Camper power distribution: smart fuse box and electronic fuses

Power distribution decides how safe, clear and easy to maintain the 12V or 24V electrics in your motorhome are. The classic setup is a fuse box, relays and switches. Modern systems combine all of this in one device with electronic fuses that switches, protects and measures every load individually. This article explains how camper power distribution is built, compares both approaches and shows what to look for in a smart fuse box.

How a 12V electrical system is built

1. Leisure battery: the energy source for everything in the living area.
2. Main fuse: directly at the positive terminal. It protects the thick main cable in case of a short circuit. With lithium batteries, it needs a sufficient breaking capacity, for example an MRBF, NH or Class T fuse.
3. Battery isolator switch: cuts power to the whole system, for example when you work on it or put the van into storage.
4. Distribution: this is where the power is split into the individual circuits, each with its own fuse.
5. Loads: lights, water pump, fridge, fans, heater, charging sockets.
6. Negative busbar: brings all negative wires back to the battery, through the shunt if you have one.

Every cable needs a fuse that matches its cross-section. The fuse protects the cable, not the device. The values that apply are in Cable size and fuse in a camper.

The classic way: fuse box, relays, switches

In the classic setup, each circuit has a blade fuse in a fuse holder. Loads that draw a lot of current or need to be switched remotely get a relay. You switch with wall switches and dim with separate dimmers. This works, but it has weaknesses:

• When a fuse blows, you have to find it behind the bench seat and need a matching spare fuse.
• You don't know which load draws how much.
• Every extension means new cables, new relays, new switches.
• With a creeping fault, such as a pump that draws more and more current, you notice nothing until something fails.

The modern way: electronic fuses

An electronic fuse measures the current constantly and switches off when it gets too high. Because it is a switch itself, it replaces both the fuse and the relay. The everyday benefits:

• Set instead of swap: you set the trip value in the interface and change it whenever you need to.
• Reset with a tap: no spare fuse, no tools.
• Selectable characteristic: fast for electronics, slow for pumps, compressors and motors that briefly draw more when they switch on.
• Measurement per output: you see the voltage, current and power of every load.
• Protection against persistent faults: if you keep resetting while the fault remains, you get a forced pause.

More on this in Electronic fuses: set instead of swap.

Classic or electronic: the comparison

	Fuse box with relays	Electronic power distribution
Fuse trips	Replace the fuse	Reset with a tap
Change fuse rating	Buy a different fuse	Set it in the interface
See consumption	No	Yes, per output
Remote switching	Only with an extra relay	Built in
Dimming	Separate dimmer	Built in on suitable outputs
Voltage protection per load	No	Yes
Extending	New parts, new cables	Set up a free output

What to look for in a fuse module

• Current per output and in total: is it enough for a compressor fridge and a water pump? Large inverters belong directly on the battery with their own fuse.
• Adjustable characteristic: otherwise the pump trips the fuse every time it starts.
• Measurement per output: only then can you see where the power goes.
• Inputs for wall buttons: so control stays in the vehicle, even without a phone.
• Behaviour after a power cut: do the outputs come back in their last state?
• 12V and 24V: does the module detect the system voltage by itself?
• Development and testing: electronics that switch power for the whole vehicle should be developed to automotive standards.

Ampy: the power distribution from Camper Jarvis

Ampy combines fuse box, relays, dimmers and current measurement for six loads in one device.

• 6 outputs with 24A continuous each, up to 32A for short periods, and 120A across all outputs combined.
• Electronic fuse per output, trip value freely adjustable, characteristic fast, normal or slow. The trip value must not exceed the maximum for the cross-section of the cable to the load.
• Measurement of voltage, current and power per output.
• Dimming on every output up to 5A.
• Wall buttons or wall switches on every output. They switch directly at the module.
• Pop-top roof and awning: two outputs form a direction pair, and both directions are never on at the same time.
• Under and overvoltage protection per load, so you can switch off in stages.
• 12V and 24V detected automatically.
• Connection: supply on two M6 threaded studs, loads in lever terminals up to 4mm², button wires in removable spring terminals.

After a power cut, Ampy restores the last state of its outputs. How to connect Ampy is explained in Connecting Ampy.

An Ampy output in the dashboard: switch it and see live what the water pump draws.

If a fuse trips, the SmartKnob shows straight away which device is affected.

Important: Even with electronic fuses, the supply cable to the module needs a fuse at the battery that matches its cross-section. And never switch off a diesel heater by cutting its power supply, because it needs its run-on. At Camper Jarvis, Heaty controls heaters through their interface.

What about 230V?

230V loads don't belong in a 12V distribution. Separate rules apply here: an RCD with 30mA and a circuit breaker for every circuit. At Camper Jarvis, Switchy switches up to four 230V channels at up to 10A and detects faulty shore power. Why every 230V channel needs a B10 circuit breaker is explained in Why a B10 circuit breaker (MCB) is needed at 230V. Work on the 230V system must be done by a qualified electrician.

Switchy checks the shore power and shows earth and polarity.

Which characteristic for which load?

Load	Characteristic	Why
Water pump, fans	Slow	The motor briefly draws several times its normal current when starting
Compressor fridge	Slow	The compressor starts with a high current
Awning, pop-top roof	Slow	Motor under load
Small inverter	Slow	Capacitors charge when switched on. Larger inverters are connected directly to the battery with their own fuse and switched via their remote switch input
LED strips	Fast	Hardly any inrush current, so a rise in current is almost always a fault
LED lights with built-in driver	Normal	Briefly draw a charging current when switched on
Sensors, control units	Fast	Pure electronics. If fast trips when switching on, use normal
USB charging sockets	Normal	Input capacitors briefly draw more when switched on
Not sure	Normal	The safe middle ground

How power distribution works together with the battery, water and heating is shown in the guide Camper van smart home.