Shore Power Question

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Night Watch

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Hi Folks!
Once again relying on your collective experiences to make this clear.
My live aboard marina has 30 amp shore power.
Incoming boat is 120/240 50 amp shore power.
I cannot use two shore power outlets.
Is it a matter of having an electrician put in a new plug?
I don't need much power, it's propane stove and ac/DC fridge,
 
I think you can get an adapter but your boat will only receive 120v 30amp. This is from one of the two incoming 120v legs. How your boat deals with this depends upon how it is wired. Some boats have onboard transformers and some split the 2 incoming 120v 30 amp feeds to two separate buses with various devices on each. If that is the case essential 1/2 of your 120v devices will operate. No 240v appliances will but perhaps you don't have any. Electric stoves and air conditioners would be possible 249 volt devices. But I would suggest you have an electrician take a look as an error could be very costly and unsafe. Don't trust the forum because each boat can be different.
 
As mentioned above, do you have any circuit breakers (other than the incoming main breaker) for appliances that are 240 volt (double breaker)? Do you have an isolation transformer? If not, there is a 30 amp to 250 volt 50 amp dog bone (adapter). There's also one for 15 amp normal receptacle.

If in doubt, take a picture of the main panel and post it. You need to check for the isolation transformer though. Would also be helpful to post make model and year of your boat.

Ted
 
If the boat uses an isolation transformer then it most likely won’t work at all with a 30a 125v supply.

If there is no transformer involved but your boat is set up to run 220v equipment it’s very possible that nothing will work.

If your boat is all 125v but uses two 50a lines, then it will work off a 50a 125/250v to 30a 125v adapter. However, you won’t be able to use much more than lights and the water heater.
 
I think you can get an adapter but your boat will only receive 120v 30amp. This is from one of the two incoming 120v legs. How your boat deals with this depends upon how it is wired. Some boats have onboard transformers and some split the 2 incoming 120v 30 amp feeds to two separate buses with various devices on each. If that is the case essential 1/2 of your 120v devices will operate. No 240v appliances will but perhaps you don't have any. Electric stoves and air conditioners would be possible 249 volt devices. But I would suggest you have an electrician take a look as an error could be very costly and unsafe. Don't trust the forum because each boat can be different.
Not sure I understand the "2 incoming 120 legs" as I would only have access to one 30 amp shore power outlet on the dock.
 
I think you can get an adapter but your boat will only receive 120v 30amp. This is from one of the two incoming 120v legs. How your boat deals with this depends upon how it is wired. Some boats have onboard transformers and some split the 2 incoming 120v 30 amp feeds to two separate buses with various devices on each. If that is the case essential 1/2 of your 120v devices will operate. No 240v appliances will but perhaps you don't have any. Electric stoves and air conditioners would be possible 249 volt devices. But I would suggest you have an electrician take a look as an error could be very costly and unsafe. Don't trust the forum because each boat can be different.
I think you can get an adapter but your boat will only receive 120v 30amp. This is from one of the two incoming 120v legs. How your boat deals with this depends upon how it is wired. Some boats have onboard transformers and some split the 2 incoming 120v 30 amp feeds to two separate buses with various devices on each. If that is the case essential 1/2 of your 120v devices will operate. No 240v appliances will but perhaps you don't have any. Electric stoves and air conditioners would be possible 249 volt devices. But I would suggest you have an electrician take a look as an error could be very costly and unsafe. Don't trust the forum because each boat can be different.
As mentioned above, do you have any circuit breakers (other than the incoming main breaker) for appliances that are 240 volt (double breaker)? Do you have an isolation transformer? If not, there is a 30 amp to 250 volt 50 amp dog bone (adapter). There's also one for 15 amp normal receptacle.

If in doubt, take a picture of the main panel and post it. You need to check for the isolation transformer though. Would also be helpful to post make model and year of your boat.

Ted
 
Thank you! I will check next week, when I see incoming boat.

I only use a Caraform heater, microwave, and water heater on current boat. And not at the same time. So just need the minimum power. There were several posts on adapters here so wasn't sure if those are temporary or live aboard solutions.
I have questions to ask now - thanks everyone
 
50a 125/250v means that you have 4 wires, a black, red, white and green. The green is ground, the white is 50a 125v neutral, the black is 50a 125v power or line in and the red is another 50a 125v power or line in.

Most of the time the two power lines are in opposite phase but this is not the case on all boats or all docks. When both lines in are in phase there can be additional issues such as over loading the neutral.

You probably need an hour's time from a marine electrician to look over your boat and explain just how it is wired and how your electrical system can work on various power options available.

While many 50a 125/250v boat can operate on a 30a 125v adapter, 30a sockets are prone to failure. They simply are not adequately designed to run above 20a for extended periods of time.
 
If your boat needs fully functional 120/240V, you could install a 120V 30A to 120/240V transformer. Ideally it would be permanently installed along with a dedicated 120V 30A inlet. But you might be able to buy or build something sufficiently waterproof and portable to place on the dock or on the deck of your boat. However I would strongly favor a permanent installation.
 
