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Old 10-27-2014, 07:11 AM   #21
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Originally Posted by kulas44 View Post
You will never have 100 amps anywhere no matter what. The service is not cumulative. 50 amp 125 or 50 amp 125/250 is still just 50 amps.
No. If you split the legs of the 50a 125/250 cord like many boats do you have 2 50a 125v incoming lines. So you have 100a of 125v available total, 50a on each leg.
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Old 10-27-2014, 07:17 AM   #22
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Sure a boat can live off 12V and use renewable power to supplement a charger....mine just isn't set up that way yet and having 100 amp surge capacity for ACs or a Microwave or any other short term surge is nice in my book with not having to dash to the panel and load shed...
While you have 100a of 125v to play with total. You don't have 100a of surge capacity. You only have 50a per leg.
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Old 10-27-2014, 07:28 AM   #23
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Correct on the math...not so on the "stupid" part.
Actually he's not wrong on the stupid part either. While you have 100a of 125v available on a 50a 125/250 cord, 50a on each 125v line, if you try to pull all those amps off the two lines for any length of time you will most likely end up burning out the cord ends or frying the receptacles in doing so.
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Old 10-27-2014, 07:34 AM   #24
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A lot of people on here have been questioning my wisdom on my 50A 125/250 upgrade...
Am I mistaken, my recollection of walking the docks along the Atlantic ICW is that many of the 40ft+ newer trawlers had 50 amp 120/420 service. I am aware of a couple of older Krogen 42s which upgraded from two 30 amp 120v service to a 50 amp 120/240 volt service. In the US southeast with the demand for airconditioning in a marina I think it would be beneficial.
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Old 10-27-2014, 07:46 AM   #25
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Correct on the math...not so on the "stupid" part...especially when you have 2 or 3 air conditioners that may kick o at the same time.

A lot of people on here have been questioning my wisdom on my 50A 125/250 upgrade...seems to me after 3 times and over 10 years living aboard, lot's of burnt 30 amp connectors and chasing popped CBs all the time because normal living shouldn't have too much load shedding involved...

I'm not sure it's my decision that should be in question...

Sure a boat can live off 12V and use renewable power to supplement a charger....mine just isn't set up that way yet and having 100 amp surge capacity for ACs or a Microwave or any other short term surge is nice in my book with not having to dash to the panel and load shed...

Yes yes Fred, I could have it done automatically...but I'm just gonna live with my 50A 125/250 service, enjoy my 100 amps when I need them and work the boat towards more 12V so eventually I can be free from marina power to a point and happier at anchor.

The wasn't directed at you. But you and me both know if you continuously try to get 100A's out of your cord you have 99% chance of meltdown somewhere on shore or on one end of the cord.

Are you going with a true 50A 125/250v or are you splitting the legs up?

All of our AC's running (64k BTU's) run 24 amps 240. With all them running I usually don't like to run the water heater, but small loads like the microwave aren't a big deal. In the Bahamas we run off two 50A cords, one dedicated to HVAC and one for ship loads that's generally enough for us and we're pretty power hungry. Our problem is the genny isn't big enough. Anyways, if ones not enough you can always add a second and dedicate it to HVAC.
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Old 10-27-2014, 08:32 AM   #26
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My last boat had a separate 30 amp circuit dedicated to the A/C. If it wasn't plugged in, it wouldn't work. I needed 2 power cords or a splitter. I felt 2 cords was better. I would plug in 1 30 amp circuit at a time and check to see if yours is set up that way. But, I agree, get someone in there that knows what he/she is doing, and get an analysis.
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Old 10-27-2014, 08:35 AM   #27
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I'm not sure why you guys think things melt at rated capacity.....

Things go wrong with high resistance...but I've never had any issue except at the ends with running full amps through shore power cords...and the 30's suffer much greater end burning than the 50's based on just the design which is 1/2 the reason I'm switching...

