Overview

The Hella Marine 933332181 is a 12V Mini ISO SPDT (Form C) relay with a mounting bracket for switching higher-current onboard circuits from a low-current switch or control output. It is rated for 40A continuous on the normally open contact and 20A continuous on the normally closed contact (at 85°C), with up to 150A inrush capacity for loads that hit hard at startup.

This relay uses a standard 5-terminal layout (30 common, 87 normally open, 87a normally closed, 85/86 coil) with 6.3 x 0.8 mm blade terminals. The coil includes resistor suppression to help tame voltage spikes at turn-off, which is useful when the trigger side is coming from sensitive electronics.

With an IP54 rating and an operating range from -40°C to +85°C, it fits well behind a helm panel, in a dry locker, or inside an electrical enclosure where it is protected from direct washdown and bilge spray. It is a solid match for boats that need a clean way to control deck or spreader lights, horns, pumps, or other accessories without running full load current through a dash switch.

Key features

• 12V nominal Mini ISO relay in SPDT (Form C) configuration with 5 terminals
• Continuous rating: 40A on N/O contact and 20A on N/C contact (at 85°C)
• Handles up to 150A inrush for high-startup loads
• Integrated coil suppression resistor (560 ohm) for cleaner switching on the control side
• IP54-rated housing for locations exposed to dust and splashing water
• 6.3 x 0.8 mm blade terminals (ISO 8092) for common relay sockets and crimp terminals
• Mounting bracket for securing the relay to a bulkhead or panel inside an enclosure

Compatibility and fit

This relay is intended for 12V DC systems. It pulls in at 8.0V or less and drops out at 1.0V or higher, which helps it stay engaged during brief voltage dips. For resistive loads, use the continuous ratings as the main guide; for inductive loads like motors and solenoids, plan around the lower inductive switching ratings and always manage load-side kickback with appropriate suppression at the load.

Installation and setup

Mount the relay by the bracket in a protected location and keep wiring supported so vibration does not work the terminals loose over time. Use properly crimped 6.3 mm female spade terminals or a matching Mini ISO relay socket, and protect the connection area from moisture and corrosion. Fuse the load circuit appropriately and keep high-current runs short to reduce voltage drop, especially when switching lighting where brightness matters.

Electrical and system integration

The coil resistance is 73.8 ohm (plus or minus 10%), so the trigger side draws modest current and can be driven by many helm switches or control outputs when wired correctly. Switching time is fast (10 ms or less for operate and release), which is helpful when the relay is used as part of a control chain. Dielectric strength is rated to 1,000 VDC.

Use cases on board

This relay is commonly used to let a small dash switch control a high-current accessory circuit. Typical placements are behind the helm, in a flybridge console, or inside a protected electrical locker close to the load feed for deck and spreader lighting circuits.

Maintenance and care

Periodically check that terminals stay tight, clean, and free of heat discoloration, especially on high-load circuits. In saltwater environments, keeping the relay inside a covered enclosure and protecting the terminals with corrosion control practices can go a long way toward preventing intermittent faults.