Why a fused distribution block is so important and how to install it

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While making the wiring of a DIY camper, the most straightforward (wrong) solution would be to just connect any 12V appliances directly to the battery, following the scheme BATTERY –> CABLE –> SWITCH –> CABLE –> APPLIANCE.

That is definitely a super dangerous install!

In case of shortcircuit, the current sent by battery would be able to start a fire. That’s all.

I am not going into details explaining you why 12V tension is more hazardous in terms of fire catching compared to 220V, check this external website in case you do not just trust me 🙂

So, how to avoid this risk? How to deal with shortcircuits?

We should always connect the battery to a fused distribution block, where each fuse protects a single electrical circuit. In case of shortcircuit in one circuit, its fuse only will blow off and everything will be fine and safe.

One fuse, one appliance or group of appliances (For example all the interior led lights).

Sounds easy, right? It is! 😉

Let’s go in details and  discover how to succesfully install a fused distribution block.

1)  Think about what appliances you really need

Dreaming about what kind of electrical equipment we would love to install is great fun! 🙂

I spent so many hours imagining what I would need in my camper, while offroading in Australia and camping in the beaches.

Off course I need lights, 12v and USB sockets to charge mobile devices, water pump, fridge and freezer, inverter and so much more.

But on simpler campervan conversion (just like my Hyundai H1 4×4 conversion project) you may have fewer needs, maybe just lights, some 12v/USB sockets and water pump.

Take your time to complete a list of what you plan to install, it will make life way easier during next steps! Take note of the current needed for each appliance too. If you just find the power (W), do your maths to calculate the current (A).

A = W / V  —> for example in case of a 12v water pump of 30W you have —> A= 30W / 12V = 2,5A

Your list should look something like this:

LED interior lights   – 1A

Water pump – 2,5A

Compressor fridge – 10A

….

P.s.: remember that often the power needed to start an electrical device is more than one needed once device is operating. Some products clearly indicate it, some do not, so do some research about it and put it down the MAXIMUM amount of A needed by the device.

2) Just power or power and ground distribution block?

Basically two models of distribution blocks exist.

1. Just power, the most common, it distributes only the power. The appliances will receive only the power by the block and will be grounded directly to the chassis. This type of block is used mainly on vehicles where the ground cable coming from battery is soundly connected to chassis.
2. Power and ground: the names says it all, they distribute also the ground to each circuit. That is nice where it is difficult or not possible to ground each device to chassis. It is the case of boats and big campers.

3) Where are you going to place it?

Our goal would be to position the block as close as possible to battery, to keep the power cable from it as short as possible to avoid any voltage drop. The ideal location would be somewhere fair easy to access, bear in mind that in case of any circuit’s failure, the first to check would be the distribution block itself, looking for blown off fuses.

4) Choose cables of correct diameter

The power (and ground) cables must be thick enough to let enough current to pass and to avoid any significant voltage drop. Same for the cables that distribute power from the fuse box to any appliance.

As a rule of thumb, consider that a cable of 1mm2 can safely carry up to 4A. So, if you need 30A in the fused distribution block, a cable of at least 7,5mm2 is needed. Off course electrical cables’ sizes are standardized: just approximate to the bigger section. In this case, you should buy a 10mm2 cable that is pretty common.

5) Make a quality terminal connection between the battery cables and the block

Probably the most difficult step – some specific tools are required. Although some people use to solder the battery terminal, that is generally considered not the best practice: the soldered terminal is so rigid that tends to break under vibration. Some serious 4wders sweared that their soldered terminals lasted a lifetime under hard abuse on the track…but…I would not take the risk.

The best would be to make a good crimp of the terminals – using a quality crimping tool. A professional grade tool of this type is quite expensive, but you may have a decent result buying this or this model. Buying even a cheap 30/40$ crimper is worth if you plan to make more than one vehicle, for just a pair of battery cable it’s probably cheaper and easier to just knock the door of a mechanic or car electrician.

That being said, take in account that a good soldered terminal is better than a poor crimped one, so do things properly or invest a few bucks having somebody doing this for you! 🙂

Personally, I use the ring terminals that are so easy to connect to the block using a nut.

6) Connect each appliance (or group) to each fuse socket

Again, you should use the right cable size for each line. Following with the same example, the 12v water pump, if it requires a maximum of 5A, you could use a 2,5mm2 cable to be safe.

7) Insert the correct size fuse and you are done!

An entire book could be written regarding this, anyway take a look at this post, I have prepared a short straight-forward guide to help you about that! 😉

Really hope this guide helped you to understand the role of a properly wired fused distribution box and how to install it quickly.

If you have any doubts or question, feel free to let me know in the comments below, I will reply personally as soon as possible.