Downgrade from 50A to 30A (Grand Banks)

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jwag956

Veteran Member
Joined
Jan 15, 2020
Messages
73
Location
US
Vessel Name
Scrimshaw
Vessel Make
1989 GB 42 Classic
We have a 1989 42CL - with a 50A/120V shore power. I am looking at adding ELCI, isolation transformer - and would love to reduce the weight of our shore power cables.
Converting to SmartPlug would be a plus.

Anyone done this?

From looking at our Amp meter - normally of course we pull almost nothing - though with Hot water (1700 watts) and a couple space heaters, battery charger, I have seen it just at 30A (No AC - we're in PNW)

Looking at Victron isolations transformers - they don't even make a >3000W 120V model that I can see.

Seems like the important thing is to swap out the main breaker to be 30A. In another thread someone mentioned their generator putting out more than 30A - but I don't see why that would be an issue unless something is drawing that??
 
I think your the first person I've seen who wants to downgrade.

My thoughts:
30 amp twist lock is a horrible connection that should never have been used for boating. While you have a choice at the boat end (SmartPlug), you almost never have a choice at the other end. Personally, I wouldn't want to draw much more than 20 amps through the average 30 amp power pedestal receptacle.

From a boat resale standpoint, it's a looser.

Here's an alternative. Read atleast post #40.


I bought the bits to tie the two cords together with a water tight connection.

The last option I will offer is to use SO cable and make your own cord. If your electrically inclined, you can buy quality SO cable as remainders on eBay. Manufacturers sell the ends off their spools at a very good price. I needed another 50' 250 volt 50 amp cable for some of my remote docking locations. Most marine cable has a much thicker jacket (maybe to go through a Glendine cable system) and adds a significant amount of weight. The 50' cable with 4 conductor number 6 wire worked perfectly and weighed significant less.

Ted
 
If you swap the main breaker to 30A you also have to change the shorepower inlet to be able to use 30A cable which is the ultimate objective, right? But as Ted notes above, the 30A twist lock is a poor connector to use for more than 20A.

Stick with the 50A breaker and the 50A cable. It may be a bit more cumbersome, but it is a lot safer.

David
 
My boat also has a 50A input but a 30A shore cable that I installed a 50A plug on. Don't worry guys, the pedestal has a 30A breaker so the 10g power line is protected.
 
i do soon downgrade, because 50A marine cable is forbidden in EU standards, don exist. all marine,house is 16(england 13A) or 32A or 3x32A socket
125-640A socket resist but for use this fee is astronomic from 500 to 10000€ month I think in Germany is more.
for that reason all small marina for to 100 yacht in Croatia have usually 3 x 125 to 3x250A max . also I don't understand USA charge first aid,if you broke neck charge you to hundred thousand $,but electric power is almost free. Tiny Croatia if want all marine have 50A socket need invest minimum 20-25 billion € and 10 years for document and another 20 year for build. Our almost all electric grid cable is underground.
 
We have a 1989 42CL - with a 50A/120V shore power. I am looking at adding ELCI, isolation transformer - and would love to reduce the weight of our shore power cables.
Converting to SmartPlug would be a plus.

Anyone done this?

From looking at our Amp meter - normally of course we pull almost nothing - though with Hot water (1700 watts) and a couple space heaters, battery charger, I have seen it just at 30A (No AC - we're in PNW)

Looking at Victron isolations transformers - they don't even make a >3000W 120V model that I can see.

Seems like the important thing is to swap out the main breaker to be 30A. In another thread someone mentioned their generator putting out more than 30A - but I don't see why that would be an issue unless something is drawing that??
I did it and love it. Most of the time when marina hopping you rarely get 50 so why drag around the cords? 30 Cords are a breeze to handle in comparison. After a while you learn what combination of appliances you can run at one time… Easy. If 50 power was anlways available and you if you rarely or can’t hop don’t change anything. But if you are adventurous I’d dump 50 for 30 and never look back.
 
I'm entertaining similar thoughts.

