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Old 02-04-2014, 03:16 PM   #1
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30 amp source with 50 amp system

I am chartering a boat with a 50 amp electrical system. It has a "Y" adapter with the power cord so when visiting a marina with only 30 amp service you can connect to two 30 amp receptacles. My question is, if there is only one 30 amp receptacle available can I connect one leg of the "Y" adapter to the 30 amp receptacle and be careful how much equipment I run? Do you think I could run reverse cycle heat and a few cabin lights? Is it dangerous to leave one leg of the "Y" adapter open?

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Old 02-04-2014, 04:27 PM   #2
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I have the same 50 amp 250 volt cord and intelligent combiner box for my boat. My understanding (I could be wrong) is that the electronics that are in the box are supposed to make sure you are plugged into 2 30 amp services of different phases so that a 220 volt AC or water heater will work. Believe box is supposed to disconnect if you lost one leg or they were on the same phase.

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Old 02-04-2014, 04:31 PM   #3
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Assuming it's a proper adapter cable supplied with the boat, it's what's more correctly called a "Reverse Y" because it combines two 30A 120V circuits into one 50A 120/240V. A "splitter" would split a 50A 120/240V circuit into two 30A 120V circuits. The connectors will be different (opposite sex), and the operation is different in a subtle, but important way.

Now, to answer your question.... No, it won't work. A proper Reverse Y detects the presence of the two 30A 120V circuits, ensures they are out of phase so they correctly combine to create 240V, and only cut through the power if everything checks out. It's an important safety feature.

I say "proper" reverse Y because there are plenty of people who hack together something that will work under certain circumstances if you really know what you are doing (most people don't) and are really careful, but it's just too dangerous in the hands of most people. But I would be really surprised if a charter boat were supplied with such a hack job.
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Old 02-04-2014, 05:05 PM   #4
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Thanks!

How about if there is a single cord adapter that mates the 50 amp cord to a 30 amp receptacle, think I can run reverse cycle heat and a few cabin lights?
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Old 02-04-2014, 05:09 PM   #5
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I think that what has been said before is mostly correct, but I am a bit surprised that one 120V, 30 amp leg won't partially work. No you won't be able to use any 240V appliances on the boat but it is rare to have any.

But it should be possible for the connected 120V leg to supply power to its respective 120V breaker buss on the main panel. There will be two such busses and only one of them will be powered if only one leg is connected.

So give it a try. I don't see anything that makes it unsafe to run off of one leg if the reverse y splitter will let it.

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Old 02-04-2014, 05:10 PM   #6
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How about if there is a single cord adapter that mates the 50 amp cord to a 30 amp receptacle, think I can run reverse cycle heat and a few cabin lights?
Most likely "no" on the heat since on a 50A boat it is most likely 240V. Lights, maybe, but now you are asking to go down the hackery path and create something dangerous. If you are asking these questions, then you are exactly the person who shouldn't be playing with it. Just use two 30A outlets and the supplied adapter like it's supposed to have.
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Old 02-04-2014, 05:15 PM   #7
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I think that what has been said before is mostly correct, but I am a bit surprised that one 120V, 30 amp leg won't partially work. No you won't be able to use any 240V appliances on the boat but it is rare to have any.

But it should be possible for the connected 120V leg to supply power to its respective 120V breaker buss on the main panel. There will be two such busses and only one of them will be powered if only one leg is connected.

So give it a try. I don't see anything that makes it unsafe to run off of one leg if the reverse y splitter will let it.

David

Dave, where it becomes dangerous is if any 240V appliance has been left on, creating a path for the powered leg to feed back to the un-powered leg. Yes, you can go make sure they are all turned off, but what if someone mistakenly switches on the hot water heater?

You are correct that it CAN be done, but in my humble opinion it SHOULD NOT be done by anyone who doesn't really know what they are doing, and someone asking how to do it is just such a person.
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Old 02-04-2014, 05:22 PM   #8
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Looks like the Hubble smart "y" will not let you use only one leg...I could be wrong but here is a snapshot from their catalog

"Features and Benefits
3 pole contactor breaks both hots and neutrals to prevent possibility of “live” plug when not engaged.

You may need a 30 to 50 single adapter....the other doesn't sound right but I can't find anything to the contrary yet.

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Old 02-04-2014, 05:23 PM   #9
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Gosh sorry I asked Twisted...

How do you learn if you don't ask?
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Old 02-04-2014, 05:27 PM   #10
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Or better yet run the genny. We had to run the genny multiple times in the Bahamas do to unreliable power.
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Old 02-04-2014, 05:40 PM   #11
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I think that what has been said before is mostly correct, but I am a bit surprised that one 120V, 30 amp leg won't partially work. No you won't be able to use any 240V appliances on the boat but it is rare to have any.

But it should be possible for the connected 120V leg to supply power to its respective 120V breaker buss on the main panel. There will be two such busses and only one of them will be powered if only one leg is connected.

So give it a try. I don't see anything that makes it unsafe to run off of one leg if the reverse y splitter will let it.

David
I would tend to agree...as not all boats with 50 amp 125/2450V are wired for 240V...

But I think that's why they are called smart "Y"s cause they may not work (see my previous post) on only one leg to prevent any backfeeding.

