Rewiring brings years of circuits added on top of each other into one orderly system. A good rewire is one where, when something fails, you know which cable goes where.
When is it needed?
- Circuits added later, unfused or run in household cable.
- Hot connections on the thermal camera and corroded terminals.
- Unexplained leakage current or batteries that run themselves down.
- A switchboard with no diagram and no labels.
Principles of a rewire
- Cable
- Tinned, multi-strand marine cable. Size chosen for current and for voltage drop over the run length.
- Protection
- Each circuit is fused as close to the source as possible; the main battery cable is protected too.
- Layout
- AC and DC run on separate routes; cables are secured and protected from sharp edges.
- Labels and diagram
- Every cable labelled at both ends; an up-to-date diagram kept aboard.
- Standards
- ISO 10133 for DC installations and ISO 13297 for AC.
The sequence
- Inventory. Existing loads and battery capacity listed.
- Design. Load calculation, battery bank, charging sources and diagram.
- Strip and run. Old circuits out, new ones run to the diagram.
- Testing. Continuity, insulation, leakage and a thermal scan under load.
- Handover. Diagram, label list and test records.
What we often see
- Overheating electrical connection: On the thermal camera, one pole of the main battery switch is markedly hotter.
- Unfused circuit added later: A circuit added for extra equipment in household cable with terminal blocks, and no fuse.
How the load calculation is done
A new system's design starts with the power and running time of every consumer aboard. Fridge, autopilot, instruments, lighting, pumps and high-current loads such as the windlass are listed one by one. From that list come both the battery bank's capacity and the current each circuit must carry. Cable size is chosen for length as well as current; thin cable on a long run drops voltage at the far end and the equipment cannot perform as expected.
The switchboard
The new switchboard is laid out with each circuit on its own protection, legible labels and access behind it for maintenance. The main switch and battery selector must be quick to find in an emergency. Adding voltage and current meters makes it easier to follow the system's state in use.
Galvanic protection and bonding
A rewire is also the time to review the boat's bonding and cathodic protection. How underwater metals are bonded, where the anodes sit and the galvanic isolator on the shore-power side are handled as part of the new installation. When the work is done, a reference electrode reading confirms the result.
Rewiring in stages
If the budget does not allow the whole system at once, the work can be staged: main distribution, battery bank and switchboard first; individual circuits after. The new diagram is followed from the first stage, so old and new circuits do not mix.
At acceptance
After the rewire, every circuit is checked against the diagram and scanned under load with the thermal camera. The diagram, label list and test results go into the handover file.
Safety and fire
A significant share of fires aboard are electrical: a loose connection, an overloaded cable, an unprotected circuit. A rewire is the chance to reduce these risks at the root. Protecting cables against chafe, covering battery terminals and protecting every circuit at the right rating are the most important parts of the work.
A good installation works quietly and makes fault-finding easy.
That saves time for years.