The 40 amp double pole single throw,Can be used to run more than a 1000 watter and fans pumps timers and anything you choose to add to your room.The larger gauge is a safety precaution.A small gauge can carry a surge and melt the insulation on the wire,Due to overload.Your so right when you say it's invisible! That's why they make meters!I go a 40 amp and it runs 2 rooms.0ne room has a 600 HPS and a 400 HPS.The other room has a 400 MH.Timers and lights and fans!That is code for this area.

Ga Grown!