5/6/2020: Updated to add approximate mineral/salt content of different waters.
Electrical Characteristics of Water:
Chemically “pure” water (“distilled water,” or laboratory-quality “deionized” water) does not conduct electricity. In real life, the water with which people have routine daily contact (think drinking water, ground water, river and lake waters, estuary waters and sea water) contains varying concentration of dissolved and suspended minerals. Dissolved minerals make water electrically conductive. Like all electrical conductors, water with mineral content possesses the electrical properties of resistance and it’s reciprocal, conductance.
Fresh water has a relatively high electrical resistance. Salt water has a relatively low electrical resistance.
The open ocean is about 3.5% salt; i.e., for every 1000 pounds of sea water, 35 pounds are dissolved salt, or 35 parts-per-thousand. “Brackish” water is a mixture of salt and fresh water in which the mineral content varies from place to place, based on the relative amounts of salt and fresh water present. Brackish conditions exist naturally in marine estuaries, where fresh water rivers flow into, and mix with, the salt water of tidal inlets. Many US intracoastal waters are brackish. Mineral concentrations vary with a number of factors, including distance from tidal inlets and the outbound flow rates of fresh water rivers feeding tidal estuaries.
The salt concentration of estuarine waters is less than that of ocean water, but more than that of fresh water. In estuarine systems, the farther upstream one measures salt content, the less salt is found. Therefore, the electrical resistance of brackish water ranges from high-to-low, where the highest resistance occurs upstream, inland, where it approaches that of fresh water. The lowest resistance occurs nearest the ocean, where it approaches that of tidal sea water. The Great Lakes and Inland River systems of the interior US are largely fresh water systems with less variability in electrical conductivity.
Here are some “typical approximations:”
- Potable Water – water fit for human consumption (generally less than 500 ppm).
- Fresh Water – water with total dissolved solids (salts & other minerals) generally less than 1,000 ppm.
- Brackish Water – water containing more than 1,000 ppm but less than seawater.
- Slightly Brackish Water – water that contains between 1,000 to 3,000 ppm salts and other dissolved minerals.
- Moderately Brackish Water – water that contains between 3,000 to 10,000 ppm salts and other dissolved minerals.
- Highly Brackish Water – water that contains more than 10,000 ppm salts and other dissolved minerals, but less than sea water (35,000 ppm).
- Sea Water – ocean water with TDS about 35,000 ppm.
- Brine – high salt waste water (generally more than 50,000 ppm).
Electrical Characteristics of the Human Body:
Human blood and body fluids contain about 0.9% sodium chloride, or about 9 parts-per-thousand. Therefore, the electrical resistance of the human body is numerically found between the electrical resistance of salt water and the electrical resistance fresh water. That means the human body is not as good a conductor of electricity as salt water, but it is a much better conductor of electricity than fresh water.
The electrical resistance of the human body depends on the manner of exposure and the magnitude of the voltage. Dry skin with low voltage has a relatively high resistance. Wet skin with low voltage has medium resistance. High voltages overcome skin resistance easily. A body fully immersed in water has a large surface contact area and relatively low resistance. If the water itself is highly conductive due to dissolved mental content, that skin resistance can be negligible.
Electric Shock Drowning:
Electric Shock drownings happen to people, pets and wildlife that find themselves immersed in an electric field that has been established in the water. This condition is almost always unintentional and accidental. There are electric “fish barriers” in some places, like the Illinois River at Chicago, the principal reason for which is to restrict/contain the free movement of invasive species of fish. These barriers intentionally introduce electric currents into the water, and they definitely could be dangerous to people. But usually, AC electricity leaking into the water is an unintended situation caused by a wide variety of faults in either shore-side or on-board electrical systems.
Electric “shock” occurs when an electric current flows through the body. Very low electric currents can cause muscle spasm and/or muscle paralysis. Muscles will contract at as little as 15 milliamps (mA) of current. Slightly higher currents – called “can’t release” or “can’t let go” threshold – result in muscle contractures that can render voluntary muscle control impossible. Once paralysis occurs, drowning can result. If the electric current becomes high enough, death from actual electrocution results. The current required to cause cardiac failure is amazingly low; only 60 – 80 mA. Because in general, electricity will tend to follow the path of lowest electrical resistance, the potential for tragedy is greatly increased in fresh water environments. The risk to a person immersed in an electric field in fresh water is high because the electric current will find its “path of least resistance” by flowing through the body and its vital organs rather than through the water surrounding the body. The risk of serious electric shock is relatively less in brackish water than fresh water, and relatively less again in salt water, because the electrical “path of least resistance” is through the surrounding water rather than through the body. However, the risk of shock – and drowning – is never zero!
