question

With a steel narrowboat the isolation transformer is being installed to separate the boats hull from the shore power earth to avoid galvanic corrosion from stray earth currents. To keep them separate when in the water J34 should not be connected to J34A nor should the PE wire be connected to J34.I

If you have had a connection to J34 then you would not have protection from galvanic corrosion but the system would still be safe, i.e. your RCD breakers on the boat would still work and protect you if there was an electrical fault to ground. It would be as if you had a direct shore power connection without a galvanic isolator. This only matters when you are on shore power, have you been hooked up for the 5 years.

The connection to J34 is made when on land is I believe for electrical safety. my understanding is that when you are in water if there is an earth fault, the boat hull can discharge the voltage into the water so you could not get a shock if you touch the boat with one hand and the dock with the other. However, if you are on land and there is an earth fault the hull could be at a high voltage because it can not dissipate that voltage to ground, therefore someone could get a shock from your hull.

On my narrowboat I had built last year I specified an IT and one of the first checks I made was to use my multimeter to see if there was a connection between the shorepower socket earth connection and the boat hull to confirm that they were not connected.

Thank you pwfarnell. I really appreciate your help. I have been connected to shore power only for 5 years. Never unplugged. I'm taking my boat our for blacking this month so I will see if I have any galvanic issues. I feel very gutted the transformer instillation was not done correctly in the first place and left without protection. Hopefully my anodes have done their job.