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Old 18-08-2014, 14:11   #1
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Adding a 2nd AC input

I've been having problems with my main AC breaker tripping a lot. The best explanation I got was from a pro who said since I'm docked at the end of the pier, in the summer when lot's of people are running their air conditioning and dehumidifiers it puts a heavy load on the dock's wiring, causing a voltage drop and an amperage spike. This seems like a reasonable explanation, since the only pattern I have been able to find is that it trips more often in the morning, when everyone else's AC would be clicking on. My air conditioning stays on all the time in the summer since I live aboard.

So my first question, is that the most likely explanation?

Then my next question is what to do about it. Right now I have a 30 amp shore power cable powering everything on board (air conditioning, battery charger, water heater, fridge/freezer, outlets running various things). I was thinking my choices are either get a new air conditioner unit, which seems like it would be the more expensive route, or splitting up the AC load by putting in a second shore power input. I have access to a 50 amp shore power connection so it seemed like the obvious thing to do would be to put in a 20 amp connection on the boat to run just the AC, then use the existing 30 amp connection for everything else. That seems like the cheaper and easier way to go and I see lots of other boats around with that kind of 30/20 input set up so it seems to be some sort of standard.

So, does that sound like a good route to take? What do I need to know to install the second outlet? Will it be difficult to set everything up to still run off of the generator when away from shore power?

Thanks!
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Old 18-08-2014, 14:40   #2
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Re: Adding a 2nd AC input

No opinion, yet, but you might try using that 50-amp shorepower access to do a test. Run your boat from that (with pigtail converter) for a while, and see if the same AC breaker problem persists.

I've never seen a boat with 30/20 amp inlets. Always twin 30s (when they have two). Kind of surprised yours isn't set up that way already. If you DO add another inlet, I'd say another 30 would make more sense, given all the marinas around here supply twin 30-amp power routinely.

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Old 18-08-2014, 14:40   #3
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Re: Adding a 2nd AC input

Is the 50 amp dock connection 50 amp 120V or 240V?
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Old 18-08-2014, 14:43   #4
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Re: Adding a 2nd AC input

By the way, if you are tripping the breaker because of low voltage, unless you go to a different 120V line, a higher amp connector won't help.

I'm guessing the 50 amp plug will be 240V. Are you familiar with 120V vs 240V wiring?
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Old 18-08-2014, 14:50   #5
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Re: Adding a 2nd AC input

It's disturbing to me that a qualified electrician would make that statement without doing the first bit of investigation into the problem.

You're proposing that you cut a hole in your boat to add an expensive plug and wire and alter a system the condition of which has not been tested. That is not the route I would take, to answer one of your questions.

Do, or hire a qualified electrician to do, some proper diagnosing.

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Old 18-08-2014, 15:14   #6
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Re: Adding a 2nd AC input

You'll need a good volt and clamp on amp meter to confirm that you don't have enough current (or low dock voltage) or both. Once you've confirmed what you think it is it's just time and money.

We've done many 30 to 50 amp upgrades. Easiest way is to replace the cord and plug inlet as well as the 30 amp main breaker with a 50amp one. From there it gets more harder and more complicated.

(If the shore power is 50/125-250 you'll just need to connect one leg of course)
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Old 18-08-2014, 15:28   #7
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Re: Adding a 2nd AC input

Quote:
Originally Posted by Scott Berg View Post
(If the shore power is 50/125-250 you'll just need to connect one leg of course)
Or split the legs and run the air con on one leg and the hot water and smaller loads on the other. However, making some assumptions from the original question I think this would be beyond the skills of the OP. Time to bring in a pro.
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Old 20-08-2014, 14:10   #8
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Re: Adding a 2nd AC input

Thanks for all the replies! I'm not a pro by any means, but my dad is very knowledgable with this stuff and will be helping me, and I'm trying to learn more.

I checked the shore power box and I definitely have a 30 amp plug and a 50 amp plug. There's no labeling about voltage on either one but the plugs look exactly the same. Is there some other way to tell?

I have a clamp on meter but I'm not sure how I'm supposed to get a good measurement on the power flowing through the shore power cable. I just get a zero reading, which is because there's multiple leads running through the cable, correct?

