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Old 08-01-2013, 05:01   #16
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Re: amp leak

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Originally Posted by boeing1 View Post
..... I checked the shore power cord with a clamp on amp meter, I get 1.5 amps reading....
They only work if they measure one cable at a time - not a shorepower cable containing more than one cable. Maybe the instruction manual is not very clear.
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Old 08-01-2013, 05:28   #17
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Originally Posted by sailinglegend View Post
They only work if they measure one cable at a time - not a shorepower cable containing more than one cable. Maybe the instruction manual is not very clear.
Measuring the total cord is a valid test and if all is well it will read zero. St. Elsewhere has the right plan of attack.

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Old 08-01-2013, 06:00   #18
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Re: amp leak

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Originally Posted by transmitterdan View Post
Measuring the total cord is a valid test and if all is well it will read zero. St. Elsewhere has the right plan of attack.

Dan
This is correct. In a properly operating shore power cord there would be equal current on the black and white wires. With say 7.9A on black and 7.9A of white you would read 0A by clamping around the shore power cord.

With 7.9A on black and a resistance issue on white causing it to only pass 7.2A you would see a reading on .7A when clamped around the entire cord set. This means .7A would be flowing back to the source on the green wire or some could be leaking back through the water path. It always gets back to Earth somehow..

If you want to use a clamp meter, rather than building your own 30A and 50A test leads, you'll need one that has low current accuracy something most AC/DC clamps lack. You can always test your clamp meter against a standard DVM on the 10A scale with a known load low amperage load, preferably below .5A, and compare the two.

If you don't have a clamp meter than you'd need to insert a standard DVM into the green/ground wire on the 10A scale. There should be no current on this wire. Remember you are dealing with AC so if you are skittish with this leave it to a competent technician...

Electric Shock Drowning is real and most often caused by improper wiring, home made plugs, adapters, lack of safety ground etc. etc...

ESD is far more common in fresh water than in salt but there is still a potential for it to occur in salt. At last check there were over 40 documented cases of ESD in the US. Because an autopsy won't show anything other than drowning these documented cases need to have someone witness the paralysis in order to be considered a documentable ESD death. It is likely the issue is a lot more common but attributed to drowning not ESD.

In fresh water 12 - 20 THOUSANDTHS of an an amp or 12-20 mA of leakage is enough to cause paralysis leading to an ESD. For this to happen there is either an undetected AC leakage fault with faulty grounding energizing the boats external metals or the docks metals. The problem can also be with the marina itself and they are technically required (in the US) under NFPA & NEC standards to conduct and keep on file annual inspections of the marinas wiring.

If your boat does not have an ELCI (basically a whole boat GFCI) or RCD main breaker then one should be considered.

Very often the issue is with bad or corroded connections in the dock pedestal, shore cord, shore cord inlet or at the AC panel on your boat. If this is the case the issue will get worse as you increase current demand on-board the boat. If it is a single source leak on an appliance the leak current won't change much as you increase loads.

These are two suitable clamps for measuring corrosion level/low amperage leaks on boats. Meter in this class are NOT inexpensive...

Extech:
380942 - 30A True RMS AC/DC Mini Clamp Meter


Amprobe (A Fluke Company)

LH41A AC/DC Low Current On Clamp Ammeter | Amprobe

Either way the OP's situation is serious enough that it should be reported to marina management so they can enure they have a safe marina for everyone. The offending boat should be UNPLUGGED IMMEDIATELY!

I would urge everyone to look up Kevin Ritz and Electric Shock Drowning. He has done tons of work on this having had his own son killed by ESD.

There is a good webinar out there done by Kevin and the ABYC that is worth looking up. Perhaps on YouTube? I did it live about 6-8 months ago, IIRC, and have attended other seminars by Kevin & the ABYC on ESD.

Getting shocked touching a prop is 150% unacceptable!!!
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Old 08-01-2013, 06:05   #19
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Re: amp leak



Short video from Extech, who ought to know how to use thir own meters. And not to clamp it over a 3-wired AC cord because the hot and neutral should cancel each other out--leaving a reading of zero on a live cord.

