electrical shore power question

Joe · Jun 22, 2012

It's an adapter, not a splitter.

centerline · Jun 22, 2012

what is your boat set up to take? coming from the boat, do you have a 50 amp cord, a 30 amp cord, or a 20/15 amp cord? having more amperage available than you need is a good thing.... having less amperage available than what you need is a very, very bad thing.... (not to be confused with voltage, too much voltage is also bad)
the two seperate legs coming from the adaptor may supply 30 amps (or only 25) each by themselves, but without going into the whys and hows of it all, and speculating on how the main circuit may actually be wired, the main supply is rated at a constant 50 amps.... even though at peak it could potentially supply a lot more depending on the main circuit breaker.... so as long as your equipment is operating at the same voltage as the supply voltage, all you need to know is that your supply amperage is higher than your demand amperage. your demand will only pull as much as it needs from the available supply..... a 50 amp circuit is a 220volt circuit, but with the connector you have it splits it to (2) 110 volt legs... hopefully this will help explain and answer your question rather than to further confuse you....

Rocket1 · Jun 22, 2012

The amp rating of the shore power receptacle is just a rating of the amount of power that is available to draw.

Much the same as any household circuit that might be on a 15 amp breaker at the panel, you'll only have an issue if you try to draw more than 15 amps.

With the Y adapter you can feed two 30 amp cords from one 50 amp receptacle. The only way you will cause an issue would be if you and the other vessel that are plugged in collectively draw more than 50 amps, in which case you'll just trip the circuit breaker on the dock.

As an added precaution, the A/C main breaker on board your boat should protect you from drawing too much juice.

Bill Roosa · Jun 23, 2012

To answer your question, you will not be able to heat water AND run the AC at the same time. In fact you will not be able to do much except run the AC and the battery charger. Coffee pots, microwaves, arc welding AND AC are right out.
You do need to insure that your Y is correctly wired with hot to hot to hot etc and no neutral to ground.

Bill Roosa · Jun 23, 2012

After thinking about it during a smoke break I think we are getting it backward. If you have a 30 amp boat and there is only 50 amp outlets at the dock then you use the 50 to 30 adapter not the Y. The Y is so you can have 50 amps service using 2 30 amp dock outlets. Course if you don't have a 50 amp service on the boat this is just dead weight.
Check the sex of the Y cables. The two arms should have male ends for plugging into the dock.

Cayennita · Jun 23, 2012

My live aboard boat used a splitter and had 2 - 30 amp cables coming in. We were able to run 2 a/c's hot water heater, coffee maker, microwave, battery charger, refrigeration, all at the same time. The only time one of the legs would trip at the panel was when the compressors for both the refrigerator and one of the a/c's kicked on at the same time. If there was only one 30 amp breaker available at the dock then I only used one cord and flipped the parallel switch at the panel and only used one a/c and refrigerator plus one other item. Always able to used the coffee maker. We lived aboard for 12 years and never had a problem.

kenn · Jun 23, 2012

When MS sees this thread he's gonna blow a fuse!

Current (Amps) doesn't 'divide' in an AC Y adaptor.

We probably need more information (make/model) on the adaptors you intend to use. If this "adaptor" simply allows you to connect one or two 120v 30A cords to a 240v 50A socket (2 x 120v 50A), and it doesn't include two 30A breakers or fuses, then I think it would be both dangerous and illegal.

The purpose of fuses and breakers is to protect the CIRCUIT from excessive current, which can lead to wiring or connector overheating and fire. A straight Y or split of a 240v 50A source into two 120 v lines means each 120 leg is protected at 50A, not 30A, which means that a hard short at the boat could theoretically draw more than 30A without blowing the 50A breaker.

jviss · Jun 23, 2012

centerline said:
what is your boat set up to take? coming from the boat, do you have a 50 amp cord, a 30 amp cord, or a 20/15 amp cord? having more amperage available than you need is a good thing.... having less amperage available than what you need is a very, very bad thing.... (not to be confused with voltage, too much voltage is also bad)
the two seperate legs coming from the adaptor may supply 30 amps (or only 25) each by themselves, but without going into the whys and hows of it all, and speculating on how the main circuit may actually be wired, the main supply is rated at a constant 50 amps.... even though at peak it could potentially supply a lot more depending on the main circuit breaker.... so as long as your equipment is operating at the same voltage as the supply voltage, all you need to know is that your supply amperage is higher than your demand amperage. your demand will only pull as much as it needs from the available supply..... a 50 amp circuit is a 220volt circuit, but with the connector you have it splits it to (2) 110 volt legs... hopefully this will help explain and answer your question rather than to further confuse you....

