Some suggestions follow that are intended for qualified, trained and experienced electrical workers. (1999) NEC Article 720 — Circuits and Equipment Operating at Less than 50 Volts. may apply.
An example of DC-rated wiring devices is Hubbell 328DC-series.
Because voltage drop is critical, consider something like roughly 4-AWG aluminum conductors, with roughly 10-AWG copper pigtailed with a tap connector like T&B 63105 installed with T&B-specified tooling. Increased box volumes should not be overlooked.
