RV 12V Auto Reset Breaker Size Guide: 30A, 40A, 50A Selection

Quick Take

For your 50A service panel with WFCO converter and dual 6V batteries, you're most likely looking at a blown fuse rather than an auto-reset breaker. WFCO converters typically use replaceable fuses (30A, 35A, 45A, or 55A depending on model) rather than auto-reset breakers. The sudden loss of all 12V power points to this main fuse blowing, which is a common failure point in WFCO systems. Check your converter's fuse panel for the appropriate amperage fuse - consult your WFCO model specifications for the correct rating.

Common Causes

Common causes of auto-reset breaker failure in RV 12V systems include repeated cycling from overloads or age-related internal component degradation. In WFCO systems, typical scenarios include when the breaker's internal contacts become worn from multiple trips caused by high-draw appliances like water pumps, furnace blowers, or slide motors drawing excessive current during startup.

The "out of nowhere" nature of your failure suggests the breaker reached its cycle limit and can no longer reset properly. This is especially common in systems that have experienced repeated overloads from failing water pumps or corroded connections that create high resistance and current draw. Temperature cycling from seasonal use also weakens the internal spring mechanism over time.

Another possibility is a short circuit somewhere in your 12V system that caused the breaker to trip and stay open. However, since you mentioned it's an auto-reset type, a permanent short would typically cause it to cycle repeatedly rather than stay open permanently.

Preparation

SAFETY WARNING: Working with electrical systems can be dangerous. Always disconnect all power sources (shore power AND battery disconnect) before beginning work. If you're not comfortable with electrical troubleshooting, consult a qualified RV technician. Improper electrical work can result in fire, shock, or damage to expensive components.

Before heading to the parts store, you'll need to identify the exact amperage and type of your current breaker. Most RV supply stores carry replacement fuses for WFCO converters. WFCO converters use specific fuse ratings (typically 30A, 35A, 45A, or 55A) depending on the model - check your converter's specifications for the correct amperage. Bring your multimeter to test for continuity and a flashlight since you'll be working underneath the trailer.

Purchase a replacement breaker rated for the same amperage - don't go higher as this protects your wiring from overload. Get the correct part for your model (verify with dealer). Also grab some dielectric grease and wire brushes in case the terminals need cleaning.

Make sure your batteries are disconnected and the shore power is unplugged before starting any work. Have your phone ready to take pictures of the wiring configuration before disconnecting anything, as WFCO installations can vary in their layout.

Repair Steps

Start by locating the breaker on the bottom of your power distribution center - it will be a cylindrical or rectangular device with two large terminals. With power confirmed disconnected, test it first with your multimeter set to continuity; if the fuse has blown, you should see no continuity (infinite resistance) across the terminals when it should be closed.

Carefully remove the two wires from the breaker terminals. Note that one wire typically comes from the converter output and the other feeds your 12V distribution panel. Clean both terminals with a wire brush and apply a light coat of dielectric grease.

Install the new breaker in the same orientation, ensuring the terminals match the wire gauge - most use 10 AWG or 12 AWG wire. Tighten the terminal screws to manufacturer specifications. Don't overtighten as this can damage the internal components.

Before reconnecting the battery, double-check all your 12V appliances are turned off, then reconnect the positive terminal first, followed by the negative terminal. The new breaker should allow 12V power to flow immediately. Test your lights, water pump, and other 12V systems to confirm proper operation. If the new breaker trips immediately, you have a short circuit that needs to be located before the system will work properly.

When to Get Help

Call a professional if the new breaker trips immediately upon installation, as this indicates a short circuit somewhere in your 12V system that requires systematic troubleshooting with specialized equipment. An RV technician can quickly isolate which circuit is causing the problem using current clamps and circuit tracers.

Also seek help if you discover the breaker terminals are severely corroded or burned, as this often indicates deeper electrical issues in your converter or wiring that could be dangerous to address without proper training. If you're uncomfortable working with electrical systems or can't safely access the breaker location, it's worth the service call to avoid potential safety hazards.

Consider professional diagnosis if you've had recurring 12V electrical problems, as repetitive breaker failures often point to undersized wiring, poor connections, or failing appliances that are drawing excessive current and will continue to cause problems until properly addressed.