Circuit Breaker vs Fuse in a Campervan: Which to Use Where
Both fuses and circuit breakers protect wiring from overcurrent. The right choice depends on where in the system you are and what you need the protection device to do.
What they have in common
Both fuses and circuit breakers open a circuit when current exceeds a threshold, protecting the cable downstream from overheating. The principle is the same; the mechanism and reset behaviour differ.
Fuses
A fuse contains a thin wire or element that melts when too much current flows, breaking the circuit. Once blown, it must be replaced.
Types used in campervans:
| Fuse type | Current range | Typical use |
|---|---|---|
| Blade fuse (ATO/ATC) | 1A–40A | Individual 12V circuits (lighting, fridge, USB) |
| Mega fuse | 40A–500A | Main battery positive cable, inverter cable |
| ANL (bolt-down) fuse | 40A–500A | Main battery cable, DC-DC charger |
| MIDI fuse | 30A–100A | Mid-range circuits |
| Glass tube fuse | 0.5A–30A | Older fuse boxes, some accessories |
Advantages of fuses:
- Very fast blow time — the element melts almost instantaneously under a severe fault
- No moving parts — extremely reliable long-term
- Low cost
- ANL and Mega fuses handle very high currents reliably
Disadvantages:
- Must be replaced after a fault — if you blow a fuse mid-trip, you need a spare
- Cannot be tested without removing them
Circuit breakers
A circuit breaker uses a bimetallic strip or magnetic mechanism to trip a switch when overcurrent flows. After a fault, you reset by pressing a button or flipping the lever.
Types used in campervans:
| Breaker type | Current range | Typical use |
|---|---|---|
| Automotive/marine blade breaker | 5A–30A | 12V circuit protection with convenient reset |
| DIN rail MCB (miniature circuit breaker) | 6A–63A | 12V fuse box, consumer units |
| Combined RCD+MCB (RCBO) | 6A–32A | 230V circuits |
Advantages of circuit breakers:
- Resettable — no replacement part needed after a nuisance trip
- Can act as a switch (trip and reset as needed)
- DIN rail breakers allow professional distribution panel design
Disadvantages:
- More expensive than fuses
- Mechanical parts can wear over time or fail to trip in rare cases
- Some automotive circuit breakers have slower trip times than fuses
Which to use where
Main battery cable: ANL fuse
The main positive cable from your leisure battery to your bus bar or distribution panel should be protected by an ANL fuse within 300mm of the battery positive terminal. This is your entire system's primary protection.
Choose ANL over a circuit breaker for this position because:
- ANL fuses reliably interrupt very high fault currents
- No mechanical failure modes
- Lower cost for the ratings needed (100A–300A)
Inverter DC cable: ANL fuse
Same logic as the main cable — use an ANL fuse within 300mm of the battery/bus bar positive for the inverter's DC cable.
Individual 12V circuits: blade fuses or circuit breakers
For individual circuits (lighting, fridge, USB sockets, water pump):
- Blade fuses in a blade fuse box: Simple, inexpensive, replacement fuses easy to carry
- DIN rail circuit breakers (e.g., Hager, Schneider): More professional installation, resettable, can double as circuit switches
Either is appropriate. Many UK builders use a DIN rail MCB consumer unit for 12V distribution — it looks professional, allows easy circuit switching, and each breaker can be labelled.
230V circuits: RCD + MCBs
For 230V circuits, use an RCD (residual current device) immediately after the hook-up inlet or inverter output, then MCBs (miniature circuit breakers) for individual 230V circuits. This is not optional — it is a safety requirement for any 230V installation.
The RCD protects against earth faults (which fuses/MCBs cannot detect). MCBs protect against overcurrent on individual circuits.
A typical UK campervan fuse/breaker layout
Battery positive → ANL fuse (100–200A) → main positive bus bar
From the positive bus bar:
- 230V mains charger: fuse or MCB sized for charger current
- MPPT solar charger: 15–40A blade fuse or MCB
- DC-DC charger: 40A blade fuse or MCB
- Inverter: ANL fuse on dedicated cable
- 12V fuse box: 60–80A blade fuse, then individual fused circuits within
FAQ
My 12V fridge keeps blowing fuses. What's wrong?
The fridge's compressor draws a startup surge of 3–5× its running current. If the fuse is rated for the running current only, startup will blow it. Use a fuse rated for the startup surge (check fridge datasheet for peak current) or replace with a circuit breaker with a short thermal delay.
Can I use a circuit breaker instead of an ANL fuse on the main battery cable?
High-current circuit breakers (150A–300A) exist and work for this purpose. They are more expensive than ANL fuses and have slightly slower fault response. If budget allows, a 250A or 300A circuit breaker on the main cable acts as a convenient disconnect switch as well.
What rating ANL fuse do I need?
Match the ANL fuse rating to the cable ampacity — use the fuse to protect the cable, not the device. If your main cable is 50mm² (rated ~160A), use a 150A or 160A ANL fuse. If the fuse is larger than the cable rating, it no longer protects the cable.