Most of the time the two power lines are in opposite phase but this is not the case on all boats or all docks. When both lines in are in phase there can be additional issues such as over loading the
I don’t think this is correct. The two 120v lines must always be out of phase or you will not get 240V between them. And if your dock is actually 208V not 240V (like many including ours is) L1 & L2 are 60° (or if you prefer 120°) out of phase, not 180° like they are in a true 240V supply.
 
Hi Folks!
Once again relying on your collective experiences to make this clear.
My live aboard marina has 30 amp shore power.
Incoming boat is 120/240 50 amp shore power.
I cannot use two shore power outlets.
Is it a matter of having an electrician put in a new plug?
I don't need much power, it's propane stove and ac/DC fridge,

As you've seen, maybe an adapter will give you something...

But it's easiest to just have an electrician change the dock pedestal... and better that way if your boat has an isolation transformer and/or any 220V appliances anyway.

Shouldn't take long, shouldn't cost much... and the marina's standby electrician has probably done things like that to the pedestals before.

-Chris
 
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I don’t think this is correct. The two 120v lines must always be out of phase or you will not get 240V between them. And if your dock is actually 208V not 240V (like many including ours is) L1 & L2 are 60° (or if you prefer 120°) out of phase, not 180° like they are in a true 240V supply.

It all depends on how the boat is wired and what equipment is on the boat. Plenty of boats bring in two lines of 50a 125v to two different busses. The system could care less if it is in phase, out of phase or 60 degrees out of phase. In all cases you will get 125v. These same systems convert the 125v to 220v on the boat. If you have one of these systems you need to be aware of when power is in phase so you don’t over load the neutral.

Many boats are wired so that they won’t work when both lines are in phase or work very poorly when the phase is 60 degrees. Nether system is perfect, one leaves you idiot proof but powerless the other provides power and a constantly tripping breaker if you are overloading your neutral.
 
Not sure we’re on the same page here. OP question is about a 125/250V 50A boat, connecting to a single 30A. His “normal’ connection is to a 50A 4-wire outlet. This has 2 hots that are out of phase and what you will find in almost all marinas. You are describing a boat(s) that has multiple (2 in your case) separate 125V 50A shore power connections. These would plug into a 125V 50A (3-wire) outlet. These are not common at all (FWIW in 40 years I’ve never seen one in a marina).

If he has no isolation transformer (I understand not) and doesn’t need 240V (I understand not) simplest and easiest would be an adapter like this https://a.co/d/2qFlPRB. Not necessarily the best solution: as has been pointed out the normal 30A twist lock outlet is not as robust as one would like.
 
Not sure we’re on the same page here. OP question is about a 125/250V 50A boat, connecting to a single 30A. His “normal’ connection is to a 50A 4-wire outlet. This has 2 hots that are out of phase and what you will find in almost all marinas. You are describing a boat(s) that has multiple (2 in your case) separate 125V 50A shore power connections. These would plug into a 125V 50A (3-wire) outlet. These are not common at all (FWIW in 40 years I’ve never seen one in a marina).

If he has no isolation transformer (I understand not) and doesn’t need 240V (I understand not) simplest and easiest would be an adapter like this Amazon.com. Not necessarily the best solution: as has been pointed out the normal 30A twist lock outlet is not as robust as one would like.

You certainly are not understanding me. I am sure if we were face to face this conversation would be easier. Do not read any condescending in this reply. That is not were I am going.

A 50a 125/250v socket by code must have two out of phase lines. We agree on that. What happens when some one grabs a two 30a 125v to a single 50a 125/250a adapter and plugs it into two 30a sockets that are in phase? What happens next depends on how the boat was wired. Some boats will simply not function. Some boats will function just fine with the exception that the neutral becomes over loaded. This is why Twistedtree is so adamant about only using smart Y adapters.

While less of an issue now, 208v was a major problem north of Seattle. Many boats would not use L1 and L2 to make 220v. Instead they would put a transformer on L2 to boost the power from 125v to 250v. This did away with any 208v issues.

The adapter you referenced feeds both the L1 and L2 with power in the same phase. Boats wired for 250v won’t work with that adapter. Boats wired as mentioned with the 208v issue will work with it. Even the 220v appliances will work. Obviously, power management is critical when you go from having 100a available to only 30a. Since we are restricted to 30a overloading the neutral is not an issue.

When you add isolation transformers things become more complicated.
 
You’re quite correct, which is why I’ll take a conversation over an email or text or forum exchange any time. Particularly in a complicated area like this, where one incorrect use of a term or a tiny miscommunication can lead one totally off into the weeds. I would also observe it makes it much quicker to determine the bonafides of the participants in the conversation. I probably don’t need to mention the TON of opinion masquerading as fact out there. And re intent, no worries but thx for clarifying. And same goes for me if I’m coming across as less than polite.

