I had a customer call today, he was wondering if his main panel could be moved as it was in a basement suite kitchen. on the wall behind the cooktop stove and counter.

Anyhow when I looked in the panel someone had loaded it up with tandem breakers on 3 wire circuits. I think some of these circuits are split appliance circuits and they took out the double pole breakers and installed tandems to free up spaces.

A home inspector had took off the panel cover and told the buyer everything was fine.

I am sure the use of the tandem QO breakers on a 3 wire circuit (mwbc) is a violation am I right ??