400 SB- 30amp-to 50amp

Ray 40

New Member
May 11, 2009
105
La Conner, WA
Boat Info
1997 400 Sedan Bridge w/ lower helm
3116 Cats
Engines
3116 Cats.-
8 kw Westerbeke
Am I endanger plugging my 30amp boat into a 50 amp service at the dock using a 50 to 30 adapter?
Thanks,
Bud :smt100
 
If you use a splitter and convert a single 50A plug into 2-30A recepticles you are ok............go to www.marinco.com and find item# 152AY.


If you try to adapt a single 50A plug into a single 30A recepticle (using a Marinco #121A) to power one cord set you are asking for trouble since the 30A cord set, the 30A inlet on the boat and the wiring from the inlet to the main power panel is all rated for just 30A.
 
The Amps in electricity is like a tube, we have 2 sizes 30A and 50A. if you need to fit 30A tube in a 50A tube is it ok it fits! but if you want to use 50A tube in a 30A it won't work.

If your boat have tow corset of 30A each and you use a "Y" and plug it to a 50A female at your dock it will work but you are using a total of 60A tube in a 50A tube (one line will be 30A and the other one 20A). so you might have some problems with the main breaker if you want to switch on all at the same time.
If you have this problem there is a way to fix it. plugging one cable from 30A to 30A at your dock and the other cable plug it to a 50A using a converter (from 30A to 50A).

Good luck
Robert
 
Beween the tubes and tow corsets, I am completely lost.

But.....do not try to power a 30A inlet on your boat with a 50A plug or cord. You will have no circuit protection between the power pedestal and the main breaker on your panel and if something goes astray, you are going to burn up the 30A cord, the power inlet on the boat or the wiring between the inlet and the main panel. I've seen this happen on a 400DB and there is a lot of hidden wire you can't get to between the inlet and the power panel. If you short something, it will smolder and do a lot of damage before you can access the wiring.
 
Am I endanger plugging my 30amp boat into a 50 amp service at the dock using a 50 to 30 adapter?
Thanks,
Bud :smt100


there is two kinds of 50A services available

50A 125V and 50A 230V
adapter 50A 125V ---> 30A 125V is not a problem and perfectly safe

50A 230V ---> 30A 125V it is very tricky and may be harmful to you or your boat
it requires special adapter or better use "Y" splitter 50A 230V ---> TWO 30A 125V and connect only to one leg.
 
This is liable to get confusing............ I agree that a 50A 240V service with the legs split to power 2 30A circuits is safe, but I'd argue with the statement that a 50A 120V circuit is safe to use with a 30A cord set/power inlet on a boat.

What if you get a short or a high resistance situation between the 50A adaper and the main panel in the boat? You are applying 50A current to wiring that is only designed for 30A and when resistance is high or you have a short, that can't be perfectly safe.

BTW, the 400DB I mentioned previously was one of those where Sea Ray did not strip the wires connected to the Marinco inlet far enough back. The lug was tightened on insulation and partial contact was made. Over time resistance grew and the plug and inlet fitting began to get hot. The owner knew something wasn't right when he began tripping the 30A breaker on the power pedestal. About 3 ft of wiring after the inlet plug was burned beyond use. I wonder how hot it would have gotten if he had used an adaper and hooked up to 120V 50A service?
 
What Frank said. It is not proper to use a wire gauge that is not able to support the current that the feed is fused to supply. Thus if the feed is 50A, all of the wiring from that feed point must be able to support a 50A draw. The safe thing to do is to either change the breaker to a 30A breaker or use a 50 to 30 adapter that is fused for 30A.

Best regards,
Frank
 
This is liable to get confusing............ I agree that a 50A 240V service with the legs split to power 2 30A circuits is safe, but I'd argue with the statement that a 50A 120V circuit is safe to use with a 30A cord set/power inlet on a boat.

What if you get a short or a high resistance situation between the 50A adaper and the main panel in the boat? You are applying 50A current to wiring that is only designed for 30A and when resistance is high or you have a short, that can't be perfectly safe.

BTW, the 400DB I mentioned previously was one of those where Sea Ray did not strip the wires connected to the Marinco inlet far enough back. The lug was tightened on insulation and partial contact was made. Over time resistance grew and the plug and inlet fitting began to get hot. The owner knew something wasn't right when he began tripping the 30A breaker on the power pedestal. About 3 ft of wiring after the inlet plug was burned beyond use. I wonder how hot it would have gotten if he had used an adaper and hooked up to 120V 50A service?

NOPE. First post states that he wants to connect 30A power cord to 50A outlet, so where is a problem? His boat amperage draw should never exceed pole's outlet limits. Or I am reading something wrong?
 
What Frank said. It is not proper to use a wire gauge that is not able to support the current that the feed is fused to supply. Thus if the feed is 50A, all of the wiring from that feed point must be able to support a 50A draw. The safe thing to do is to either change the breaker to a 30A breaker or use a 50 to 30 adapter that is fused for 30A.

Best regards,
Frank

yes Frank said, but original poster asked
"Am I endanger plugging my 30amp boat into a 50 amp service at the dock using a 50 to 30 adapter?" not 50A cord into 30A outlet!
 
