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1.3.2 Firewall CONSTANT Bus Bar

Blue Sea 2105 MaxiBus

Type: Bus Bar

Model: Blue Sea 2105 MaxiBus (250A) or 2107 PowerBar (600A)

Manufacturer: Blue Sea Systems

Product Page: MaxiBus 250A

Overview

Forward distribution bus mounted on the firewall (passenger cabin side). Receives a single protected feed from the AUX battery and fans out to the cabin/firewall-mounted accessory controllers.

Location: Firewall (cabin side, passenger area), co-located with SwitchPros power module, BODY PDU, and JL Audio amplifier.

Two-Stage Distribution Architecture

The AUX battery has no local CONSTANT bus. Loads are distributed in two stages:

1. **AUX battery+ → inline CBs → 3 protected feeds** (forward to this firewall bus, local to SafetyHub, local to audio amp)
2. **Firewall CONSTANT bus → per-load CBs → 2 distribution controllers** (SwitchPros + BODY PDU)

The firewall bus is fed by a 2/0 AWG cable through a 300A master CB at the AUX battery (within 7" of battery terminal). This places power distribution *near the loads* (most SwitchPros outputs are forward, BODY PDU is at firewall; audio amp is fed directly from the AUX battery, not from this bus) and keeps the cabin trunk to a single heavy cable instead of multiple medium-gauge feeds.

Specifications

  • Rating: 250A continuous (Blue Sea 2105) or 600A (2107 if oversized for future expansion)
  • Terminals: 14× 1/4"-20 studs (2105) or 8× 3/8"-16 studs (2107)
  • Wire Range: Up to 2/0 AWG (2105) or 4/0 AWG (2107)
  • Features: Tin-plated copper, corrosion resistant
  • Recommendation: 2105 is sufficient for ~154A combined load; 2107 if future expansion is anticipated

Input Feed (from AUX battery)

From Cable Distance Protection Voltage Drop @ 200A Notes
AUX battery+ 2/0 AWG ~13 ft 300A CB at battery (<7") ~2.0% @ 20°C Routed via cabin trunk (path TBD)

Load Distribution

Connection Wire Gauge Distance Voltage Drop Protection Load Notes
Feed INPUT 2/0 AWG ~13 ft <1.5% @ 20°C 300A CB (at battery) ~154A max From AUX battery via cabin trunk
SwitchPros 2 AWG ~2 ft <0.5% @ 20°C 150A CB ~100A max Auxiliary lighting
BODY PDU 2 AWG ~2 ft <0.5% @ 20°C 100A CB ~54A max Cabin circuits

Combined max realistic load: ~154A (well within 250A bus rating, comfortable in 600A bus)

Stud utilization: 3 of 14 used on 2105 (11 available), or 3 of 8 on 2107 (5 available)

Circuit Breakers (co-located with bus)

Both per-load CBs mount within 7" of the bus on a small bracket near the cluster:

Load CB Rating Model Notes
SwitchPros 150A Mechanical Products 174-S2-150-2 150% of max load
BODY PDU 100A Mechanical Products 174-S2-100-2 185% of max load

See Circuit Breakers for full specs.

Power Systems:

Connected Systems: