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Old 26-07-2020, 13:37   #16
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Re: Wiring dual 240V 50 amp shore power, USA

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Originally Posted by Thumbs Up View Post
2x50A to 100A Y adapters do have special electronics. https://www.imarineusa.com/HubbellMarineYQ100PLUS.aspx
L1 and L2 are randomly assigned so you would have a 50/50 chance of a dead short when you plugged into that second outlet.
If you had two onboard 50 amp inlets, one would have hot male prongs when only using one. If one of the 50 amp shore plugs came loose, it would also have hot male prongs. You can't rely on the pedestal breaker to test the polarity, a 50 amp "spark" can ruin a plug and burn your hands and flashburn your eyes. You would need "special electronics".
Yep I was wrong. I do not think L1 and L2 are randomly assigned but I can believe there are places where every electrician is an idiot. Of course the spark would be inside the circuit breaker which is rated to deal with a dead short safely. Who said the breakers were to test polarity? (hint: you) The breaker protect the cables, that’s all.

Indeed, if one plug is taken out without first flipping the breakers, you get hot male prongs. Not idiot proof so not allowed. But more than 3 grand for a couple of contactors and a microcontroller is pretty stiff profit margins...
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Old 26-07-2020, 17:33   #17
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Re: Wiring dual 240V 50 amp shore power, USA

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It is easy to make a simple tester to see if the wiring is in phase or 180 degrees out of phase with an incandescent light bulb. That test would have to be performed every time he visits a new slip and he would have to make wiring adjustments to correct errors.

When I added a 16.000 BTU air conditioner to a 30 amp service boat I added a completely separate 30 amp inlet for it. Splitting the load would be the simplest way to to go.

That is a lot of power. How big it the boat?
Rewiring an adapter or cable or anything isn't an option in this case. Needs to be plug and play as son in law is not an electrical whiz.

Boat is a 56' Viking and it has more stuff than my house and boat combined. Twin 21 kW generators (for redundancy, only one runs at a time); Five separate air conditioners, five or six separate refrigerator and/or freezer systems, water maker, washer dryer, electric stove, commercial size ice maker for the fish box and probably more stuff that I haven't even seen yet.
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Old 26-07-2020, 17:39   #18
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Re: Wiring dual 240V 50 amp shore power, USA

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Originally Posted by Quadrille in JB View Post
Thanks for all of the good information. Do you think a reading of 260 V AC at the boat panel is out of limits.
I measured this using a good fluke meter that I had Factory calibrated recently.
What would cause the voltage on the boat to read 260 vac when the pedestal reads 240 vac?
Are you using the same Fluke to read the power at the dock and on the boat? Which Fluke meter and how is it set for reading the AC volts? AC voltage can be read as peak, average or RMS voltage and all are different.

Another possibility, if the boat has an isolation transformer or the AC runs through an inverter that could be boosting the volts on the boat.
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Old 26-07-2020, 17:46   #19
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Re: Wiring dual 240V 50 amp shore power, USA

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Yep I was wrong. I do not think L1 and L2 are randomly assigned but I can believe there are places where every electrician is an idiot. Of course the spark would be inside the circuit breaker which is rated to deal with a dead short safely. Who said the breakers were to test polarity? (hint: you) The breaker protect the cables, that’s all.

Indeed, if one plug is taken out without first flipping the breakers, you get hot male prongs. Not idiot proof so not allowed. But more than 3 grand for a couple of contactors and a microcontroller is pretty stiff profit margins...
This is also my understanding, L1 and L2 are not randomly assigned according to standards BUT I would be a large sum of money that it is fairly common to have them randomly wired on a dock.

If one is wired wrong and two cords are connected there will definitely be some sparking somewhere.
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Old 26-07-2020, 17:54   #20
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Re: Wiring dual 240V 50 amp shore power, USA

Well just made a discovery. Panel has switches for Shore 1 and Shore 2 but it was assumed that this was an uninstalled feature. But I opened the panel and found wires to the Shore 2 switch, traced and found a connection for a second shore power cord. Shore 1 is hard wired and on a reel, Shore 2 is behind a panel and just a connection for a cord.

So looks like there's a provision for two 50 amp supplies. Now I just have to figure out how to operate all the switches on the AC panel. There are three, the main and two secondary panels. With two shore power supplies, two generators and the loads divided up into several different 120 and 240 groups the panel looks like the control panel on a 737.