That this cord does NOT test as zero indicates there's an imbalance.
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Old 08-01-2013, 06:20   #20
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Re: amp leak

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Originally Posted by hellosailor View Post

Short video from Extech, who ought to know how to use thir own meters. And not to clamp it over a 3-wired AC cord because the hot and neutral should cancel each other out--leaving a reading of zero on a live cord.

That this cord does NOT test as zero indicates there's an imbalance.
Yes in your house that is what you'll see with a properly operating power cord. That is also what you SHOULD see on a marine shore power cord but often don't due to the environment..

In the marine environment where corrosion and high resistance are an everyday occurrence you CAN get a reading by clamping the entire cord IF there is an imbalance on white/black and current is flowing back to Earth via other paths...

This is a very, very standard test...

While this Fluke, all I had with me at the time this measurement was taken, is only fairly accurate into the tenths, it shows exactly what you don't want to see...
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Old 08-01-2013, 07:50   #21
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Re: amp leak

Maine Sail is exactly correct. Posts #18 & 20 are a primer on AC leakage and should be considered as a "sticky" for future reference. The OP has discovered a dangerous condition that must be corrected immediately. This is a life safety issue.
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Old 08-01-2013, 08:16   #22
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Re: amp leak

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Originally Posted by transmitterdan View Post
Measuring the total cord is a valid test and if all is well it will read zero.
Very helpful - and thanks to Main Sail as well.

My brand new not used yet MS2108 has a a constant 0.1Amp measurement when not around the cable - which stays the same when put on a mains cable. This is not a Fluke, but it's also not the cheapest clamp meter on the market. This has an auto DC zero but not an AC zero. Do these have an internal AC zero if not the I suppose you just have to be aware of the imbalance before you start to measure.
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Old 08-01-2013, 09:06   #23
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Re: amp leak

Just a stray thought...but if there was a GFI or other safety device in that power line, wouldn't it have tripped out and shut him down long ago?

Something to pick up and install while the issue is at hand.
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Old 08-01-2013, 09:53   #24
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Re: amp leak

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Originally Posted by hellosailor View Post
Just a stray thought...but if there was a GFI or other safety device in that power line, wouldn't it have tripped out and shut him down long ago?

Something to pick up and install while the issue is at hand.
How about there is nothing wrong with his boat such that the hot and neutral are balanced so a GFI would not trip. Then all the imbalance current measured on the shore power cable would be through the ground wire caused by external problems. Measuring all three wires individually will help troubleshoot.

Reworded repeat of St. Elsewhere's posts.
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Old 08-01-2013, 10:19   #25
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Re: amp leak

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Originally Posted by Don Lucas View Post
Is this really possible? This would mean that the current would have to go though the body of a diver then into the water to ground? I would think the current would always just go though the water to the ground and that the body of a diver would be higher resistance.

And just think of how high the potential would have to be to shock the diver.

Someone talk me out of it as my BS meter is going off.
No, it is quite possible, due to the internal capacitance of the human body. It is 60hz AC that is causing the shock. DC would not give you much of a shock, if any, while in the water. 60 times a second, the AC is charging, discharging, and then charging again with reversed polarity, the human capacitor, and so there is current in the extremities, particularly the extremity touching live metal. Very little current actually passes through the body core, though.

Would you touch one side of a 220 circuit? You aren't making a circuit if you are not connected to the other leg of the circuit, right? Logically you might think it is okay to do so. Hopefully your illogical fear of electricity would make you stop listening to the logic and make you scared to touch it. That is because your own internal capacitance does indeed make a sort of a circuit for AC. Touch one side of a DC circuit? Sure. Probably won't feel a thing if you are well isolated from ground or the other side of the circuit. Touch a terminal of one of your batteries, for instance. You know your battery is quite capable of sending dozens of amps through something, and you can die from a tenth of an amp passed through your body core. But nothing happens with DC unless you have a connection to the other side of the circuit! AC doesn't need that, to give you a jolt. Such a contact is more likely to scare the crap out of you than actually harm you, but the potential is there.
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Old 08-01-2013, 14:15   #26
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Re: amp leak

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Originally Posted by sailinglegend View Post
Very helpful - and thanks to Main Sail as well.