Re para 2: I agree, and am also adamant about Smart Y’s. Respectfully, a little of the “what happens….’ you refer to here is just people not knowing what they’re doing, and doing stuff they shouldn’t be and getting into trouble. Lots of that out there.

Re 208V, I’ve never heard of just boosting a single leg. That sounds like a very dodgy solution that has all kinds of ways to go sideways. The methods I am most familiar with are just live with it - your 120V supplies are good because of the phasing between the legs, and the 240V stuff you might need? Meh, tough luck. Many appliances used in environments like this are rated 208/240 (like the Marinairrre reverse cycle heat pumps), although they are much happier at 240V. If that isn’t satisfactory, then on to plan B - a boost transformer that boosts both legs. Even better, an isolation transformer with selectable boost. Charles used to make one that automatically detected your shore voltage and boosted/no-boosted accordingly. (There are some issues to be navigated though with iso xfrmrs, but benefit exceeds problems in my opinion). I’m curious, you say “less of a problem now”, why is that?

And your final paragraph, I do not understand. To clarify: I’ll use my own boat as an example; straightforward factory Silverton, 125/250V 50A service. Prior to my major rework the last two years, it has a panel with two banks of 120V breakers fed by L1 and L2, and a bank of 240V breakers. L1 and L2 are opposite phase, but none of the 120V load know that or care. If you take that “dumb” Y that I posted a link to, you are quite correct L1 and L2 would be in phase *and limited to 30A by the shore breaker*. 240V panel would be useless of course, because with L1 & L2 in phase, it would be 0V. But the 120V panels should work just fine, no? Am I missing something, or misunderstanding you?

Cheers
 
I think you are understanding me. With the dumb Y on same phase your L1 and L2 would not know but you run the risk of overloading the neutral but only by 10a. (not saying that is ok, just that it would take a long time before any issues surfaced)

Taking L2 and running it to a transformer that produces 250v is not dodgy. It is exactly what is happening when you boost 208v to 250v. Instead of having 50a 125v you just have two 25a 125v out of phase. Now, when you plug your 50a 125/250 shore cord into an adapter to a single 30a 125v socket you can still run your dryer at 15a 250v. You won't be able to operate anything else without tripping the shore breaker.
 
At the risk of dragging this out longer 😉…..how could there be an overload on neutral? The scenario has a maximum of 30A coming into the boat, not 2 x 30A. I’m still looping back to the OP’s requirement: no 240V, doesn’t require more than 30A total….that adapter I linked to above would do the job.

Re the second bit….gotta digest that some.
 
NoRain, my Mainship is set up the same way yours was, before your refit. Probably because they were both made by Luhrs. I made my own adapter by joining the L1 and L2 together in the plug. All my 120 volt loads work fine. I just can't use my 240 volt air con when plugged into 30 amp shore power. Not a real problem in the PNW.
 
With a dumb Y adapter or Two 30a 125v to Single 50a 125/250v you can tap into 2 30a sockets. With the Single 30a 125v to Single 50a 125/250v you can only tap into one 30a socket. The first scenario runs the risk of overloading the neutral. The second scenario can't overload the neutral.
 
NoRain, my Mainship is set up the same way yours was, before your refit. Probably because they were both made by Luhrs. I made my own adapter by joining the L1 and L2 together in the plug. All my 120 volt loads work fine. I just can't use my 240 volt air con when plugged into 30 amp shore power. Not a real problem in the PNW.
What you have done is made your own Single 30a 125v to Single 50a 125/250v adapter. It works but it doesn't work fine because you can't use your 240v. It's possible to wire the boat with a boosting transformer to get your 240 to work. I doubt it would be worth the effort for most.

My boat was wired in such away to nullify the 208v issue. A by product of that is I can run a 240 appliance off of a single 30a socket.
 
With a dumb Y adapter or Two 30a 125v to Single 50a 125/250v you can tap into 2 30a sockets. With the Single 30a 125v to Single 50a 125/250v you can only tap into one 30a socket. The first scenario runs the risk of overloading the neutral. The second scenario can't overload the neutral.
The first scenario is not an issue here because the OP has already stated he can’t get access to 2 x 30A outlets, just one. Otherwise I and others would have suggested a Smart Y straight off.

But you are quite correct a dumb Y not a good idea for the reasons you mention.
 
What did you end up doing? The majority of these answers are incorrect and you cannot make everything work with 30/120 power if your boat is requiring 50/240. If the pedestal has a 20 amp circuit like most do AND it is on the other leg then you can do that, just have to watch how much stuff you operate
 
Hello All those who responded!
I think the take away is to see that (new boat) has a Smart Y Adapter and perhaps get the gizmo the Boat Show Seminar showed where I can test the shore power as well.
To run the washing machine at the dock I can use the generator. Air conditioning- never heard of it, it’s 55° in salon right now (old boat).
I’ll know more in a few weeks when boat closes, but at its current marina everything worked on the survey with just a 30 amp shore power cord.

Thank you everyone!!!
 
You will not make any friends running your generator at the dock for the time it takes to do laundry. I know some marinas prohibited running it at the dock.
 
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