This is a confusing explanation that contains incorrect information. One such item is that 50A shore power outlets are not 220V - they are either 125V or 125/250V. There is a key in the plug/receptacle for the 125/250V type.

To the OP, I recommend looking at the Hubbell marine products catalog, or the West Marine advisor for good info on this plugs and receptacles, adapters, etc.

Regarding the Amperage, the capacity of the outlets and cords, that refers to the capacity of the outlet, i.e., the maximum current you can draw from it, and the rating of the cords and adapter, i.e., the most they will handle, and also the plug and receptacle configurations that are assigned to various configurations. That said, with "Y" adapters, there are no guarantees that your won't exceed the capacity of the circuit (and pop the breaker), depending on what the load is.

In addition, there is no guarantee that two 30A outlets found on the dock will be out of phase such that you can combine them to drive a 125/250V 50A load. There are "smart" adapters available that will indicate whether this is working or not.

Bill Roosa · Jun 23, 2012

Well the circuit is not going to draw more than it needs and connecting it to a 50 amp when it only needs 30 is not a problem. If it shorts then it really does not matter what the service is as you are going to exceed the capacity in all cases.
Kenn's comment of mixing 120 and 240 is a serious consideration. I don't think there is any dock that has this kind of set up though. I believe that the 240 volt plugs are different as they have 4 prongs (hot-hot-neutral, ground) not 3 (hot-neutral, ground) so it would be difficult to have a brain fart
Best to get out the ohm meter and check to see exactly what you have. You might want to put a label on each adapter indicating what it is actually designed to be used for.

jviss · Jun 23, 2012

Bill Roosa said:
I believe that the 240 volt plugs are different as they have 4 prongs (hot-hot-neutral, ground) not 3 (hot-neutral, ground) so it would be difficult to have a brain fart

Then you believe wrong. First, the common higher voltage circuit in use is a 125/250V circuit, not unlike the kind of circuit used for electric ranges. And, it uses a three prong plug, 'though it's keyed differently to prevent accidentally connecting it to a mismatched circuit. The cable is four conductors; the ground on the 125/250V is the barrel of the connector, not another prong.

Gunni · Jun 23, 2012

Bill, the reason there are two 30 amp circuits on a boat is because the AC units power off their own 30 amp leg. The house load (charger, WH, outlets) have their own 30 amp circuit. My 2 ac units draw about 25 amps total on their own 120vac 30 amp circuit.

Your comments above suggest that you have never seen or used a 50-30 amp y-adaptor. It simply adapts a 50 amp dock supply for a boat with 1, or more commonly 2, 30 amp. shore-power installation.

Windsock: You are good to go, the Y-adaptor should meet your needs for your 2, 30 amp shore power cords.

jviss · Jun 23, 2012

kenn said:
When MS sees this thread he's gonna blow a fuse!

Current (Amps) doesn't 'divide' in an AC Y adaptor.

We probably need more information (make/model) on the adaptors you intend to use. If this "adaptor" simply allows you to connect one or two 120v 30A cords to a 240v 50A socket (2 x 120v 50A), and it doesn't include two 30A breakers or fuses, then I think it would be both dangerous and illegal.

The purpose of fuses and breakers is to protect the CIRCUIT from excessive current, which can lead to wiring or connector overheating and fire. A straight Y or split of a 240v 50A source into two 120 v lines means each 120 leg is protected at 50A, not 30A, which means that a hard short at the boat could theoretically draw more than 30A without blowing the 50A breaker.

A hard short will pop the 50A breaker long before the 30A cord warms up - like, in less than a second.

Nothing dangerous or illegal about these adapters, as long as the boat and dock are wired properly; they are commonly available and used.

centerline · Jun 23, 2012

jviss said:
This is a confusing explanation that contains incorrect information. One such item is that 50A shore power outlets are not 220V - they are either 125V or 125/250V. There is a key in the plug/receptacle for the 125/250V type.

In addition, there is no guarantee that two 30A outlets found on the dock will be out of phase such that you can combine them to drive a 125/250V 50A load. There are "smart" adapters available that will indicate whether this is working or not.

