Shore Power Voltage Ratings

Is there an electrician out there that can explain this too me? My home marina uses 50A 125V outlets for their 50A 120V shore power outlets. When I'm visiting other marinas most of them use 50A 125/250V outlets but they are wired to provide only 120 volts. My boat as well as most boats in the 50 foot size range require only a 120V service. Now, here is the catch, at my marina they only use the 50A 125/250 volt outlets for 120/240 volt service! This means that if the majority of the boaters were to plug their 50A 125/250V cords into my marina they would end up with 240V to their boat! I find this confusing and down right dangerous to have some but not all marines use the 125/250V plugs for only a 120V service. They make an adapter but that too is dangerous. According to NEMA (not NMEA) the industry standard for a 125/250V plug should ONLY be used for 240 volt service. My marina is in accordance with this standard. Can anyone explain to me why a marina uses this 125/250V cord at 120V? Not only does this not meet code but it could cause severe damage to a unsuspecting boater who thinks they are connecting to a 120V source. I have discussed this with several people and most agree that marinas that are using the 125/250V outlet at 120 volts are wired incorrectly per the NEMA standards. I purposely purchased a 125V cord but now I find that I can't connect at many public marinas like Roche Harbor and Friday Harbor in the San Juan Islands.

Yes, it certainly has you confused, because it is a bit confusing.... Let me try to unravel it for you..

There are 50A 120V outlets which provide only 120V service. These have a certain shape plug so you only plug in a 50A 120V cord.

In addition, there are 50A 120/240V outlets which provide BOTH 120V and 240V service. The key here is that they provide BOTH voltages, not just one or the other. These outlets are also unique so you can only plug in a compatible cord.

What's interesting about the 120V/240V service is that whatever is at the other end of the cord you plug in can choose to use the 120V, 240V, or both services in any combination. And there are adapter cords that break out one of these services and make it available on a different receptacle type. For example, there are adapter cords that plug into 120V/240V service at a dock and allow you to plug in a 120V cord which would otherwise not fit the dock receptacle.

With this in mind, here's what I think you are seeing in your original posting:

Is there an electrician out there that can explain this too me? My home marina uses 50A 125V outlets for their 50A 120V shore power outlets.

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If these are correct outlets then a 50A 120V/240V cord wil not plug into these outlets.

When I'm visiting other marinas most of them use 50A 125/250V outlets but they are wired to provide only 120 volts. My boat as well as most boats in the 50 foot size range require only a 120V service.

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This doesn't really make sense. A properly wired 120/240V outlet should have both voltages available. Perhaps what you are seeing is the result of plugging in an adapter cable that only picks up the 120V service. Such adapter cords are made to allow 120V boats to plug into and use these more common outlets.

Now, here is the catch, at my marina they only use the 50A 125/250 volt outlets for 120/240 volt service! This means that if the majority of the boaters were to plug their 50A 125/250V cords into my marina they would end up with 240V to their boat! I find this confusing and down right dangerous to have some but not all marines use the 125/250V plugs for only a 120V service.

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Hopefully my earlier explanation will help clear up this part for you. The key is that BOTH 120V and 240V is present on these outlets, and the connected boat can use either or both as it desires. There is no danger, assuming of course that everything is wired up properly. Also note that you cannot plug a 120V cord directly into a 120/240V outlet. The pin configuration is different and it will not plug in.

They make an adapter but that too is dangerous. According to NEMA (not NMEA) the industry standard for a 125/250V plug should ONLY be used for 240 volt service. My marina is in accordance with this standard.

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I can't say one way or another if NEMA that a device plugged into a 120/240V outlet use the 240V service. I just don't know.

Can anyone explain to me why a marina uses this 125/250V cord at 120V?

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Now I'm confused. I though you said that your Marina only allows 120V boats to use teh 120V outlets, and 240V boats to use the 240V outlets? I'm missing something here.

Not only does this not meet code but it could cause severe damage to a unsuspecting boater who thinks they are connecting to a 120V source. I have discussed this with several people and most agree that marinas that are using the 125/250V outlet at 120 volts are wired incorrectly per the NEMA standards. I purposely purchased a 125V cord but now I find that I can't connect at many public marinas like Roche Harbor and Friday Harbor in the San Juan Islands.

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The plug incompatibility that you have encountered trying to hook up at Roche Harbor exists precisely to protect you against the hazard that you describe. You can't plug into the wrong service - the plugs won't go in. The only way to "convert" is via an adapter cord of some sort. Assuming everything is wired properly, you can only plug things together in a safe way.

Does this make more sense to you now?

