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Old 05-13-2017, 09:12 AM   #41
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I know the 50A, 125 volt is rare, but my 1984 Albin has this inlet and I find it more convenient than the dual 30 amp cords, I just need more adapters than most other boats.
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Old 05-14-2017, 06:40 AM   #42
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For your boat you might consider a std 50A240V plug with a 50A 120V socket on each of the leads of a Y .

In many marinas the 240 is split to create the 120V , and it happens that one leg has way more boats than the other.

Selecting the leg with the higher V will give your electric goodies a break.
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Old 05-14-2017, 07:47 AM   #43
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Looking at a a new-ish (two year old boat) that has a 50 amp connection. My dock only has 30 amp connections available. I am more confused after reading this thread but am guessing I can just get a 30 amp to 50 amp adapter and just need to manage my load to keep the boat draw under 30 amps as to not trip any breakers?
You are 100% correct. This is exactly what I do at my home dock.

I have two 30A power inlets which feed independent breaker panes. I can theoretically consume 60A of power by running everything at once. I have an adapter which allows me to run the two panels off one 50A outlet.

I've found that I don't need to do that. I can manage the loads to keep the total draw under 30A. I feed that with a "Y" adapter - one 30A to two 30A.

In the past three seasons, over three thousand miles of travel, I've never removed the 30A to 30A "Y", feeding BOTH panels from ONE 30A outlet. Even when more is available, it's not worth the effort of changing out adapters.

It's actually easier for me to use a 50A to 30A pigtail adapter if 50A is all that's available.

I've also been able to scrape by on 20A or even 15A "household" style outlets, with the appropriate pigtail. It requires a closer watch on load, but it keeps the essential systems running, and maybe even an air conditioner or water heater.

My point is you may find you don't NEED 50A power, at which point your options become much easier, and many of the admonishments and proclamations above may not apply to you.
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Old 11-04-2017, 10:07 PM   #44
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so the reverse Y 2x 30a shore power males that have a 50a boat-side female means the boat will have 50 amps of power available or is it only 30 amps? if only 30 amps, why not just use the straight (non Y) adapter so its 1x 30a shore to 1x 50a boat-side? thanks
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Old 11-05-2017, 06:07 AM   #45
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so the reverse Y 2x 30a shore power males that have a 50a boat-side female means the boat will have 50 amps of power available or is it only 30 amps? if only 30 amps, why not just use the straight (non Y) adapter so its 1x 30a shore to 1x 50a boat-side? thanks
The Smart Y starts with twin 30s and provides twin 30s to the boat -- but through a 50A cord and follow-on distribution system. 60A total.

A straight single non-Y 30-to-50A adapter delivers only one 30A (total) feed to the boat, which would then mean 15A per leg on the boat.

But then some boats also have isolation transformers... and I understand in that case, the single 30-to-50A adapter won't energize the boat systems at all.

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Old 11-05-2017, 06:13 AM   #46
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so the reverse Y 2x 30a shore power males that have a 50a boat-side female means the boat will have 50 amps of power available or is it only 30 amps? if only 30 amps, why not just use the straight (non Y) adapter so its 1x 30a shore to 1x 50a boat-side? thanks
If the boat is 125/250V 50A, then you will have 2 legs of 30A each. A total of 60A.

A 125/250V 50A boat normally has almost 100 amps (50 per leg) available.

I always thought it was 50A per leg, but an engineer showed how it wasnt quite a full 100A possible. I forget the engineering and just live with it.
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Old 11-05-2017, 01:52 PM   #47
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If the boat is 125/250V 50A, then you will have 2 legs of 30A each. A total of 60A.

A 125/250V 50A boat normally has almost 100 amps (50 per leg) available.

I always thought it was 50A per leg, but an engineer showed how it wasnt quite a full 100A possible. I forget the engineering and just live with it.


