I think that manufacturers sometimes struggle with recommendations on equipment that have safety implications. To reduce exposure to liability, it?s always best to quote established regulations based on recognized independent testing. The problem that I see is that there may be no definitive standard test for some limited applications. The most often recognized current carrying capacity of #10AWG wire is 30 amps as recorded in tables in the NEC and CEC standards.
However, there are rules linked to the tables that adjust this rating depending upon other factors. The table numbers usually start with a proviso that the ampacity listed is for wires when bundled in cable or conduit having no more than 3 conductors in contact to account for the effect of mutual heating. Wires of the same gauge, but different insulation temperature ratings will have different ampacities. The ambient temperature of the surroundings is also considered. Another consideration is whether the load is continuous or intermittent. These numbers are all taken into consideration for the sole purpose of maintaining the integrity of the wire?s insulation to avoid hazardous failures and not the performance of your appliance.
So, does the manufacturer?s recommendation take into account that there may be only 2 wires, not 3 in contact? Perhaps these wires are considered ?single conductors? since they are not contained in an outer cable sheath or within a conduit, so they can dissipate heat more readily. The manufacturer might think that a marine environment has, by nature, a cool ambient temperature or perhaps he?s considered that these wires are likely to be exposed to direct sunlight on a hot day. The manufacturer might also expect that when the wire gauge is increased to reduce voltage drop, the increase will easily compensate for otherwise undersized wires.
Circuit breakers are rated for no more than 80% for continuously applied loads; but is this use in fact a continuous load? Just as each member on this website may have a different opinion, so do the manufacturer?s employees and their advisors. My opinions? For a 42 amp maximum load, I?d increase the wire size to #8 AWG with a 90 degree Celsius insulation rating to cover voltage drop and current carrying capacity. I?d consider the 50 amp breaker as appropriate. 42 amps is more than 80%, but I don?t consider this load to be continuous. A 60 amp breaker may not adequately protect a 10 AWG wire.
- Grandad
