Good thread, Jim.
I would like to comment on each of your suggested sites:
1. Wire ampacity is determined by three factors; length, the cross section of copper wire and the type of insulation. Voltage and Watts mean nothing. Current creates heat.
Insulation performs two tasks, it determines the wire's voltage limit and the rate at which the wire sheds heat. These ratings are always printed on the wire. I use (minimum) 60°C stranded copper wire that is gas and oil resistant.
We commonly use automotive wire, MTW, or THHN. They are all covered in the National Electrical Code, and those tables should be followed for real safety.
There is more... Automotive loads are DC, which 'never lets go'. 60-cycle house current is derated .707 times DC current. in real terms, 10-amps of DC equals 7.07-amps of AC (or RMS). This means your car wire needs to be larger than AC applications. Duty Cycle plays a big role for intermittent loads, like horns, starter motors, or flashers because the wire cools down between loads. Never skimp on alternator, headlight, or tail light wire sizes.
2 & 3. Don't solder. None of the OEM's do (and neither do utility companies) for good reasons. Use quality, plated, copper lugs (like in the picture) or splicing sleeves and crimp. How often do you need this service? Rarely. Any electrician will be more than happy to crimp a few connections for you for free OR, you can use a hammer. The idea is to squeeze the conductors tightly together to keep resistance at a minimum. Solder spreads the strands and keeps them far apart, (and it wicks up the wire). When serious current arrives, the solder will melt first and the spliced conductors may fall apart. Mechanical lugs work better than solder connections.
The picture shows 'Welding Wire' which has hundreds of very fine strands. This is the ultimate starter motor and engine ground wire. Welding wire tends to spread out when stripped. Some electricians use copper foil to keep all the strands together before inserting in the lug. Crimping makes it all one solid piece. - Dave
Last edited by simplyconnected : 07-18-2011 at 05:57 AM.