Rather than confuse the issue by trying to total up amps per leg, figure watts. No, you can't wring 100A out of a 50A cordset. You can get 2 legs of 120V @ 50A for a total of 12kW, or a 240V @ 50A for 12kW, but 2 legs of 240V isn't in the equation. 240V IS 2 legs of 120V each.
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Old 11-05-2017, 07:57 PM   #48
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Rather than confuse the issue by trying to total up amps per leg, figure watts. No, you can't wring 100A out of a 50A cordset. You can get 2 legs of 120V @ 50A for a total of 12kW, or a 240V @ 50A for 12kW, but 2 legs of 240V isn't in the equation. 240V IS 2 legs of 120V each.
thank you!
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Old 11-06-2017, 11:00 AM   #49
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240/120V, 50A service is 4-wire (L1,L2,N,G) 240V L1-L2, 120V L1-N and L2-N. If you plug into a 120V/30A 3-wire service (L,N,G) the adapter will usually connect L to both sides of your service panel so that all 120V loads can get power. No harm to 240V devices, they just won’t work. If you plug into two 120V/30A outlets, then two possibilities. If both outlets are on the same hot leg, your 240V devices still won’t work, but you now have 60A available for your 120V loads, assuming the two outlets are on separate circuit breakers. If the two outlets are on different legs (L1 and L2), then you get 240V/30A service and 120V/30A to each side of your panel. Not familiar with the expensive “reverse Y” adaptor, but from what has been described here it sounds like it will only permit power to flow if the two 30A outlets are on opposite legs. I fail to see the advantage of that. BTW: Most circuit breakers will only carry ~80% of the rated value continuously. Thus a “50A” breaker will carry about 40A continuous without tripping and a “30A” breaker about 24A. YMMV. There are breakers that will carry their full rated load continuously, but they use a different, and more expensive, technology.
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Old 11-06-2017, 11:27 AM   #50
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These Blue Seas breakers have intetesting trip curves.

Seems like thrir breakets hold the rated amperage. Think my Paneltronics do too.
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Old 11-06-2017, 11:39 AM   #51
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Looks like you have excellent circuit breakers. I presume these are the ones in your boat. It’s the breakers at the shorepower pedestal that matter.
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Old 11-06-2017, 03:27 PM   #52
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In case the OP didnt get his answer on "what would run on 240"; this would typically be something like a laundry dryer, or perhaps a large air conditioner system.
I too have a 50A cord on board but i don't do a lot of brain damage when i come to a marina with 30A, nor do i mess with a reverse-Y. I just use a simple 50 to 30A adaptor cord, and I don't run my dryer or in winter, i dont run all my heaters at the same time.
You'll need the cord on board if you cruise around and visit other marinas.
By the way i've run into that prob where my cord is in the cockpit and they have those bow angle slips;often I will just go ahead and back stern-in anyway as long as your bow isnt sticking out too much in the fairway.
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Old 11-06-2017, 06:07 PM   #53
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One more time: Two 30 amp 120v outlets through a Smart Y thence to a single 50amp/250 cord yields you 30 amps of 240v at the boat, comprised of two separate 30 amp 120v legs. You will not have 60 amps of anything on any one circuit.
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Old 11-06-2017, 06:18 PM   #54
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No, but you will have 30 amps available on each of your two legs, inlets...etc....if only asking 120V per leg.....?

Except not full power if the CBs are as what someone posted before, derated ....that I am not sure about.
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Old 11-06-2017, 06:22 PM   #55
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Agreed caltexflanc. What I forgot to mention is that there is a potential downside to using two 120V/30A outlets if they are on the same leg. In a true 240/120 service the L1 and L2 currents flow in opposite directions in the Neutral, so the maximum current in the Neutral is 50A and the neutral conductor is usually sized for that, i.e., the same as the L1 and L2 conductors. If the two 120V/30A outlets are on the same leg, one on each side of the distribution panel, the currents in the neutral will add. Thus it might be possible to have 60A in the neutral and it typically is not sized for that. That would like only be a problem if someone was drawing a full 30A on both legs for a long time, which from the other posts here seems unlikely.
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Old 11-06-2017, 06:27 PM   #56
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some unfortunate semantics at work here. Popular opinion is that if you supply 2 x 30A conductors plus a neutral, then you have 60Amps of 120V power available. That is true, but it is also true that no conductor has 60Amps on it. So, no ammeter will read 60 Amps. clear?

H3: a proper panel has overcurrent protection for the hots plus neutral. 240/120 panels should have 3 pole main breaker. so, a 60A neutral, caused by 30A on each side, should trip out a 50A panel.
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Old 11-06-2017, 06:29 PM   #57
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I beg to differ. If the two 30A supplies are in phase and not 180 degrees out of phase, the currents will add in the neutral and could be as high as 60A.
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Old 11-06-2017, 06:30 PM   #58
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... in the neutral. The current would have to be measure in the neutral.
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Old 11-06-2017, 06:37 PM   #59
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And thats the purpose of a smart y...not to allow you to plug into 2 30s in the same phase and get power.
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Old 11-06-2017, 06:47 PM   #60
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... in the neutral. The current would have to be measure in the neutral.
Yes, you are correct. I left out the part about reading the panel ammeters, which don't read N current. my bad.
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