8 pin PCI Expre ss power cable. It's just an 8 pin version of the 6 Pin PCI Express power cable. cable. Both are a re primarily used to provide supplemental supplemental power to video cards. The older 6 pin version officially provides a maximum of 75 watts (although unofficially it can



usually usually provide much more) whereas the new 8 pin version provides a maximum of 150 watts. It is very easy e asy to confuse the 8 pin version with the very similar-looking EPS 8 pin 12 volt cable ca ble.. The 8 pin PCI Express and the EPS 8 pin 12 volt connectors are polarized polarized differently so you won't be able to plug one kind of cable into the other kind of conne ctor. That is, you won't be able to plug the wrong kind kind of cable in unless you try rea lly lly hard. Unfortunately, Unfortunately, the Molex Mini-fit Mini-fit Jr. connectors used by both kinds of power cables can sometimes be forced into a differently-polarized differently-polarized connector if they only have a fe w pins and you push hard enough. If the t he cable won't slide slide in easily then you're probably trying to insert the wrong kind kind of cable. ca ble. The 8 pin PCI Express connector does have a small plastic plastic bridge which which prevents it from being plugg plugged ed into an EPS 8 pin 12 volt motherboard connector. You You can see the bridge bridge in the image image above between the t he rightmost rightmost two pins in the top row of the connector. But there's no such protection to prevent EPS 8 pin 12 volt cables ca bles from being plugged plugged into an 8 pin P CI Express connector connec tor on a video card. That combination combination may fit if you shove hard enough. And if you plug in in the wrong kind kind of ca ble then expect expe ct fireworks. Some Some of the t he grounds and 12 volts wires for an EPS 8 pin 12 volt are reve rsed compared to an 8 pin PCI Express. Fortunately, most most 8 pin PCI Express connectors are labeled "PCI-E" so people won't confuse them with EPS 8 pin 12 volt cables. If the connectors aren't labeled then you can t ell an 8 pin PCI Express power cable from an E PS 8 pin 12 volt cable by checking the color of tthe he wires which plug into into the clip side side of the t he connector. connec tor. On the EPS 8 pin cable, cable , the yell ye llow ow wires (the 12 volt wires) go go into the clip side of the connector. On the 8 pin PCI Express cable, the wires on the clip side side are all black (grounds). (grounds). That's the same as it is with the 6 Pin PCI Express power cable. cable. Of course, none of this helps you if your cable uses the trendy all-the-same-color-wires design which is popular with high-fashion power supplies. supplies. In that case you'll just just have to be very careful or hope the connectors connec tors are labeled. Pinout Pins 1 through 3

Pins 4 through 6

Desc Descrip riptio tion n Wire ire color color Pin num numbe berr Pin num numbe berr Wire ire color color Desc Descrip riptio tion n +12 volts

yellow

1

5

black

ground

+12 volts

yellow

2

6

black

ground

+12 volts

yellow

3

7

black

ground

ground

black

4

8

black

ground

Connector part numbers Video Video card conn connector ector Cable Cable connector connector Terminals erminals Maximum Maximum current current p per er circuit circuit ?

?

?

?

Official cable/connector maximum wattage delivery Voltage oltage rail Number Number of lines Maximum Maximum current current Maximum Maximum wattage wattage +12 volts 6+2 pin PCI Express power cable

3

4.167

150 watts



Some Some video cards ca rds have 6 Pin PCI Express power connectors and others have 8 Pin PCI Express power connectors.. Many power supplies connectors supplies come with a 6+2 PCI PC I Express power cable c able which is compatible compatible with both kinds of video video cards. The 6+2 PCI Express Expre ss power cable is made up of two pieces: a 6 pin piece, and a 2 pin piece. If you put the two pieces together then the n you have a full 8 pin pin PCI Express power cable. But if you split the connector into two parts then t hen you can plug the 6 pin part into the older 6 pin PCI Express connector and leave the 2 pin part unplugged. unplugged. That way, your power supply only needs to ha ve one 6+2 cable to be compatible compatible with both 6 pin and 8 pin PCI Express E xpress 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 DVI compatibility for sticklers Troubleshooting AGP Troubleshoot your video card by underclocking Diagnose Diag nose your video card problems by comparin c omparing g with example corrupted screens scre ens Troubleshooting DVI problems The basics of 3D graphics without making your eyes glaze over - just enough to get you started How to uninstall your current displ display ay drivers How to install display drivers for your video card Understanding video RAM memory bandwidth What kind of expansion e xpansion slot slot should you use for your video card? c ard? VGA video card outputs Useful technical information How to install your motherboard chipset drivers Test your motherboard memory with Memtest86 Torture test t est your CPU with Prime95 How to find specifications for your computer Create a system restore point in case ca se something goes wrong Getting administrator privileges



Fiddling with your BIOS How to boot into safe mode or VGA mode Rate your CP U speed at games Glossary Glos sary of technical t echnical terms Random stuff My favorite RollerCoaster Tycoon Tycoon 3 coasters c oasters PeepFactory PeepFact ory peep generator for RollerCoaster Tycoon Tycoon 3 The view from my old backyard

Copyright © 2005 - 2008 by Mark Allen

All About the Various PC Power Supply Cables and Connectors

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