high-currentoutdoorswire
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?
This isn't really a full answer but just to contribute.
I once spent a lot of time designing an enclosure that had to live outside in the full sun, near the beach so we had to deal with salt spray. Oh and of course management wouldn't stand for any color changes in the plastics, and metal couldn't be formed to the pretty shape ID wanted...
Most plastics either degraded in the sun or yellowed over time. We had to pick white for the sun loading effect (shining sun down on the box heats it up etc). In the end after working with our injection molding house and looking at tons of different plastics the only thing we found that met all our needs was fiberglass. Something we hadn't even considered at the start.
Then as we started looking at what would happen if we needed a fan. We started thinking about designing an air flow system that could still block water (although not salt fog)... Then someone pointed out that in the south there were problems with fire ants making their homes in electrical enclosures. Here's a pic of some wiring damaged by fire ants:
In the end we were trying to work out a way with the injection molder to include a metal heat sink around which the case could be formed to get a tight seal. Then some heat pipes from the main chips to the underside of the heat sink. Not off the shelf but we were trying to do some crazy things at the time. Never tested that to see how well it worked though.
The best way is to desolder the old cables from the scale's circuit board, and solder on the new ones. That way there are no messy splices. However, to do that easily you may need a solder pump (cost: about $5-$10 USD) to vacuum away the solder from the existing joints. Without a solder pump, you can desolder a through-hole-mounted wire simply by pulling it away while the solder is liquid, but solder may clog the hole. To get around this, you can heat the solder that remains in the hole while inserting the new wire; if you can't get at it with the tip of the iron, then simply add more solder to the area.
The next choice after that is to make rat tail joints (stripped ends of wires twisted together) between the new and existing cable (or else Western Union splice which is neater), and then strengthen these joints with solder and perhaps cover with electrical tape or hot glue. The Western Union is not well-suited for braided wire, but this is only true of the splice alone, not if the splice is flooded with solder.
Best Answer
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.