30amp reverse Y adapter

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Newtrawlerowner

Newtrawlerowner

Senior Member
Joined
Nov 16, 2019
Messages
347
Location
USA
Vessel Name
PartnerShip II
Vessel Make
2003 Mainship 400
2003 Mainship 400
I would like to buy a reverse Y adapter to plug into 2 30amp receptacle and connect my 50amp shore power plug.
My question for you all is will the AC and water heater work using this adapter?
 
Assumption made, you have a 50A 120V cord. You want to connect two 30A 120V plugs into the 50A. It will work but only if both 30's are on the same phase. At a pedestal two side by side 30A may well be on opposite phase and would pop the breakers, maybe cook the adapter, by being 240V.
 
Best to check the voltage between the two 30's on the shore power pedestal for 240V with your voltmeter before attempting. The two 30s on my pier are same phase, and my brother connects his two 30-Amp to single 50-Amp connector and the connects his big 50-Amp boat power cable when he visits. He runs all the electrics in his boat he needs being mindful not to overload.
 
Are we talking two 30a/125v to one 50a/125v?
Or
are we talking two 30a/125v to one 50a/125/250v?

It makes a difference.
 
I want to connect two 30a/125v to one 50a/125/250v
 
SteveK said:
Assumption made, you have a 50A 120V cord. You want to connect two 30A 120V plugs into the 50A. It will work but only if both 30's are on the same phase. At a pedestal two side by side 30A may well be on opposite phase and would pop the breakers, maybe cook the adapter, by being 240V.
Click to expand...
Thanks Steve. I am aware of them being on the same phase.
 
Newtrawlerowner said:
I want to connect two 30a/125v to one 50a/125/250v
Click to expand...
In this case you need the outlets to be out of phase.

Everything will work up to a draw of 30a per side.

You do not say how many BTU’s the AC is or if anything is 240v.

The water heater is typically 11 amps and resides on the primary house leg. AC is typically 11 amps per 16,000 btu and lives on leg 2.
 
The only way you should even consider doing this is with a "smart" reverse Y. They are expensive, but sense power on each of the 30A inlets, and only connect through to the boat if both are present, and correctly phased. One will cost you $750 to $1000.

That said, "smart" reverse Y adapters are going the way of dinosaurs, because they will not work with newer RCD dock outlets. The neutral currents in the two 30A dock outlets will virtually never match the line current, and trip the RCD.
 
West Marine sells this smart Y adapter for about $500.
Model # 10072957 Mfg # RY504-2-30
I connect 2 30A 120v to my 50A 125/250 v cord. Works OK on my 1976 Hatteras. But I do have some beefy isolation transformers so no guarantee it will work for you. But I suspect it will and don't think it would cause any problem if it doesn't work. At least it is easy to return to WM if it does not work. I don't think the 30A outlets are opposite phase.
 
READY said:
West Marine sells this smart Y adapter for about $500.
Model # 10072957 Mfg # RY504-2-30
I connect 2 30A 120v to my 50A 125/250 v cord. Works OK on my 1976 Hatteras. But I do have some beefy isolation transformers so no guarantee it will work for you. But I suspect it will and don't think it would cause any problem if it doesn't work. At least it is easy to return to WM if it does not work. I don't think the 30A outlets are opposite phase.
Click to expand...
If the sockets are not out of phase you could end up running 60 amps down the neutral. This could turn into a fire. This is why TT only recommends Smart Y adapters, so you don’t inadvertently plug into two sockets in the same phase.
 
READY said:
West Marine sells this smart Y adapter for about $500.
Model # 10072957 Mfg # RY504-2-30
I connect 2 30A 120v to my 50A 125/250 v cord. Works OK on my 1976 Hatteras. But I do have some beefy isolation transformers so no guarantee it will work for you. But I suspect it will and don't think it would cause any problem if it doesn't work. At least it is easy to return to WM if it does not work. I don't think the 30A outlets are opposite phase.
Click to expand...
That's the type of smart reverse Y that I'm talking about. Good to see they are less $$ than I recall.
 
twistedtree said:
The only way you should even consider doing this is with a "smart" reverse Y. They are expensive, but sense power on each of the 30A inlets, and only connect through to the boat if both are present, and correctly phased. One will cost you $750 to $1000.

That said, "smart" reverse Y adapters are going the way of dinosaurs, because they will not work with newer RCD dock outlets. The neutral currents in the two 30A dock outlets will virtually never match the line current, and trip the RCD.
Click to expand...

Both responses above are correct. The 30A 125V outlets need to be OPPOSITE PHASING not the same and it will only work on older marina power systems so their usefulness will decline as marinas get upgraded power.
 
SteveK said:
Assumption made, you have a 50A 120V cord. You want to connect two 30A 120V plugs into the 50A. It will work but only if both 30's are on the same phase. At a pedestal two side by side 30A may well be on opposite phase and would pop the breakers, maybe cook the adapter, by being 240V.
Click to expand...
Above is not correct and is an important consideration before purchasing / experimenting.
 