My shore power is a 50A (HVAC) plus a 30A (everything else)
The HVAC only needs 50A capacity if all three units are running. As I never plan to run south in summer, I don't think I'll ever need to run all three simultaneously. I could get away with dual 30A. I might even be able to cut it all down to a single 50A.

I'm going with smartplug either way, just need to settle on a Plan.
 
Here in the PNW you are very unlikely to find a 50a 125v socket. You will find plenty of 50a 125/250v sockets. So converting a 50a 125v to 30a 125v SmartPlug makes sense.

On the other hand I am not a fan of 30a twist lock sockets. They have too high of a failure rate. I would more likely install a 50a 125v end to a 30a cord for protection of the boat and leave the 50a 125v socket on the boat.
 
sorry i wrong write.
all small marina for to 100 yacht in Croatia have usually 3 x 125 to 3x250A max

must be: all small marina for to 100 yacht in Croatia have usually 3 x 125 to 3x250A max connection for grid to share all 100 yacht. 1A 230v per boat.
i don't think so also in USA have real 50A connection for all boat
 
Depends on how you use your boat. We made the mistake of going to 30 amp when we rewired our boat when we bought it five years ago. We live aboard in Sitka, Alaska, and have to turn off heaters and dehumidifier when we use the microwave. Remember, 30 am is about a quarter of the power of 50 amp.
 
Depends on how you use your boat. We made the mistake of going to 30 amp when we rewired our boat when we bought it five years ago. We live aboard in Sitka, Alaska, and have to turn off heaters and dehumidifier when we use the microwave. Remember, 30 am is about a quarter of the power of 50 amp.

I want to point out that there is 50a 125v and 50a 125/250v. They are very different. While 30a 125v is approximately 1/4 the supply of 50a 125/250v it is 60% of what is supplied from 50a 125v.

OP specifically mentioned 50a 125v.
 
Here in the PNW you are very unlikely to find a 50a 125v socket. You will find plenty of 50a 125/250v sockets. So converting a 50a 125v to 30a 125v SmartPlug makes sense.

On the other hand I am not a fan of 30a twist lock sockets. They have too high of a failure rate. I would more likely install a 50a 125v end to a 30a cord for protection of the boat and leave the 50a 125v socket on the boat.
Would you then change the 50A main to 30A main on the boat?
 
Would you then change the 50A main to 30A main on the boat?

Assuming that the wire was correctly sized for 50a on the boat, there is no need to change the breaker. Since the cord being used is 30a and the shore has a 30a breaker, nothing on the boat is at risk.
 
Our boat had 1 each, 30 amp plug when we purchased her. Inadequate if you are using shore power for AC or heat, as you have to do the Power Management Dance . . . Okay I want to use the microwave, so what do I have to turn off . . . ???
We had looked into upgrading to 50 amp, but after we installed 1,200ah of LiFePO4, the Victron Quattro 12/5000 inverter charger with pass through, our power issues went away. If we overload the 30 amp shore power (actually 28 a, since I limited the input from shore power to 28 amps), the quattro automatically begins to invert 12v house bank power to 120v to supply the power draw. Our boat seldom draws more than 28 amps continuously. Once the draw goes back down below 28 amps, the additional amps now charges the batteries back up to full . . . . Rinse and repeat.
At anchor, our solar keeps the batteries charged without the need for the generator in most cases.
I can't see that I'll ever need 50 amps the way we set it up!
 
When we bought our boat, the previous owner had a 50a 125v plug on the boat end of a 30a cord. His dock only offered 30a. When I installed 50a Smart Plugs (port and starboard) on the boat, I noticed the 30a cable was fried. I use 50a 125 cable now whether I’m plugged in to 30a or 50a. Definitely heavier, but I don’t worry about it.
If you do this, I recommend a 50a Smart Plug on the boat end so that you can use the 50a cord when you’re going to leave the boat, and you pay close attention to how much power your pulling through the 30a cord when you use it while cruising.
 
