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Old 07-11-2019, 10:50 AM   #1
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Boat pulling excess shore power

There are lots of very knowledgeable people on this forum, so I am hoping that someone can volunteer some advice which will help what seems to be a sticky situation.

I got a call from the marina the other day, saying that my boat was pulling so much shore power that they had disconnected it. And that I should come down and check to see what might be wrong. To give you an idea of the magnitude of the problem, they said that I had used about $2,000 worth of electricity before they disconnected it. (My slip rent and the power usage are separate).

Needless to say, I went down immediately. The power station on the dock has a meter, so I connected the power, and sure enough the meter began whirling. Disconnected it.

Then disconnected the power cable from the boat, but connected it to the power station. Not using any electricity, so no short in the cable itself.

Went on board and checked for any burning smells. None. Connected to power again and tried turning things on such as fans and the dehumidifier. They all worked fine, with no smell of burning anywhere. The meter on the electrical panel inside the boat did not show any particular drain on the 120v line.

So I disconnected everything again (of course!), turned off everything inside the boat which runs from 12 volts, and came back home to have a stiff drink and ponder.

Any thoughts?
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Old 07-11-2019, 10:57 AM   #2
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Maybe a bad Inverter?
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Old 07-11-2019, 10:57 AM   #3
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First thing I would try is to plug it into a different power pedestal and see if it does the same thing. If it does then plug it in with everything turned off. Does the meter go crazy with everything off? Add 1 breaker at a time and see when it starts using a lot of power. Then check the power usage of whatever device is on the breaker. You will have to find a label on the device or look in the owners manual to see how much power the device is supposed to use.
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Old 07-11-2019, 11:37 AM   #4
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You are very fortunate to have a marina that notices that sort of thing. My (old) marina would have been quite happy for the bill to run to 20x that amount without noticing a problem.
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Old 07-11-2019, 11:55 AM   #5
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I would back up a moment and think outside the box as you will get plenty of what could be wrong with the boat side.


The average circuit on the boat is 15 or 20 amps....if something tried to draw more than that, it should pop a circuit breaker.


20 amps X 120V X 24 hrs X 30 days = 1,728,00 watt hrs or 1,728 KWH


At 10 cents a kilowatt hr 1,728 x 0.10 = $172.80


Please check my math....


But either the meter is wrong or you have a bad breaker/short someplace....


Even a full 50A service would only draw 5 times that without something popping all the way back to and including the post...plus at those amperages...I would have to see something being hot and you smelling it.


Just sounds too strange..... I know many marinas charge more than the power companies, but don't most states have some limit on it...surely not 10X. Last time I heard in one state it was something like 15%.


My first step would be try another post or plug some small load directly into the power post.
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Old 07-11-2019, 12:00 PM   #6
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I'm having a math problem. How many volts and amps is your electrical service? What do you pay per kilowatt-hr?

A 30A connection at 120V can supply 3600w, which is 3.6kw. So, even at a really high rate of $0.20/kw-hr, that is only $0.72/hr. 24hrs/day, 30 days/mo, that is only $518.00/mo.

50A service at 120v can only supply 6000w, which is 6.0kw. So, even at a really high rate of $0.20/kw-hr, that is only $1.20/hr.,24hrs/day, 30 days/mo, that is only $864.00.

And, the average energy cost in the US is about $0.13/kw-hr. Even NY and Cali are only about $0.18/kw-hr.

$2000/mo, 30 days/month at $0.20/kw-hr would require something like a 115A draw at 120v. Even at 240V that would be 57.5A draw.

...unless I am messing up the math, I'm not seeing it. Especially on a single 30A or 50A breaker!

I'd put a clamp type meter on the hot wire right after it comes into your boat. See what current it is drawing there. Then do same at pedestal. It would be shocking rare for meter to run fast. But, since the numbers don't seem to work, I'd get clarity there and check that early on

Id also feel the shore power cord and outlet at both ends for heat and check for low voltage (a sign of loss/usage along the way) at the main panel.