That is one of the problems with forums........writing a clear description. I looked at Marinco's product list and found both an 30A to 50A splitter and adapter. That is why I wrote the answer both ways. I still think powering the 30A entrance to the boat with a 50A adapter is unsafe...........unless the adapter splits a 240V service into 2 legs.....but we are all guessing without a schematic or photos.
 
I still think powering the 30A entrance to the boat with a 50A adapter is unsafe

Because it is unsafe. A problem that develops between the breaker before the 30A breakers on the boat could cause all of the wiring that's rated to only carry 30A to carry as much as 50 before the shore side breaker fails.

There's a reason why we fuse at the source rather than at the load.
 
OK....maybe I'm missing something....but whenever you convert a 50A shore power down to 30A service to the boats inlet...regardless of wether the pedestal is 50A 125/250V or 50A 250V.....you will always have a 30A rated power cord/adapter in there somewhere and a 50A breaker at the pedestal protecting everything.

The boat's wiring is circuit protected at the boat's inlet breaker.....which is your protection for the 30A rated wire 'in' the boat. There is no 30A protection for the 30A cord going from the shore pedestal to the boat....that's all 50A circuit protected.
 
Right, Dom.

But the 30amp rated cordset could be fed as much as 50A. If the main breakers are inside on the panel, then the 30A wiring from the cordset inlet to the panel also could see as much as 50A, too. A fault that develops before the 30A breakers on the panel could therefore allow as much as 50 amps to be placed on wiring both inside and outside the boat that is not sized to carry more than 30. That's OK if you want to collect the insurance money on your boat for a total loss, but otherwise a bad thing.

yes Frank said, but original poster asked
"Am I endanger plugging my 30amp boat into a 50 amp service at the dock using a 50 to 30 adapter?" not 50A cord into 30A outlet!

The answer to his question is, "Yes." On the other hand, there is no safety issue in connecting a 50A boat to 30A service other than having to turn some stuff off in order to avoid nuisance trips.

Best regards,
Frank
 
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Ok there is a lot of misinformation on this tread that needs to be cleared up.
As Frank (FC3) said connecting up a boat with a 30 amp cord to a source that is protected with a 50 amp breaker is unsafe. I will add that it is unsafe even if one uses a Y adapter that Frank (fwebser) is suggesting.

First a couple of facts to get clear.

The breaker is there to protect the wiring on its load side.
Any wiring on the load side of a breaker must be able to handle the load that a breaker will trip at.
When another breaker is on the load side of a breaker the wiring on the load side of the second breaker has to be able to handle the load of the smallest breaker in the chain.
When going from split phase (240 volts between L1 and L2) to single phase (L1 or L2 to neutral) the wiring must still be able to handle the load that the breaker will trip at.

SO what does this all mean.

If you have a 50 amp breaker all your wiring up to the main breaker on your main panel must be able to handle 50 amps. So if you use a connector adapter to insert a 30 amp cord in this path (either a straight adapter or a y adapter) you now have a cord that is only capable of handling 30 amps that could potentially see 50 amps. The wiring from your shore power connector to your breaker will also be rated to carry only 30 amps, unless Sea Ray oversized this wire.

If you have a 30 amp breaker and you connect a 50 amp cord via an adapter you are fine.

It all gets done to the fact that you can oversize a wire but you can’t undersize it.

Note that I did not go into details on the overload ratings of wiring vs temperature and duration of current and the trip time of breakers vs amount of overcurrent. I think this would complicate things too much with out really adding anything.

The bottom line is the answer to the original posters question is that it is unsafe.

Disclaimer.
I am not an electrician nor do I play one on TV.
I am an Electrical Engineer who has done a small amount of power distribution calculations in the past.



NOPE. First post states that he wants to connect 30A power cord to 50A outlet, so where is a problem? His boat amperage draw should never exceed pole's outlet limits. Or I am reading something wrong?

The key wording in the above quoted text is "should never exceed". It should really say "should never exceed durring normal operation" But what about when it does due to a fault? The breaker is there for safety reasons not normal operating conditions.

A boat should never sink, yet we all carry lifejackets (and some carry liferafts)
 
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http://www.marinco.com/files/media/guides/AC Boater'sGuide.pdf

I believe the adapter you are looking at is model # 110A
50amp shore side to 30amp boat. Again perfectly safe to use, your boat's main breaker should be rated at (according to your statement) 30amp but AGAIN I would monitor power load and make sure you are not exceeding the 30 amps your are rated for....(not trusting your 30amp breaker entirely). I carry over $1500 in adapters on board.
 
http://www.marinco.com/files/media/guides/AC Boater'sGuide.pdf

I believe the adapter you are looking at is model # 110A
50amp shore side to 30amp boat. Again perfectly safe to use, your boat's main breaker should be rated at (according to your statement) 30amp but AGAIN I would monitor power load and make sure you are not exceeding the 30 amps your are rated for....(not trusting your 30amp breaker entirely). I carry over $1500 in adapters on board.

Bad advice
 
Quote:
Originally Posted by The Bill Collector
http://www.marinco.com/files/media/g...#39;sGuide.pdf

I believe the adapter you are looking at is model # 110A
50amp shore side to 30amp boat. Again perfectly safe to use, your boat's main breaker should be rated at (according to your statement) 30amp but AGAIN I would monitor power load and make sure you are not exceeding the 30 amps your are rated for....(not trusting your 30amp breaker entirely). I carry over $1500 in adapters on board.


Bad advice

+1
 

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