How would I find the maximum Voltage & Amperage/Wattage of any piece of wire if I don't know what gauge the wire is?


For example, I have want to take some wires out of a spare 200 watt PC power supply to use in one of my projects. How would I figure out what the max Voltage/Amperage is of each piece of wire that I remove? Would the "Ohms" setting on a digital multimeter work?

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Buy one of those cheap digital verniers, measure the wire with that, and work out the gauge - a useful, cheap and universal tool.
.  About three years ago, I found a vernier caliper at an auto parts store (O'Reilly's?) for 5 $US. Made of stamped steel and the zero is off a little, but it works well enough for this type of measurement. I can throw it in the bottom of my toolbox and not worry about it - if I wreck it, it's cheap to replace. Don't want to do that with my Starrett dial caliper. ;)
ListysDad6 years ago
Just be a little careful about voltage.

If its for a low voltage application (say up to 30v DC almost anything will be fine. However, if its for mains voltage buy new as it is the sheath (the outer covering) that is rated NOT the cable.

Using a low rated cable for mains means that the voltage could literally jump across the plastic sheath.

Have fun.
orksecurity6 years ago
The simplest answer is "measure the gauge and look it up". Or "buy wire rated for your application."

With a long enough piece of wire to measure the resistance, you could figure out how much energy will be wasted as heat for a given amount of current. You then need to find out what the wire is made of and insulated with, and at what temperature each of those materials will start to oxidize significantly. That will tell you now long the wire will be able to survive carrying that amount of current before either shorting out or blowing open like a fuse. (Don't forget to factor in the starting temperature as well.)

This presumes you're working with DC (with AC you need to start worrying about inductance, which means looking at the shape of the wire and what it's near). It also presumes you're working with relatively low voltages which won't exceed the breakdown potential of your insulator -- if you go past that, you risk it shorting out, which will melt insulation, which will cause it to continue shorting out, which.... Generally nasty. Most common wire's insulation is good for a few hundred volts, but if you're looking at something like enameled wire the answer may be different.

Finally: If, at any time, a wire gets significantly warm, you're putting too much current through it. Unless it's something like a heating element which is _designed_ to get warm and to survive doing so.


BucketBasher (author)  orksecurity6 years ago
Ok, thanks for the tip. I just was hoping I would be able to calculate the max current b/c I'm currently lacking a decent enough wire gauge. I remember seeing pictures of circular ones on wikipedia a while back, and since then have been trying to find some but to no avail. Any idea where I could find such a wire gauge by any chance?
.  Those type of wire gauges can be found at most electrical supply stores or online. Remember to only measure the conductor, not the insulation.
Or compare it to samples whose gage you know. Or use a micrometer to measure the wire and look up what gage it is.

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