Shore power

[uncledom]

...As long as you don't draw more than the branch circuit provides, you will be fine.) So, the marina's branch circuit breaker protects their circuit from breaker to receptacle; your boat's input breaker protects your boat's AC input wiring, including your shore power cord.

That said, I'm open to hearing a substantiated argument for why this isn't so, or safe. I know I can learn something new every day, and I'm all ears.

Actually, even though the pedestal on the dock is a branch circuit from the marina the cord to your vessel is considered a service entrance just like the service on your house.
The problem begins right after you put in the adapter and then connect equipment that is only rated for 30 amps to the 50 amp adapter and breaker. Now your putting 50 amps of potential power down a 10 gauge wire system that is only rated for 30 amps. That is way under rated and can easily cause a fire if there is a fault, long before the breaker trips.

Your input breaker, or your first main breaker in your vessel is the first place that has now started to protect the vessel at 30 amps. Up until this breaker every current carrying device is at risk for overload and fire. The 50 to 30 and the 30 to 15 are both against code and are a hazard and both are covered in my patent.

When using an adapter on my vessel, and I do use one occasionally, here is a list of what is in jeopardy.
The 30 amp shore power cord, the shore power plugs on the side of the vessel (where fires have started), the wiring from there to the 30amp rated isolation transformers and the transformers themselves and then the wiring from the transformers to the main disconnect breaker in the aft cabin. From that first 30 amp breaker you are back in compliance but there is a lot of room for fault. Also breakers don't trip as soon as you hit Xamps plus .01. They have a curve based on heat over time. Technically you are suppose to "continually" pull only 80% of a circuit's rating which would mean that on a 30 amp circuit you should only be pulling 24 amps under full load. I know the boat builders don't calculate to that spec. The problem really lies in the fact that without a properly sized breaker to protect you from over current you might not be fine. They don't call it a fault for nothing. Wire chafe, loose connections or a short circuit of any type can lead up to a fire especially when there is more current available than the circuit is designed to operate.

 

[jviss]

I'm not buying it, uncledom. If what you assert is so, then any case of plugging an appliance, or even a lamp into a 20A household outlet would have to be rated for 20A continuous, all the way through. They are not, and this is not how electrical distribution systems are designed or operate. It should be intuitively obvious that downstream components consume less that the rating of the source, and are built to the load rating, not the source rating. So it is with boats.

I might add that the current in a loop is the same at any point on the loop. The boat's breaker will see a current overage at nearly the speed of light, and will respond according to the characteristics of the breaker, which of course are substantially slower, but fast enough.

If there's a fault, i.e., short, in the line between the boat and source, then yes, the cord might burn before the source breaker trips, but it will burn upstream of the fault.

I'd like to know more about your patent application: where filed, what your claims are, if you don't mind sharing.

I'd also like to know what code, exactly, is violated by the adapters, and if so, why vendors still make and sell them. (Better tell Marinco!)

 

[jviss]

here is a list of what is in jeopardy.
The 30 amp shore power cord, the shore power plugs on the side of the vessel (where fires have started), the wiring from there to the 30amp rated isolation transformers and the transformers themselves and then the wiring from the transformers to the main disconnect breaker in the aft cabin. From that first 30 amp breaker you are back in compliance but there is a lot of room for fault.

I admit you have a point here, uncledom. Anything upstream of that main, 30A duplex breaker in the boat is potentially at risk, and I imagine that there's no way to tell what component might fault, fail, or burn. But I just don't know; everyone does this, uses a pigtail to plug a 30A shore power cord into a 50A outlet, and the pigtails (or other mechanical format adapters) are commercially available and not disallowed in marinas, which have insurance requirements. Do any insurance companies exclude these? I don't know. I don't think so.

I imagine one could build an adapter that plugs right into the 50A receptacle that has a duplex 30A breaker integrated. Is this your invention? I have some experience with patents, and I don't think that is patentable. I don't think it would pass preliminary scrutiny for non-obviousness or not being a simple combination of existing items. But then, I have seen some pretty simply things patented, so you never know. It's one thing to be granted a patent, it's entirely another to 'use it' to pursue infringers and to license it to manufacturers. Regardless, good luck! If you build it, they will come. I might buy one, myself.

(I need to do more research on this topic.)

