I have a customer with a full 100 amp main panel. She needs more spaces. I tried to make her understand that she needs an upgrade to a bigger panel. She only wants a 50A sub panel. Well ok then.(shes an idiot). I had told her the sub would be cheaper so thats what she wants. This panel has two main lugs that feed the main breaker. Can I put my 50A ser wire under those lugs to feed my sub panel, or do I need to put a 2 pull 50A breaker in her existing panel to feed my main lug sub panel? I am pretty sure you can. And I was told to do it when I was an apprentice.(long time ago). But now my buddy says I can't do that. I'm breaking out the code book now just wondering what you guys think? Thanks for your time!!!