Amp Leak

[chala]

Originally Posted by Maine Sail

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...

In clear: before someone start disconnecting an earth wire, or do some electrical work it should make sure that such actions does not endanger anyone.

[sailinglegend]

Originally Posted by Maine Sail

The MS2108 is a decent "cheap" clamp meter but not for low current use............Also keep in mind that the claimed "in-rush" feature does not work on DC.....

Thanks for that. I have been in touch with the ebay seller who contacted the manufacturer. They say it will measure inrush DC current - just use the AC scale!!!!

After looking at all the other meter options I chose the inrush model as a bonus.
It does appear to work, 79 amps on my starter battery for a small car, but how accurate is it???? Sounds a bit low to me. In a month I will be able to test it on my watermaker DC motor which should have a inrush current of 90 amps, continuous of 22 amps.

[boeing1]

we have moved the boat down the dock to another slip and using the same shore power cord plugged into a different shore power box I get a reading of 0.15 amps,
moved boat back to the origin slip using same shore power cord in the original power box and get 1.5 amps.
would you agree the problem seems to be the shore power.....

[hellosailor]

Boeing, any hardware store will carry a little $5 socket tester, plugs into a standard 3-prong outlet (you'd need an adapter obviously) and has 3 LEDs that light red or green to show faults across all 3 side of a grounded AC connection. If you can use one of them--they also make it fairly simple to show someone else (like management) "You have a dangerous problem here."

Or you can, after all, just use your meter with conventional test leads, stick 'em in the three holes and measure the voltage difference across each pair of them. If anything is showing voltage from neutral to ground, bingo again. But really...no matter how you do it, some measurements on the posts should show whether the problem is shoreside or boatside.

[St. Elsewhere]

Originally Posted by boeing1

we have moved the boat down the dock to another slip and using the same shore power cord plugged into a different shore power box I get a reading of 0.15 amps,
moved boat back to the origin slip using same shore power cord in the original power box and get 1.5 amps.
would you agree the problem seems to be the shore power.....

boeing1,

No. It indicates that the problem is not on your boat, but it is likely caused by a boat near your slip that is leaking current into the water that is going to ground via your boat's grounding system. If you do as previously suggested, and unplug nearby boats one at a time, you will likely find that the current in your slip goes away when the leaker is disconnected. It is far less likely to be the wiring on the dock, but it is worth using a polarity tester as hellosailor suggested. You can simply plug it into an outlet on your boat to test for correct dockside power.

This is a serious problem that should be resolved quickly.

[sailinglegend]

Originally Posted by hellosailor

......Or you can, after all, just use your meter with conventional test leads, stick 'em in the three holes and measure the voltage difference across each pair of them. If anything is showing voltage from neutral to ground, bingo again.....

You can get a voltage between neutral and earth simply because the pontoon cables are not large enough, so when carrying a large current there is a voltage drop along the neutral cable. If the earth is carrying no current then at the boat there will be a voltage between neutral and earth equal to the voltage drop along the neutral cable. This will cause any reverse polarity diode to start to glow slightly.

[Maine Sail]

Originally Posted by sailinglegend

You can get a voltage between neutral and earth simply because the pontoon cables are not large enough, so when carrying a large current there is a voltage drop along the neutral cable. If the earth is carrying no current then at the boat there will be a voltage between neutral and earth equal to the voltage drop along the neutral cable. This will cause any reverse polarity diode to start to glow slightly.

This is very often caused by dirty connections/resistance in shore power cord boat side inlet, cord sockets or dock pedestal & sockets. The poor contact area of this standards coupled with even minimal levels of corrosion causes resistance and can force some current onto the green.

We can't get rid of the "Marinco/Hubbel" NEMA plugs and standard fast enough.... I HOPE that someday the SmartPlug or similar GOOD connection will be the STANDARD and the others will be banned from marine use, as they should be.....

Rant over...

[fstbttms]

Originally Posted by Blue Stocking

I would REALLY like to hear Fastbottoms (sp) on this. Serious.
I refuse to participate in marina work when divers are changing zincs.

