Most reed switch blades are made of nickel/iron that has a relatively high resistance to current flow when compared to copper and silver. Most of the time it is not a problem. However, when the reed switch is asked to pass high current, whether DC or AC the contacts will heat up. The heat can become so high that the curie point is reached > 700°C. At this point, the nickel/iron loses it ferromagnetic properties. Therefore, the relay coil or magnet holding the contacts together will no longer hold the contacts open due to the excess heat. To solve this problem plating the entire reed switch with 50 to 100 µm of copper will improve the conductivity so much that the problem will disappear.