What are the specifications of the three wires inside a PC cable that is used to connect the switching power supply to a US AC outlet.

The positive, negative and ground appear to be the same gauge stranded cable, and I've heard that it can handle 10A, but beyond that I don't really know what the rest of the specifications for the wire are.

  • $\begingroup$ What's the question exactly? What specification are you looking for? Wires can have plenty of specifications like minimum bending radius, but they aren't really of interest for you if you just want to connect the power supply to the outlet. $\endgroup$ Commented Jan 25, 2016 at 17:19
  • $\begingroup$ Well how many AMPs it's good for and what the metric and AWG Wiresize is; the strand number... here's a chart that has a list: zierick.com/pdf/wire.pdf but I don't know which one it is... $\endgroup$
    – leeand00
    Commented Jan 25, 2016 at 18:06
  • $\begingroup$ Why do you need to know the wire size if you already know that it's good for 10A? You probably used this cable before to connect your PC (or other device) with the outlet without asking these questions. What's the specific concern that you have now? It looks like this belongs on Electrical Engineering $\endgroup$ Commented Jan 25, 2016 at 18:12
  • $\begingroup$ Well I just want to learn what I'm doing...and I'm using the wire to attach a switch and plug to the printer. I'm going to crimp terminals using a crimping tool; and I want to make sure the switch, it's fuse as well as the electrical connection terminals are correct for the wire, so they don't melt. I bough a stripper/crimper, not that cheesy thin black one that everybody uses but one that's between that and the $78 ones...it's a Commercial Electric Double Jaw Stripper Crimpper. Ultimately, I'd like to avoid a fire, or damage to the house wiring. $\endgroup$
    – leeand00
    Commented Jan 25, 2016 at 18:20
  • 1
    $\begingroup$ It's not the wire or its specifications that melt anything, it's the power that goes through them, which is determined by the load: the power supply that supplies your printer. The standard wire can handle what the outlet can supply. If your printer draws more power than that, you have other problems. If you buy a bigger TV you don't start thinking about metric wire sizes either, do you? $\endgroup$ Commented Jan 25, 2016 at 18:27

2 Answers 2


Very basically speaking, electricity works like this:

  1. There's some source that delivers a certain voltage.
  2. You have a device that operates at a certain voltage. The device voltage and supply voltage should always match. No, don't put that 120V US device in a 230V outlet in Europe.
  3. The device does something. By doing something it draws current. Most devices also draw some current when not doing anything.
  4. How much power your device draws is the product of these two values:voltage x current = power

So far, so good. In your case:

  1. US AC outlet.

    the voltage is 120V.

  2. On this other question of yours you linked to this power supply on amazon. Besides being available gift-wrapped, it states the following feature:

    You can choose the input voltage (110V/240V) by switch.

    110V ≈ 120V, which means the device voltage matches your supply voltage.

  3. The supply can deliver 30A at 12V on the DC side which means 360W. If it could transform the electricity ideally, without any inefficiency, that would be 3A at 120V on the AC side. But your supply is unlikely ideal. Wikipedia suggests 60-95% efficiency. Let's be super pessimistic and assume 50%. That means half the power that goes into the switch power supply is turned into heat. In order to still get the 360W out, you have to insert 720W. That means your device draws 6A on the AC side.

What does this all mean for your wire? What wire size do you need for this supply?

Coincidentally, the above link to the amazon website showing your power supply also suggests the following PC ATX power supplies to me:

Let's get this straight: You can buy a power supply for a PC and plug it into your outlet without even thinking about what a wire size is. You'd just plug and play. That PC power supply will potentially draw more current than the power supply of your 3D printer. A standard wire would be able to supply either one of the PC ATX power supplies linked above and would not have a problem delivering a lower current to the power supply of your 3D printer.

The switching supply doesn't have a plug like a PC ATX supply, but that on its own doesn't make it any less secure (if wired up properly). It's just less common for household appliances.

Ultimately, I'd like to avoid a fire, or damage to the house wiring.

That's a good and valid concern.

PC Power supplies deliver 12V and supply more than enough current (like the examples above). They are probably in use in your house already and did neither set it on fire nor damage the house wiring.

A switching mode power supply is just as secure and if bought from a known brand unlikely to do you any harm either if used properly and within its specifications.

Ultimately, this is not a question of secure electricity but a trade-off between secure electricity and the price to pay for it. The standard wire and it's specifications have little to do with this.

Personally, I also use a cheap switching power supply made in china for my printer. It's very noisy and I pull the plug when I leave it unattended.

  • $\begingroup$ "Besides being available gift-wrapped"... ROTFL! $\endgroup$
    – mac
    Commented Jan 29, 2018 at 21:58

It's somewhat unclear what you mean by "standard PC cable", but virtually all desktop computers use IEC C14 sockets/IEC C13 plugs. Such connectors/sockets are rated for 10A 250V and thus you can safely assume that the cord itself will also be able to handle this voltage and current. 10A is what is specified by the IEC, certain North American standards agencies rate C13 cords for up to 15A.

The IEC standard also specifies that the conductors inside of a C13 lead have a cross sectional area of at least 0.75mm^2 and at least 1mm^2 if the cord is longer than 2m.


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