Dumb question about CPU power cable

[Cutechri]

So I'll make this brief, I'm currently running a PBO setup of 165/115/150 PPT/TDC/EDC and I have a single 8-pin EPS cable powering my CPU. From what I know that cable can only deliver 150W. Is it safe to have the limit be increased to 165W from the default 142W in the long run? Or should I connect the additional 4-pin CPU power on my board?

 

[tabascosauz]

I'm pretty sure it's the 8-pin PCIe that's specced for 150W.

You will literally never max out a modern 8-pin EPS, assuming you aren't using a dodgy cable or some extremely dodgy brand of motherboard no one has heard of. I don't remember the exact number but they're all capable of pulling upwards of 300W per 8-pin (maybe even 400W? can't remember). For one, buildzoid brings it up just about every time he reviews a board with 2 or more 8-pins.

All thanks to the move to thick solid power pins ubiquitous in just about any modern motherboard. Compare the size of the EPS pins on your board to something from 12 years ago.

Especially for AM4, there is zero purpose in having anything beyond the single 8-pin, outside of XOC.

 

[DarkDreams]

I agree with tabascosauz. The 150W rating is for PCIe power cables not 12V EPS. According to what I found there is an unofficial rating of 336W for the 8 pin CPU connector so you should be absolutely fine (source and source)

 

[Cutechri]

Alrighty thanks! Again, dumb question but better safe than sorry lol

assuming you aren't using a dodgy cable or some extremely dodgy brand of motherboard

Nope, ROG and Seasonic here

 

[GerKNG]

EPS 4 Pin 16A/193W
EPS 8 Pin 28A/336W

 

[Deleted member 202104]

Alrighty thanks! Again, dumb question but better safe than sorry lol

It was actually one of the more useful questions on the forums in a while.

The info is good to know, and now I know that the dual 8-Pin EPS and the single 6-Pin PCIe connectors on my B550 are really dumb.

 

[qubit]

I'd connect that extra cable for that little tiny bit of extra peace of mind. It won't be needed, but it can't hurt either either. It will certainly help to have that extra margin of safety if that connection starts to become high resistance over time due to oxidation or some other issue comes up.

 

[Cutechri]

I'd connect that extra cable for that little tiny bit of extra peace of mind. It won't be needed, but it can't hurt either either. It will certainly help to have that extra margin of safety if that connection starts to become high resistance over time due to oxidation or some other issue comes up.

Now that I know the 8-pin provides 336W, I'm good lol. I'd have to move my top fan to get to the CPU connectors and that's a pain.

 

[qubit]

Now that I know the 8-pin provides 336W, I'm good lol. I'd have to move my top fan to get to the CPU connectors and that's a pain.

If the connection becomes faulty, then it doesn't matter how much power it can deliver, it's gonna fail and the hotspot that develops can destroy the mobo.

Having two gives you redundancy and spreads the load so that there's lower voltage drop and less heating of the cable, especially the joint in the plug between pin and cable where there's significant resistance, all of which can lead to faults over time. Using both plugs puts half the stress on the cables and the sockets. Also, think, if it totally wasn't needed, then why is the second connector there? Manufacturers would rather save money by leaving it out, so they had a good reason for including it. It's not like there's any great diifficulty in connecting it, is there?

It's your hardware, but I'd connect both on mine for that extra peace of mind.

 

[ir_cow]

I agree with tabascosauz. The 150W rating is for PCIe power cables not 12V EPS. According to what I found there is an unofficial rating of 336W for the 8 pin CPU connector so you should be absolutely fine (source and source)

This "unofficial" rating is based on a higher electrical rating and not the ATX standard. 16 AWG is 13 Amps. Times that by 6 because 2 of the 8 are ground pins. that gives you 78 Amps which is 936 watts. But to be conservative for all power supplies. 18 AWG at 5 Amp. which would be 360 watts. Basically a single Seasonic PSU with 1x 8pin PEG using 16AWG wire would be able to handle a NVIDIA RTX 3090 just fine.

Know your wire gauge, know your power limits.

Also, think, if it totally wasn't needed, then why is the second connector there? Manufacturers would rather save money by leaving it out, so they had a good reason for including it. It's not like there's any great diifficulty in connecting it, is there?

