A planer is a hard start as the head requires a fair bit of power to get the iron moving, my 25" planer has a 10 hp motor and my 15 hp RPC starts it, but if I had the planer before the RPC I would have purchased a 20 hp. Thankfully my RPC was designed to handle hard starts and can deliver the current needed to get the 6" diameter head turning. Better to have a little extra capacity than too little capacity.