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A luxury yacht or commercial vessel is an important asset worthy of the best corrosion and safety grounding protection available. While protective coatings and anodes can help protect your boat, a sure method is required to deal with the galvanic corrosion circuit created by the shore power connection. The DEI Galvanic Isolator provides the safest isolation of any technology on the market
The Galvanic Corrosion Problem:
Whenever a boat is connected to shore power, the hull and drive system is connected to the shore grounding system and to other adjacent vessels (also connected to shore power) via the grounding conductor in the shore power cable. This connection, while required for safety, creates a galvanic corrosion cell involving the dissimilar metals between boats and between a boat and the shore grounding system, as shown in the following diagram.
1) Anode – a metal surface which gives up metal ions (corrodes). 2) Electrolyte – a medium which conducts ionic current between the anode and cathode. 3) Cathode – a metal surface that picks up metal ions. 4) Metallic Bond – a continuous metallic path that allows current to flow from cathode to anode.
The Solution:
A simple method which virtually eliminates this galvanic corrosion problem is to insert an appropriately rated and certified Galvanic Isolator in series with the grounding conductor of the ship-to-shore power cable. The function of the Galvanic Isolator is to provide AC continuity of the grounding conductor (required for safety in the event of an AC fault) and to block the flow of corrosion-causing galvanic current.
Product Selection:
DEI Galvanic Isolators are the most highly rated products available on the market. DEI Isolators are typically applied using an industry standard method of matching the device to the steady-state current rating of the shore power service. DEI Isolators are offered in 30A, 50/60A, 100A and 200A ratings. For dual 30A services, one 50/60A DEI Galvanic Isolator can be used in place of two 30A units.
Review the DEI fault current rating for the selected model, to confirm that this value is adequate for the application. In the event that the anticipated fault current magnitude and duration in the shore power service is higher than that of the selected GI model, choose a higher rated model. This can be accomplished by examination of our product ratings, via our online guide in the product section, or by contacting DEI for assistance.
What model Galvanic Isolator do I need?
DEI Isolators are typically applied using an industry standard method of matching the device to the steady-state current rating of the shore power service. DEI Isolators are offered in 30A, 50/60A, 100A and 200A ratings. For dual 30A services, one 50/60A DEI Galvanic Isolator can be used in place of two 30A units.
What does the term "fail-safe" mean?
To be considered "fail-safe," an independent laboratory must confirm that the isolator will either remain fully functional or remain a permanent, effective grounding path if it fails when subject to the maximum current capability of the grounding conductor for a given galvanic isolator current rating. This provides guaranteed safety grounding, even when the product is failed, thus the "fail-safe" designation.
What is the difference between Fail-Safe Plus and Fail-Safe MAX?
All DEI Galvanic Isolators are categorized as either Fail-Safe Plus® (FSP) or Fail-Safe Max® (FSM). Fail-Safe Plus models not only meet the fail-safe test criteria in the proposed revision to A-28, but also have considerably higher fault current ratings than are required and have substantial lightning current ratings, which are not required by A-28; hence, the "Plus" designation unique to DEI.
Fail-Safe Max models provide even higher AC fault current ratings than Fail-Safe Plus models and will still be functional and meet all other requirements of A-28 after being subject to the fail-safe test criteria, thereby providing the ultimate in performance and safety grounding; hence, the "Max" designation.
Do DEI products meet ABYC A-28 standards for Galvanic Isolators?
In the marine industry, the criteria for galvanic isolators is defined by the American Boat and Yacht Council (ABYC) recommended standard A-28, which has recently been revised. Due to recommendations to the A-28 galvanic isolator standards committee concerning the need to retain safety grounding under all conditions, as required by the U.S. National Electrical Code for all similar applications outside of A-28, the new revision of this standard now makes provision for fail-safe galvanic isolators, which guarantees the isolator will never compromise the ground. DEI Galvanic Isolators have been tested to meet or exceed all requirements of the revised ABYC A-28 for fail-safe galvanic isolators and were certified by Imanna laboratory.
Do DEI Galvanic Isolators need a monitoring system?
No. According to the revised ABYC A-28, any isolator meeting the fail-safe criteria will not require a monitor. Isolators not meeting the fail-safe requirement in the revised ABYC A-28 will still require a monitor. Since DEI Galvanic Isolators are tested to meet and exceed all ABYC A-28 standards, monitoring is not required.
How can I purchase DEI products?
DEI products are available for purchase from Farwest Corrosion Control Company, America's leading distributor of corrosion control products.
Product Selection
Selecting an appropriate Galvanic Isolator and installing it is a simple process. The device is installed in series in the safety grounding conductor on the boat, usually near the main shore power panel. Please see the schematic below for more detail.
Typical Product Selection
DEI Isolators are typically applied using an industry standard method of matching the device to the steady-state current rating of the shore power service. In order to select the best product for your vessel you must know the size of the shore power service on your boat and choose the Galvanic Isolator accordingly. In some cases, one unit can be used for dual shore power services (such as the GI-50/60A devices, which can be used for dual 30A shore power services.
Fail-Safe Plus and Fail-Safe MAX
DEI offers two versions of the GI-30A and GI-50/60A products, designated by Fail-Safe Plus (FSP) and Fail-Safe MAX (FSM). Fail-Safe Plus models meet the requirements of ABYC A-28 for fail-safe galvanic isolators, while the Fail-Safe MAX versions offer even more robust performance. Fail-Safe MAX products have fault current ratings so high, that the ground wire would melt before the product will fail. The choice between these two models can be made at the customer's discretion.
If assistance is required to determine whether these ratings are adequate for your application, contact Farwest for assistance, or visit our Alternate Product Selection page.