I dont see that crazy amperage on any standard amerage shorenpower cord without it getting hot.

Beyond that, if the load is real, Comdave has it exactly right. Turn everything off, then just the main, then each circuit one at a time. Check after each one to see if the usage is crazy. When you find the one that you can flip on to cause the problem and flip off to relieve the problem, you've narrowed it down a lot. Then turn on and off devices at that one circuit.

But, again, I'm having problems....a single 15A/120v circuit, for example, can only supply
1800w, 1.8kw. $432/mo computed as above. The wiring would fry,otherwise.

Something seems off. Maybe just my math rushed between tasks.
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Old 07-11-2019, 12:05 PM   #7
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Also, if these numbers are real, another thing you can try is using an infrared thermometer or camera on the shore power connections, inside shore service, any isolation transformer, and the back of the main panel.

...something should be toasty!
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Old 07-11-2019, 12:59 PM   #8
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bad kWh meter
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Old 07-11-2019, 01:06 PM   #9
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Looks like a consensus has emerged!
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Old 07-11-2019, 01:16 PM   #10
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If you suspect a bad KWh meter, and I am also in that camp, remove the metal cover inside the shore power pedestal so you can get to the internal wiring. Then put a clamp on AC or AC/DC meter set on AC around the black wire going to the 30A socket. Turn your power on and see what you measure.


You could do the same thing inside your boat at the main AC panel, but that would not include the possibility of a live wire dropped in the bilge water or somehow getting to ground before the main AC panel. But that is very unlikely.



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Old 07-11-2019, 01:20 PM   #11
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Thanks. Some good suggestions there. And one absolute nugget -- I didn't know about clamp meters! I should add that the marina has not charged me anything yet at this point. The owner (Chuck Shields) is an old acquaintance from way, way back, and he is the one who called me. He was going to check the dock power pedestal and see if it might have a problem. If it is entirely my problem, I'm sure that I will have to pay something, which I should. Good suggestion to try plugging into a different power pedestal. I'll do that the next time I am down there. But am going to order a clamp meter today. I can see where it would be a very handy item to have!
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Old 07-11-2019, 01:33 PM   #12
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This is what you are looking for.

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Old 07-11-2019, 02:06 PM   #13
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I think that $2000 is a whole lot of electricity to use as some have said with the math figured out. That is why I suspect the meter may be bad. I always like to try the simple stuff first. Swapping power pedestal is the easiest thing I can think of. The KISS principle in action. I used to be an engineer for a computer company and many of the engineers would skip the simple stuff because every problem had to be an intricate one. They would get burned by skipping the simple things and diving deep into the problem. Many times it was as simple as is it turned on.
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Old 07-11-2019, 02:11 PM   #14
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Quote:
Originally Posted by Comodave View Post
First thing I would try is to plug it into a different power pedestal and see if it does the same thing.

That would be my first action as well. As Scott mentioned, the amps required to draw that much power would be way more than any of the breakers on your boat could handle.
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Old 07-11-2019, 02:18 PM   #15
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Is the power cable dangling in the water? I often see boats with power cables dangling in the water - always considered it bad practice. Are there many dead fish around your boat?
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Old 07-11-2019, 02:38 PM   #16
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Quote:
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Is the power cable dangling in the water? I often see boats with power cables dangling in the water - always considered it bad practice. Are there many dead fish around your boat?
No. No cables in the water (I am careful about that), and no dead fish.
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Old 07-11-2019, 02:50 PM   #17
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John,
Do you have 120VAC@30A
120VAC@50A
240VAC@30A
240VAC@50A
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Old 07-11-2019, 02:54 PM   #18
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The meter that Capt Lee recommended above is an AC only ammeter, ie no DC amps. For a few bucks more you can get an AC and DC ammeter. On a boat I use the DC ammeter 95% of the time.


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Old 07-11-2019, 02:56 PM   #19
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We are discussing an AC amperage problem
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Old 07-11-2019, 03:01 PM   #20
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I agree with David, if you buy one, get the one that also does DC. Extremely useful
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