Originally Posted by steve77
A boat came in to Horta with large power requirements - 50 Amps 240 Volts in the US and we are trying to connect to the European 230 V shore power outlets.
The shore power pedestals here have four 16 Amp outlets. We discovered that these outlets contain multiple phases of the power distribution system so that the voltage between two outlets (at least the two I checked, I did not try all combinations) is 400 Volts.
We made up an adapter pigtail to allow them to plug into one of the 16 Amp receptacles, but it really limits them as to what they can run onboard. My question is, how can we make a Y-adapter for this boat? All I can come up with is to wire two 16 Amp plugs in parallel to the feed the 50 Amp plug that connects to the boat. Then it becomes a safety
issue to check the pedestal with a voltmeter to ensure you are plugging in to two 230 Volt receptacles that are in phase, with the voltage between them at 0 Volts.
1) Are you sure that ALL on board are 220V/240V loads (which in the US would usually be fed by two live/hot wires, each of them 180 degrees away form each other and 120V away from earth) and you do not have any 120V loads that in a US boat would be fed by one of the hots and a neutral)
2) Are you sure that the boat is properly wired to ABYC standards, ie no connection of green wire to (what is supposed to be) AC Neutral wires onboard?
If the answer is YES to both questions then keep going, otherwise stop right there because stuff is going to break and people may get hurt.
I take as a given that there are no inductive loads ie motors, that would be sensitive to the change in frequency.
You said you will check that the two outlets that you are going to connect in parallel are indeed fed by the same phase and have same polarity, ie voltage between L in one outlet to L in other outlet is at most a fraction of a volt, and same for N and N.... So far so good
Also make sure that the two shore outlets belong to the same circuit in the marina installation
.. Otherwise someone could get killed if they turn off a breaker to work in one of the circuits, just to get zapped when you plug in your Y adapter and backfeed the "disconnected" circuit. This is the golden rule
of never "paralleling" two circuits downstream of the panel where they are born..
Note that the American boat will most lilely be wired to take two hots (call them L1 and L2) that are 180 degrees away form each other and 120V away from earth (one going each way). Now you will feed one of them with the N from shore and the other one with one of the Ls from shore. So far so good. Thw problem is that there may (or MUST) also be some 120V loads (light or fan in the oven
, wall outlets, etc) that are connected between one of the two hots and a white "neutral" wire onboard the boat. In your "jury rigged" setup that "neutral" wire will not be connected to anything ashore , hence you will have what is called a "broken neutral" and it will be very easy to expose those 120V loads to almost 240V with catastrophic consequences.
Underlying all this is that the combined 120-240W wiring
system you find in the US relies on having two 120V hots phased 180 degrees away form each other. Two hots give you 240V, hot to neutral gives you 120V.
you will most likely have three hots that are 120 (not 180) degrees away form each other and 220-240V away from earth, which is makes it impossible to make the combined US system delivery
both 120V for outlets and 240V for heater, etc) at the same itme. In Trinidad ( at least Crew´s Inn) they have 3-phase systems but each hot is 127V away from neutral and earth, hence you can make a proper 4-wire connection between that boat and shore and get 127V in the 120V circuits and 220V (= 127 x 2 x cos 60 degrees) into teh 240V circuits.
Having said all that, my recommendation is that if you or the owner need to ask about it you probably should not be doing it. The owner can buy an isolation transformer that will do everything that is required except the frequency, and do it safely.