Wire oxydation

I've got two DS18B20 waterproof sensors connected on an Arduino Mega. They've been collecting data pretty flawlessly for 2 years now. We recently noticed that on of the two wires of the cable go serious oxydation all along the cable to the Arduino. The coper turned all black causing the sensor to not function properly. This is not heating up cause the wire's rubber insulation isn't melted or disformed.

What would cause this and how to prevent it?

Note: the probes are immerged in sea water (verry salty environement)

I read some documentation in electricity manuals and it seems to be a common problem in damp, humid environments. Could be the cables I'm using that are not made for this kind of environment leaving some humidity pass through?

Could be sulphur products and humidity in the air.

elwayno:
I've got two DS18B20 waterproof sensors connected on an Arduino Mega. They've been collecting data pretty flawlessly for 2 years now. We recently noticed that on of the two wires of the cable go serious oxydation all along the cable to the Arduino. The coper turned all black causing the sensor to not function properly. This is not heating up cause the wire's rubber insulation isn't melted or disformed.

What would cause this and how to prevent it?

Note: the probes are immerged in sea water (verry salty environement)

Chemical alert! Copper oxidation is GREEN/BLUE. Not black. Rubber contains sulfur. It is part of the manufacturing process.

Neither will cause immediate problems with your sensor unless the connection was not properly made.

Hint: use wire that is made for direct burial in the ground.

Paul