Dual 30A Dock to 50A Boat Adapter

[rslifkin]

Originally Posted by waterman46

Are you in USA? In the US, I don't think we have 240V on the dock except for the superyachts, and a power cord for that will have 4 pins and not be compatible with the 120V 50A outlet. We generally have 50A 120V single phase only on the dock, and that supplies a 50A breaker and a 30A breaker in parallel at the pedestal.
I assume your 50A receptacle on the boat has three pins. Go to the dock outlet with your multimeter and check between the hot side of each of those 30A outlets. If I am right, you will get close to zero volts difference between the hot sides of each 30A outlet on the dock. If so just plug in your two 30A cords.

I've only ever seen 50A/125V dock outlets once. Almost everywhere has 30A/125V and 50A 125/250V. So with my twin 50A/125V inlets, I'm typically using a Y adapter to connect to a 50A 125/250 outlet or a pair of pigtail adapters to the 30A outlets.

[Dsanduril]

Originally Posted by waterman46

On my old boat the 120V breakers are both 2 pole. The neutral and hot are both disconnected when breaker is open. This may be by code I don't know.

Originally Posted by smac999

Yes 120v. Needs 2 pole main and 240 needs 3 pole.

But 2 poles does not mean 120. It could just be 240 done wrong.

Yes, two-poles is not definitive of anything, could be a 240V split phase wiring with the neutral left connected, could be a 120V system with the neutral disconnected, could be a 240V single phase system with the neutral disconnected.

A single-pole breaker, given that the OP says the boat is 120V, is pretty definitive.

And given that the boat is North American from the '70s it is entirely possible that a single-pole breaker was installed. A Euro boat, even from that era, would be a different question.

Can only wait until the weekend and the OP can post back about what he actually finds on the boat.

[RobertAB]

So the adapter worked great!

I wasn't able to reach the back side of the plug so couldn't see the cables. After digging though, the back side of the switch that changes between 30A and 50A clearly stated it was 50/240, was very hard to get the camera in there to see it though.

Interestingly, i have two other boat power plugs that come out of the hull vs the one I use on the coaming. The hull plugs I could get to the back of, they are 50A 125V but the boat no longer uses them and the cables that are attached look nasty, I need to pull the cables and bin them.

[valhalla360]

Just to clean up some of the discussion....in the USA/Canada.
- Standard 30amp plug is 30amp @ 120v.
The voltage is a nominal rating. For most practical purposes 110v, 115v or 120v are the same thing (there are some technical differences but nothing you really need to worry about). Actual measured voltage may range between 108v-130v. if it gets much outside of that range, something may be wrong with the power source.
The 30amp rating is for short duration surges. Long term draws are only good for 24amps (derated by 20%).
There are 3 prongs on the male end. Hot, Neutral and Ground. If you measure voltage, Neutral to Ground should be 0v. Hot to either of the others should be around 120v (again nominal, it will vary in real measurements).
- Standard 50 amp plug is 50amp @ 120/240v.
Again the voltage is nominal, so you may see 220v, 230v and real life measurements will vary.
There are 4 prongs on the male end. 2 Hot, Neutral and Ground. Neutral & Ground will again be 0v. Hot to Neutral or Ground will be 120v nominal. Hot to Hot will be 240v nominal.
If you want to run a 120v device, you connect Hot to Neutral
If you want to run a 240v device, you connect Hot to Hot. This can be a problem for your adapter, though generally it will show up as a device with no power. If you plug into 2 - 30amp outlets that are on the same hot leg, the Hot to Hot will be 0v.
Many boats have no 240v devices. In this case, it works fine even if 30amp adapters are both on the same hot leg.
You have available...50amp at 240v or 50amp on each leg at 120v (again short term peak loads...longer term loads need to be derated by 20% or 40amp). So you can run multiple loads up to 80amps total if you keep them balanced between the hot legs. You won't be able to run a 60amp @120v device as that will be on one leg and overload the leg.

Your 30amp connector works similar but instead of 50amp per leg, you have 30amp per leg (roughly double what a single 30amp plug will provide but again), that assumes you split the loads between the legs.

Other areas of the world may be different, though general principals still hold.

