Recently I’ve been wondering about one of the more common wiring schemes that I see on both power and sailboats, primarily made outside of the US but certainly quite popular here in the US. The DIN rail mounted terminal strips you see here in my lead photo illustrate what has me wondering what’s up. These terminal configurations come in a few different flavors. Some have a small slot to insert the wire and a screw to tighten to clamp directly against the individual wire strands. I recently had to double check myself on this to see if the applicable ISO standard that would apply to this situation had changed, thereby making this sort of thing compliant on European boats seeking the CE mark. Well, much to my surprise, the European standard that discuses screw type terminals essentially mirrors what the US ABYC standards states, that screws shall not bear directly against the conductor strands. The fear being that as the screw gets tightened, damage will occur to the fine individual strands of the wire, thereby reducing the theoretical conductivity of the wire or cable.
Now, understand that not all DIN rail mounted terminal blocks that look quite similar to the one in the photo above are designed the same. Some have a little lever vs. a screw that simply activates a clamp that grips the wire. There is no screw on that style. Other will use a crew but will have a compression plate vs. direct contact with the screw. Both of those types comply with both the US and European standard. Many builders will use small ferrules or crimp-on pin connectors to facilitate complying with the standards. But, most I’ve seen in recent years simply tighten the screws directly against the wire strands.
Now I’ve taken more than a few of these terminals apart and removed the wire from them as well and frankly I can’t see any damage to the individual strands as we worry about. Simply put, the screws are quite small and it’s nearly impossible to apply enough torque to the screw to cause any damage to the wire. But, no matter here, these terminals still are not in compliance with either US or European standards the way I interpret things. So, my question is, how do the boats utilizing this method of wire termination achieve the CE compliant designation? I’d love to hear from some of our readers outside the US on this one……….