Shorepower connections/leakage, starting with some simple tests

[The Brockerts]

Starting with a few simple tests.
Shorepower breaker on, boat breaker on, in other words a Normal running boat.
Is this a valid way to test for stray currents and should this be zero?

Second test.
Shorepower on, connected to nothing
Should this be zero?

 

[ksanders]

My opinion is no. You need a different test setup.

leakage is in miliamps, and current clamps like the one you are using are not good at detecting small amounts of current.

If... if you had a industrial high resolution current clamp, then theoretically you could sense the hot and the neutral on a 120 volt system, and any difference would be leakage, but again the equipment in your photo is not capable of that kind of accuracy.

The easiest test you can do to check for leakage current would be to let the GFCI or ELCI trip, and then remove things until it stops tripping.

 

[The Brockerts]

I'm not tripping GFCI or ELCI, just getting ready to travel and see where I stood.

 

[ksanders]

I'm not tripping GFCI or ELCI, just getting ready to travel and see where I stood.

If you are not tripping, you are good to go...

 

[Iggy]

There was this video, sad to say the mans son died. The Father said his son did not drown! He was a good swimmer.

He came up with this, to prove that he's son did not drown. Take a wooden pole and attach a 6'x'6' copper plate to it. Than attach a wire to the plate and the other end to a amp meter in the Milli Amp range. You need a very good meter for this. Now ground the other test lead to the power station.

Take the pole and test the waters around the boat. If you get any reading other than zero, than there is some leakage.

Disclaimer: If your not knowledge/uneasy in doing this, than don't!

 

[READY]

Yes not advisable to swim in a marina although it is done all the time. Not just concern about electrical...

 

[Comodave]

I'm not tripping GFCI or ELCI, just getting ready to travel and see where I stood.

Does the dock where you are is there GFI breakers on the dock pedestal? If there is and you are not tripping WITH everything on the boat turned on then you should be good.

 

[Bmarler]

Like Kevin said, you may need a meter with better resolution. You need three decimal places on the scale when you have the selector on ac amps, or better yet, ac milliamps.
Clamped around all three conductors on a 120 volt cord in service, should read zero amps.
If you read anything, then clamp around the hot and neutral together, Then the ground by itself.
This will help you narrow down where the problem lies.

 

[twistedtree]

For starters, your meter should be on Amps, not Volts. In principle what you are doing is the correct way to test, and the current reading should be zero. But Kevin's got a good point about the accuracy of the meter, so I would take the reading values with a grain of salt. That said, if there is any current showing, then you likely have an issue.

 

[ksanders]

Unfortunately or fortunately I am long retired, but... at one point I worked in protective relaying at the local power company. What we used there to measure the 5A secondary of current transformers was a clamp on current transformer, with a 1000:1 ratio, so 1A would be 1 miliamp of current going through the current measuring input on our fluke meters.

This was as accurate as it got. If we needed to get more accurate we brought out the big relay test set, but that was ruggedized lab grade equipment.

 

[Fleming]

Like Twisted Tree said, you need to be on Amps not volts. I have a clamp that's more sensitive that I regularly use, and boats are almost never zero, but shouldn't be more than a couple of milliamps or you have some kind of problem. You also want every piece of AC equipment running, ideally. Equipment that's not running is not being checked when you clamp on the cord.

 

[tiltrider1]

In my experience if your meter actually reads 0 on a leakage test then it is not accurate enough. My leakage tester always shows some leakage on every circuit I test. It is usually in the 1.5 to 2.3 milliamp range. If I get a reading of 6 milliamps or more I can usually track that down to something.

 

[CharlieJ]

I troubleshoot one leaking AC on a shore power supplied boat about three times a month. A lot of the comments upthread where surprisingly accurate or near so but I want to provide some clarity.

