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Old 08-16-2016, 08:18 AM   #1
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30A vs 50A Twist Lock vs Smart Plugs

I didn't want to Hi-jack Roguewave's post on replacing 30A cord ends so started this thread.

My question... and I'm here to learn - not trying to convince anyone one way or another
I've dissected / autopsied several 30A plugs but have never done a 50A and I've read & reread RC's comparison at Compass Marine How To on Shore Power Cords

I've read here on TF that the over heat / meltdown problems etc experienced w/ 30A Twist-Lock cord ends shouldn't be extended to 50A Twist-Lock ends as they "are more robust"
or that the (purported) advantages of of Smart Plug apply to 30A NOT 50A cords / ends

What makes the design of a 50A Twist-lock that much better than the design of the 30A?
Why do advantages of of Smart Plug apply to 30A NOT 50A cords / ends


I get that the blades may be thicker, etc but isn't the reduced contact area - due to the need to twist the plug to lock it - similar for both?

My marina / dock supplies 50A/125V and my boat has 2 X 30A/125V inlets.
I use a 50A/30A 125V splitter and 2 30A power cords. Can't change anything on shore but I am considering changing to 30A Smart Plugs & Boat Inlet in the future - I believe there is a benefit and willing to pay a premium - when I need to change plugs / inlets but so far cord ends are good and no overheating. I am aware of the issue and check often - also I'm in a relatively good fresh water environment so corrosion concern is lessened.
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Old 08-16-2016, 08:37 AM   #2
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The 50 amp 125/250 cords don't hang from the contact blades, the 30s do.

While people talk corrosion being the enemy, my cut is that corrosion is secondary to the loose fit many 30A twist locks achieve/maintain. Many a time I have had a good twist and yet by the next morning it has almost fallen out of the inlet/outlet into my hands.

The 50s are locked on by nubs in either a metal to metal male/female sleeve, or in some cases plastic on the female with metal ground inside. These sleeves are robust enough to practically stand on, except the socket in the pedestal may not support that. Once twisted on, I have never had one work loose from wind, people kicking the cord, cord motion from the boat tugging on it, et, etc.

As far as less contact area...not sure who wins that with the 50 plugs, but yesterday I had 3 air conditioners, a 75 amp battery charger, and all the boat outlets on just one leg. True it may valve only exceeded 30 amps part of the time..... but there was no perceptible difference in temp on the shore power inlet or wires to the rear of it.

But that is also the point of using a 50A for the in between small and larger boats like mine. It came with one 30A inlet. Add air conditioning, add another 30.

But the boat was wired where EVERY outlet on the boat, water heater, stove, fridge, newclarger battery charger, etc..etc... was still on that one 30A circuit. So taking both 30s to their limit was common.

My argument to upgrade is 2 fold, one because you just may need the higher amp service, but even not, the 50A twist plugs just don't suffer the same loose connections that the 30 do routinely.

Just like a partially connected lamp cord, it may not be drawing many amps, but the tiny surface contact is heating up like crazy....and ultimately the whole connection.

Smart plugs are a great upgrade for 30A setups, they haven't convinced me yet for 50A.
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Old 08-16-2016, 08:46 AM   #3
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Can't change anything on shore but I am considering changing to 30A Smart Plugs & Boat Inlet in the future - I believe there is a benefit and willing to pay a premium - when I need to change plugs / inlets but so far cord ends are good and no overheating. I am aware of the issue and check often - also I'm in a relatively good fresh water environment so corrosion concern is lessened.
The link you provided from Compass Marine says it all. I can't add anything to it other than the convenience of plugging in the SmartPlug (Obvious orientation, no twisting, better locking, etc) is really nice! I had a 30a chord & inlet on my last boat and now have a 50a chord & inlet on my present boat. They are the best! (IMO)
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Old 08-16-2016, 08:53 AM   #4
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First on your setup you have a 50amp breaker supplying 2 30amp cords if I read your post correctly. Remember the purpose of the breaker is to protect the wire not the device. If it were me I would have a 50 amp cord set going to the boat and splitting into 2 30 amp at the boat end... 50 amp blades are more robust but the metal sleeve that surrounds the plug is the ground connection so there is a much larger surface area... In reality if you just keep the connectors clean and don't max out the amp draw for an extended period of time you will be just fine.... At our marina we installed 120 50 amp receptacles on the shore power pedestals because everyone put a 50amp to 30 adapter than ran a 30 amp cordset, we changed the breakers to 30amp....
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Old 08-16-2016, 10:46 AM   #5
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First on your setup you have a 50amp breaker supplying 2 30amp cords if I read your post correctly. CORRECT

