Whenever a boat is connected to shore power, the hull and drive systems are 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 below:
Four Components are Needed for Corrosion:
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 metallic path that allows current to flow from cathode to anode.
A simple method which virtually eliminates this galvanic corrosion problem is to insert an appropriately rated and certified DEI 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.
DEI Galvanic Isolators (GI) are fail-safe, solid-state DC isolation / AC coupling devices with ratings and characteristics that significantly exceed those of all known galvanic isolators designed for marine applications. The proven fail-safe construction assures that the galvanic isolator never compromises the integrity of the grounding conductor, even in the unlikely case of the product failing.
In the marine industry, the criteria for galvanic isolators is defined by the American Boat and Yacht Council (ABYC) Standard A-28, which has a publication date of July 2008 and an effective date of July 2009. 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 Electric Code for all similar applications outside of A-28, this standard now makes provision for fail-safe galvanic isolators.
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 rating. Per the new A-28 standard, galvanic isolators meeting the fail-safe requirement will not require a monitoring system since the integrity of the grounding wire will not be compromised should the isolator fail. All galvanic isolators not meeting the fail-safe criteria will still require a monitoring system to alert the boat owner that their grounding system may be compromised.
Fail-Safe Plus & Fail-Safe Max Technologies
DEI offers a Fail-Safe Plus® (FSP) or Fail-Safe Max® (FSM) model for each rating except for the 100A and 200A models, for which only the Fail Safe Max model is offered. Fail-Safe Plus models not only meet the fail-safe test criteria in the new A-28, but also have considerably higher fault current ratings than are required and have very substantial lightning current ratings, which are not even required by A-28; hence, the "Plus" designation unique to DEI.
Fail-Safe Max models provide even higher AC fault ratings than Fail-Safe Plus models and will still be fully functional when tested to the A-28 fail-safe fault criteria, thereby providing the ultimate in performance; hence, the "Max" designation. The FSM models will fail in the safe mode, at a level in excess of the A-28 fail-safe definition - a point at which the grounding conductor would have previously failed.
DEI Marine Galvanic Isolator Features & Characteristics
- Fail-safe construction with Fail-Safe Plus™ and Fail-Safe Max™ technology
- Certified to ABYC A-28 July 2008 publication
- Highest AC fault current ratings available
- Ignition protected
- Maintenance-free solid-state design
- Rated for high levels of lightning current
- Very low DC leakage current allowed