YES.... even at its best it can be confusing.... and for the record, the older designated 110v has been bumped up to 120 volts, and the 220 service is now 240... and has been for several years....
But 50 amp service IS in fact 220 volt service... it is now and always will be. BUT.... you may plug into it and only get 110v from it.... depending on how the adaptor or boat/vehicle is wired.... in this case it is single phase power, but there are 2 legs of 110 power that combine to make 220... for ranges and clothes dryers.... but they can be split to create 110 volt so that half the load requirements can draw amperage from one leg, and the other half can draw from the other leg without overloading one individual circuit.....

and YES.... even at its best it can be confusing....

centerline · Jun 23, 2012

windsock1 said:
I started this whole thread because I was looking through the WM catalog and saw a splitter made by "EEL", sku#12998415. The description is: Boat Side-30A/125V, Dock Side-50A/125V. There's another one described as Boat Side 30A/125V, Dock Side-50A/125V/250V.

The boat system is two shore power inlets, Bus1 and Bus2. The air-conditioner/heat unit runs off Bus2. When running the genset (6KW) I can run the A/C with anything else - microwave, charger, outlets, EXCEPT the hot water heating element at the same time. When I'm plugged into shore power with two 30A cords coming in, I can run the A/C (Bus2) and the heating element which is on Bus1.

Reading the replies to this thread it looks like I could get that EEL Y-adapter and run everything as if I had two 30A cords coming in from two 30A shore outlets.

Correct?

that is correct! that is exactly what the "y" is offering you. two 30mp shore power outlets on seperate legs of the shore power.....

kenn · Jun 23, 2012

jviss said:
A hard short will pop the 50A breaker long before the 30A cord warms up - like, in less than a second.

Nothing dangerous or illegal about these adapters, as long as the boat and dock are wired properly; they are commonly available and used.

I've only ever used the 30A shore-power feeds... so you have me thinkin...

Given that there's a safety factor in wire ratings, and assuming gear in good condition... sure, I would agree that there wouldn't likely be a problem with a 30A shore cable fed from a 50A circuit. Like you said, a hard short should trip the breaker quickly, and even drawing between 30 and 50 A from a 30A cable shouldn't immediately cause problems.

And I see that for a properly-wired boat where the A/C has its own 30A input, a 120v 50A circuit could safely feed both the normal and the A/C services.

I do know this: when I added a 60A subpanel to our house electrical and fed it from a 60A breaker, I had to use the properly-rated wire; if i'd used a size smaller, I wouldn't have passed inspection.

Maine Sail · Jun 23, 2012

kenn said:
I've only ever used the 30A shore-power feeds... so you have me thinkin...

Given that there's a safety factor in wire ratings, and assuming gear in good condition... sure, I would agree that there wouldn't likely be a problem with a 30A shore cable fed from a 50A circuit. Like you said, a hard short should trip the breaker quickly, and even drawing between 30 and 50 A from a 30A cable shouldn't immediately cause problems.

And I see that for a properly-wired boat where the A/C has its own 30A input, a 120v 50A circuit could safely feed both the normal and the A/C services.

I do know this: when I added a 60A subpanel to our house electrical and fed it from a 60A breaker, I had to use the properly-rated wire; if i'd used a size smaller, I wouldn't have passed inspection.

The key words are "on a properly wired boat". A properly wired boat would have two 30A main breakers that break both hot and neutral in the case of an over load. Thus you can not pull 50A through a 30A cable or "Y" connector for either leg as they should be protected by their own 30A breaker in the boat. If the AC panel is further than 10' wire run from the inlet a second set of 30A breakers would be close to the 30A inlet.. The 50A to 30A "Y" is a common adapter..

That said many boats are not properly wired. I see many boats connected to 50A posts with a 50A to 30A adapter and then these boats have no internal main breaker... I had one boat this past winter that had no less than five 1500W ceramic disc heaters running off one shore power cord. The boat had no main breaker and was relying on the dock pedestal... This is what happens when you have an IMPROPERLY wired boat...

Stu Jackson · Jun 23, 2012

jviss and MS are right. I recommend you read the referenced material at the West Advisors online and in the printed catalog. Hubbell and Marinco are also good resources. When we go to Half Moon Bay we pick up an adapter, NOT a splitter to use the 50A shorepower. Do some research and you'll see the differences. As noted above, much of what has been presented in this topic is a bit off the mark, sorry...

Rick486 · Jun 23, 2012

I have a headache after reading this thread. All I can say is that I have 2 "30 amp" cords. Often, and I do mean often, when cruising we will go into a marina for a night or two which offers only "50 amp" receptacles. When I see this I ask them "please bring down a splitter to dock ABC". The splitter shows up, I connect my 2 cords to the splitter and the splitter to the 50 amp receptacle, and life is good. I run 2 AC's, charger, microwave, coffee maker, and so forth, with never a thought and never a problem. Of course I can presume my boat is wired correctly.