It’s an exchange I have on a regular basis; the dialog goes something like this: “During my inspection I noticed you didn’t ground any of the electronic gear. Why is that?” I ask. To which the tech or boat builder responds, “Yeah, you don’t need that unless it’s a metal boat.”
The fact is, no such guideline or exemption regarding metal hull vessels exists (ironically, when I encounter this same scenario aboard a metal vessel, the invariable and predictable response is, “Oh that’s only needed on fiberglass vessels”); if a piece of equipment is equipped with a grounding stud, then you can be certain the manufacturer placed it there for a reason, and if the installation instructions are consulted, they will almost certainly call for the equipment’s chassis to be connected to the vessel’s ground system, or at the very least it’s recommended to reduce interference.
The challenge is that “interference” is a subjective term. It can be as benign as static or as profound as irreparable damage caused by a near or direct lightning strike or voltage spike. These anomalies often don’t manifest themselves until the vessel is in use, by which time the boat and installing electronics tech have gone their separate ways. Furthermore, adding an electronics bonding bus after the installation is complete is nearly always more challenging and time consuming, so why wait and why assume it’s unneeded?.
Every piece of gear equipped with a ground stud or connection point, regardless of hull material, should be connected to the vessel’s ground bus, in order to comply with the equipment manufacturer’s instructions or recommendations, as well as standards established by and codified in both the American Boat and Yacht Council’s (ABYC) Standards, and the National Marine Electronics Association’s (NMMA) installation guidelines (here: NMEA Installation Standards Grounding Schematic).
It’s important to remember that the entire vessel’s ground system, bonding, DC negative, AC safety ground, lightning, if equipped, and electronics ground are common and should be interconnected and at the same potential. Therefore, it should not matter where your electronic gear is grounded, provided sound, low resistance connections are made. However, best practice calls for installation of a bus bar dedicated to electronic component bonding, located at the helm or electronics area. That bus bar is then connected to the remainder of the vessel’s grounding system, which again should be common with all of the vessel’s grounding and bonding systems.
Each piece of bonded gear should rely on a dedicated wire run or ‘drop,’ which leads directly from its chassis to the bonding bus bar, avoid interconnections between gear, or using a chassis as a conductor, by connecting multiple bonding wires to it in different locations, a practice known as ‘daisy chaining.’ Bonding wires in all but a few cases, including electronics, should be at least the same size as the DC-positive conductor supplying the gear and no smaller than #16. The accompanying diagram, from the National Marine Electronics Association (NMEA) manual, details this guideline. Savvy marine electronics installers are NMEA members and are therefore afforded access to this material.
If any bonding connections are made in damp locations (what area aboard a boat isn’t damp?) particularly on smaller vessels, they will benefit from the use of a conductant paste such as Thomas and Betts Kopr Shield, applied to the contact surfaces on ring terminals and bus bars, and an after-assembly coating such as CRC Heavy Duty Corrosion Inhibitor. Ideally, resistance in bonding circuits should not exceed one ohm between bonded gear and bonding busses. Under no circumstances should bonding or any other electrical connections rely on tapping or lag screws, especially and including fasteners used to secure gear to bulkhead or shelves, as these are prone to loosening; the resultant poor connections and use of such fasteners in this role is a violation of ABYC Standards. Bonding connections should always be made using machine screws.
What happens if this gear isn’t grounded? That’s a question that isn’t asked often enough. It’s difficult to predict for certain. Grounds have been likened to seat belts; you don’t need them until something goes wrong. While it’s anecdotal, in my former position as the manager of a boatyard located on the Chesapeake Bay, where lightning repair projects were a regular occurrence, vessels that were equipped with ABYC-compliant bonding and NMEA-compliant chassis grounds, seemed to suffer less damage than those that lacked proper ground systems. In one case, a properly grounded vessel’s masthead VHF antenna was struck by lightning. It melted and fell into the cockpit, damaging the gelcoat and the dodger canvas; remarkably the VHF radio was undamaged. After the antenna was replaced, it worked properly. I believe that when vessels suffer a near or direct lightning strike, wholesale destruction of equipment is simply expected, and the issue of chassis grounds, or the lack thereof, and the role this plays in the level of damage that is incurred, are neither considered nor discussed. They’re simply chalked up to bad karma, and hopefully the insurance company pays the bill. Each time I quiz an electronics manufacturer about chassis grounds, the answer is the same: “It’s a good idea.”
Check your electronic gear. If it’s equipped with a ground stud or screw, which is sometimes symbolized by three successively smaller, cone-shaped horizontal lines and one vertical line, make sure it’s utilized, and don’t let anyone, professional or otherwise, tell you it’s unnecessary. If you are preparing to have electronic gear installed, make certain the installer is willing to abide by this guideline, doing so in a manner that complies with the gear manufacturer’s installation instructions as well as standards established by ABYC and NMEA.
About the Author: Former boatyard manager, technical writer, and lecturer, Steve D’Antonio, consults for boat owners and buyers, boat builders, and others in the industry. Visit stevedmarine.com for his weekly technical columns.