My boat came with two huge, old-looking, heavy bricks that I later learned are Isolation Transformers.
I'm not an expert, but as a boat owner I try to do as much DIY
as possible and learn from the experts. My electrical
was done by a master boat electrician and I learned a lot from him, including the incredible value of my isolation transformers.
First, due to their function, size, weight, and cost, it only makes sense for a full time cruiser to install as they will protect your boat from shore power faults. Your boat is not physically connected to the shore power ground, which is the path of problems if nearby boats or the shore power system isn't up to snuff.
If your boat stays in one marina you don't need this protection unless you don't trust that marina's shore power service
Second, due to the way they function, it can be a problem connecting with newer shore power systems with sensitive GFCI breakers. The IT creates a short power spike as it connects the shore power to the boat that can trip sensitive shore power pedestal
breakers. This has happened twice in the past 2 years when we started full time cruising.
But this problem is rare, and if you're interested I'll described both below.
The first time this happened was at an older, remote
small harbor and I contacted my electrical
guy and he informed me of the above and emailed me a diagram to bypass the IT if I really wanted to connect with that power source. I decided not to as we were only there for a couple of days to sit out a storm on our way to our destination
The second time this happened was at a marina that I really wanted to return to in the future and followed the bypass procedure, which was easier than I thought it would be, involving switching some wires around (carefully!).
In the process I discovered a fault- the hot and neutral were reversed on the boat-side shore power connection! This hadn't been a problem visiting some 30 different marinas until the sensitive, new system of the one we were at. Amazing. Corrected the fault and now we can connect without tripping the breaker.
I've made friends with and have come to love my IT as it provides me a lot of peace of mind when connecting to different shore power systems when we visit unknown marinas (which is not often nowadays as we like to live on the hook).
Would I pony up the bucks if it wasn't already on my boat? As a full time cruiser, knowing what I know now, yes I would.