1. Residual current devices (RCD’s) are required in shore power pedestals, whether in a commercial marina or behind a condo or private house by the NEC.
2. RCD’s have the same specifications as the Equipment Leakage Current Interrupters (ELCI’s) that have been required by ABYC E-11 for about 6 years. The RCD/ELCI must trip when challenged with 30mAAC mismatch between L and N in < 30mSec.
3. @Iggy #5: The man in the video is Kevin Ritz, a close friend of mine, who lost is son Lucas to “death by drowning” according to the coroner. As Lucas’ death was witnessed by Kevin’s wife (an RN), and he was wearing a PFD and in an inner tube, Kevin would not accept that cause of death. Through his efforts the entire concept of electric shock drowning (ESD) was developed.
4. @READY #6: Per the NEC, all marinas are to have signage warning against swimming in a marina.
5. ESD takes far less current in fresh water than in saltwater.
6. Using a high resolution (.001 mAAC) and clamping the entire shore cord doesn’t really provide useful information.
7. Clamping the entire shore cord, or just the safety ground conductor, with the main panel breaker open will always (+/-) show some leakage. This is created because the safety ground conductor on the dock is not a zero potential for a variety of reasons. This junk potential finds its way to the water via the AC/DC connection and to the underwater metal bits.
8. To determine AC leakage, a breakout adapter that provides access to the individual conductors is a must. Although the meter is not measuring amps and lacks sufficient resolution, @The Brockerts #1 second photo shows this breakout adapter.
9. @Fleming #11: This is not correct. Remember the safety ground wire is not broken by opening a breaker and for branch circuits protected by a SPCB, N is not broken. A N>G bond other than at a source of power will cause leakage.
10. I rarely find a boat with zero leakage.
11. Don’t rely on #5 above to keep you safe if you do have leakage. In estuarial bodies of water fresh water floats on top of salt water and depending on the amount of rain/FW feeding the estuary, there could be a lens of fresh water a couple of feet deep.

We just finished an AC leakage job last week. When we started the boat was leaking 90mAC. After correcting miswiring a GFCI and rewiring a very badly wired inverter/charger, the leakage is now 3mAAC.

 

[CharlieJ]

Here is the link to an excellent article on this topic written by Jim Healy, currently a CLOD, but formerly cruising full time on a Monk 36: Electric Shock Drowning – Cruising Aboard Monk36 Trawler Sanctuary

 

[SteveK]

@CharlieJ The explanations here are for your shore power cord.
Is there a simple layman test for leakage into the water from other sources nearby?
Divers go and clean bottoms in marinas all the time, does the neoprene protect them?

 

[CharlieJ]

During an ABYC managed/USCG funded survey of marinas in FW and in SW, it was determined that a voltage gradient of 2VAC/foot would create a current flow that was considered lethal.

To make a test rig, use a piece of Starboard with copper bars attached one or two feet between them and attach the rig to a broom handle. Solder wire to each copper bar and lead the wire to the end of the handle. Use a good quality DMM set on mVAC with leads clipped to the ends of the wires.

Submerge the copper bars and read the mVAC potential. Rotate the rig 90 degrees and re-measure. Probe around docks, finger piers and boats. There will be low level background voltage present. Real leakage will be very obvious.

 

[CharlieO.]

During an ABYC managed/USCG funded survey of marinas in FW and in SW, it was determined that a voltage gradient of 2VAC/foot would create a current flow that was considered lethal.

To make a test rig, use a piece of Starboard with copper bars attached one or two feet between them and attach the rig to a broom handle. Solder wire to each copper bar and lead the wire to the end of the handle. Use a good quality DMM set on mVAC with leads clipped to the ends of the wires.

Submerge the copper bars and read the mVAC potential. Rotate the rig 90 degrees and re-measure. Probe around docks, finger piers and boats. There will be low level background voltage present. Real leakage will be very obvious.

Thanks Charlie, I think I would like to build one. I will have to see if my current multimeter has the proper settings. Any other tips for building a rig?

So, if I put my copper bars 1 foot apart 2 volts AC would be considered lethal and 2 feet apart 4 volts would be lethal?
What would be considered safe?
We are in freshwater and many people swim in our marina and it makes me nervous.

 

[CharlieJ]

@CharlieO. #17: Make the “broom handle” long enough to reach the water. Goes without saying but I have used this in some marinas that have very high fixed docks and I had to lay down on the dock to reach the water!!

 

[Fleming]

1. @Fleming #11: This is not correct. Remember the safety ground wire is not broken by opening a breaker and for branch circuits protected by a SPCB, N is not broken. A N>G bond other than at a source of power will cause leakage.

I still stand by my comment. A neutral to ground connection is not the only source of current leakage on the grounding conductor. Imagine a hot water heater with a low resistance to ground between the ungrounded (hot) conductor and the metal casing (grounded with the grounding conductor). It may not be enough current to trip the breaker but it will pass current through the grounding conductor and show up as leakage, but only if the water heater breaker is closed and powering the water heater. Same with a motor that has low resistance to ground.

 

[Fleming]

1. Clamping the entire shore cord, or just the safety ground conductor, with the main panel breaker open will always (+/-) show some leakage. This is created because the safety ground conductor on the dock is not a zero potential for a variety of reasons. This junk potential finds its way to the water via the AC/DC connection and to the underwater metal bits.
2. To determine AC leakage, a breakout adapter that provides access to the individual conductors is a must. Although the meter is not measuring amps and lacks sufficient resolution, @The Brockerts #1 second photo shows this breakout adapter.

