What are the tax penalties for going over the 401-k non taxable with holding limits?

No penalties. It's just post-tax money put into your 401k after the allowance amount. You should put the extra money in a Roth IRA if your income allows or just put it in a nonretirement investment account. Putting additional money above the taxfree amount in a 401k plan serves no purpose other than just limiting your investment options, which isn't a good thing.