Through Lorient Grand Large, I had attended an online course given by Henri from TEEM and this proved extremely useful and provided me with the fundamentals I needed to work out how to go about my rewiring. One of the really key takeaways was the importance of knowing how the diagram related to real life - rewiring was going to give me a much-needed first hand knowledge of this!

The first time I opened the distribution box, I got very scared and shut it very quickly, being sure to screw the lid on tightly. Rewiring was going to force me to face this demon which was super important because out at sea is not the place to try and understand what is going on!

Planning

With help from a very friendly, Jersey marine electrician called Peter, I had a plan for my project. Step 1 - Diagram / Step 2 - Order parts / Step 4 - Build new distribution box / Step 5 - Run new wiring / Step 6 - Make connections to equipment and distribution box / Step 7 - Connect to batteries / Step 8 - Test.

With my new design, I intended to keep things as simple as possible and to keep the distribution box as tidy as possible. On a boat this is often easier said than done because generally, each piece of equipment has its own circuit so that a problem in one circuit should not affect the other circuits. This means that for every red positive wire going out, there is a black negative wire coming back. Peter gave me the idea of taking the negative wires to a bus and to have this bus outside of the main distribution box. This would halve the number of wires inside of the distribution box!

Distribution Box

Now to find myself a waterproof box (technical term "enclosure") to make into my distribution panel. After much searching, I came across Phoenix Mecano and really liked the look of their enclosures. All I had to do was choose the correct size - queue measuring tape and another diagram.

I was really excited when my box turned up in the post because it meant I could get started on the rewiring!!! Obviously there was a bit of work to make my off the shelf box into the power distribution box I needed....

Next step was to take apart all the old connections and wiring......

I ended up with cable all over the boat and a fair few bags full of cables from inside the old distribution box. With tape and cable ties I managed to bring a bit of order to the chaos which allowed me the space needed to work on my new cable runs.

Cable Management

Cable runs require a bit of thinking because to be tidy and efficient, you want there to be a limited number of individual routes which are as short as possible. However, there is electrical equipment in all corners of the boat and certain pieces of equipment need to "talk" with other pieces of equipment. Add to this the different sizes of wire and the need to be a contortionist, it's quite a challenge!

The reason we want routes to be as short as possible is because of a phenomenon called 'voltage drop' which results from the resistance of the cables themselves and the connections. The effect of this can be quite extreme in 12V system because the supplied voltage is not very high and so voltage drop can reduce the voltage supplied to the equipment to below a level where the equipment can function. Because it is in part a function of the resistance of the cable, this problem is also linked to cable sizes which we will mention a bit later on.

The other challenge is finding a way to get the cable-tie mounts to stick to the hull of the boat. These mounts are pretty fundamental to any wiring project because they provide the anchor points for the cable-ties which support the cables. However, the self-adhesive ones don't stick and even if they pretend to for 5 minutes, they fall off as soon as you attach your cable so you need to use some sort of adhesive. And the adhesive is not likely to create a very good chemical bond between the plastic cable-tie mount and the fibreglass hull so you must use sandpaper to key both surfaces to give the adhesive a chance. This means that rewiring is a three step process: (1) Plan the routes (2) Place and fix the cable-tie mounts (3) Run the cables after the adhesive has set.

I started off with the easiest part of the job, organising the cable-runs inside the escape tunnel and then moved on to the NKE network and finally I ran the cables for my other equipment (VHF/AIS/solar panels etc).

Cable Sizes

One of the things I learnt quite quickly was that not all cables are equal. There are different sizes, there are different configurations, different thicknesses of insulation, different colours, the list goes on.....

Perhaps the most important aspect in cable sizing is its current carrying capacity. This is the max current that a cable can carry without exceeding its temperature rating. The problem with exceeded the max current capacity is that this generates heat because the resistance of the wire increases as it gets hotter. This could melt through the insulation which could lead to a short circuit or could eventually lead to a fire.