>I purposely purchased a 125V cord but now I find that I can't connect at many public marinas like Roche Harbor and Friday Harbor in the San Juan Islands.<

It will only be of use in a very few marinas , as 120/50a is about 30 years dated.

To cruise you will need to install the modern 120/240v socket and get a power cord to fit.

The boat will require a minor rewire to bring this two 120 lines aboard , and power 120v.

AS you are set up for 50A , and the 120/240 line will handle 50a per leg , it would be possible to NOT use one leg and not rewire the boat.The second 120v terminal would simply not be hooked to anything.

However by splitting the system to 2 120v legs the voltage drop should be less , and big load systems would work better.

Twistedtree has most of it right I think...but that's because trying to answer the OPs post is hard enough.

There is no 240v at any of the power posts that most of us plug into...you have to get to the big boy stuff before that happens.

The power posts only have 120 at them...the 120/204 outlets just have a 4 wire service where 2 "hot" legs are 180 out of phase (just like a house service). The straight 3 wire 50A 125 service just has 1, 120 volt leg.

As long as they are all standard marine plugs and standard marine adapters everyone should be safe...happy is another story if you want 120/240 and all they have is 3 wire outlets.

The only way you would have 240 volts someplace in at your panel inside your boat where the breakers span 2 hot legs to give 240. No worries as long as everyone including the marina follows the correct plug game.

To connect to other marinas...an adapter is all you need...the boat right next to me has one as we have the 120/240 outlets thankfully. Just hope the marina an big enough dock wires to satisfy the bigger boats and liveaboards they have now.

This is kinda off topic but really related.

Unless I'm staying at a guest marina for quite a long time I just avoid using their power.

The generator is super quiet, so quiet as to not be an issue, so why bother.

I know I'm not alone in this thinking as when I walk the docks at my home marina (which has good but very expensive power) I notice the transient comercial fishing boats almost always have a generator running.

ksanders said:

This is kinda off topic but really related.

Unless I'm staying at a guest marina for quite a long time I just avoid using their power.

The generator is super quiet, so quiet as to not be an issue, so why bother.

I know I'm not alone in this thinking as when I walk the docks at my home marina (which has good but very expensive power) I notice the transient comercial fishing boats almost always have a generator running.

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Alsaka...FORTUNATELY ...is a different world.

Along the Atlantic ICW...you would be asked to turn it off by many marinas or other boaters because of either noise or fumes. If it's really that quiet or doesn't give off ANY diesel exhaust smell..then you might get away with it.

Gotta remember...there's sensitive folk down here in the lower 48...

<There is no 240v at any of the power posts that most of us plug into.>

IF it is the common standard 120/240 marine setup , you are DEAD Wrong.

Open the box and measure between the red and black wires and there is 240V!

It is true that few boats actually can use 240v , bit it IS THERE!

FF said:

<There is no 240v at any of the power posts that most of us plug into.>

IF it is the common standard 120/240 marine setup , you are DEAD Wrong.

Open the box and measure between the red and black wires and there is 240V!

It is true that few boats actually can use 240v , bit it IS THERE!

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You are correct...hence the 120/240 right on the plug...but there is not 240 on any one wire...

The amout of people who understand electricity is surprisingly low and trying to get them to understand that's it's a combination of wires that gives them what they need is hard to explain.

Money Sponge said:

Is there an electrician out there that can explain this too me? My home marina uses 50A 125V outlets for their 50A 120V shore power outlets. When I'm visiting other marinas most of them use 50A 125/250V outlets but they are wired to provide only 120 volts. My boat as well as most boats in the 50 foot size range require only a 120V service. Now, here is the catch, at my marina they only use the 50A 125/250 volt outlets for 120/240 volt service! This means that if the majority of the boaters were to plug their 50A 125/250V cords into my marina they would end up with 240V to their boat! I find this confusing and down right dangerous to have some but not all marines use the 125/250V plugs for only a 120V service. They make an adapter but that too is dangerous. According to NEMA (not NMEA) the industry standard for a 125/250V plug should ONLY be used for 240 volt service. My marina is in accordance with this standard. Can anyone explain to me why a marina uses this 125/250V cord at 120V? Not only does this not meet code but it could cause severe damage to a unsuspecting boater who thinks they are connecting to a 120V source. I have discussed this with several people and most agree that marinas that are using the 125/250V outlet at 120 volts are wired incorrectly per the NEMA standards. I purposely purchased a 125V cord but now I find that I can't connect at many public marinas like Roche Harbor and Friday Harbor in the San Juan Islands.

