| There are two concerns here. The I-squared-R heat transferred to the insulation from the 30 amps being carried by the wire and the external thermal environment that the insulation sees. Any in-line connector will be the point of highest in-line resistance, especially if the connectors become corroded as they are prone to be. That's why the insulation gets crispy adjacent to the connector and why it's a good idea to solder the wires together.
The wires that are connected to the stator see a quite hot environment since they are run in a common sheath near the engine. This common sheath is a major factor in regulator failures because it holds the wires together along it's length, and as the wire's insulation property degrades, the wires short together intermittently and cause damage to the regulator. The sheath is probably there for abrasion resistance to provide additional insulation to adjacent engine and chassis parts. I took it off.
The first evidence is usually burnt insulation adjacent to the connector to the regulator and most people just cut out and replace this section of wire. But if you check the wires inside the sheath you'll find that the insulation there has also been damaged and should be replaced as well. The insulation on my 916 in the sheath was so soft that I could cut it with my fingernail. I had to replace several regulators until I found this root cause.
The answer to your question about wire sizes is that the size required is larger in hot environments to avoid insulation degradation. The insulation material and thickness selected is also a function of the service environment as well as voltage and current carried.  |