 

[uncledom]

When you plug something in, it is a device and not subject to the rules of distribution, as you so properly put it. The boat is seen as a structure and the wiring to it and in it are part of the distribution of electric, this is where code compliance comes in. Breakers only see the load put upon them, they only look down stream not upstream to the source. So when there is 50 amps available to the plugs and wiring right up to the far side of the first over current device rated for 30 amps those parts are in a dangerous state as they have the potential to conduct the heat of 50 amps on wire and plugs only rated for the heat of 30 amps. Make no mistake that electricity is really a heat potential and that is the real danger. A loose connection is not a short but it will raise the resistance and therefore the amperage and the heat passing through the area of the bad connection. That is a fire hazard. Adding to that the fact that you have almost doubled the amount of power available to that loose connection is a recipe for disaster. Usually bad connections do not trip breakers. But if you look at all the pictures of 30 amp twist lock shore power cords that Maine Sail shows on his site https://secure2.pbase.com/mainecruising/boat_projects these are caused by bad connection and possibly the application of more current than the plug was designed for by using an adapter cord that allows 50 amps down a 30 amp circuit.
My patent is filed with the United States Patent and Trade Office. I am awaiting review and any critique they might have. The patent is all about over current applications caused by people who are ignorant of the rules. I don't have the book handy but you can consult almost any version of the National Electrical Code and find the actual article number that applies. There will be a chart for the ampacity of conductors and separate article that shows required over current protection of said conductors.

 

[uncledom]

@jviss my patent is pretty much for an over current device, circuit breaker, to be built into the adapter. It is obvious, but it also makes the adapter NEC compliant. The ignorant are the ones manufacturing an adapter with out over current protection. As with many things in life they are playing the odds in favor of profit. I saw a gap and I'm trying to fill it with a safer solution.

 

[JamesG161]

20A household outlet would have to be rated for 20A continuous, all the way through

It should be. Why?
You are assuming one big factor, that the Boat/House or anything on the "receiving" end is...

OFF!

Current surge is a real thing!

Also in an AC circuit, that "Surge" is met with not only resistance, but Impedance by the completed circuit.
Most of my boat breakers are "heat" tripped.

Jim...

PS: I am sure you have heard of a "Arc Arrester" Breaker.
PSS: Current flows in a room temperature copper wire at no where near the speed of light.

 

[walt]

Sort of interesting... for some reason there is a 110 30 amp plug that RV's use that is slightly different than the 110 30 amp plug used by marina's.

I dont know if this is a local thing but where I spend the winter, the house has a RV 110 VAC 30 amp outdoor socket in the side yard. I was able to go to the local Lowes hardware store and purchase an adapter that had the male prongs for the 30 amp socket and the female socket for standard 15/20 amp service. This allows you to use a standard hardware store or Walmart extension cord and admittedly, that is exactly what I have done to provide AC power to the boat when its in the side yard.

This is the same exact dangerous condition being discussed (using an underrated power cord for the service) yet I was able to easily find and purchase this adapter at a local hardware store. Surprised me as I thought the threat of an even remotely potential lawsuit would have prevented the hardware store from selling such a thing. I checked the adapter for any sort of underwriter marking (like UL), there was none. But.. so easy to find and buy that you would assume it was safe to use. Lots of RV's in this area during the winter, Lowes probably sells plenty of these.

FYI, I am still going to keep using that "dangerous" adapter..

 

[jviss]

A loose connection is not a short but it will raise the resistance and therefore the amperage and the heat passing through the area of the bad connection. That is a fire hazard. ... Usually bad connections do not trip breakers. But if you look at all the pictures of 30 amp twist lock shore power cords that Maine Sail shows on his site https://secure2.pbase.com/mainecruising/boat_projects these are caused by bad connection and possibly the application of more current than the plug was designed for by using an adapter cord that allows 50 amps down a 30 amp circuit.

O.K., so agreed, you are right, the loose connection is often the culprit. And, they usually don't trip a breaker. So, a circuit breaker isn't going to help here. I think the increased current capacity is a marginal consideration here, but maybe I'm wrong about that. It seems to me that the loose connection for a 50A cord used from a 50A outlet will be just as bad as a loose connection on a 30A cord used from a 50A outlet.

A breaker won't protect against this, you would need a thermal shutdown device, no? Mainesail talks about this feature of the Smartplug, but I don't think that product includes that at this time.

 

[SEMPERAVANTI41]

I agree with Uncledom, it just doesn't make sense to have up to 50 amps feeding a shore power cord and boat wiring up to the main breaker that is only rated for 30 amps. If there is anyplace to observe electrical safety, it is around water, marinas & boats. Unfortunately the electrical standards only seem to get updated when a tragedy occurs.

