Somebody explain this please

[hardworker]

I was inspecting a 10 year old professional installation in a commercial basement It was wired with 12 awg mc cable. Some of the mc cable was fastened with single hole mc cable fasteners to the stone basement wall. The mc cable aluminum shield was completely eroded away at the contact point of fastening and the single hole fastener is rusty. The wire was still insulated fine, but the mc aluminum shield was now just white mush. Gone completely. What was the science behind this? I have never seen such a thing. The aluminum shield was not just soft, it was no longer there. Just white mush.

No issue where the mc cable was fastened to the wood structure, just a problem to the stone. It is a basement with moisture.

Please explain.

 

[ramsy]

Look up Galvanic corrosion.

Masonry minerals may provide dissimilar metal ions, not evidenced at wood structure.

PVC straps may be one solution, if available in 3/8 Inch.