Remember the purpose of the breaker is to protect the wire not the device. If it were me I would have a 50 amp cord set going to the boat and splitting into 2 30 amp at the boat end... I don't get this point - see below - are you thinking one 30A cord could get shorted and not trip the CB? a short should trip either - No? if one 30A gets overloaded the boat inlet CB will trip

50 amp blades are more robust but the metal sleeve that surrounds the plug is the ground connection so there is a much larger surface area... In reality if you just keep the connectors clean and don't max out the amp draw for an extended period of time you will be just fine.... Agree but larger ground isn't the point of overheating - size of current carrying connection is still small due to the need to twist the 50A to lock the same as the 30A - isn't the contact area still a dimple?

At our marina we installed 120 50 amp receptacles on the shore power pedestals because everyone put a 50amp to 30 adapter than ran a 30 amp cordset, we changed the breakers to 30amp.... Understand and agree a preferable arrangement - also agree 50A plugs are not as subject to movement as a 30A
So my thinking on 1 - 50A cord split at boat vs 2 - 30A cords split ashore and run to the boat...

Per ABYC current carrying capacity of a 10Ga cord w/ insulation rated at 60*C (Marinco 30A cord spec) is 28A - vs capacity of the same 6Ga cord at 56A (Marinco 50A cord spec)
2- 30A cords roughly equivalent to 1 - 50A

you still have to have the Y splitter w/ 1-50A & 2-30A plugs - If the 30A plugs are a weak point does this really create a better situation at the boat?

I do agree the 50A cord eliminates on set of 30A plugs - is this the benefit you are getting at?
At least in my situation they are sitting on shore on concrete - w/ threaded ring connectors for mechanical & weather resistance and don't normally get disconnected unless I'm cruising for an extended period... not a high risk problem in my mind?

Is there anything significantly different in the design of the 50A twist lock current carrying connection vs the 30A that increases the contact are?
I get the difference on the ground but that's not where the heat is generated???
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Old 08-16-2016, 12:11 PM   #6
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It's not just the fact that the 50a plug is superior to a 30a plug that makes the 50a system less likely to burn out its plugs.

It's the fact that with a proper 50a system you have so many more amps available that on most boats you are rarely, if ever, pulling anywhere near enough amps to stress the plugs contact points.
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Old 08-16-2016, 12:13 PM   #7
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Look at a 50A 125/250V setup and judge for yourself .....for what you trust your boat with.

Sure a 50A splitter to 2 - 30s is resolving the problem....at the dock end.

At the boat end it is still an issue where the smart plug would generally be better.

I just upgraded, yes at significant cost...but now I have 50% greater current capacity and better ends..so for me, smart plugs are a non-issue.

If you have any 30 A twist locks going into a boat or dock pedestal, you could do better in my experience.
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Old 08-16-2016, 12:26 PM   #8
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http://www.hubbell-wiring.com/press/pdfs/H4574.pdf
I know it is fruitless talk as things are what they are regarding all the differing plug designs. I always thought the pin and socket offered the biggest - best surface area for power connections like the 100 amp cordsets use. It simply could have been scaled for any desired amperage rating.

I have the typical twin 30 amp setup. I added a 30 amp double pole manual switch (leviton bought on Amazon) that allows one cord to power the entire split system. And I keep off the 30 amp breaker so that the plug socket remains dead at the shore inlet. So only need one cord. I have digital amp and voltage gauges and have not had any situations needing to draw over 30 amps. And of course there is still a 30 amp breaker. So all I ever use is a single 30 amp cord from the power plug on shore.



My heat pumps draws 13 amps, fridge 0.9 amp, vacuum cleaner about 7 amps, drills 3 amps, jig saw 2 amps, circular saw 12 amps. Microwave about 14 amps. But see most of these things are only used for a very short time.

