The repeated heating up and cooling down resistance wires are subject to during use imparts thermal stresses into the wire. Whilst the alloy combinations have been developed over many years, and ensuring they have low temperature coefficients of linear expansion has been a key design influence, minimising these stresses will improve longevity. In cases where it is difficult to replace the heating elements, in underfloor heating cables for instance, bunching or stranding the conductors will help. Scott Precision wire stranded and bunched conductors are subject to the same inspection regime as solid wires, so whatever the format, the conductor will exhibit the same consistency.
A 12-gauge wire is wider than 14-gauge wire and thus has less resistance. The lesser resistance of 12-gauge wire means that it can allow charge to flow through it at a greater rate - that is, allow a larger current. Thus, 12-gauge wire can safely support a circuit that uses an appliance drawing up to 20 Amps of current. In fact, a 20-Amp circuit is protected by a fuse or circuit breaker that will flip off when the current reaches 20 Amps. If a 14-gauge wire was used on the same circuit, then the breaker would allow up to 20 Amps to flow through it. It could overheat and thus lead to the risk of fire. A 20-Amp circuit should never be wired using 14-gauge wire.