I had a nightmare job once where we wired a stamping shop that had a lot of machinery with electric motors in it. The customer insisted on unshielded cable due to the cost difference.
After it was all installed, they kept having network problems. After a lot of expensive troubleshooting, they figured out that the high-frequency motors in the machines were causing interference and messing up the way the network performed. Just like I said it would.
He was not amused when he got the quote to redo it the way it should have been done in the first place. I never heard back. I wonder why?