Because not all power supplies are equal. Alot of junk ones for sale. They don't want to be blamed for the fire.

 

[DoLlyBirD]

Having two gives you redundancy and spreads the load

That's one hell of an assumption, do you have anything to confirm this is the case when using both? I'm not sure it does load balance and spread the load, and would hazard a guess that they are both their on higher end boards kinda like the k1ngp1n and other GPU's with 3x 8pin PCI-e connectors for high end overclockers and such that no "normal" user would ever need.

 

[GerKNG]

there is absolutely no problem running with just one 4 or 8 pin.
i do this since many years and even a 300W pulling overclocked 10900k under heavy load is completely fine on one 8 Pin. Zero influence on stability or "safety".

 

[qubit]

That's one hell of an assumption, do you have anything to confirm this is the case when using both? I'm not sure it does load balance and spread the load, and would hazard a guess that they are both their on higher end boards kinda like the k1ngp1n and other GPU's with 3x 8pin PCI-e connectors for high end overclockers and such that no "normal" user would ever need.

No assumption, you clearly don't know much about electric circuits.

Put two wires / resistors in parallel and the two will carry half the current of just one, all other things being equal. Therefore, less heating and less voltage drop on each one. Why else do you think manufacturers put multiple wires in a plug all connected in parallel when just two would complete the circuit? A PCIe connector would need just two wires if extra wires weren't needed for load sharing to reach the current carrying capacity required.

Just find a YouTube video on electric circuits and you'll see that this is true. It's about as basic as it gets.

 

[DoLlyBirD]

No assumption, you clearly don't know much about electric circuits.

Put two wires / resistors in parallel and the two will carry half the current of just one, all other things being equal. Therefore, less heating and less voltage drop on each one. Why else do you think manufacturers put multiple wires in a plug all connected in parallel when just two would complete the circuit? A PCIe connector would need just two wires if extra wires weren't needed for load sharing to reach the current carrying capacity required.

Just find a YouTube video on electric circuits and you'll see that this is true. It's about as basic as it gets.

They are separate circuits/ connectors, you are assuming they are load balancing between the 2 when there is no proof this is actually going on, being condescending doesn't make you right, also, referring to pcie connectors, I think you'll find that they don't balance the load, the first will take more of the load and the 2nd will will provide the rest where required.

Also, think, if it totally wasn't needed, then why is the second connector there?

Also think... wouldn't this be on all boards and not just high end ones if that was the case? you basically admitting you're not 100% sure but you think this is why....

 

[qubit]

They are separate circuits/ connectors, you are assuming they are load balancing between the 2 when there is no proof this is actually going on, being condescending doesn't make you right, also, referring to pcie connectors, I think you'll find that they don't balance the load, the first will take more of the load and the 2nd will will provide the rest where required.


Also think... wouldn't this be on all boards and not just high end ones if that was the case? you basically admitting you're not 100% sure but you think this is why....

Pathetic responses. I really don't care whether I convince you or not. When you make such a basic mistake, I know that you don't know what you're talking about.

And it doesn't matter if it's a PCIe connector or any other type as the principle is the same.

Just calm down ok? Your attitude stinks.

 

[DoLlyBirD]

Pathetic responses. I really don't care whether I convince you or not. When you make such a basic mistake, I know that you don't know what you're talking about.

And it doesn't matter if it's a PCIe connector or any other type as the principle is the same.

Just calm down ok? Your attitude stinks.

If you're right you don't have to resort to spitting your dummy and insulting people, I'm sorry for having a differing opinion than you, was just joining in the conversation, take care.

 

[qubit]

If you're right you don't have to resort to spitting your dummy and insulting people, I'm sorry for having a differing opinion than you, was just joining in the conversation, take care.

The one who's spitting out his dummy and insulting people is you matey. It's not a matter of opinion how the current splits with parallel wires. Go and educate yourself and stop bugging me.

 

[DoLlyBirD]

The one who's spitting out his dummy and insulting people is you matey. It's not a matter of opinion how the current splits with parallel wires. Go and educate yourself and stop bugging me.

