Error Returns After Every Reset: Corroded Outdoor Terminals

A communication code returning some weeks after the outdoor terminals were last cleaned. The clean worked at the time it was done. This has now happened more than once, and the interval gets shorter each round.

A repair that works and then fails on a shortening cycle is reporting how much material is left rather than how well the cleaning was done. Corrosion removes metal, and cleaning removes only the layer above it. Each clean therefore starts from a slightly worse position than the last, which is exactly the pattern of shortening intervals. Looking at the terminal faces for lost material, not just for deposit, is the check that settles it.

Corrosion works downward into a metal face rather than sitting on it. A clean removes the products of that corrosion and exposes what is left, which is a smaller and rougher contact area than the original. The connection works again for a while, then degrades faster than it did before because there is less metal to lose. Nothing about the cleaning is wrong; there is simply less to clean each time.

The terminal block is replaced rather than cleaned a third time, and the new one shielded from the conditions that took the old one. This is the point at which cleaning stops being maintenance and becomes a delay. Two cleans on a shortening cycle is enough evidence to stop, and the replacement usually costs little more than the next visit would have.