Motorhome Electrical Systems continued --
Almost all automobile electrical wire has two components. In focusing on the internal metal wire, I almost forgot the other component -- the insulating jacket, usually just called insulation.
The insulating jacket on wire is usually some form of flexible plastic. Solid copper wires tend to have a relatively rigid form of plastic, in part to keep the wire bending and flexing too much. On the other hand, stranded wire is intended to withstand repeated movement and bending so automotive wire (often just called auto wire) should have a more flexible, rubber-like plastic.
It's important for the insulating jacket to be continuous, without any cracks or gaps that can allow the electricity to "escape."
Regardless of the degree of flexibility, the plastics used for wire insulation all contain volatile compounds to help maintain flexibility. Over a span of decades, these compounds can leach out and evaporate, causing the insulation to become more rigid and brittle. So, very old wires are more likely to develop cracks and breaks in the insulation, making it much harder to ensure the electricity only goes where you want it to go.
The ambient temperature around the insulation has a direct bearing on how quickly the volatile compounds evaporate. Likewise, very low relative humidity tends to speed up the rate of evaporation, although to a lesser extent than high temperatures.
Very high ambient temperatures, such as in an engine compartment, can cause the insulation to degrade quickly, in as little as a few years. So, automotive wire (as well as marine wire) often has a temperature rating, using the Celsius scale. (On automotive wire, the temperature rating is often hard to notice or even missing. However, it's worth looking for the rating and avoiding any wire that doesn't have a rating, as well as any wire rated at 60 degrees C or below.)
The Blue Sea Systems online
Circuit Wizard app includes a drop-down menu that allows you to select the wire insulation temperature rating.
It's worth noting plastic insulation, regardless of how flexible, gets stiffer as it gets colder. As long as it's not flexed significantly even severely subzero temperatures will not damage the insulation. (The main reason I prefer arctic grade wire is the insulation remains relatively flexible even at extremely subzero temperatures.)
There's nothing technically wrong with using wire with insulation rated at 105 degrees C (221 degrees F) exclusively. However, it costs a bit more and is a bit harder to work with because the insulation tends to be stiffer at normal outdoor temperatures.
