I don't know anything about marine regulations, but on land you generally only have a breaker or fuse on one side of a transformer (usually the "powered" side)

I don't know anything about marine regulations, but on land you generally only have a breaker or fuse on one side of a transformer (usually the "powered" side). If you're in US, the mains transformer feeding your residential service almost certainly has no overcurrent protection on the secondary, it has a fuse on the primary.