 

[JamesG161]

Unfortunately the electrical standards only seem to get updated when a tragedy occurs.

Unfortunately Safety standards and most code is just a History Book of past Tragedies.
Jim...

 

[SEMPERAVANTI41]

Jim
Well said!!!

 

[plenny7]

It was my understanding that NFPA 70 (NEC) was the law across the entire US & NFPA 303 was also law for marinas & some types of similar marine facilities. Is this not correct?

Here is a map where you can find out which states have adopted the NEC, and which edition. I find it interesting that several states are several editions behind in their adoption of the Code.

https://www.nfpa.org/NEC/NEC-adoption-and-use/NEC-adoption-maps

 

[jviss]

I very glad this topic came up. To answer the OP's question, no, the 50A capacity outlet will not damage any properly working system.

On these wiring systems, I think it's important to note wherein the responsibility lies at each part of the system. Let's use the example of U.S. home wiring. The circuit breaker in the distribution cabinet is sized to protect the wires in the wall, and of course, the 'device' at the end, that is, the receptacle. That's it. Plug in whatever you want, a house fire starter, electric chair, whatever, as long as it doesn't exceed the circuit rating, typically 15A or 20A, the breaker won't trip. It is the responsibility of the supplier of the 'appliance' to ensure safe operation from the receptacle downstream. A lamp make can provide a 100W lamp with a 12' 18WG cord, and as long as it's designed and constructed properly, all is well. Note that the lamp's implicit rating is somewhere around 1 A max., despite the fact that it's fine to plug it into a 15 or 20A outlet.

Likewise, your dock's outlet breaker should be sized to protect the wiring, and a 50A outlet is expected to be able to provide 50A within some voltage tolerance. The responsibility for safety of downstream devices if that of the device - your boat, for example. Your boat should be well designed and maintained enough to not cause a fire or other dangerous fault. Relying on the branch circuit's protection to ameliorate a fault downstream is not a good idea.

 

[JimInPB]

... Make no mistake that electricity is really a heat potential and that is the real danger. A loose connection is not a short but it will raise the resistance and therefore the amperage and the heat passing through the area of the bad connection. That is a fire hazard. ...

Actually, unless we are talking about a motor load, the loose connection does not increase amperage. It does increase wattage dissipated at the point of the connection, which can be calculated via the I squared R equation. In this case, I remains constant, but R goes up, so wattage goes up. This is your source of heat in that example. It is increased watts not increased amps. It happens in corroded old breaker boxes all the time. It is a common & well documented occurrence in older & poorly maintained electrical equipment.

The rest of it, you two have pretty well hammered out. The use of a 50 to 30 amp connector is safe except for the portion of the run from the 50 amp outlet to the 30 amp breaker. If a short occurred in that area, then the undersized wires in that area would lack proper over current protection. I have seen twist lock adapters for generators that go from 30 amp male to 20 amp female, & have a 20 amp breaker built in, so somebody has already realized that this issue exists.

The fires that start at the corroded connectors can happen even when using a 30 amp plug in a 30 amp receptacle with a 30 amp breaker. Obviously, this issue is compounded when more amperage is available because once the plastic melts, you might also get a short in addition to resistance heating.

 

[JimInPB]

Here is a map where you can find out which states have adopted the NEC, and which edition. I find it interesting that several states are several editions behind in their adoption of the Code.

https://www.nfpa.org/NEC/NEC-adoption-and-use/NEC-adoption-maps

Wow, 3 states don't respect NFPA70. I did not know that. I guess that the "National Electric Code" isn't actually national. That really surprised me.

 

[plenny7]

Actually, unless we are talking about a motor load, the loose connection does not increase amperage. It does increase wattage dissipated at the point of the connection, which can be calculated via the I squared R equation. I remains constant, but R goes up, so wattage goes up. This is your source of heat in that example. It is increased watts not increased amps. It happens in corroded old breaker boxes all the time. It is a common & well documented occurrence in older & poorly maintained electrical equipment.

This is essentially correct, but actually, an increase in resistance to the circuit will decrease the current, but since that additional resistance is at the connection, not the load, then you do get an increase in watts dissipated as heat at the connection.

 

[JimInPB]

Sort of interesting... for some reason there is a 110 30 amp plug that RV's use that is slightly different than the 110 30 amp plug used by marina's.