I've had way more marina CBs pop when at capacity than meltdowns...well...never had a meltdown except with a bad shore power power post.

When I discussed surge...I was just saying that if I was and probably will continure to run at 60-75 amps normal loads...then I still have about 30 amps in reserve for the surges on some appliances and the times I add a heat gun or ceramic heater to an outlet circuit.

Don't worry guys...I've researched this so much that I have found I had to go way beyond the normal sources of info around here including the marina electricians, the large marine electronics outfit here, Paneltronics tech help etc..... I'm pretty sure I have a good handle on it...to the point that I'm scared that the "pros" have so little.
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Old 10-27-2014, 08:42 AM   #28
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The numbers above the circuit breaker switch on the panel actually reads "50 amps 230 volts"
I'm still leery to say for sure what's going on with your boat.

You should also have a panel with something that says 110V or 115V.

If you don't something is definitely a bit strange...unless the 50A inlet is wired directly to a 230V panel and then one or several of your appliances must be 220.

And again..with a used boat...looking at just the front of panels is a bit dangerous...you really need to understand what is going on behind them.

As a boat owner you have 2 choices in my way of thinking....know everything about your boat yourself and know enough to know what is going on isn't dangerous...or hire experts that you trust with your boat/life to certify that the boat checks out and then they write up a basic operating and systems diagram so you understand at least the basics and the next owner/tech doesn't have to reinvent the wheel.
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Old 10-27-2014, 09:13 AM   #29
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You will never have 100 amps anywhere no matter what. The service is not cumulative. 50 amp 125 or 50 amp 125/250 is still just 50 amps.
50 amps is 50 amps.......unless you have two of them. 50 plus 50 is 100.

I have a 50 amp 125/250 service cord and its two 50 amp split phase leads give me 100 amps on my 40 foot boat. I will take you downtown Miami and give you an hour to draw a crowd and kiss your you know what if I don't have a 100 amps.
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Old 10-27-2014, 09:21 AM   #30
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I did something very similar for the new owner of my old Mainship Sedan Bridge. I had added 6 DC circuit breaker sub panels to various areas of the boat, installed a Xantrex 2500 invert/ charger with a Link 2000R controller, added an extensive NMEA2000 buss. I ended up using a Word document with embedded PDF's on every piece of equipment and instructions for what each DC panel controlled. I also included an updated AC and DC schematic showing the power distribution. I found it less expensive to run heavy gauge wire to various DC sub panels than to run home runs to a single large DC breaker panel. The boat also had 2 stand alone Xantrex battery chargers, one for the starting batteries that could also charge the house bank if the 2500 failed and a stand alone 40 amp charger in the front of the boat to charge the bow thruster, windlass and wash down pumps battery bank. I could get the boat ready in a few minutes with my eyes closed but not the new owner. I hear he's having fun with the boat and he uses it for cruising much more than I ever did.
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Old 10-27-2014, 09:31 AM   #31
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Put an amp meter on it and show me 100 amps, not gonna happen. You have a 50 amp service, it is not cumulative. Although I am impressed that a Texan can do simple math
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Old 10-27-2014, 09:54 AM   #32
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Put an amp meter on it and show me 100 amps, not gonna happen. You have a 50 amp service, it is not cumulative. Although I am impressed that a Texan can do simple math
I told you I have two 50 amp phases. (50amp125/250) With two amp meters I can show you 100 amps. You have to add them together. Maybe thats why you can't get to 100. You have to add.
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Old 10-27-2014, 09:55 AM   #33
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Put an amp meter on it and show me 100 amps, not gonna happen. You have a 50 amp service, it is not cumulative. Although I am impressed that a Texan can do simple math
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Old 10-27-2014, 10:25 AM   #34
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I'm not sure why you guys think things melt at rated capacity.....
I guess cause I've seen it first hand so many times. Unless ever connection, plug and deceptively is in very good condition at every location you connect to, your cord ends and recepticals are not going to be happy running at full capacity hour after hour, day after day. Then you have start up loads.
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Old 10-27-2014, 10:40 AM   #35
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Our 44' trawler has 3 electrical inlets for shore power: 30 amp, 50 amp, a/c. We have only used 30 amp which sometimes leaves us a little short and the main circuit snaps off. We have been told that if we get the bigger cord and kick up to use the 50 amp inlet we will have more available juice but it will not operate the a/c. We have also been told that the only way we can run a/c from shore power is by using a 50 amp source (available at our marina) and getting a splitter and an additional 30 amp cord and run one cord from the splitter to the 30 amp inlet and the other to the a/c inlet. We are told this will allow us to run the a/c but it will be a separate circuit and will add no more available power for the rest of the vessel. Would appreciate any thoughts.
As so often happens on boating forums, people have taken your question and turned it into an irrelevant argument among themselves.