[Beausoleil]

Originally Posted by valhalla360

Just to clean up some of the discussion...
--snip--
- Standard 50 amp plug is 50amp @ 120/240v.
Again the voltage is nominal, so you may see 220v, 230v and real life measurements will vary.
There are 4 prongs on the male end. 2 Hot, Neutral and Ground. Neutral & Ground will again be 0v. Hot to Neutral or Ground will be 120v nominal. Hot to Hot will be 240v nominal.
If you want to run a 120v device, you connect Hot to Neutral
If you want to run a 240v device, you connect Hot to Hot. This can be a problem for your adapter, though generally it will show up as a device with no power. If you plug into 2 - 30amp outlets that are on the same hot leg, the Hot to Hot will be 0v.
--snip--

And to add to valhalla's excellent info:

The connection from Hot to Neutral for 120Vac and 240Vac should already be done by the AC wiring panel.

Half the boat's 120Vac loads should be connected to the BLACK (line 1) wire coming in from the shore power 50A connection, and the other half should be connected to the RED (line 2) wire. The return (Neutral) is the WHITE lead.

Because of the possible confusion of mistaking a 240Vac RED lead for a 12Vdc RED lead in distribution wiring in the boat, we only have RED leads in four-plex sheathing (BLACK/RED/WHITE/GREEN) to feed 240Vac appliances on the boat. That's one of the reasons for DC wiring's move from RED/BLACK to RED/YELLOW...

Of course, EU AC electrical standards are a bit better - they learned from our mistakes and use BROWN for load, BLUE for neutral, GREEN/YELLOW stripe for ground/earth, and BLACK and GREY for 2nd/3rd phase in 3-phase systems...

[Kally13]

Thanks to Beausoleil and Valhalla for cleaning this up. I just have one clarification to make if this wasn't clear before. The reverse-Y adapter allows you to connect to the boat's 50 amp (125/250V) inlet, but it does NOT support 50 amps. Please reference Marinco's spec and manual which indicate it can only draw 30 amps max. The adapter is still limited by the 30 amp connectors and wiring (from the adapter and the dock).

https://www.marinco.com/en/~/media/i...5182-41463.pdf
https://www.marinco.com/en/~/media/i...6679-11524.pdf

The boat owner will need to ensure that the boat is not pulling more than 24-30 amps from each hot side. 24 amps on an extended basis, 30 amps for temporary loads.

[Kally13]

Thanks to Beausoleil and Valhalla for cleaning this up. I just have one clarification to make if this wasn't clear before. The reverse-Y adapter allows you to connect to the boat's 50 amp (125/250V) inlet, but it does NOT support 50 amps. Please reference Marinco's spec and manual which indicate it can only draw 30 amps max. The adapter is still limited by the 30 amp connectors and wiring (from the adapter and the dock).

https://www.marinco.com/en/~/media/i...5182-41463.pdf
https://www.marinco.com/en/~/media/i...6679-11524.pdf

The boat owner will need to ensure that the boat is not pulling more than 24-30 amps from each hot side. 24 amps on an extended basis, 30 amps for temporary loads.

[SCarns]

Originally Posted by RobertAB

Looking at the back side of the plug is great idea. I'll look and report back. It's a Canadian built boat from 1973. I see other boats on the dock with the adapter, so I'm pretty sure the dock side will be compatible. I'm on the boat Saturday and will report back.

The boat is in Channel Islands Harbor down in Oxnard, I'm planning to leave it down there for at least the winter and might bring it north in the spring, we'll see if I get enough time anchoring at the islands by then...

RobertAB, I’m in Ventura (although I’m out of town until March 1-ish. The info here is good, but if it helps, I’m happy to come down a take a look.

Steve

[Cadence]

Originally Posted by Dsanduril

US power is 120V from hot leg to neutral/ground. If you have opposite phases you get 240V. This is very typical, nearly every house in the US has 240V (or possibly 208v) but most appliances only use one side of the circuit or 125V. You balance the load on each side (at least that's the plan).

