We’ve had a galvanitic isolator (protecting the boat’s hull against earth current leakage) installed since launch, but I’ve recently taken shorepower isolation and galvanitic protection to the next level.
1) It physically isolates the boat’s 240V electrics from the shore power by the use of physically separate transformer coils which transfer electricity from one coil to another via electromagnetic induction.
2) The primary coil has switched multiple windings which allow either 110V or 240V input, and a constant 240V output.
This provides me with complete physical isolation from the shore power in marinas. If there are any wiring faults or current leakage they do not affect our boat or aluminium hull.
Isolation transformers provide galvanic isolation and are used to protect against electric shock, to suppress electrical noise in sensitive devices, or to transfer power between two circuits which must not be connected.
The transformer is rated at 5kw, which means it’ll handle up to 20 Amps at 240v. This far exceeds our boat’s power requirements, but to be safe, I also upgraded all the main 240V supply wiring to 6mm cable, which will easily handle the load.
I have also bought a replacement 6mm shore power cable to handle the additional current draw when connected to 110v. To supply the theoretical maximum 20A at 240V, the transformer could potentially draw approximately 40A from the 110V supply, so it requires a very chunky cable.
The unit itself is quite bulky and heavy, so I bolted it securely to a wooden bulkhead in the transom area. This keeps the cable run from the shore power connection to a minimum, keeps the weight low, keeps it mounted safely and secure.
The transformer has two cable glands – one for the supply input from the shore power, and one output feeding to the supply crossover switch (for selecting either the shore power or generator supply), on to the breaker switches through the inverter and out to the 240V circuits.
Costs and Supply
There are plenty of production marine isolation transformers on the market, but because of my dual 110V/240V supply requirement, I found a UK company Airlink Transformers Ltd that could produce a custom unit at a reasonable price.
Michael Harris at Airlink Transformers Ltd discussed my requirements and designed and made the unit for me. They provided a very professional and helpful service. The transformer cost just under £500 including VAT. It is solidly built and is CE certified.
The shorepower cable came from a company called IndustrialExtensionLeads.co.uk, who have a great stock of quality cables at non-marine inflated prices. Their 25m off-cuts of 6mm Arctic Yellow flex are ideal for a shore cable, and instead of costing several hundred pounds, cost me just £65.