As previously mentioned, almost all electric shock drownings occur in freshwater. Not to say that it can't happen saltwater and I do know hull cleaners who have reported being shocked. But I've been working underwater in marinas for over 18 years and I have never had a problem nor have I heard of any hull cleaner being seriously injured or killed here or anywhere else, for that matter.

That being said, I always unplug the boat I'm diving on from the shorepower. Always.

[GrowleyMonster]

Originally Posted by fstbttms

That being said, I always unplug the boat I'm diving on from the shorepower. Always.

A very sensible precaution!

[senormechanico]

From MainSail's post:

"
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."

To put a finer point on it, that amount of current would only light up a LED Christmas string at 120 volts.
A diver exposed to that current would probably have a lot less voltage available to cause the same result.

Don't mess with electricity unless you REALLY understand it.

Steve

[senormechanico]

Originally Posted by GrowleyMonster

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.

Sorry, the body has some capacitance, but at DC or only 60 hz, it's effectively a resistor.

I used to repair TV sets back in the '70's.
A horizontal output transformer operating at 7875 hz with 6kv output could do some serious drilling into your skin, but underwater, you're simply a resistive load.

20 milliamps is enough to do you in. AC or DC.

Steve
Steve

[hellosailor]

fast-
"That being said, I always unplug the boat I'm diving on from the shorepower. Always. "
You might want to add a lockbox, or at least tape over the outlet. I used to think electricians using lockboxes were just paranoid, but found out the hard way that yes indeed, some helpful idiot can re-energize what you KNEW was a perfectly safe dead line.
Very much the opposite of the cleaners who kept unplugging a corporate server because they needed an outlet for their vacuums.
Ah, the wonders of electricity.

[bill cartwright]

I had this same problem before and it was caused by the AC wiring ground being tied down to the boat grounding and you could watch bubbles form on the zinc after a minute or so and bubble up to the surface.
There was a 2 fold problem, First everything was bonded on the boat to the shaft zinc for electrolis as well as the 12Vdc was also laid down and the AC Neutral/Ground was also. This is a absolutely no no.
The second problem was the dock power, the ground wire was broken at the gangplank hinge area and the return was going thru the boat, thru the water to the land, where the 10 foot ground rod was which was a 100 yards away. As the Borg says " Resistance is Futile"
Solution: take a volt meter and check your power at the dock and verify you have a potential (120vac) across the plug between hot and neutral. If the answere is "No" then tell the dock managers office! Also do the same test for the ground and the positive 120vac as well. Now you know which one is hot and the 2 that is either ground or neutral. You can check and see if there is anything across them. Make sure your dock power is correct 1st before taking the boat apart!

Go on the boat and turn all breakers and power off that is AC from the dock. then plug in your power to the load center on the dock, put your clamp on the AC wire hot and there should be zero amps or MA of current. Turn on your Master AC and it should be zero current. Now try each breaker seperately and check each breaker after you turn it on to see if there is any current. There may be more than one that shows currrent as mentioned up the thread where someone laid down the neutral for the ground on the hot water heater or the stove or whatever. This will show you where the problem lies.
To completely get away from Electrolis at docks and AC power, you can purchase a 1 to 1 transformer (about 1500 dollars but cheaper if used) to take care of the problem. You just need to know the watts you need for your boat. Generally a 5K or a 7.5K for smaller boats(20-40 foot) and this solves the problem. The transformer is 100% isolated from the shore power and your power will be clean and no distortions on the electronics like someone using a drill 2 boats down and you hearing it on the radio. They are sortta big though, about 10" thick about 12" across and 16" tall. plus heavy, about 50 pounds of insulated wound copper wire with iron core and steel frame.
Check your bonding, grounding (both AC & DC) DC should not be grounded to the boat and go back to the battery only. The AC should be isolated as much as posiable and not tie into the DC. This can mess up charging rates thru the battery charger and potentially cause a failure. This is getting long so PM me if you need to go farther.
I think it is a ground problem but I can't be there to check it. Good luck with your troubleshooting. Take note: the AC neutral and ground do come together back at the Meter Main and they both go to the grounding rod where ever it is, generally within a few feet of the meter. Have a good one.
bill cartwright

[GrowleyMonster]

The isolation transformer is a great idea, Bill.