From: Dennis Haynes
Sent: Saturday, January 22, 2022 10:12 AM
To: Derek Drew <derekdrew@DEREKMAIL.COM>; vanagon@GERRY.VANAGON.COM
Subject: RE: Best Wire Selector -- Voltage Drop Charts Mayhem

Derek,
Sorry about the delay in responding. Answering your question is a bit tough as there are so many variables. Wires size selection for low voltage circuits is a bit of a compromise act. Amongst some of the variables include the temperature rating of the insulation, wire in free air or bundles or in conduit, and the quality-strand count of the copper. Much primary automotive wire today is cheap copper clad aluminum.

Marine wiring methods can be a bit overkill and with good insulation and proper weather shielded terminations there is no reason for tinned wire to needed. There are marine grade rated wire that is not tinned. Another major difference in marine use is using the chassis for ground is not common. Most devices actually get 2 wires to/from the source. This is also common in RVs with wooden cabinets and furniture.

For simplicity I pretty follow the NEC electric code for wire size based on ampacity. Rarely will I use anything under 18 AWG just for reliable terminations and mechanical strength. 14 AWG up to 15 amps, 12 AWG for 20, 10AWG for 30A, and 8 AWG for up to 50A non continuous. By definition we use continuous load as three hours or more. Battery charging, lighting, and some other loads can fall into this category. For mixed loads such as feeding a fuse block diversity can be applied such as your house. You have a 200 A main but adding up all the branch circuits is much more. Diversity is that all the circuits will not be loaded at the same time.

So for example you run a fused at 40 A #8 to a distribution fuse box and can have multiple branch circuits at 20 A each feeding #12 wire.

Over current protection and fuse coordination comes the next step. Point is as systems become complex and large current some good engineering should be part of the plan.

Dennis