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I know this is going to sound like a dumb question but is there a way to test a power cable?

Background: I was having issues with my 3D printer. I brought it over to a friends place and it worked fine using a 14 AWG. The power cable I was using that was causing troubles was 18 AWG. So I brought it home and replaced it with the 14 AWG power cable and it worked fine. The power cables themselves are regular PC power cables. The power cable is plugged into an APC surge protector. Some variables are -

  • Maybe the power supply for the printer needs a 14 AWG cable?
  • Maybe the cable was just went bad and it can still use an 18 AWG?

I would like to know if it is possible to (safely) test a power cable to determine if there is a fault or was made with cheap materials?

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  1. Use a multimeter to test for continuity from the plug end to the line socket end.
  2. Test the cable on another appliance. Flex the lead and see if the appliance switches off. Pay particular attention to where the lead enters the plug or line socket as this is a common point of failure due to flexing.
  3. Apply a known current of several amps through each wire of the cable in turn and measure the voltage drop along the conductor carrying the current. Calculate the resistance from \$ R = \frac V I \$. Compare this with the value calculated on one of the many web voltage drop calculators. Compare the readings from the L, N and E conductors. Is one higher than the other?
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With the cable completely disconnected from power, you can perform a continuity test. Use your multimeter to check that each of the three wires from one end to the other are conducting properly. Physically moving/wiggling the cable (especially near the ends where the molded plug and socket are attached to the cable) may result in an intermittent connection which would indicate a bad cable.

The difference in current rating between 18 and 14 AWG is about double. For example, according to this table at a power cord manufacturer site, 18 can safely carry 10 amps while 14 AWG can carry 18*. Unless your device was pulling more current than the cable is rated for, the gauge shouldn't be a concern. (You would have noticed the cable getting warm or hot if that were the case.)

* These charts are based on some amount of allowed temperature rise and can vary based on application and local electrical codes.

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  • \$\begingroup\$ I think the currrent ratings you mention are extremely conservative. In North America, 14 AWG is rated at 15 amps for house wiring, and I have a AWG16 extension cord rated for 13 amps. \$\endgroup\$ Aug 31, 2020 at 18:50
  • \$\begingroup\$ @PeterBennett You're absolutely right. I'll exchange the chart and figures for more common values. \$\endgroup\$
    – JYelton
    Aug 31, 2020 at 19:49

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