In Europe, cable sizes are expressed in cross-sectional area in mm2 and so a bigger cable has a larger number. For use on the boat, flexibility is really important so it is normal to have mutliple strands making up the cable rather than a single core. For additional resistance to the marine environment, the copper strands in these cables are all individually coated in tin, hence "tinned" cable. In the US, wire sizes are expressed using American Wire Gauge where larger numbers indicate smaller cable until you get to cables larger than 50mm2 (1/0 AWG) and after this, a larger number means a larger cable. European and AWG sizings are not however directly comparable so it is important again to check the current carrying capacity and ensure that this is sufficient for the load (with a safety margin).

Connections

Once I had run my cable, I needed to join the positive cables to the fuse box (blade terminals) and the negative cables to the negative bus bar (ring terminals). These terminal fittings are generally fixed to the wire by crimping (for which you need crimping pliers with the correct jaws). The connectors are either insulated or non-insulated and if they are insulated, the second stage is to apply heat using a heat gun (in extremis a soldering iron or lighter) to heat shrink the plastic insulation. The connectors I found contain glue inside the insulation which melts when the heat is applied to provide a better seal around the cable.

To accommodate the different sizes of cable from 0.5mm2 to 6mm2, the connectors come in 3 sizes: Red, Blue and Yellow.

To make the cable runs the right length, it is often useful to be able to shorten the cable or to splice in a section of cable and so I also needed butt connectors to join cables together. This can be achieved with crimps or by soldering and covering with heatshrink but I found some really useful "solder-seal" connectors which use glue-filled heat-shrink sleeves around a solder bubble in the middle to join cables.

Finally, the connect up my NKE instruments to the NKE bus bars, I needed to use solder to galvanise the wires I had stripped and then insert the galvanised ends into the connection terminals.

Fuses

Once I had made all the connections, it was time to think about fuses. Fuses protect a system's wiring from excessive current which could otherwise cause an electrical fire. In designing my new system, fuses were something I particularly wanted to think about because the fuses in the previous system were spread over the boat in different fuse holders and there were quite a few different types of fuses. I wanted to simplify the fusing of the system to make it easier to replace a blown fuse and to reduce the number and types of fuses I had to carry in spares.

My new fuse box uses exclusively blade fuses which are very commonly available in a range of current ratings. Having the fuses centralised in the distribution box means that if I suspect a fuse has blown, there is only one place to check.

The fuses are marked with their continuous current rating and will blow if they are subjected to a current greater than this. However, for excess currents which only just exceed the fuse rating, the fuse may take up to a few minutes to blow whereas if it were subjected to a higher current, it would blow much faster.

In short, when selecting fuses, the fuse rating should be somewhere between: (1) the current rating of the smallest cable in the circuit (upper bound) and (2) the expected current draw of the equipment (lower bound).

Testing

With the fuses in, it was time to connect up the batteries to see if it all worked...... and nothing. The batteries were completely flat! Although it had been cold, I thought that the batteries should have kept at least some of the charge but I had maybe 4V across the terminals. Time to order a battery charger. In the meantime, to get some charge back into the batteries with my solar panels, I had to bypass my solar panel regulators which had shut down because there was so little juice.

However, I came back after a sunny day and was really disappointed to find that I still had zero juice in the batteries. I was very perplexed and decided to re-check the battery cables. I found some crimped connections which had corroded and the negative battery wire was a very dubious shade of black.

After cutting away as much of the corroded cable as I could, I reconnected the batteries and waited for my battery charger to arrive. It came fast and excitedly I plugged it in - I bought a Victron smart charger and so I could monitor it using Bluetooth!! It started off great and then two minutes later it quit charging. I imagine it must have decided the batteries were dead because there was so little charge. On a hunch, I thought I would try to charge each battery individually. The first one I connected didn't charge (of course) but the second one was much better behaved and started to charge properly. Now at least, when it was charged, I would be able to test my system!

This time when I turned the switch, lights started flashing and I could hear the GPS's familiar pings as it started to try and acquire a satellite fix. I tested each piece of equipment and found a few that didn't work so I tightened all the connections and magic!! It's amazing how a nut that looks tight is actually too loose to provide an electrical connection!

Final job was a liberal coating of dielectric grease to all the connections to help prevent corrosion and the job was a good'un!!