Overview

The Perko 8504DP is a medium duty battery selector switch with a key lock and alternator field disconnect for 6 to 32 VDC marine electrical systems. It is rated for 250 amps continuous load and 360 amps intermittent load, so it fits the kind of battery management setup found on many small to mid-size boats with separate start and house batteries.

This switch gives you OFF, 1, ALL, and 2 battery selection in one surface-mount body. That layout lets you isolate one bank, combine both banks for emergency starting, or route charging and onboard loads the way your system is wired. The ignition-protected housing also makes it suitable for gasoline engine room installations when the rest of the system is wired correctly.

Key features

• 4-position selector with OFF, 1, ALL, and 2 battery settings
• Make-before-break action between 1, ALL, and 2, so switching between those positions can be done with the engine running
• Rated for 6 to 32 VDC systems used with alternators and generators
• 250 amp continuous rating and 360 amp intermittent rating for battery selection and emergency parallel use
• Ignition-protected construction for installations in gasoline engine spaces
• Alternator field disconnect circuit for systems that use non-unitized alternators
• Key lock secures the switch in the OFF position
• Polycarbonate body with brass terminals, 5/16 inch terminal studs, 5-1/4 inch diameter, and 2-5/8 inch depth

Installation and setup

This switch is built for surface mounting and works best where the cable run can stay short and service access at the rear is still practical. The 5-1/4 inch body diameter and 2-5/8 inch depth are worth checking before replacing an older switch in a tight battery compartment, console, or machinery space.

The terminals use 5/16 inch studs, which suits common marine battery cable lugs. On boats that use larger battery cables, rear clearance matters as much as the panel cutout area because the cable bend radius can take up more room than the switch body itself.

Compatibility and fit

This model makes sense on boats that carry two batteries and need clear battery selection at the helm, in a battery locker, or near the engine space. It fits common layouts where one battery is reserved for engine starting and the second bank supports house loads, and it also works in twin-engine systems that use selector switches to manage battery choice at each engine.

The alternator field disconnect feature is relevant on systems with non-unitized alternators. In that setup, the field circuit is routed through the F1 and F2 terminals to reduce the chance of alternator damage if the switch is turned to OFF with the engine running. On unitized alternators with a built-in regulator, that field disconnect circuit is not used.