I went thru this on my boat, which was a mix of 220/50 & 120/60.
What I found -
- the distribution wiring
was all 2.5mm2 which is slightly larger than 14awg
- the breakers were either 10amp or 16amp
- the hot water
heater element was already a 120v 750w unit (they were running it at 220v)
- AC was installed in NA, so it was already 120v 60hz (although will run at lesser capacity on 120v/50hz via an auto transformer)
Since the wire size more than supports the breaker size, I changed the receps and the shore power
cord and used all the existing breakers and wiring. My boat already had Berker Integro (Germany) receps (& matching 12v light switches), so I went to the trouble to get the North American receps from Berker in order to maintain the look and use the same cover plate & box. I like the look, but it was a pain and $$$ to get them. I also replaced the 220/50 inverter
with a 120/60. The shore power charger
If you read the technical data you'll find the claim that ELCIs built for 50hz shouldn't be used for 60hz. My investigation found that when using the 'wrong' ELCI, it will trip at a different unbalance value. I did the simple math and figured that if the ELCI trips at +/- 20%, I don't care, it'll still trip on a fault (somewhere between 24ma to 36ma). If you want exactly 30ma trip, you should probably replace the ELCI(s) that are built for 50hz. I don't have any GFCIs on my boat (5ma trip).
Now my boat is all 120v/60hz & NA receps. I've since added a 6250va isolation transformer, fed with 240v/60hz using the secondary as 120v/60hz. The shore power is 240v/50a with a 30a ELCI on the input to the IT & 50a breaker on the output. I also wired my genset to the input of the IT via a transfer switch. This allows the IT to clean up some of the harmonics in the genset output.