I once went to a service call, complaint was that every time they turned the new dryer on the lights house lights went out. When i opened the panel I could see why. the "maintenance" man that had wired the dryer had landed one of the #12's to a new 20a single pole breaker and the other to an existing 15a single pole with the lighting circuit. When the tenant asked him why the lights went out he told them it was because the dryer was new and because of that all the power would go to it first! Luckily, the tenants kept complaining to the property management company and they finally called us. We ended up rewiring the dryer, range and doing a service change. We also rewired a window AC receptacle to replace the 12-2 Romex run 1/2 way around and stapled to the outside of the house.
