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Old 02-12-2010, 23:55   #1
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How to Measure Stray Current in the Water

I have read horror stories about the effects of stray AC current in fresh water. They have made me curious to know how prevalant this issue is in my marina.

How can I measure this? Do I set my multitester to AC amps and simply lower the leads into the water?
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Old 03-12-2010, 04:41   #2
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It's a little more complicated than that. Here is an article to get you started:

ABYC Article by Stanley G. Konz
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Old 03-12-2010, 05:58   #3
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For more information on corrosion testing, check out:

Corrosion Testing (Fluke) ➥
http://assets.fluke.com/appnotes/ele...r/B0269b_u.pdf

And ➥ Electrical Study Hall:

And ➥ The Galvanic Series and Corrosion

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Old 03-12-2010, 06:44   #4
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Originally Posted by GordMay View Post
For more information on corrosion testing, check out:

Corrosion Testing (Fluke) ➥
http://assets.fluke.com/appnotes/ele...r/B0269b_u.pdf

And ➥ Electrical Study Hall:

And ➥ The Galvanic Series and Corrosion
Is this problem worse in fresh water as opposed to salt water? All our dockside outlets have GFCIs and was wondering what level of protection these offer.
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Old 03-12-2010, 07:37   #5
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Is this problem worse in fresh water as opposed to salt water? All our dockside outlets have GFCIs and was wondering what level of protection these offer.
Fresh water is a higher risk than salt, but salt water doesn't cure the problem.

GFCIs offer almost no protection from stray current, because corrosion begins at a much lower currents levels than required to trip a GFCI.

ABYC has been working very hard on the issue of stray AC currents in marinas and they have collected much data. It is not a simple subject, nor are there simple solutions. Once again, I point to this article that appeared in the ABYC newsletter:
ABYC Article by Stanley G. Konz
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Old 03-12-2010, 08:33   #6
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The Case of the Hot Marina ~ by Jim Shafer

The Case of the Hot Marina
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Old 03-12-2010, 09:28   #7
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Thanks for the article, Doug. It describes interesting test cases. In terms of current leakage, sounds like they inferred it by measuring ground faults using a clamp on meter. I am looking for something a little different--measuring the current in the water at a specific location in the water and for that I need to know how to place each test lead (and type of leads to use).

"Protection" can apply to either the boat, as in protection from corosion, or to people, as in protection from shock. GFCIs offer great people protection. A properly functioning ELCI as the boatside AC main breaker goes a long way towards eliminating AC current leakage from boat to water and thereby protecting people in the water from electrocution or electrically induced drowning.
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Old 03-12-2010, 10:01   #8
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That's interesting stuff. But, all the initials such as GFCIs and ELCIs are leaving me a little blank. Are these the abbreviations for earth trip residual currant devices?

One presumes also that if the boat isn't properly grounded, then we will also have problems with electrolitic reaction on skin fittings and propellers and the like. Am I correct in that thinking?
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Old 03-12-2010, 10:09   #9
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There's a whole ocean of alphabet soup surrounding ELCIs, GFCIs, and related devices. Here's an excellent intro, complete with diagrams:
AC Ground Faults, the Boater, and ABYC—Understanding Equipment Leakage Circuit Interrupters (ELCIs) and Ground Fault Circuit Interrupters (GFCIs) to make your boat safer. - Resources - Blue Sea Systems
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Old 03-12-2010, 10:09   #10
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GFCI: Ground Fault Circuit Interrupter (trips @ 5 mA)

ELCI: Equipment Leakage Current Interrupter (trips @ 30 mA)

More ➥ http://bluesea.com/files/resources/t...und_Faults.pdf


An undetected AC ground fault which produces a water path current in salt water may not create enough current density to affect a swimmer, even with a defective grounding conductor.
Because of the much higher resistance of fresh water (about 70 times more than salt water), the swimmer becomes the fault path conductor when the boat or dock ground is missing. A voltage rise will occur on the underwater gear of the affected boat and cause a paralyzing low level current to flow in the swimmer.

See: “The Case of the Hot Marina” ~ by Jim Shafer
The Case of the Hot Marina

And: “The Critical Ground System” ~ by James D. Shafer
http://www.halifaxharbor.net/Marina%...g%206%2004.pdf
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Old 03-12-2010, 10:29   #11
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That's interesting stuff. But, all the initials such as GFCIs and ELCIs are leaving me a little blank. Are these the abbreviations for earth trip residual currant devices?

One presumes also that if the boat isn't properly grounded, then we will also have problems with electrolitic reaction on skin fittings and propellers and the like. Am I correct in that thinking?
AC current doesn't cause electrolytic corrosion.
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Old 03-12-2010, 11:07   #12
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Perchance, that is correct. However, AC wiring, specifically the ground wire, provides the electrical connection that creates a galvanic cell. This is the reason a galvanic isolator or an isolation transformer should be part of the system.
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