My brand new not used yet MS2108 has a a constant 0.1Amp measurement when not around the cable - which stays the same when put on a mains cable. This is not a Fluke, but it's also not the cheapest clamp meter on the market. This has an auto DC zero but not an AC zero. Do these have an internal AC zero if not the I suppose you just have to be aware of the imbalance before you start to measure.
The MS2108 is a decent "cheap" clamp meter but not for low current use..... I own one too and it is great for testing alt current and loads higher than a few amps but it really gets sketchy below 1A... The fact that it "hunts" to the tenths, and won't zero, I find is kind of typical of less expensive clamp meters...

Also keep in mind that the claimed "in-rush" feature does not work on DC. The don't make this clear but do list as an AC/DC clamp meter with in-rush function.. It's not an inexpensive meter unless you compare claimed features then it becomes a pretty inexpensive meter...

Heck my little 30 AC/DC Extech was $380.00 but only because it is in a class ofvery few meters that can do mA level clamping with accuracy. Chasing corrosion issues this little meter has paid for itself over and over, even at $380.00 USD...

Certainly not for the average boat owner but a useful tool I would not be without....
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Old 08-01-2013, 14:47   #27
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Re: amp leak

Probably what is happening here is the boat owner was having problems with electrolysis so the green ground wire was cut to remove other boats with more noble metals from eating his boat up. The problem then is that if an electronic or electrical device suffers a short in its electrical parts, the boat becomes hot from AC power short. The offending device needs to be isolated by methodically pulling circuit breakers, and/or unplugging electrical devices, then re-establishing a proper ground circuit for the boat. My preference; however, would be an isolation transformer. This takes care of the electrolysis problem for sure, and isolates the electrical devices from the shore AC ground so no current can flow through water from the metal parts of the boat
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Old 08-01-2013, 22:22   #28
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Re: Amp Leak

Let's define leakage current. Understanding what it is will help avoid following other processes such as measuring the loads with an amp clamp meter.

For boats connected to shore power, leakage current is a condition where the current entering the boat (via the black wire) is greater than the current leaving the boat (via the white neutral wire), because a portion of the supplied current has found an alternate route back to the grounded neutral at power source. This is usually due to a fault due to insulation wear, or a wiring error.

The most efficient way to learn if your boat has leakage is to clamp the black power wire and the white neutral simultaneously. If there is no leakage the reading will be very close to zero. The reason that it may not be exactly zero is that some electronics may run a milliamp level of current to the green ground wire, and that very small amounts of current may pass through insulation. If you see 5 miilliamps (mA's) you do not have a problem. The OP appears to have a 1500 mA problem which is clearly in the lethal range. Such a large leak can be detected with the conventional amp clamp meter that he is using.

If it is not found by simultaneously clamping the black and white wires, it is likely from an adjacent boat, and the 1.5 amps would appear on the green ground wire.

The cause of the leak can be isolated by disconnecting things, one at a time, and observing when the leakage current disappears.

Some have suggested installing a GFI on the whole shore-power system. They are effective for a few outlets, but would be problematic for the whole boat. The typical GFI trips at about 2 mA. The whole shore-power system is likely to have more than that amount of transient leakage fairly often which would cause a lot of trips. Devices are available for a whole shore-power circuit, but they trip at about 30 mA's. The problem is that level is in the lethal range.

I hope that boeing1 will tell us what he finds.
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Old 09-01-2013, 10:28   #29
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Re: Amp Leak

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Originally Posted by St. Elsewhere View Post
Devices are available for a whole shore-power circuit, but they trip at about 30 mA's. The problem is that level is in the lethal range.

I hope that boeing1 will tell us what he finds.
For personal protection the trip time must be not greater than 40mS.
Electric shock - Wikipedia, the free encyclopedia
AC Grounding
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Old 09-01-2013, 14:13   #30
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Re: Amp Leak

The following links explain the importance of a green wire ground to prevent electrocution. The first link is by Don Casey, the second link by West Marine

BoatUS – BoatTech – Safe Shorepower by Don Casey


The West Advisor: Marine Grounding Systems
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