I am conducting an experiment where I would like to heat up 18 AWG copper cables outdoors using to 50-60°C using 60 amps. The wires are wrapped with teflon to prevent damage to the cable. Can I use a generic waterproof wire connectors (ex. Small Waterproof Wire Connectors, Aqua/Orange (20-Pack)) for my connections (link the image below) or do I need something special?

Small Waterproof Wire Connectors

  • \$\begingroup\$ How hot do you expect the wire to get? \$\endgroup\$ Mar 17, 2019 at 22:38
  • \$\begingroup\$ It seems pretty doubtful, but you may have difficulty finding the temperature and current ratings. What temperature do you expect? \$\endgroup\$
    – user80875
    Mar 17, 2019 at 22:39
  • \$\begingroup\$ Why are you thinking of PTFE wrapping? Be aware of en.wikipedia.org/wiki/Polymer_fume_fever \$\endgroup\$
    – D Duck
    Mar 17, 2019 at 22:45
  • \$\begingroup\$ Information I could find indicates that 29 amps is the maximum current for 18 AWG teflon insulated wire. \$\endgroup\$
    – user80875
    Mar 17, 2019 at 22:53
  • \$\begingroup\$ pushing 60 amps through 18 AWG wire does not sound like a good idea by any stretch of the imagination. I'd use at least 8 gauge, maybe even 6 for that. \$\endgroup\$
    – Hearth
    Mar 17, 2019 at 23:08

2 Answers 2


60 A through 18 AWG copper is going to raise the temperature of the wire to much greater than 60°C. Calculating the steady-state temperature of an insulated wire depends on the ambient temperatures, how it is installed, and the materials it is surrounded with.

According to Table 310.15(B)(17) of the 2017 NEC, 18 AWG copper insulated with PVC installed in free air at 30°C will reach a steady-state temperature of 90°C with current of 18 A.

By the way, Teflon insulation would not be necessary if your goal is 60°C. Common TFFN building wire (PVC insulation with a nylon skin) is designed for a maximum temperature rating of 90°C. All standard electrical splices will be rated for at least 60°C, there should not be any need for special materials.

I would expect about 15 A would result in a temperature of 60°C on the copper surface of 18 AWG wire. Since the DC resistance per foot at 60°C of 18 AWG is 7.38 ohms / 1000 ft, a voltage from a perfect voltage source of only 5.5 V would result in 15 A.

  • \$\begingroup\$ Thanks for this. I am actually a hydrologist using metal braided fiber optic cables for soil moisture experiments. As you may be able to tell, my understanding of electrical wiring is limited. \$\endgroup\$
    – Rob
    Mar 19, 2019 at 20:11
  • \$\begingroup\$ I have 1600m of cable that I want to heat at 10 w/m at minimum (22 amps minimum). The cable resistors are 18 AWG, so I am definitely going to use more amps than what the cables are rated for. The cable manufacture says its fine to heat the cable at this rating, but I am unsure about the connections. The total resistance is 16.8 ohms \$\endgroup\$
    – Rob
    Mar 19, 2019 at 20:17
  • \$\begingroup\$ Are you sure your heating wire is 18 AWG copper? It's likely a different material with a higher resistance. If everything is kept at 60°C, the temperature won't be a problem, but if the connectors are designed for copper and are used with a different metal, it could cause galvanic issues. \$\endgroup\$ Mar 19, 2019 at 21:24
  • \$\begingroup\$ To the OP: beware of creating a shock hazard. Going by YOUR NUMBERS, you have 16.8 Ohms and you are talking about up to 60A, which is 1008V. Running something like that through soil could easily electrocute someone if there is any continuity anywhere to the soil, and they happen to touch a grounded metal surface while standing in the soil. \$\endgroup\$
    – user57037
    Mar 21, 2019 at 3:38

Based on expected temperature rise for your conditions, your connections must be cooler with heat sinking on the terminations such as a thermal heatsink, bus bar or conductor with much lower thermal resistance to avoid fusing. The insulation if any, must be non-fuming non PVC as chlorine gas is dangerous.


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