Not sure about that one. Perhaps mechanical code? As for the switch I believe it must be located out of the room that houses the oil burner. If the burner is in an open basement the switch must be outside of the basement, such as on the first floor outside the door leading to the basement stairs.
Bob, I looked in the Interenational Mechanical Code and also the International Residential Code and couldn't find anything regarding this. All that I could find is a requirement for a shut-off valve, nothing electrical. Perhaps you have a state amendment to the code...?
It may be required in NH too. My parents had to have one installed above their Oil-fired Hot-Air Furnace when the house was built 10 years or so ago. At that time the AHJ was the local Fire Marshall (if that makes a difference).
Guys I live in NH and they are required for oil and gas burners. They are thermo cut-out switchs. The type I see around here are black with a push in black "switch" which has a temp rating of I believe of 185 degrees which is supposed to melt at that temp and shut off the heating equipment(It is wired in series with the hot wire). This is also known as a "new england safety kit" which includes the fire-o-matic, a switch at the head of the basement stairs with red plate(oil or gas) and a fire-o-matic on the oil feed that looks like a black wheel and is used to shut off the flow of oil to the burner. This also has a temp rating and will melt if there is a fire and shut off the flow of oil to the burner.