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Originally Posted by skipmac View Post
Or split the legs and run the air con on one leg and the hot water and smaller loads on the other. However, making some assumptions from the original question I think this would be beyond the skills of the OP. Time to bring in a pro.
This is exactly what I was thinking about doing. Unless I'm missing something big, I don't see why it would be that hard to do this work myself. Like I said, my dad is much better with these things than I am, and he's going to be helping me, I'm just trying to get some initial research done and learn a bit for myself.
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Old 20-08-2014, 14:57   #9
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Re: Adding a 2nd AC input

Quote:
Originally Posted by Toubab View Post
Thanks for all the replies! I'm not a pro by any means, but my dad is very knowledgable with this stuff and will be helping me, and I'm trying to learn more.

I checked the shore power box and I definitely have a 30 amp plug and a 50 amp plug. There's no labeling about voltage on either one but the plugs look exactly the same. Is there some other way to tell?

I have a clamp on meter but I'm not sure how I'm supposed to get a good measurement on the power flowing through the shore power cable. I just get a zero reading, which is because there's multiple leads running through the cable, correct?



This is exactly what I was thinking about doing. Unless I'm missing something big, I don't see why it would be that hard to do this work myself. Like I said, my dad is much better with these things than I am, and he's going to be helping me, I'm just trying to get some initial research done and learn a bit for myself.

The plugs for all the different varieties of shore power are different. The two most common are 30 amp 125V and 50 amp 250V. You occasionally find a 30 amp 125V. Some also have 15 amp 125V which looks similar to a regular house plug. One place to see the different type plugs is here.

http://www.westmarine.com/WestAdvisor/DIY-Shore-Power

Since they are uncommon I wouldn't think about 50 amp 125V. Your marina almost certainly has 50amp 250V.

If you add this to your boat you will have to buy a new shore power cord and either change the receptacle on your boat to a 50amp 250V or add a second 30 amp 125V and a Y adapter to the boat end of the cord. Obviously the first was is the correct way to do it. If you are going to change the boat receptacle you should definitely go with a Smart Plug.

If you go with the 50 amp 250V you will essentially have 2 separate 125V supplies so you will also have to either

1. add a second AC panel in your boat
2,.completely rewire the existing panel and probably change some of the breakers.
3. Replace the old panel with a panel set up for 250V.

About the clamp on meter, the reason you read zero current is the meter reads the total current in and out. You have to separate one wire to read the current just going through that wire.
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Old 20-08-2014, 15:27   #10
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Re: Adding a 2nd AC input

Quote:
Originally Posted by Toubab View Post

I checked the shore power box and I definitely have a 30 amp plug and a 50 amp plug. There's no labeling about voltage on either one but the plugs look exactly the same. Is there some other way to tell?
No, as skip said, they're different. Here's another resource: Outlets/Receptacles | Marinco

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Old 20-08-2014, 15:37   #11
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Re: Adding a 2nd AC input

Test them with your volt meter at the pedestal.
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Old 20-08-2014, 19:06   #12
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Re: Adding a 2nd AC input

surely if the problem is dockside voltage drop, adding a second feed wont really solve anything
You could just update the offering breaker thats tripping if its inn the boat
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Old 20-08-2014, 19:08   #13
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Re: Adding a 2nd AC input

surely if the problem is dockside voltage droop, adding a second feed wont really solve anything

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Old 23-08-2014, 23:22   #14
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Re: Adding a 2nd AC input

Quote:
Originally Posted by skipmac View Post
Since they are uncommon I wouldn't think about 50 amp 125V. Your marina almost certainly has 50amp 250V.
You are absolutely correct. I didn't look closely enough. I have a 30 amp 125V and a 50 amp 125-250V.

Quote:
Originally Posted by skipmac View Post
If you add this to your boat you will have to buy a new shore power cord and either change the receptacle on your boat to a 50amp 250V or add a second 30 amp 125V and a Y adapter to the boat end of the cord. Obviously the first was is the correct way to do it. If you are going to change the boat receptacle you should definitely go with a Smart Plug.
At the risk of asking a stupid question, why is the first way the correct way? Is it because I wouldn't have to cut a 2nd hole in the boat? I was thinking keeping the 30 amp 125V plug could be useful if I was visiting a different marina that only had that option, for example.

Quote:
Originally Posted by skipmac View Post
If you go with the 50 amp 250V you will essentially have 2 separate 125V supplies so you will also have to either

1. add a second AC panel in your boat
2,.completely rewire the existing panel and probably change some of the breakers.
3. Replace the old panel with a panel set up for 250V.
I like the idea of having a second AC panel because, if I'm understanding everything correctly, if my air conditioning were to trip the breaker, I'd like to still have power to my refrigeration, batteries, etc. That's why I originally thought of adding a 2nd AC input.