The AC I only use in the summer heat and I keep the hot water heater off since I dont shower on the boat.

I have a 6500 watt genset, I have tested the output by turning on as many things as I can, and it is hard to draw more than 50 amps thru the electric system. It would be almost impossible in my normal use of power to use that much power at once.
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Old 08-16-2016, 12:56 PM   #9
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Quote:
Originally Posted by Bacchus View Post
My marina / dock supplies 50A/125V and my boat has 2 X 30A/125V inlets.
I use a 50A/30A 125V splitter and 2 30A power cords. Can't change anything on shore but I am considering changing to 30A Smart Plugs & Boat Inlet in the future
I agreed with your assessment on the 30A Smart Plug connectors which is why I switched out my sailboat.

However, you said that your dock has 50A/125V and that you use a splitter to give you two 30A/125v. I am a complete dunce when it comes to anything electric, but I thought that the 50A/250v could be split to provide 2 125v feeds since the 250v is carrying two hot wires. The 50A/125v still only carries the one 125v supply. Am I confused?
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Old 08-16-2016, 01:29 PM   #10
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i h,ave 50 amp splitter that goes to 2, 50 amp 110s it is for sale you an buy a adapter that will go from 50 amp 110s to 30 amps 110s. it is a heavey duty Hubbel. asking 150$ or OBO
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Old 08-16-2016, 01:40 PM   #11
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don,

On my '09 Mainship I have two 30amp SmartPlugs plugged into two SmartPlug outlets on the boat. The two 30amp cords (bought new from SmartPlug) are attached to the 2-30amp to 50amp pigtail. I use the 50 pig tail where ever I can as I think the connection to the pedestal is much better. The 30amp cords have a ring collar that screw onto the two 30amp pigtail connections so they are much more secure than just twisting into the dock pedestal. I don't know if it makes a real difference but make me feel better.
Up and back from CT/FL this year I would say I was able to use the 50amp connection 80% of the time.
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Old 08-16-2016, 04:07 PM   #12
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However, you said that your dock has 50A/125V and that you use a splitter to give you two 30A/125v. I am a complete dunce when it comes to anything electric, but I thought that the 50A/250v could be split to provide 2 125v feeds since the 250v is carrying two hot wires. The 50A/125v still only carries the one 125v supply. Am I confused?
Dave... I wouldn't say confused...Maybe just mixing apples & oranges

A 50A / 250V outlet can indeed be split to provide 2 50A / 125V connections (splitting the V in this case)
While some marinas have that arrangement ours doesn't

My marina provides 50A / 125V outlets which can only be split to provide 2 30A/125V outlets (splitting the Amps in this case)

Ka_sea_ta stated that a 50A cord to the boat (and I assumed split at the boat) would be superior to 2 - 30A cords split at the dockside pedestal and run to the boat...I just don't see the benefit - unless I were to eliminate all 30A plugs??
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Old 08-16-2016, 04:09 PM   #13
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Dave... I wouldn't say confused...Maybe just mixing apples & oranges

A 50A / 250V outlet can indeed be split to provide 2 50A / 125V connections (splitting the V in this case)
While some marinas have that arrangement ours doesn't

My marina provides 50A / 125V outlets which can only be split to provide 2 30A/125V outlets (splitting the Amps in this case)

Ka_sea_ta stated that a 50A cord to the boat (and I assumed split at the boat) would be superior to 2 - 30A cords split at the dockside pedestal and run to the boat...I just don't see the benefit - unless I were to eliminate all 30A plugs??
Makes sense now, thanks.
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Old 08-16-2016, 05:45 PM   #14
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In over 50 plus marinas from NJ to Florida...I have never seen or heard of a 50A - 125V service.


In hundreds of boats that I have run or been acquainted with, there has only been 2 that I can think of that had 50A 125V services.


If my boat was set up with a 50A 125 V service, I don't necessarily think I would mess with it....just adapt.


But I think many members here are confused with the types of plugs and what they will or won't do for your boat.


If you have a 50A 125V service...you are in such a minority, even to plug into a dock, that I suggest you either know or get a good explanation before doing anything.


