Ampacity Testing

Just a simple understanding question. If I obtained a DC bench power supply that has a current limit, could I test the ampacity of a wire by connecting said wire across the terminals? So when I slowly increase the current limit, more current will flow through it, causing it to heat up? A basic question but I'm learning and want to make sure this would be safe to do! Thank you :)

• What you suggest is indeed a possibility but how will you know that you didn't heat up the wire too much and changed the properties of for example the insulation? It will be easier to just look up what a certain wire can handle, there are tables for that like on this Wikipedia page: en.wikipedia.org/wiki/American_wire_gauge Also, when you're starting with electronics you generally stick to low currents like 1 A or less. Then only very thin wires will pose a problem. As you get more experience and move to higher currents then you can look into this further. Feb 21, 2019 at 10:23
• Thank you, i'm just interested in seeing if I could sort of recreate these in the table. For example, putting 20A through a 12AWG wire and measuring the temperature to see if it matches. I like being able to see it happening. I'd just like to make sure from experts that what I'd like to do would be safe! Feb 21, 2019 at 10:28
• Then don't use 12 AWG and 20 A but much thinner wire at a lower current. It might not be easy to recreate the exact same situation as is used for the table though.In general EEs don't test/question that table but use it as a guideline to determine what the minimum conductor size needs to be. So generally we would not select a wire and operate it "on it's edge" but we'd use a wire that can easlily handle the largest current. Wires are "low tech" and it is fairly easy to choose the correct one so EEs prevent problems and use a wire that is more than thick enough. Feb 21, 2019 at 10:33
• Electronics engineers are often more concerned with the voltage drop down a cable than its absolute current rating, and so will often use a much thicker cable in order to keep the voltage drop within spec. Feb 21, 2019 at 12:24
• You would need a load that would draw 20A and a fair amount of wire. Now 20A is dangerous. As others suggest, a smaller wire with a smaller current would still demonstrate the effects. Feb 21, 2019 at 20:20

It is safe to do, yes. The current limiting of your power supply will only output the maximum selected current. You can do this for testing, learning by doing is always a good thing.

The question is, what you hope to achieve by this action. You will certainly see, that at some point your cable/wire is going to get warm due to the current flow, when you increase the allowed current. But you won't be able to make precise measurements and there are already tables online, that give you the values you are looking for under basically all conditions you can think of.

Therefore it will be a nice and safe to do experiment, but it does not make sense to really try to measure new data =)

• Thank you to everyone that helped with lots of different information. I found a fairly cheap 5A supply that can operate in constant current mode. Instead of cables or wires I am actually using PCB traces of different widths, thicknesses, and builds and measuring the temperature rise. I have found data on circuit board traces to be quite limited, especially when there is so many different builds there can be! Thank you again everybody! Mar 14, 2019 at 12:54
• Although in german, I always find this table very helpful: mikrocontroller.net/articles/Leiterbahnbreite Mar 14, 2019 at 12:56

and you have to control the ambient temp starting temp etc.

ampacity tables are all over the internet. look it up. don't know the wire size? measure an individual strand / count the strands - look it up in the wire tables

Ampacity values are determined be usage, insulation, inside conduit? etc. the only thing you WILL find is the fusing current. 12 ga. Cu fuses at ~12,000 Amps.

A smart person learns from others work (mistakes).... no need to do whats been done