I started working for a new builder and they are claiming that the building inspector is requiring that they make the gas furnace be able to turn on the exhaust fan in the utility room a couple times a day for whole house ventilation. This is fine with me but the HVAC crew is running a 18-2 conductor to a junction box directly under the switch that controls the exhaust fan. They are claiming that as long as I junction the 18-2 into a 14-2 NM-B before it goes into my switch box then I don't have to separate the high and low voltage in the box. I have never heard of this. Can anyone confirm that this is true?