If you have 30A or 50A 125/250V service, you are in the mainstream along the Atlantic Seaboard and just need to convert or adapt...your choice.
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Old 08-16-2016, 06:01 PM   #15
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Psneeld

Just to clarify...
My Mainship has 2 30A 125V inlets and came w 2- 30A cords...fairly common from my experience.

My marina which is a NY state park has 50A 125V outlets and most of us have to provide some sort of adapter...not all that uncommon as the major mfgs have 50A 125V to 2 - 30A 125V splitters avail...and the park has some 50A to 30A loaner adapters avail for transients that need them
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Old 08-16-2016, 06:49 PM   #16
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In over 50 plus marinas from NJ to Florida...I have never seen or heard of a 50A - 125V service.


In hundreds of boats that I have run or been acquainted with, there has only been 2 that I can think of that had 50A 125V services.


If my boat was set up with a 50A 125 V service, I don't necessarily think I would mess with it....just adapt.


But I think many members here are confused with the types of plugs and what they will or won't do for your boat.


If you have a 50A 125V service...you are in such a minority, even to plug into a dock, that I suggest you either know or get a good explanation before doing anything.
Oddly enough, there is 50A/125V service at my dock, and I have a 50A/125V inlet on my boat. However, I think all of breaker on my boat are actually 30amp breakers.

It is definitely a less than common plug type.

I end up using a 50A/125V to 30A/125V adapter at the dock end, then a 30A/125V to 50A/125V adapter at the boat. Not a very convenient arrangement.
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Old 08-16-2016, 07:43 PM   #17
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Remember the purpose of the breaker is to protect the wire not the device. If it were me I would have a 50 amp cord set going to the boat and splitting into 2 30 amp at the boat end... I don't get this point - see below - are you thinking one 30A cord could get shorted and not trip the CB? a short should trip either - No? if one 30A gets overloaded the boat inlet CB will trip

It's not if the cord shorts, it's if one cord opens... That means the a 50amp breaker can feed the other shore power cord that is rated only for 30 amps.


A analogy: in your house if you had 50 amp breaker and connected 2 10 gauge wires to the breaker instead of a 6 gauge wire with 2 10 gauge wires connected at the terminal end of the run.... Think of a lamp plugged into an outlet in your house the breaker is sized to protect the wire that feeds the plug not the wire that connects the lamp to the plug..

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Old 08-16-2016, 08:13 PM   #18
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The difference with the boat example is there is a correct sized breaker where you plug the lamp in.


There is no way to put more than a 30 amp load on the shore power cord other than some sort of short between the pedestal and the boat...and as I said...it would be weird to have a greater than 30 but less than 50 amp short or other fault.


They make the adapters and no one bats an eye at that very common setup.
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Old 08-16-2016, 08:43 PM   #19
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The difference with the boat example is there is a correct sized breaker where you plug the lamp in.

There is no way to put more than a 30 amp load on the shore power cord ...
Exactly... Agree w psneeld

Each 30A leg has miltiple breakers to protect them... one at the inlet another at each half the panel main.
If one leg opens those loads drop out and are NOT picked up by the other leg.

This whole discussion is tangent to my original question...
Is there something significantly different about a 50 A twist lock vs a 30A that provides significantly larger contact area on current carrying contacts?
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Old 08-16-2016, 10:51 PM   #20
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[QUOTE=psneeld;470479]In over 50 plus marinas from NJ to Florida...I have never seen or heard of a 50A - 125V service.


In hundreds of boats that I have run or been acquainted with, there has only been 2 that I can think of that had 50A 125V services.


If my boat was set up with a 50A 125 V service, I don't necessarily think I would mess with it....just adapt.


But I think many members here are confused with the types of plugs and what they will or won't do for your boat.


If you have a 50A 125V service...you are in such a minority, even to plug into a dock, that I suggest you either know or get a good explanation before doing anything.


If you have 30A or 50A 125/250V service, you are in the mainstream along the Atlantic Seaboard and just need to convert or adapt...your choice.[/QU OTE]
yrs ago the old Hatts had that set up 50 amp 125 i delivered a lot of them back in the day in the 60s and 70s
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