Our boat had 1 each, 30 amp plug when we purchased her. Inadequate if you are using shore power for AC or heat, as you have to do the Power Management Dance . . . Okay I want to use the microwave, so what do I have to turn off . . . ???
We had looked into upgrading to 50 amp, but after we installed 1,200ah of LiFePO4, the Victron Quattro 12/5000 inverter charger with pass through, our power issues went away. If we overload the 30 amp shore power (actually 28 a, since I limited the input from shore power to 28 amps), the quattro automatically begins to invert 12v house bank power to 120v to supply the power draw. Our boat seldom draws more than 28 amps continuously. Once the draw goes back down below 28 amps, the additional amps now charges the batteries back up to full . . . . Rinse and repeat.
At anchor, our solar keeps the batteries charged without the need for the generator in most cases.
I can't see that I'll ever need 50 amps the way we set it up!
Thanks - it never occurred to me that an inverter could/would augment shore power - a great solution
 
Thanks - it never occurred to me that an inverter could/would augment shore power - a great solution
Just to support this usage. Currently have the stove top and oven using average 250A through inverters while the 30A shore supply is heating water and running electric heaters. Oh this is while watching TV.
 
Ok, let's think about this.

If your inverter has sensed that the demand is larger than the 30 Amp shore power supply and has now sync'd to this shore power supply and added 250 Amps of 12 V dc sourced inverter power to the ac circuit, that means the ac circuit downstream of the inverter is now carrying about 50 Amps at 120 V.
30 Amps + (250 A x 12V ÷ 120V x .8 (for losses))= 50 Amps.

What size are the conductors that leave the inverter? And the breaker?
 
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Perhaps I was drawing 250A from a 12V bank of LFP? Dont overthink it.
The shore 30A was supplemented by the inverter with an additional 23A 120V. Even a 50A 120V shore connection would not have worked.

ETA: the cable size carries 30 Amps. BTW, two of them actually, each asked to carry 30A. So no problem there.
 
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The chemistry of the battery does not matter. The math is not over thinking anything.

If your shore power was suppling 30 Amps and the inverter was supplementing this with 23 Amps at 120 V. then the inverter's output conductors are carrying 53 Amps. In that instance a 50 Amp shore power connection/breaker, given enough time would likely not have held.

The question remains, what size are the downstream conductors and the breaker?
 
Have you heard of a selector switch? What makes you think 30A shore was going through the inverters which then added 23A. That would be silly.
10 gauge wire handles 30A, two of them handle 60 amps. Since 23 amps were split between two, I think I was safe tonight.
I originally replied to post 16
Thanks - it never occurred to me that an inverter could/would augment shore power - a great sonlution
 
Normally selector switches select a source of power, like a generator or a grid/shore power connection.
I have two such switches that select between 5 such power sources. My inverters, of with I have 3, are not switch selectable as they don't need to be, each has their own on/off button. Provide power to them and then determine if you want them on.

Ok, if as you say your inverter is powering your stove top and oven to the tune of drawing 250 amps from the batteries all the while knowing that it (the inverter/charger) is not connected to the grid, then how once your tea is brewed and your goose is cooked does your inverter/charger charge the batteries? It has no 120 V. power to it!
 
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ok. victron have more option for any situation. for example me
I am limited to monofase system. meen max 16-32A from shore power
victron multiplus 2 can be assisted from shore depend model 32A or 50A or 100A
12v model usually limited 50-100A assisted current.

what I make before AC current come in Victron I install ATS automatic transfer switch 125A. main is generator slave is Grid. on end electric cable go in Victron multiplus 2 5000W 100A max switch. now I can start my chiller on any grid connection in marina. what I see with my experience after sunset in marina all charter boat,big catamaran turn on AC unit and continius marina breker go off. in reality all connector to shore power is limited to 10A max usually couple Amp.Only off-grid marina don't have this problem.on remote island without grid where marina produce his electric from solar hybrid inverter -lifepo4 battery and 700-1400 kwp generator don't have this problem.

i don't know is available multiplus 2 for USA electric 110V
The MultiPlus-II combines the functions of the MultiPlus and the MultiGrid.
It has all the features of the MultiPlus, plus an external current transformer option to implement PowerControl and PowerAssist and to optimize self-consumption with external current sensing (max. 32A).
It also has all the features of the MultiGrid with built-in anti-islanding
 
@luna Ok, if as you say your inverter is powering your stove top and oven to the tune of drawing 250 amps from the batteries all the while knowing that it (the inverter/charger) is not connected to the grid, then how once your tea is brewed and your goose is cooked does your inverter/charger charge the batteries? It has no 120 V. power to it!
After the heavy load is done, I turn on shore power to inverters, they pass thru power and also charge. Batteries at 100% this morning. We really should start a thread on this topic.
 
