PSU Tech Look: Cable Length and Voltage Regulation


When building a “new” PC one of the components that enthusiasts often pay less attention to, or often reuse, is their power supply. And, why not? For the most part, the ATX12v/EPS standards over the years have not changed nearly as much as other facets of the market and, barring some issues with efficiency and low power sleep states, most of the changes that have impacted power supplies are not noticeable to the end-user so long as they push the “on” button and their system powers up.

Therein we find one of the problems. What happens when you get everything installed in your brand new shiny case and you go to connect your EPS or 24pin ATX cable only to find out that, between the placement of those connectors on your motherboard and the layout of your case, your cables won’t reach? Or, if they do reach, the cables are sitting right on top of your CPU HSF and forget about cable management even being possible? Or, if everything does reach you are left over with what seems like 40 feet of extra cabling to now hide? What now? Well, most of the time you swear for a while, then it is time to problem-solve with shorter or longer cables as needed (or you grab another power supply). Today, with modular power supplies on the market, that problem solving is a bit easier in some circumstances as there are options for longer and shorter cable sets. However, one of the questions that still hits my inbox more than a few times a month even though things have gotten easier is; how does this change in cable length affect the voltage regulation?

Is It A Downer?

There is an obvious answer to this. The longer the wire of the same gauge the more resistance you will encounter and the greater change in voltage regulation you will see. In theory, this is fairly easy to calculate. However, the saying “in theory” exists for a reason. If everything worked “in reality” like it did “in theory”, then we would have no need to say “in theory”. Now, relevant to our interests today, there are a lot of variables that go into what is going to affect the voltage regulation in both fixed and modular cables. We have the wire length and gauge (easy to account for), the various Mini-Fit and other connectors needed to make modular connectors (can be accounted for), we have the interface quality between these connectors (hard to account for), we have the presence or absence of sense wires, and we have the quality of the cable construction overall (quite variable). At some point, that makes for a lot of variables to account for “in theory”.

So, what are we going to look at today exactly? Well, today, we are going to take a single modular power supply with its normal length cables and then a short cable set that is also sold by the same brand. We are then going to see if the difference in the two cable sets make, what appears to be, a meaningful difference. Now, obviously, with one power supply and just one set of each cables we can’t give you a large enough sample size to do real statistics on. However, what we can do is get an idea about whether or not this is something that might warrant further examination on our part or concern on the reader’s parts. If we do get what seems to be a large difference, then this can be revisited. However, for today, sticking with one brand and one model with just two cables sets limits a lot of other variables that would make the numbers hard to examine initially. So, without further ado let us move on to see what we are working with today.

Paul Johnson
Paul is a long time PC hobbyist and tech enthusiast having gotten his start when he broke his first C64 quickly followed by breaking his first IBM XT. Most notably however, for 12 years, he served as the Power Supply Editor for one of the truly early, groundbreaking, and INDPENDENT PC enthusiast sites ([H]ardOCP) until its mothballing in April of 2019. Paul now brings the same flair and style of his power supply reviews to

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