Boats as a Source of Electric Shocks:
Boats attached to shore power are a major source of unintentional leakage of electrical energy into the water. The details of this topic are enormously wide-ranging and complex, involving current dispersal patterns, voltages gradients in the water, tidal ebb and flood movement, dissolved mineral ion concentrations, water temperatures and a plethora of other factors, but all of the theoretical factors taken together are mainly of interest only to researchers. For boat owners and marina operators, items of actual, practical interest boil down to eliminating the conditions that cause electricity to enter the water in the first place. The assumption has to be that there is no “safe” level of electrical leakage into the water.
Fortunately there are just three conditions that boaters and marina operators really need to understand. All three are necessary, and all three must all be present concurrently – at the same time – in order for electricity to leak/flow from a boat into the water:
- the power’s origin point – the “derived source” – of AC electricity on the boat must be on-shore; i.e., shore power, fed from the shore-based electrical infrastructure (as opposed to an on-board generator, inverter, solar system or isolation transformer; and
- a ground fault condition on the boat must result in an unintended voltage being placed on the safety ground aboard the boat; and,
- the electrical integrity of the shore power AC safety ground must itself be compromised by any condition (internal high resistance due to corroded, loose or broken connection(s), worn/frayed insulation, wiring error or omission, electrical failure within a protected device) which impairs the ground’s ability to, or altogether prevents it from, carrying a fault current safely back to the shore-side earth ground.
If all three of the above conditions exist concurrently, fault current from the boat will return to the shore power infrastructure via the ground bonding system of the boat, to and through the major zincs and underwater metal components connected to the boat’s bonding system, into the water and back to shore through the water to get back to the shore power infrastructure’s earth ground.
Anyone who dives on a boat – professionally or personally – must be aware of the possibility of this set of circumstances, not only on their own boat, but on boats in neighboring slips as well. Marinas, yacht clubs and condominium docks must have policies forbidding swimming in their boat basins. Homeowners with “backyard” residential boat docks must be aware of this phenomena. Homeowners with waterfront properties are at-risk even if they, themselves, do not have boats or boat docks. Electrical fault conditions on neighboring properties are equally a threat to the safety of swimmers. Not going into the water is the major preventive measure in electric shock drowning!
In the United States, the National Fire Protection Association (NFPA) develops, publishes and maintains the National Electric Code (NFPA 70). The Canadian Standards Association (CSA) maintains the Canadian Electric Code (CEC). The two country’s codes are not always identical, but they are generally compatible.
Land-based Electric Codes:
In the US, the National Electric Code (NEC) is revised every three years. The 2011 revision of the NEC contained major changes in articles pertaining to marinas, condo docks and boatyards. Individual state legislatures adopt the NEC in order to give it the force-of-law within the state’s jurisdiction. As of 4Q2012, only 21 states had adopted the 2011 NEC. Thus, there are state-by-state variations in compliance standards. Individuals must always check with local code authorities for local requirements. This is particularly true for persons holding properties in multiple states. Articles of the NEC code that might be of specific interest to boaters include:
- Article 553 – Floating Buildings, and
- Article 555 – Marinas and Boatyards.
The scope statement for Article 555 covers: “fixed or floating piers, wharves, docks and other areas in marinas, boatyards, boat basins, boathouses, yacht clubs, boat condominiums, docking facilities associated with residential condominiums, and any multiple docking facility, or similar occupancies, and facilities that are used, or intended for use, for the purpose of repair, berthing, launching, storage, or fueling of small craft and the moorage of floating buildings.”
Sections of the NEC-parent NFPA70 Fire Code that might be of interest to boaters include NFPA Section 303, Chapter 5 – Fire Protection Standard for Marinas and Boatyards.
Code enforcement for marinas and boat yards is often handled by municipal code enforcement personnel who are employed by local or state governments. In some jurisdictions, code enforcement is handled by private, independent contractors, certified by the Board of Fire Underwriters, and working on behalf of insurance underwrites who provide fire, casualty and liability insurance to the marina facility owner/operator.