Have you heard of a selector switch? What makes you think 30A shore was going through the inverters which then added 23A. That would be silly.
10 gauge wire handles 30A, two of them handle 60 amps. Since 23 amps were split between two, I think I was safe tonight.
I originally replied to post 16
Thanks - it never occurred to me that an inverter could/would augment shore power - a great sonlution
The Victron inverters with powerassist can do exactly what you described there. You'd wire the output with larger wiring than the input, so the inverter can dynamically assist shore power to handle higher loads without exceeding the configured limit on the input side. Basically, as you approach the limit, it scales back charging to stay below it. Then once it's down to 0 charging, it starts inverting to supplement the output to prevent exceeding the input limit. No manual switching involved.
 
@rslifkin
Yes there is a variety of inverters and their capability.
The Magnum 2012 I have will decrease charging if other loads want power. They even will accept 60A input L1L2 and always pass thru 30 L2 and adjust the other 30 L1.
I chose not send 30A to inverter only to bring it back to the 120V distribution panel as it would. So there are various configurations available. My inverters invert output 17A stand alone, that is why I have two. I have not found a configuration to send 47A out combined.
As individuals we use what we have to best suit our needs.
 
The Victron inverters with powerassist can do exactly what you described there. You'd wire the output with larger wiring than the input, so the inverter can dynamically assist shore power to handle higher loads without exceeding the configured limit on the input side. Basically, as you approach the limit, it scales back charging to stay below it. Then once it's down to 0 charging, it starts inverting to supplement the output to prevent exceeding the input limit. No manual switching involved.
Exactly what I was trying to achieve with my big electrical project last year, and succeeded; works like a charm. Here’s a screen shot from just this morning, when we had a pretty heavy load of heaters running, and turned on the microwave to heat up a coffee. A year ago we would have popped the mains.
 

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Exactly what I was trying to achieve with my big electrical project last year, and succeeded; works like a charm. Here’s a screen shot from just this morning, when we had a pretty heavy load of heaters running, and turned on the microwave to heat up a coffee. A year ago we would have popped the mains.
Yep, that looks familiar. Some people try to make easy hard. Guess that's just the way they're built :whistling:
 
It does not surprise me that your inverter/chargers will not sync. their waveform to the incoming ac power and then augment this ac with the inverter's output. Many newer inverter/chargers have this feature and I would expect that most operators of such inverters would not call it silly.

I have read an account where one operator yanked the existing (almost new) system that was advertised to perform this function but did not and at great expense replaced it with another one that did provide this function. Thats how important this feature is to some operators. If sized right, no more power management dance.

You have chosen to power your stove top and oven individually through their own inverter/charger which is just fine, as it suits you. This system allows you to replace (not augment) the grid or genset provided ac power to your stove/oven with inverter produced power. One downside to this is that the stove and oven may well consume almost all of you inverter capacity. What else, if anything is connected to these inverters?

I chose to power 2 of my water heaters by way of an inverter and left my range powered only by the grid or genset.
One reason for this is that nothing can replace the water heaters, so it's nice that when we are aboard they are always energized. With just 2 aboard no genset is required to heat water as long as we move about 4 hours daily.
No., I won't risk an engine overheat to heat domestic water. To me that would be silly as other methods (alternators, batteries, inverters and heating elements) used to produce hot water already exist.

The BBQ, microwave, electric skillet and kettle (the last 3 are all inverter powered) can all, to a large extent replace the range without using any grid or genset power. Options are almost always good.
 

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