If you did have only 2 separate 110 panels and no 240...then I have to ask someone better in electrical than me...could you just wire up a "dumb" "Y" ? or is something going on with the neutral that I don't know about that may be dangerous? (yes you would have to cap the unused 30 prongs even though they wouldn't be hot unless you had an internal problem in the boat.)
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Old 02-04-2014, 07:07 PM   #12
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I am chartering a boat with a 50 amp electrical system. It has a "Y" adapter with the power cord so when visiting a marina with only 30 amp service you can connect to two 30 amp receptacles. My question is, if there is only one 30 amp receptacle available can I connect one leg of the "Y" adapter to the 30 amp receptacle .......... ?
I'm going to go out on a limb here and suggest that you ask the person or company that is providing the boat.

Regardless, you can only get 30 amps from a 30 amp receptacle so you're not going to be able to run some appliances.
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Old 02-04-2014, 10:00 PM   #13
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I have a Mainship 36. I have two 30A cords to a 50A "Y" which is normal.
Inside my boat on my power board with all the circuit breakers, I have a 3 position switch at the top. Line 1 - Line 1&2 - Gen
Pos. Line 1 is for when you only have one 30A receptacle. It will run the entire boat on that one line which is also the forward plug outlet outside the boat.
Pos Line 1&2 is when I have either the 50A "Y" with the 2 30A cords going to it or 2 separate 30A receptacles on the doc.
Pos. Gen is when I use either the Gen or my Inverter.

There is no magic inside the "Y" adapter. It is simply wired so that the 50A 220V AC plug wiring is broken down to two 30A 120V AC circuits inside the cord.

If you have only one 30 A circuit avail on the dock, your boat is limited to 30A total
by both the dock 30A circuit and your boats 30A Circuit breaker. Also on my boat, my Ckt Breaker Panel is broken down into 2 separate panels. Like I said earlier, if I use the Line 1 position with only one cord (my forward one), both panels will have elcctricity but limited to 30A total.
I hope this isn't too confusing.
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Old 02-04-2014, 10:04 PM   #14
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If it is a 50amp panel than no it will not work on that splitter. You need a 30-50A adapter and than only the 110V side will work. We have both for our 50A boat.
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Old 02-04-2014, 10:27 PM   #15
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With 50A 220V you have two hot leads and one neutral.
With 30A service you have 110V - 0ne hot, one neutral and 1 ground.
If you think you know what you are doing you can make it work on 110V but wont have a ground wire. Not good. So you really don't know what you are doing.
If you really, really don't know what you are doing you will have 110V where your ground should be and it wont be a pretty ending.
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Old 02-04-2014, 10:46 PM   #16
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With 50A 220V you have two hot leads and one neutral.
With 30A service you have 110V - 0ne hot, one neutral and 1 ground.
If you think you know what you are doing you can make it work on 110V but wont have a ground wire. Not good. So you really don't know what you are doing.
If you really, really don't know what you are doing you will have 110V where your ground should be and it wont be a pretty ending.
Most marinas are 50A 125/250V 4 wire...red, black, white, green..and so is a 50A 125/250V power cord. The green is the ground like normal so I'm not quite sure where everyone is going with this.

The interior panel is what varies with some boats taking advantage of the 250V and some just using the increased power to have 2-50 amp 125V busses. Thus the advantage over 2-30 amp panels (busses).

The OP's question about using a smart Y cord adapter is a good one...I didn't know if they would allow hooking up only one leg and still have it work...from the quick read in the catalog...no the smart Ys need both legs hooked up and a single 30-50 adapter is needed. I'm guessing that a 30-50 amp splitter (to a 125/250V 50 amp cord) only powers on leg (panel).
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Old 02-04-2014, 10:54 PM   #17
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I've got a 50-amp outlet at my berth. Since my boat's systems use 30 amps, I need to use an adapter. Most every time at other marinas, the power is 30 amps. Seen many boats with dual cords, but I'm ignorant of their workings.

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Old 02-04-2014, 10:56 PM   #18
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My older 1986 model is low tech
All I could contribute is what I have.
Never know if they have the same set-up or not.
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Old 02-05-2014, 07:02 AM   #19
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The simply wired no brain Y will be happy to function .

As it will only light off 1/2 the boats 120, you will have to select which 120 circuit has the fridge and other goodies , the other circuit may mostly be for added air cond.

Beware as each 120 leg is expecting 50A , not just 30A the adapter/power pole can provide.

The CB on the dock post will let you when you get too power thirsty.

Folks that cruise have 2 choices for low power pole areas.

1. is a following inverter that can boost the amperage during high use times , and recharge the batt set at low consumption times , about $4,000

2. install load shedding relays , about $60. each EG so the HW heater will be shut off when the reefer turns on.

With a handful installed living on 120V 15A can still be a fine lifestyle , but no air cond.
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Old 02-05-2014, 07:03 AM   #20
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The OP's question about using a smart Y cord adapter is a good one...I didn't know if they would allow hooking up only one leg and still have it work...from the quick read in the catalog...no the smart Ys need both legs hooked up and a single 30-50 adapter is needed. I'm guessing that a 30-50 amp splitter (to a 125/250V 50 amp cord) only powers on leg (panel).
Your guess is correct. They won't work unless both ends are correctly connected. That's where the "smart" part comes from. It's a safety precaution to prevent inadvertently creating an energized, exposed 30A plug when you have just the other 30A side plugged in. And it also verifies that the two 30A outlets you are supposed to be plugged into are indeed out of phase so you have 120/240V on the 50A end.
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