Clamping the entire shore power cord with an accurate AC clamp on meter is not without merit. Sure, using the breakout adapter is better and more accurate, but by clamping on the whole shore power cord you are still accurately measuring the leakage current into the water. In salt water environments it's a faster, one less tool, easier test that tells you exactly what is going into the water from the boat and can quickly and easily tell a person if there's a problem.
Technical Bulletin: Understanding AC Leakage Current | Marina Dock Age

 

[CharlieJ]

@Fleming #11

Equipment that's not running is not being checked when you clamp on the cord.

I was taking “equipment” in this statement literally. I have found that the salt tracks left behind when the shore cord boat end is submerged in salt water will cause enough leakage current to trip the pedestal RCD.

Your water heater example is on the list of usual suspects. Most non-liveaboard owners turn the water heater on when the board and turn it off when they leave. Over time, this thermal cycling causes micro cracking of the ceramic insulation on the heating element and the path you described causes leakage.

I think we are in violent agreement.

 

[CharlieJ]

@Fleming #20:

Clamping the entire shore power cord with an accurate AC clamp on meter is not without merit.

We used to teach marina owners to perform this test. The problem is that the shore side of the safety ground system may have enough potential on it and have a poor electrical connection to the transformer ground to cause significant “fault current” even with the pedestal breaker and the vessel’s main shore power breaker opened. I have seen as much as 300mAAC leakage using this test which erroneously condemns the vessel being tested.
I consider this test without merit because of the false positives.

 

[ksanders]

My opinion, the best solution is to isolate your boat completely from the shore power by using isolation transformer(s).

This protects not only your boat from issues you do not know crop up over time. It protects your neighbors, and anybody in the water as well.

 

[twistedtree]

@Fleming #20:

We used to teach marina owners to perform this test. The problem is that the shore side of the safety ground system may have enough potential on it and have a poor electrical connection to the transformer ground to cause significant “fault current” even with the pedestal breaker and the vessel’s main shore power breaker opened. I have seen as much as 300mAAC leakage using this test which erroneously condemns the vessel being tested.
I consider this test without merit because of the false positives.

Charlie, what are you clamping around in a break out box vs "everything" when you clamp around the cord?

 

[CharlieJ]

@twistedtree #24
With a clamp meter as previously described, emulate the pedestal RCD by clamping L & N together in a 30A cord and L1, L2 and N together in a 50A cord. Sensing exactly how an RCD/ELCI senses leakage current.

The device is not a “break out box”, rather it is male and female shore power plugs joined by appropriately sized conductors. I also cut the safety ground wire and install ring terminals. I join the ring terminals with a machine screw and a thumb nut so that I can break the G connection for additional granularity in reading current in the green wire.

 

[CharlieJ]

@ksanders #23
True enough if the vessel has the room and the owner has the boat bucks necessary for the modification.

 

[SteveK]

Does the isolation transformer also cut off the ground wire. And what about the AC ground bonded to the battery negative and bonding system?
Seems to me the AC is grounded into the water if there is a leak inside an appliance.

 

[CharlieJ]

Does the isolation transformer also cut off the ground wire.

Speaking only about a conventional iron core IT, the safety ground is terminated at the electrostatic shield that is placed between the primary and secondary windings. It is not connected to any onboard system.

And what about the AC ground bonded to the battery negative and bonding system?

And what is the question? This is a compliant system in the USA (ABYC E-11) and in Europe (ISO 13297).

Seems to me the AC is grounded into the water if there is a leak inside an appliance.

Correct. And the water path for leakage current will be back to the source which is the secondary of the IT where safety ground and neutral are bonded. The leakage current electrical field will still be present but it will be a much shorter path and very close to the hull of the boat.

 

[twistedtree]

@twistedtree #24
With a clamp meter as previously described, emulate the pedestal RCD by clamping L & N together in a 30A cord and L1, L2 and N together in a 50A cord. Sensing exactly how an RCD/ELCI senses leakage current.

The device is not a “break out box”, rather it is male and female shore power plugs joined by appropriately sized conductors. I also cut the safety ground wire and install ring terminals. I join the ring terminals with a machine screw and a thumb nut so that I can break the G connection for additional granularity in reading current in the green wire.

OK, so leaving out the ground wire. Got it.

 

[SteveK]

Correct. And the water path for leakage current will be back to the source which is the secondary of the IT where safety ground and neutral are bonded. The leakage current electrical field will still be present but it will be a much shorter path and very close to the hull of the boat.

so a leak into the internal AC GRD goes into the bonding system and then comes back into the boat and does not go to the shore. I was wondering if that is still a shock hazard then.