Fair enough, maybe you should tell this guy that's not how pcie connectors work as well whilst you're at it

Sorry, whats the problem?
Theres nothing wrong in that video. You have your FPS capped at 60, so the GPU simply doesnt need to run at 100% all the time.

Some parts of that video you're at 100% GPU usage, some you're not. In those higher usage areas, you simply have graphics set too high for a 970 to maintain 60FPS.
I feel like you've made a lot of assumptions without verifying things... the second PCI-E power rail doesnt get used until the first ones loaded. They're never even, nor meant to be.


GPU will downclock and save power, if it has no work to do (FPS capped to 60, low demand area)
GPU will run at 100% load and FPS will drop, if you're asking too much from it.


Your FPS raises in the menu because it's easier to render.

 

[looniam]

I agree with tabascosauz. The 150W rating is for PCIe power cables not 12V EPS. According to what I found there is an unofficial rating of 336W for the 8 pin CPU connector so you should be absolutely fine (source and source)

funny thing is those are the same exact 7 amps per pin for pci-e power connectors, but pci-sig says NO the limit is 150 watts

fwiw and use extreme caution but many decent PSUs and motherboard headers can handle ~50% for short terms . . like benching and such.

but YMWV.

 

[Bones]

What I'm failing to understand is why folks don't just go ahead and plug in the extra plug - This kind of thing shoudn't even be an issue but lack of power due to it not being plugged in could be.
It's not going to make the system use any more power than it would, except in a case if the extra power is actually needed and it's calling for the plug to be inserted into the board to provide it.

I guess some think the PSU will try to cram power into the system - It doesn't do that.

A PSU only supplies what the system needs, it doesn't just cram power into a system if it's not calling for it.
That's why the PSU is called a Power Supply, not a power stuffer.

 

[DoLlyBirD]

What I'm failing to understand is why folks don't just go ahead and plug in the extra plug - This kind of thing shoudn't even be an issue but lack of power due to it not being plugged in could be.
It's not going to make the system use any more power than it would, except in a case if the extra power is actually needed and it's calling for the plug to be inserted into the board to provide it.

I guess some think the PSU will try to cram power into the system - It doesn't do that.

A PSU only supplies what the system needs, it doesn't just cram power into a system if it's not calling for it.

Agreed, though most motherboards don't have the 2 EPS sockets and a lot of PSU's only have the 1 EPS connector, so a lot of the times it's a non-issue, though, yea, if you have both connectors on the motherboard and both cables on the PSU why not?

 

[Bones]

If you have it, just plug it in already = No problem.

If you do have a problem it's probrably one that the extra plug being in or not won't make a bit of difference about.

 

[GerKNG]

What I'm failing to understand is why folks don't just go ahead and plug in the extra plug

extra cables, problems with top fan mounting (for example my new H510 Flow can not mount a 140mm in the top with the second 8 pin plugged it. without it it fits just fine)
there is just no reason to do this except for running P95 with ice water cooled 12900ks or similar.

 

[ir_cow]

What I'm failing to understand is why folks don't just go ahead and plug in the extra plug - This kind of thing shoudn't even be an issue but lack of power due to it not being plugged in could be.
It's not going to make the system use any more power than it would, except in a case if the extra power is actually needed and it's calling for the plug to be inserted into the board to provide it.

I'm lazy and if the second EPS is 4pin, I just don't bother. That and if I know I'll be under 300~ CPU load, I simply do not care enough.

 

[Cutechri]

If the connection becomes faulty, then it doesn't matter how much power it can deliver, it's gonna fail and the hotspot that develops can destroy the mobo.

Having two gives you redundancy and spreads the load so that there's lower voltage drop and less heating of the cable, especially the joint in the plug between pin and cable where there's significant resistance, all of which can lead to faults over time. Using both plugs puts half the stress on the cables and the sockets. Also, think, if it totally wasn't needed, then why is the second connector there? Manufacturers would rather save money by leaving it out, so they had a good reason for including it. It's not like there's any great diifficulty in connecting it, is there?

It's your hardware, but I'd connect both on mine for that extra peace of mind.

It's a top quality Seasonic PSU on a fairly high end board, I'm not concerned. I just wanted to know if the limit was above 150W and I got my answer several times. It's 336W.