@Bacchus Hi Don. Yes that P/N provided is a smart adapter. Thus the $500 price. It is an older dock so the RCD issue did not come up.
Ken
 
I carry both double 30 to 50 and 50 to double 30 for different situations.
Biggest thing is to measure first before plugging in so you know if you can double up or not. Marina installations vary.
Also suggest you spend time mapping your panel so you know which leg your various devices are on.
I see boat systems where there is an attempt to balance the draw and others with all the ACs on one leg. I guess the thought was if you only had 1 30A available you could do without AC.
 
SteveK said:
Assumption made, you have a 50A 120V cord. You want to connect two 30A 120V plugs into the 50A. It will work but only if both 30's are on the same phase. At a pedestal two side by side 30A may well be on opposite phase and would pop the breakers, maybe cook the adapter, by being 240V.
Click to expand...

Bacchus said:
Above is not correct and is an important consideration before purchasing / experimenting.
Click to expand...
so you are going to drop that comment and not bother to explain yourself?
 
Bacchus said:
Above is not correct and is an important consideration before purchasing / experimenting.
Click to expand...
I don't see anything wrong with what Steve said. I suspect Bacchus accidentally read in 125/250 when Steve in fact said 125 or missed that he used the words in phase and accidentally read out of phase.

If you combined two in phase 30a 125v sockets you would still have 125v. How many amps you could pull thru such an arrangement would vary depending on the resistance of each path. If one path had high enough resistance you would be in fact limited to 30a.
 
tiltrider1 said:
If you combined two in phase 30a 125v sockets you would still have 125v. How many amps you could pull thru such an arrangement would vary depending on the resistance of each path. If one path had high enough resistance you would be in fact limited to 30a.
Click to expand...
Paralleling two power sources like that is a big no-no, violating pretty much every electrical code and standard on the planet. It's only ever acceptable in conjunction with fancy phase alignment and paralleling gear like you would find for paralleling multiple large generators on a big ship, or paralleling separate grid segments.
 
SteveK said:
Assumption made, you have a 50A 120V cord. You want to connect two 30A 120V plugs into the 50A. It will work but only if both 30's are on the same phase. At a pedestal two side by side 30A may well be on opposite phase and would pop the breakers, maybe cook the adapter, by being 240V.
Click to expand...
I do apologize to Steve as I missread his assumption... 50A 120V boat inlet.

Those, however, are uncommon vs 50A 240/120V arrangements and are NOT what newtrawlerowner reported hehas on his boat.

My reason for strong wording was to catch readers attention as missing that comment / assumption can be dangerous and costly. Apologies if anyone was offended... that was not my intention.

If anyone has that arrangement I'd suggest replacing the panel and going to (2) 30A inlets supplying a split panel. My Mainship has exactly that kind of split panel that provides a safe way to combine separate bus bars and run off one 30A cord OR keep them separate and use (2) 30A cords / sources w/o concern if the 30A sources are in or out of phase.

Smart Y combines only work for 50A 240/120V inlets and provide protection for the user as they will not connect if connected to improper/ in phase 30A sources.
A dumb Y combiner is a dangerous accessory and not sure if a mfg even offers one. I'd caution anyobe/ everyone from even considering a DIY Reverse Y for use in combining in- phase 30A sources.
 
Don,
My boat OEM comes with three 30A inlets. That was a surprise, but then I remembered that most marinas in the day it was built only had 15A & 30A pedestals. Along came the 50A 120V cable followed by 50A 125/250 as we became power hungry.
In this thread it was important to know what the inlet splitter was combining.
 
twistedtree said:
Paralleling two power sources like that is a big no-no, violating pretty much every electrical code and standard on the planet. It's only ever acceptable in conjunction with fancy phase alignment and paralleling gear like you would find for paralleling multiple large generators on a big ship, or paralleling separate grid segments.
Click to expand...
Thank you TT. I was not suggesting it to be an acceptable solution but my language didn’t spell out the negatives very clearly.
 
My shore power connection at the home marina has to use this system. Everything operates normally.
 
sailorskip said:
My shore power connection at the home marina has to use this system. Everything operates normally.
Click to expand...
It operates normally until it doesn't. As TT pointed out its against the rules for safety reasons. I would talk to the marina to see if there is a possible long-term solution.

We are not talking about 2x 30a 125v to 50a 125/250v. We are talking about 2x 30a 125v to 50a 125v. At first glance people won't notice the difference between 50a 125/250v and 50a 125v when written but there is a big difference when you try to plug in.
 
Got it. Sorry I didn't read all the posts. My scenario is 2x 30a 125v to 50a 125/250v.
 
sailorskip said:
Got it. Sorry I didn't read all the posts. My scenario is 2x 30a 125v to 50a 125/250v.
Click to expand...
That's fine with a smart reverse Y, as long as the dock doesn't have RCD outlets. As soon as you get to a dock with RCDs, a reverse Y will trip them.

For anyone wondering why it's a problem, it's because there is a common neutral between the 50A 120/240 side and both of the 30A 120V sides. As a result, there is no way to control how much current runs through each of the 30A outlet neutrals. But an RCD expects the line and neutral currents to be equal in each 30A outlet, and will trip if it's not.
 
Fortunately, docks built to RCD regulations will come with a 50a 125/250v outlet so no Y needed.
 
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