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Here ya go...over in classifieds....talk it over with this poster if confused...

http://www.trawlerforum.com/forums/s9/marinco-y-adaptor-154ay-11288.html#post173858

Wow, thank-you for the detail and the time it took you to respond to my question. You mention several things in your post and I will comment on several of them to leave this thread as complete as possible should others refer to it. It was also clear that even after carefully crafting my original post I see that I left some misunderstandings to everyone trying to help me.

There are 50A 120V outlets which provide only 120V service. These have a certain shape plug so you only plug in a 50A 120V cord.

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Yes, I am familiar with the plug types which is why I ended up wanting a detailed understanding of how they were wired. I bought my 50A 125V cord because that's what my marina has at the pedestal. It is a three wire cord with only one leg of the utility service coming aboard.

In addition, there are 50A 120/240V outlets which provide BOTH 120V and 240V service. The key here is that they provide BOTH voltages, not just one or the other. These outlets are also unique so you can only plug in a compatible cord.

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Here is where my misunderstanding was originating but later in your reply you give me the needed tidbit as did some other posts. The plugs are indeed unique and the 125/250V outlets at the other marinas will not accept my cord and they shouldn't. In the case of the 125/250V rated cords they are four wire cords and bring both sides of utility transformer aboard the boat. This is why I was concerned about accidentally getting 240V on a boat that was wired for only 120V service. What I didn't make clear is why I had this concern in the first place, it wasn't because I thought the plug would fit in a wrong outlet but because I assumed that the outlet would be wired differently by the shore power electrician depending on whether or not the second hot leg was needed for the boat. I fell in this trap because I jumped to a conclusion when my marina told me they only install this outlet when 240V service was required.

What's interesting about the 120V/240V service is that whatever is at the other end of the cord you plug in can choose to use the 120V, 240V, or both services in any combination. And there are adapter cords that break out one of these services and make it available on a different receptacle type. For example, there are adapter cords that plug into 120V/240V service at a dock and allow you to plug in a 120V cord which would otherwise not fit the dock receptacle.

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This single yet so simple paragraph actually answered my question. Knowing now that the plug is always wired for 240 volt service and that the 125V rated cords, and adapters, simply use just one of the available two hot legs made me feel pretty silly.

This doesn't really make sense. A properly wired 120/240V outlet should have both voltages available. Perhaps what you are seeing is the result of plugging in an adapter cable that only picks up the 120V service. Such adapter cords are made to allow 120V boats to plug into and use these more common outlets.

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By this time I had already found my missing link in your reply but this made it crystal clear.

Now I'm confused. I thought you said that your Marina only allows 120V boats to use the 120V outlets, and 240V boats to use the 240V outlets? I'm missing something here.

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I think it was my wording of my original post based on my then incorrect assumptions of the wiring that confused everyone. It was my translation of what the Harbormaster told me that was incorrect. You are right on. My marina uses almost all 125V outlets but when a boat needs the other they change it. But now I know they never need to change them back! Just get an adapter that pics up only one of the two now available legs and your good to go. I see now why the newer marinas use the 125/250V outlet.

Does this make more sense to you now?

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Absolutely! And thanks again for your time. I'm embarrassed that with my understanding of this subject that I missed something that was clear to everyone else!

As an aside, it may be worth mentioning that my new 50A cord is a replacement for 2-30A cords run in parallel using a reverse wye 50A adapter. This is fine when using the adapter connected to either the 125V or the 125/250V outlets but I was very concerned that when plugging into two different 30A outlets, when no 50A power outlet was available, that I could accidentally create a short between the outlets if they were on opposite legs of the utility transformer. Each time I had to do this I had to check voltage to be sure that both 30A outlets were on the same utility leg. I am much better off with this installation. I left the second 30A inlet at the boat connected and wired it to Shore Power B so that when 50A power isn't available I simply use one of my old 30A cords to this inlet and live with 30A service.

It will only be of use in a very few marinas , as 120/50a is about 30 years dated.

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Wow, really! I wish I would have posted sooner and got all this valuable help before I started this project. If I had this understanding sooner I would have realized the advantage of the 125/250V cords and would have purchased a different cord and inlet. I don't like adapters but I think I will just buy an adapter for when I'm away from home port.

The boat will require a minor rewire to bring this two 120 lines aboard , and power 120v.

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That's sure correct but now that I'm where I'm at I would have to replace the cord and the inlet at the boat. I'll save that project for another day.

However by splitting the system to 2 120v legs the voltage drop should be less , and big load systems would work better.

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You are so right, this is exactly what I should have done. Had I not just matched what was available at my home port I would have ended up with a much better system. I could have even changed the gen-set to 240V. I hope this thread will help others that are considering this kind of upgrade to make a better choice than I did.