I've been away from this forum for a while. This similar situation has been a baffling question for me also. When I started in the trade, we had to wire for OTR microwave interlocks in every new home. A few years ago we stopped. Occasionaly we will still wire for an interlock on larger hood fan units. Seems to be up to the HVAC contractor if they are going to install a makeup air setup. Often I just run the wire just in case if its a larger CFM unit. 18/2 is cheep compaired to the cost of fishing and the service call later because the electrician is always at fault when they decide to add a MUA at finishing stage and there is no wiring for it.
