Originally Posted by Emmalina
What the hell does anybody want more than 30A for anyway ? Cruise
Well, in my case the following:
2 - 15000 BTU air conditioners - ~2000 watts each
1 - watt hot water
heater - ~2000 watts (new is 1200 watts)
1 - washer/dryer - ~1800 watts in dryer mode
1 - microwave - ~1200 watts
1 - holding plate compressor
- ~1000 watts
1 - blow dryer for GF - ~1800 watts
1 - Charger
- ~4500 watts
Now these don't all run at once but combinations do. One can argue that with care you can turn on and off things to manage the load. Would you do that in your shoreside home?
I routinely exceed 3600 watts (the size of the isolation transformer) luckily the inverter
can support the load. However, during the winter if both air conditioners come on I am loosing ground, someone takes a shower
and even with a 7000 watt isolation transformer I am going to be in deficit.
This is my primary residence so that is somewhat different than a vessel which is rarely used.
Now, the previous 35' vessel, I did install the second 30A panel when I was living in MD. The reasons were twofold
1) If the dock
power went off I did not want the inverter to try to carry the resistive loads if it was accidently left in automatic invert mode.
2) Resistive loads (hot water heater, oil
radiator heater for cabin
, cube heater for cabin) coupled with regular loads of the boat tended to burn up the shore power cable connection at the dock. If loaded for extended periods at near rating (lets say 25A) I found that the less than perfect shore power connections would heat up. After the first 3 winters aboard in MD I added the second shore power and never burned up a cable again.
It is essential to keep the two neutrals completely independent as well as the hots (obviously), in my case I used a pair of galvanic isolators (one for each 30A service) which were then each independently connected to ships ground (and the ground bus of each panel)
For this "resistive service" panel I used #10 wire throughout, not just from the shore power connection to the panel but to each point of service (hot water heater, a plug
in the forward cabin
, two plugs in the main cabin. Each point of service was supported by a single 15A breaker, the 30A main breaker on this panel (and the other panel) were double pole.
In my case, the second panel was physically separated from the main panel which resulted in two independent systems and was very useful when maintaining the primary electrical system
I had drop lamps and heat available if necessary.
One of the other significant advantages of the dual 30A service is that the shore power cables
are far more manageable. A single 125/50 or 250/50 shore power cable is rather heavy due to the wire size required for the 50A service. In addition, I can generally by 8 or more 30A shore power cables on sale
for the price
of a 50A cable which I have never seen go on sale