Over the last 10 or so years, I’ve spent a lot of time digging into the electrical systems on new boats being imported to the U.S. from all over the world. One thing is clear: The vast majority of these boats, and now some custom or semi-custom U.S.-built boats, are utilizing one of what I believe are four variations of terminal connectors typically mounted on DIN rails.
Ed Sherman At least four connector types are used with DIN rail terminal tracks, whose original specifications are now internationally adopted as the standard.
Increasingly, I hear questions about whether these terminal types are compliant with American Boat & Yacht Council (ABYC) standards. Some people say categorically, “No, they are not.” I’m not in that group, and I work for ABYC. It depends on which of the four types is being employed. The first that I’m familiar with is a spring-loaded connection that by my eye is really designed for single-strand conductors, whereby you simply push the wire into the slot and the spring-loaded connector captures the wire. The wire is held in place by spring tension. These are probably not compliant unless crimp-on pin connections are employed. Others have argued that solder-tinning the ends could achieve the same net effect—not an unreasonable argument, considering the amperage values involved are relatively low.
In a screw terminal, the screw head bears down on the strands of wire captured inside the terminal housing. Again, compliance is questionable. Considering the screw’s size and how much torque can be applied under normal circumstances, will it be enough to damage individual strands? Those that I’ve inspected indicate the answer is no.
In this same screw-type category is the compression plate that the screw bears against. I consider these compliant, based on the current wording in the ABYC E-11 Standard.
Courtesy Wago Corp. The Wago lever-type connector clamps the wire strands under a compression plate.
Finally, in the Wago lever-type connector, a small plastic lever lifts up to open the gate for inserting the stranded conductor. Lowering the lever locks everything into place. Are individual strands damaged here? Will the connection meet pull-test requirements? What about galvanically incompatible metals? I’m not sure, as I’ve only seen photos of this type in use on boats. Wago’s website (www.wago.us.com) shows a detailed cutaway of the metal clamping mechanism inside the plastic housing. The curved surface of the compression piece strikes me as equivalent to any compression plate with the screw-type mechanism. If it meets pull-test requirements and the metallurgy issues pass muster, I’d say this type is compliant.
Consider here what ABYC actually says about wire terminations in its E-11 Standard:
WIRING TERMINALS—DC & AC.
Wiring connections shall be designed and installed to make mechanical and electrical joints without damage to the conductors.
Metals used for the terminal studs, nuts, and washers shall be corrosion resistant and galvanically compatible with the conductor and terminal lug. Aluminum and un-plated steel shall not be used for studs, nuts, and washers.
Terminal connectors shall be the ring or captive spade types.
The exceptions here are important as I consider the connector types in question to be friction-type connectors.
EXCEPTION: Friction-type connectors may be used on components if:
1) The circuit is rated not more than 20 amperes or the manufacturer’s rating for a terminal designed to meet the requirements of UL 310, Electrical Quick-Connect Terminals, or UL 1059, Terminal Blocks, and 2) The voltage drop from terminal to terminal does not exceed 50 millivolts for a 20-amp current flow, and 3) The connection does not separate if subjected for one minute to a six-pound (27 Newton) tensile force along the axial direction of the connector, on the first withdrawal.
Connections may be made using a set-screw pressure-type conductor connector, providing a means is used to prevent the set-screw from bearing directly on the conductor strands.
One could reasonably interpret it this way: The DIN rail-mounted screw-type terminals might be compliant as long as a compression plate is part of the design of the terminal. One could also interpret this as meaning that if the installer uses ferrules or crimp-on pin-type connectors with this style of terminal, all is well—again as long as metallurgy and pull-test requirements pass muster.
I present this discussion more as a question than an answer. I see thousands of boats globally using the screw-clamp connector type, some with long-standing, excellent reputations, and with these terminal types in use approaching the 25-year mark with no known issues. I’d like to see the ABYC Electrical PTC (project technical committee) take on this issue and consider the compliance issue. As our market becomes more global, I think it’s time to make decisions about this connector type. It seems that the Europeans already have, as the boats I’m referring to are all CE marked and therefore compliant with minimum ISO requirements for recreational boats.