This adapter requires that the two 30A receptacles be on opposite phases. Only your marina electrician can tell you that (or trying the adapter, it has lights to tell you). Basically it is really using two 25A circuits to make one 50A one. It also requires your boat to be wired to use power that way. Some are, some aren't. The manual is pretty clear:



Take a look at the plug on the boat. What markings does it have? Should tell you if the plug is 120(5)V or 125/250. If you can access the back of the plug on the boat there should be 4 wires for a 125/250 - white, green (or green/yellow), and two colors (probably red and black). If there are only three wires (white, green (or green/yellow), and black) then it is a 120V only plug and the adapter won't help you. (Those wire colors are for US built/wired. If the boat was built in Europe or elsewhere post back with the wire colors you have).

That's the easiest way, look for the wire count on the back of the boat plug and see what you've got.

Where are you in the SFBay area? I happen to be in Oakland at the moment....

I have to call BS on opposite phases. 120/ 240 is single phase in the US.

[rslifkin]

Originally Posted by Cadence

I have to call BS on opposite phases. 120/ 240 is single phase in the US.

120/240 in the US is typically split phase. You have L1 - Neutral - L2 with L1 and L2 being 180 degrees out of phase. Line to Neutral is 120V (from L1 or L2). L1 - L2 gives 240V. So when people talk about needing 30A outlets on different phases, they mean one that's wired as L1 - Neutral and one that's L2 - Neutral.

[Flatswing]

Originally Posted by ikanode

I've heard that depending on how your boat is wired that you can end up with one of the male plugs being "hot" when you plug in the other one. It wouldn't be an issue if you followed good practice and didn't turn on the dock breakers until you have everything hooked up.

Any comments on this possibility from the experts here?

Definitely not an expert, but some ongoing experience using these devices. The quoted concern only occurs with home made devices or old legacy adapters for all intents and purposes. Modern, commercially made Marinco & Others prevent this - that's why they is called a "Smart Y" and costs a small fortune. The 2nd 30A male leg is not hot if the 1st 30A male is plugged in. The 50A 125/250v female end is only energized when both male 30A plugs are energized.

Bad news: You will only get 30A to the boat, not 50A. So you may still need to manage power use. Quite safe to plug a smart Y in and try on the dock. Worst thing that can happens is no 240v power for AC - possibly stove/hot water heater depending on how your boat is wired. (if both 30A dock sockets are on the same phase/leg). Many of us carry a 25' 30A extension, since at some marinas, need to stretch one arm to another pedestal to get both phases/legs on the 30A receptacles

[SCarns]

Originally Posted by rslifkin

120/240 in the US is typically split phase. You have L1 - Neutral - L2 with L1 and L2 being 180 degrees out of phase. Line to Neutral is 120V (from L1 or L2). L1 - L2 gives 240V. So when people talk about needing 30A outlets on different phases, they mean one that's wired as L1 - Neutral and one that's L2 - Neutral.

Yes, and that is an issue. While two 30a circuits phased the same will work just fine w/ the L1/L2 scenario, it assumes two neutrals. A cable only has one neutral. If you’re pulling a full 30amps of the same phase down both legs, it’s possible to overload that neutral and that’s not good. Phasing helps minimize that.

[rslifkin]

Originally Posted by SCarns

Yes, and that is an issue. While two 30a circuits phased the same will work just fine w/ the L1/L2 scenario, it assumes two neutrals. A cable only has one neutral. If you’re pulling a full 30amps of the same phase down both legs, it’s possible to overload that neutral and that’s not good. Phasing helps minimize that.

Exactly. And if both legs are on the same phase and have GFI breakers on the pedestal, they'll trip due to the shared neutral. In practice, however, the shared neutral isn't an overload issue in a marine application, as a 50A cable is made of 6ga and is really fine to handle 60A down the neutral conductor.

[Cadence]

Originally Posted by rslifkin

120/240 in the US is typically split phase. You have L1 - Neutral - L2 with L1 and L2 being 180 degrees out of phase. Line to Neutral is 120V (from L1 or L2). L1 - L2 gives 240V. So when people talk about needing 30A outlets on different phases, they mean one that's wired as L1 - Neutral and one that's L2 - Neutral.

You might want to research delta and Y power line cofigurations.

[rslifkin]

Originally Posted by Cadence

You might want to research delta and Y power line cofigurations.

Delta vs Y configuration comes into play for 3 phase, but I don't know of it having any relevance for a typical 120/240 setup. I guess you could consider a 240 volt connection to a 120/240 setup as a Delta, being that it doesn't use the neutral.