I dont know if this is a local thing but where I spend the winter, the house has a RV 110 VAC 30 amp outdoor socket in the side yard. I was able to go to the local Lowes hardware store and purchase an adapter that had the male prongs for the 30 amp socket and the female socket for standard 15/20 amp service. This allows you to use a standard hardware store or Walmart extension cord and admittedly, that is exactly what I have done to provide AC power to the boat when its in the side yard.

This is the same exact dangerous condition being discussed (using an underrated power cord for the service) yet I was able to easily find and purchase this adapter at a local hardware store. Surprised me as I thought the threat of an even remotely potential lawsuit would have prevented the hardware store from selling such a thing. I checked the adapter for any sort of underwriter marking (like UL), there was none. But.. so easy to find and buy that you would assume it was safe to use. Lots of RV's in this area during the winter, Lowes probably sells plenty of these.

FYI, I am still going to keep using that "dangerous" adapter..

You are in good company. Lots of people in my area do lots of things that are off the books when using generators that have those same RV outlets. Here in South Florida, is is common to see all sorts of unsafe temporary practices in place when people have few other palatable alternatives after a hurricane. "Suicide cords" with a male on each end are often used to backfeed a house with a generator. Those things are even more of an invitation for catastrophe, but they are commonly used in my area when the lights go out. Unsafe equipment is available. There is no shortage of it out there.

I too have that same "dangerous adapter" that you speak of. I try not to use it when I don't have to, but I have used it.

 

[JimInPB]

This is essentially correct, but actually, an increase in resistance to the circuit will decrease the current, but since that additional resistance is at the connection, not the load, then you do get an increase in watts dissipated as heat at the connection.

Thank you for catching my goof. With a pure resistance load, that is correct. For some reason I failed to consider that detail. The resistance of the load gets added to the resistance of the bad connection & that drops the current in the loop.

 

[jviss]

If a short occurred in that area

then the 50A breaker would trip before the wire burnt.

 

[plenny7]

I very glad this topic came up. To answer the OP's question, no, the 50A capacity outlet will not damage any properly working system.

On these wiring systems, I think it's important to note wherein the responsibility lies at each part of the system. Let's use the example of U.S. home wiring. The circuit breaker in the distribution cabinet is sized to protect the wires in the wall, and of course, the 'device' at the end, that is, the receptacle. That's it. Plug in whatever you want, a house fire starter, electric chair, whatever, as long as it doesn't exceed the circuit rating, typically 15A or 20A, the breaker won't trip. It is the responsibility of the supplier of the 'appliance' to ensure safe operation from the receptacle downstream. A lamp make can provide a 100W lamp with a 12' 18WG cord, and as long as it's designed and constructed properly, all is well. Note that the lamp's implicit rating is somewhere around 1 A max., despite the fact that it's fine to plug it into a 15 or 20A outlet.

Likewise, your dock's outlet breaker should be sized to protect the wiring, and a 50A outlet is expected to be able to provide 50A within some voltage tolerance. The responsibility for safety of downstream devices if that of the device - your boat, for example. Your boat should be well designed and maintained enough to not cause a fire or other dangerous fault. Relying on the branch circuit's protection to ameliorate a fault downstream is not a good idea.

I can't find fault with any of this.

I am not familiar with the marine electrical codes, but I am familiar with electricity, the NEC, and like @jviss I am an electrical engineer.

Any main circuit overload on the boat will be tripped by the boat's incoming 30A breaker. Since you can't have an overload without load, there can be no overload between the 30A and 50A breakers.

A short circuit downstream of the 30A breaker will be tripped by the 30A breaker, or by the 50A shore power breaker if the time-current curves between the two breakers are not coordinated. Either way, one of them will trip.

A short circuit downstream of the 50A, but upstream of the 30A, will be tripped by the 50A breaker.

What's left for discussion is a condition which occurs on the cord which will be higher than the cords 30A rating, but too low for the 50A breaker to trip. A loose connection will create heat as @JimInPB states, but that increase in resistance will decrease the current, not increase, so I'm not sure that even a 30A breaker at the shore power pedestal would trip in that case. All I can think of which would cause there to be current greater than 30A, but less than 50A on the cord is parallel arcing, such as if the jacket and insulation were cut and there was a high resistance fault from the cord to something else. This is why you should inspect your cord on a regular basis, if not every time.

If I'm missing something, I welcome being corrected.