I was just informed that there is a manual on board that's about the size of the Oxford English Dictionary, unabridged version.
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Old 26-07-2020, 19:32   #21
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Re: Wiring dual 240V 50 amp shore power, USA

Have you looked into the availability of twin 50A supplies on the dock? If you are in the super-yacht dock its probably OK but many dock only have a limited number of berths with a 50A supply let alone 2.
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Old 26-07-2020, 19:47   #22
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Re: Wiring dual 240V 50 amp shore power, USA

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Have you looked into the availability of twin 50A supplies on the dock? If you are in the super-yacht dock its probably OK but many dock only have a limited number of berths with a 50A supply let alone 2.
Really? In Florida we have 2x30A, 2x50A plus 1x 100A at every slip...
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Old 27-07-2020, 16:46   #23
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Re: Wiring dual 240V 50 amp shore power, USA

Let's just make this clear.


Never, under any circumstances, should you connect together two outlets. As mentioned earlier, L1 and L2 are random. Plus many docks are 3 phase so each outlet has some combination of L1, L2, or L3. In that case, you have a very good chance of creating a dead short when you parallel two outlets.


Pre-made combiners are fine, but they combine the lines to create an L1/L2 power source. That's not paralleling two output. Or they have smarts built in to check and only combine safely.
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Old 27-07-2020, 17:09   #24
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Re: Wiring dual 240V 50 amp shore power, USA

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It’s okay and I’m pretty sure within code as long as the panel aboard is 100A rated or upgraded to 100A.

Many boats use the 2x50A to 100A Y adapter. There is no need for special electronics because both L1 and L2 are present in each of the two legs.

If 2x 50A inlet is used then each cable is a standard 50A cable. These cables are protected by the 50A breakers in the pedestal. When some idiot reversed L1 and L2 on one of the outlets then the breaker will pop and someone will have to correct the wiring... this is to be expected with bad mistakes like that

On the in-board end of the inlets need to be separate 50A breakers after which conductors can be paralleled. From there on everything needs to be 100A rated.
You do need special electronics because you need to match up the two phases and reverse them if necessary.

While two different 240V 50A outlets are guaranteed to have two 120V hots on opposite phase from each other they aren't guaranteed to be in any particular order. To get 240V 100A the phases from each outlet need to be aligned.

Some pairs of outlets will never work at all. You have incompatible phases that can't be aligned. The electronics would need to detect that and prevent a circuit or there will be instant and catastrophic damage.

Honestly having two seperate 50A panels simplifies a lot of things.
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Old 28-07-2020, 03:48   #25
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Re: Wiring dual 240V 50 amp shore power, USA

The boat in question that I was discussing has 2-50 A pigtails that are connected to a gray Hubbel box that has the 100A receptical built in. I guess this box must contain the electronics and relays needed to keep things safe.
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Old 28-07-2020, 04:13   #26
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Re: Wiring dual 240V 50 amp shore power, USA

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Originally Posted by tanglewood View Post
Let's just make this clear.


Never, under any circumstances, should you connect together two outlets. As mentioned earlier, L1 and L2 are random. Plus many docks are 3 phase so each outlet has some combination of L1, L2, or L3. In that case, you have a very good chance of creating a dead short when you parallel two outlets.


Pre-made combiners are fine, but they combine the lines to create an L1/L2 power source. That's not paralleling two output. Or they have smarts built in to check and only combine safely.
I’m European so never professionally worked on US systems and I have been wrong before as well... but I am pretty sure that the 120/240V split service is -single- phase and both L1 and L2 are from the same 3-phase leg. All the systems I have seen use a 240V secondary winding with center tap which is grounded and becomes the neutral. So L1 and L2 are 180 degree shifted which is why you get 240 between them.

So no, there will not be different legs from 3-phase used for L1 and L2. On the next dock they probably bring another leg from the 3-phase. The equipment that I got to look at in a bit more detail, brought 440 (480) V onto the center of the dock where the transformer was and all the branch circuits to pedestals came together. Those docks did have 100A but no 3-phase service so however that works for mega yachts I don’t know.
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Old 28-07-2020, 09:12   #27
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Re: Wiring dual 240V 50 amp shore power, USA

That is correct. An infinite source of confusion is L1 and L2 being referred to as phases which is technically incorrect. They are the separate legs of the same phase split by the transformer of one of the 3 hot wires from the power grid. A problem is that large commercial marinas are wired for 3 phase and you can't derive 120/240 from a 3 phase without a center tap transformer. Some of these marinas provide a 120/208 voltage to the 50 amp (120/240) outlets. In this case there will be two phases (of the 3 phase supply) at L1 and L2. These phases are 120 degrees apart (instead of 180 as in split phase) which is why you only get 208 volts (instead of 240). For the OP's scenario to work in this instance (2 50 amp 120/240 into same panel on boat) He would need to find 2 50 amp outlets using the same 2 of the 3 phases. It is probably a code violation to wire these 50 amp outlets at 208 volts but is common practice at 3 phase marinas.
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