Quote:
Originally Posted by skipmac View Post
About the clamp on meter, the reason you read zero current is the meter reads the total current in and out. You have to separate one wire to read the current just going through that wire.
I understand this, but am I supposed to cut open my shore power cable? Or the cable coming out of the plug on the inside of the boat? Neither of those things seem like a great idea... it just seems like an invitation for water and corrosion in my electrical system. Am I missing something?

Thanks so much for your help! I'm sorry if I'm asking really dumb questions but I'm trying to learn as much as I can.
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Old 24-08-2014, 05:31   #15
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Re: Adding a 2nd AC input

Hi Toubab,

First, not to worry. You aren't asking dumb questions and better to ask than to burn up your boat. Besides I know that others are not born knowing everything like my teenage daughter was.



Quote:
Originally Posted by Toubab View Post
At the risk of asking a stupid question, why is the first way the correct way? Is it because I wouldn't have to cut a 2nd hole in the boat? I was thinking keeping the 30 amp 125V plug could be useful if I was visiting a different marina that only had that option, for example.

The reason I suggest the first method, changing the plug on the boat and using a single 50 amp, 125/250V cord from dock to boat is to avoid the Y adapter to make two 30 amp connections on the boat. The problem is these old design Hubbell plugs tend to make poor connections, corrode, get hot and even start fires. Every one is a potential trouble spot. The more adapters and additional connections you can avoid the better.

But I understand this will sometimes limit your options if you stop at a marina with only 30 amp supply. I that case you can use an adapter that will plug into the 30 amp dock and allow you to connect your 50 amp cord. You will only have one of the two hot wires in the cord connected so only half of your circuits on the boat will be active. So you would have to plan for that.

Whichever way you go I still highly recommend you remove the old connection on your boat, throw it in the trash and replace it with a SmartPlug. You will of course have to also put a matching SmartPlug on that end of your shore power cord. I changed over about 4 years ago and will never go back. 2013 Maine Sail endorsed the SmartPlug on his web site. Read all about it here. Shore Power Cords - SmartPlug vs. 1938 Photo Gallery by Compass Marine How To at pbase.com

By the way, the smart plug should install right in the old hole on your boat and even use the same holes for the bolts so an easy job with one caution. When you loosen the clamping screws to insert the stripped wire ends DO NOT LOOSEN TOO FAR. It says this in the directions but I wasn't paying attention and if you do this the little clamp falls off inside the plug and is a huge pain to get back onto the screw.


I like the idea of having a second AC panel because, if I'm understanding everything correctly, if my air conditioning were to trip the breaker, I'd like to still have power to my refrigeration, batteries, etc. That's why I originally thought of adding a 2nd AC input.

Correct.


I understand this, but am I supposed to cut open my shore power cable? Or the cable coming out of the plug on the inside of the boat? Neither of those things seem like a great idea... it just seems like an invitation for water and corrosion in my electrical system. Am I missing something?

No, neither is a good idea or recommended. This is just a limitation of a clamp on ammeter.

Thanks so much for your help! I'm sorry if I'm asking really dumb questions but I'm trying to learn as much as I can.
By the way, as I mentioned in an earlier reply and also by Dave, goboatingnow. If your problem is low voltage then adding another circuit is NOT going to fix the problem. Adding the capacity for more amps is not going to fix a low voltage problem.

Example, you have a shower in your house that doesn't put out a good stream of water because your water pump won't make much pressure. It won't make the water come out any faster if you hook the pump up to a bigger well, you still will have low water pressure. Same thing with electricity. Doesn't matter how many amps you have available, if the voltage (which can be thought of as electrical pressure) is low then you will have problems.

Before you spend a lot of money fixing all this you need to find out why you're having the problem. Is it low voltage at the dock power (possible) or are you losing voltage due to bad, loose or corroded connections somewhere between the dock and your onboard system (very possible). You could have bad connections in any of the plugs: dock, either end of the cord, or the boat plug OR where the wires from your boat connect to the back of the plug on your boat (especially if it was not well bedded and has leaked a little), or even at your panel.

You need to check the system from one end to the other to find out.

Skip
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