Alternate Product Selection
DEI Galvanic Isolators are typically sized to match the steady-state AC rating of the shore power service, which typically also provides an appropriate associated AC fault rating. If a higher AC fault current rating is needed, the following alternate methods may be used to select an isolator rating and model.
Alternate Product Selection Method - AC Fault Current
Exposure level: The grounding conductor of an AC voltage system is designed to carry the full phase-to-ground fault current in the event of a fault (e.g. shorted conductors or motor winding failures). Placed in this grounding conductor, the DEI device would be exposed to the entire available fault current, and should be rated for such.
Calculation method: The full available fault current from the shore power system is the value that we need to size for. The methods for sizing include (in order of preference):
a) using the breaker clearing curve for the circuit in question, b) comparison of the grounding conductor size to fault withstand graphs for cables, or c) calculation of the fault current at the shore transformer (worst case).
The three methods are described below:
a) Comparison to fuse/breaker clearing curves
If a fault occurs within the shore power cord up to the boat’s main breaker panel, then the shore breaker will clear the fault and ideally the shore breaker current/time trip ratings would be used. However, realistically sizing to the main breaker on the boat will adequately define the needed Galvanic Isolator fault rating. The breaker “total clearing time” curve should be used, and a DEI device rating should be chosen to exceed these curve values. On a clearing curve graph, the DEI device ratings should appear to the right of the breaker clearing curve. If you would like DEI assistance, please provide breaker clearing curves, or provide data so that we can find the curves in our library or on the web, including the breaker manufacturer’s name, model number, and ratings or settings.
b) Comparison of the grounding conductor to fault withstand graphs for cables
Device ratings can also be indirectly estimated by comparison to the AC fault capability of the conductor used on the circuit of interest. This is based on the assumption that the conductor was originally sized correctly for the available fault current, and will generally result in a conservative selection. Determine the grounding conductor size used in your shore power cord, then compare the current/time values in the withstand graph to the DEI device, choosing a product rating that approximates or exceeds the conductor rating. As this is an indirect method of fault sizing, it may be appropriate in some cases to have a DEI product rated below the conductor withstand value, if other factors, such as total conductor length, indicate that the fault current is substantially lower than the maximum conductor withstand.
c) Calculations based on the source fault current at the transformer
Unless the user has fault data for the exact circuit of interest, a conservative estimate can be achieved by starting with the fault current at the marina transformer. If desired, further refinement can be done by calculating current reductions due to conductor impedance due to the length of the service. This method is most useful for smaller electrical facilities; use at larger facilities may provide overly conservative values. Because the data needed will not likely be readily apparent, except to a site electrician, the other methods of sizing are recommended first.
The maximum fault current available at the transformer terminals is determined by the following formula, using data from the transformer nameplate, which can be supplied by a site engineer.
Secondary full load current =
Single-phase transformer kVA
Secondary kV
or
Secondary full load current =
Three-phase transformer kVA
(Secondary kV)(√3)
then
Secondary fault current =
Secondary full load current x 100
Percent transformer impedance
This is the maximum fault current at the transformer, which will be reduced by conductor impedance. This reduction can be estimated using wire characteristics for various cross-sections and lengths. Please contact Farwest for additional assistance.
Comparison to other industry galvanic isolators
DEI manufactures Galvanic Isolator models to a higher level of performance because we recognize the safety and liability implications due to inadequate grounding from our experience with similar products in the energy industry. DEI brings this experience to the marine industry by offering a much more complete and conservative approach to boat grounding and galvanic isolation.
A key feature of DEI's approach is the assured safety grounding of the boat under all conditions. This important feature, a fail-safe design, provides assured safety grounding even in the rare event of product failure. The fail-safe design is essential for safety and required for any shore-based application which comes under the U.S. National Electrical Code (NEC). The most recent revision of ABYC A-28 (July 2008 publication) makes provision for a fail-safe GI that will not require monitoring, as it assures safety grounding under all conditions. The DEI fail-safe design avoids the nuisance issue of the monitoring system, which has been troublesome for boat builders and users alike.
Additional advantages over other isolators include much higher AC fault ratings, ratings for lightning surge current (not even required in the standard), cool operation, and robust construction.
Comparison to Isolation Transformers
DEI offers the Galvanic Isolator to the marine market as an alternative to isolation transformers. Where voltage or frequency conversion on the boat (from shore power) is not required, the Galvanic Isolator offers a lower cost option to obtain isolation.
The size and weight of a DEI Galvanic Isolator is significantly less than an isolation transformer. DEI's Galvanic Isolators range in weight from 3.5 to 13 pounds (1.6 to 6 kg) and are a small fraction of the size of any isolation transformer.
Comparison Polarization Transformers
Even where an isolation transformer is installed, a Galvanic Isolator is beneficial, by keeping the boat hull and grounding system referenced to shore ground. By converting the isolation transformer to a polarization transformer arrangement, a fault from the primary phase to the transformer enclosure can be conducted through the galvanic isolator, avoiding injection of fault current into the water, which has significant safety implications.
Other Benefits of DEI Marine Isolators:
DEI has many years of experience designing, manufacturing, and testing electrical products for electrical generation, transmission and distribution systems, as well as low voltage industrial systems. If power utilities can trust us to protect their largest generator step-up power transformers at a power generating plant, you can also be assured of solid product designs for boat grounding. Our engineers will gladly assist any customer with the proper rating and selection of a Marine Galvanic Isolator.
Elimination of all customer calls pertaining to "monitor alarms."
Extensive experience in providing fail-safe products to the corrosion prevention industry.
