The key words here are "Should have". Now that you went ahead and asked for permission and have been turned down, you may be on the landlord's radar for a surprise visit one day to make sure you are not messing with his electrical system and end up burning down his rental unit. I am not commenting on if it is better to ask permission or not (it probably is), just to realize that now you may be under scrutiny simply for asking, the world is funny that way sometimes.