Electrical systems have some inherent dangers: direct dangers (electrocution) or indirect dangers (e.g. causing fires through overheated conductors).

Avoiding these dangers (in particular the latter one) is one of the primary purposes of this course.

This course focuses on low voltage DC systems (typically 12 V and 24 V), where there is very little risk of electrical shock. However, most boats will also have at least a minimal AC system on board.

In order to avoid accidents, ALWAYS unplug any shore power connection and turn off any generator or inverter before you start touching any wire on your boat. 

You should also make sure that no one accidentally plugs the AC power back in while you are working on the system. Storing the shore power cord away in a safe place is a good idea while working on your system.

The risks in DC systems are mostly fires caused by undersized conductors and bad connections or short circuits in conductors with missing overcurrent protection devices. But there is also a risk of explosion and chemical burns from lead acid batteries when they are improperly treated and lithium-ion batteries have their own hazards.

Before you start working on your system, make sure to watch all the lessons in the modules on conductors and batteries. That's where we will talk in detail about how to avoid danger.

A note about our illustrations

In most cases, the drawings and diagrams of circuits shown in this course are meant to give an overview of the devices and their connections. For reasons of simplicity, we sometimes omit the overcurrent protection devices and switches that would be required for a safe operation of the circuit.

Don't simply replicate one of the example circuits, but make sure that all conductors are equipped with the necessary overcurrent protection devices. We will show you how to do this in the relevant lesson in the module on conductors.

Before we start with the course, we have to give you the following disclaimer:


You are responsible for any modification you do on your boat. Even though we created this course to the best of our knowledge and belief, we cannot take responsibility for any damage or harm resulting from following any of the advice given here. Whenever you make changes to your boat's electrical system, make sure to have the system checked by a professional before connecting the power supply.

But now, let's get started with the first module! 

Have fun with the course!

Nigel, Michael, & Jan

  • It’d be helpful having the lessons numbered, vs “next lesson”, if we’re re-reviewing mtl, it’s easier knowing which lesson # we’re looking for, just an observation.

    • Hi Scott,
      Thanks for the suggestion. I’ll note that down for the next revision of the course. For now I’m afraid you’ll have to stick with the lesson overview in the menu or save the link to a lesson if you plan to go back to it later.

    • Jeff,

      Typically, solar is installed at 12v or 24v, and very occasionally 48v, so below the safety voltage but we are seeing some higher voltage installations, especially on catamarans with large solar arrays, so you are correct, these need to be disabled before tearing into the systems.

      Generally speaking, these series connected, higher voltage systems prevent full optimization of the solar array because of shading issues, different angles to the sun, etc. In this case it is better to have individual controllers and then use boost controllers if you need higher voltages.


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