These national standard shore-side marina electrical codes will directly affect boaters more-and-more as time goes on.
Boat-based Electric Codes:
Boats with on-board, non-compliant wiring problems will be “caught” and “identified” with ever increasing during visits to marinas that have been updated to the newer land-based codes which require ground fault sensors on shore power pedestal outlets. For a boat with non-compliances, this will result, at a minimum, in the inconvenience of not having shore power for the duration of their stay at that marina. Depending on the attitude of the particular marina where this happens, boats could be asked to depart. Boats with a properly installed and working Equipment Leakage Circuit Interrupter (ELCI) device installed, and the ELCI device does not experience problems aboard, the shore power infrastructure will also be happy. My more detailed post on ELCI devices is located on this site, here: https://gilwellbear.wordpress.com/category/boat-technical-topics/electrical-topics/boat-ac-topics/elci-primer/. (More on ELCIs below.)
The American Boat and Yacht Council (ABYC) adopts an updated E-11 Electrical Standard on a three-year cycle: July, 2012, July, 2015. This standard is fully compatible with it’s NEC and NFPA land-based counterparts, but applies specifically to AC and DC electrical installations aboard boats. It applies to all pleasure craft operating in the United States. Enforcement of ABYC E-11 is not handled through municipal code enforcement authorities. Compliance to the ABYC standards is voluntary. It is inconsistently “enforced” through yacht surveyors (AMS, SAMS) depending on that individual’s knowledge of electrical systems, and the influence that survey reports carry with insurance underwriters who write casualty and liability insurance on pleasure craft. This is approximately analogous to residential inspections performed by independent “home inspectors.”
The 2012 and 2015 versions of the ABYC E-11 electrical standard include a requirement for boat manufactures to install a device called an Equipment Leakage Circuit Interrupter (ELCI) on all new boats built after December 31, 2012. This device is technologically very similar to GFCI devices installed in residential AC systems and on boats. GFCI devices are very sensitive, and are intended to protect people directly. ELCI devices are less sensitive, and protect people indirectly by monitoring and automatically disconnecting faulty equipment. The theory here is very simple! All of the AC electric current flowing onto the boat in the hot supply wires of the shore power cable (“black” for 120VAC shore power, or “black” and “red” for 240VAC shore power) should flow back off the boat, returning into the shore power source via the same shore power connection from which it arrived. The returning current flow can be in the neutral (“white”) wire and/or any of the “current carrying conductors” feeding a 208V/240V circuit. The return current will be in the neutral (“white”) current-carrying conductor for 120V circuits.
The ELCI senses the hot and neutral lines using a device called a Current Transformer. It detects any difference in current flowing onto and back off the boat within those “current carrying conductors.” Any difference in flow, however large or small, represents current flowing somewhere else, perhaps into the water. ELCI devices are designed to be less sensitive than the GFCI devices to minimize “nuisance trip” or “false trip” problems leading to customer dissatisfaction. The 2012/2015 disconnect threshold for ELCI devices is an AC current imbalance of 30 milliamps (mA) or more that lasts for a duration of at least 100 milliseconds (mS). If the trip threshold is reached, the ELCI device will shut off all shore power feeding the boat. Such a condition is, after all, a potentially lethal safety issue, so correction of the fault condition(s) causing the device to trip will be necessary in order to get power restored on the vessel.
A two-part series of webinars on Electric Shock Drownings was sponsored by the ABYC in the Summer of 2012. Part 1 deals with the phenomena, itself, and the related boat-side issues. Part 2 deals with the shore-side infrastructure. Part 1 is easier to understand. Part 2 is technical and oriented to code compliance for marina owner/operators. The two videos were bootlegged, and are available on http://www.youtube.com. They are best watched in order.
Part 1 is located here: http://www.youtube.com/watch?v=O7-s_mdEPb0&feature=youtu.be;
Part 2 is located here: http://www.youtube.com/watch?feature=player_detailpage&v=nlBIbgBtCoE.
Note that the second video was recorded live from a computer session. There are two places where the audio is interrupted by phone calls received by the person doing the recording. The charts remain visible, and the interruptions are distracting, but do not seriously diminish understanding.