Why does my fuse keep blowing right when I turn something on?

This usually points to a startup surge exceeding the fuse rating — common with motors, compressors, and inverters, which draw a brief spike (often 2x running current) on startup. If the fuse is sized correctly for the device's running current but blows on startup, check the device's surge/inrush spec against the fuse rating.

Is it ever OK to just put in a bigger fuse?

No — the fuse must be sized at or below the wire's safe ampacity, regardless of what trips it. If a correctly sized fuse keeps blowing, the fix is to find and fix the underlying cause (a short, an oversized load, or a surge issue), not to install a fuse that exceeds the wire's rating, which removes the wire's protection.

How do I find a short circuit that's blowing a fuse?

With the circuit de-energized and the fuse removed, use a multimeter in continuity/resistance mode between the positive and negative conductors at the load end. A reading near 0 ohms indicates a short. Then work along the circuit, checking at intermediate points (connectors, switches) to narrow down the location.

RV Fuse Keeps Blowing? Causes and How to Fix It

A fuse that blows repeatedly is doing its job — but the goal is to find out why, not to work around it. Here's how to diagnose the real cause in a van or RV 12V system.

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Rule one: never just upsize the fuse

The fuse protects the wire, sized at or below its safe ampacity. If a correctly sized fuse blows, the fix is to find the cause — not install a larger fuse, which removes the wire's protection and can let it overheat in a real fault. See RV fuse sizing for how fuses should be sized in the first place.

Most likely causes, in order

1. Startup surge exceeds the fuse rating

Motors, compressors, and inverters draw a brief surge on startup — often 2x their running current. If a fuse is sized correctly for running current but blows only at startup, the surge is the culprit. The fix is usually a slow-blow fuse type appropriate for the load (many ANL/MIDI fuses already have this characteristic) — not a higher-rated fuse of the same type.

2. The load draws more than expected

Check the actual draw of the device with a multimeter or your battery monitor, and compare to its rated spec. A device drawing more than its datasheet (a failing compressor, a degraded inverter) can blow a correctly sized fuse — the fix is repairing or replacing the device, not the fuse.

3. A short circuit

A genuine short — bare wires touching, a pinched cable against metal, water ingress at a connector — draws very high current instantly and blows the fuse immediately on connection, often with a visible spark. To find it:

Remove the fuse and disconnect the load.
Set a multimeter to continuity/resistance between the positive and negative conductors at the load end.
A near-zero reading indicates a short. Work back along the circuit (check connectors, switches, anywhere cable passes through metal) to narrow down the location.

Inspect for chafing where cable passes through metal

A common short location is where a cable passes through a hole in sheet metal (a wall, a cabinet frame) without a grommet — vibration over time wears through the insulation and the conductor contacts bare metal. Always use grommets or edge protection at metal pass-throughs.

4. Wrong fuse type for the application

A blade fuse used where an ANL/Class T is needed (or vice versa) can have a mismatched interrupt rating or response curve for the load — particularly relevant for LiFePO4 main fuses, which need a Class T's high interrupt rating.

When the fuse blows only intermittently

Intermittent blowing often points to a marginal load (close to the fuse's rating, occasionally pushed over by a combination of devices on the same circuit) or an intermittent short (a connection that only shorts when jostled). Check what else was running at the time, and inspect connections for looseness.