Like a couple posters mentioned, this setup, if it really works as you describe, is "less than optimal" at best. Your best bet is to find someone who understands boat wiring and have him or her examine your boat in person and determine the best way to power all your appliances efficiently and at the least cost. Many marinas charge for electricity based on amperage or the number of power cords.

I would think it's a pretty big or complicated boat that couldn't be powered by one 50 amp shorepower service.
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Old 10-27-2014, 11:33 AM   #36
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Depends if it's 50A 125 or 50A 125/250....especially if the stove is electric

A water heater, air Conditioner, hair dryer can be almost 40 amps....someone using a large and small burner cooking breakfast on an electric stove can use another 15 amps easy...there's always a few parasitic chargers on a boat plus the main charger that may kick on at 5-10 amps...so 50 amps is easy to hit....having another 50 in reserve from a 50A 125/250 cord split into 2 busses is nice to have.

My friends Viking 55 had 2 - 50A 125/250 inlets and with an all electric boat and 6 people aboard or so...much like any house these days....even a 200 amp house service is there for a little cushion.
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Old 10-27-2014, 01:35 PM   #37
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As a former electric company employee/lineman/wireman/forman/ of 15 years then lead electrician for an oil field electrical contractor I am possibly qualified on this subject. Most folks think they can "add" there electric service. It is still only and exactly what the breaker allows. If I have 2 air compressors each putting out 120 psi (the potential) then add them together do I get 240 psi.? No,,, but I can run a larger cfm load. I still have 120 psi. Same with electric service. Some large boats have 50 amp 3 phase service. The do not consider it to be a 150 amp service. Generally the captain of these boats actually does know his stuff.
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Old 10-27-2014, 02:16 PM   #38
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As a former electric company employee/lineman/wireman/forman/ of 15 years then lead electrician for an oil field electrical contractor I am possibly qualified on this subject. Most folks think they can "add" there electric service. It is still only and exactly what the breaker allows. If I have 2 air compressors each putting out 120 psi (the potential) then add them together do I get 240 psi.? No,,, but I can run a larger cfm load. I still have 120 psi. Same with electric service. Some large boats have 50 amp 3 phase service. The do not consider it to be a 150 amp service. Generally the captain of these boats actually does know his stuff.
I may be wasting effort here but; In your air compressor example psi is voltage and CFM is amperage.

I have 2 50 amp 125 breakers. They do add and therefore I have 100 amps at 125. Many boats are like this.

In your 3 phase example you would have 150 amps if each phase were provided with a neutral. You would have three services of 50 amps each.
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Old 10-27-2014, 02:24 PM   #39
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Actually the larger boats have 100a three phase service.

And it's the engineer on board that knows his stuff in that case. Not necessarily the captain.
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Old 10-27-2014, 02:26 PM   #40
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I have 1 50 amp 120 volt cord going to two 30 amp breakers onboard. That's max for that 50 amp service and 50 amp cable. Run another cable from your neighbors box and you will have 100 amps available. I am not an electrician and will never be an electrician but that's what I did to enable a welder to work. The smiley means you can't jump all over me right?
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