Mass Spectrometer Device that has a vacuum inside it and can sense the presence of helium gas when checking around the joints in a vacuum system for leaks. The molecules in helium are small and are able to pass through the microscopic leaks that would place a limit on the vacuum. Mast Heavy conduit, through which incoming electrical supply wires pass, which runs from the service drop to the meter. Mast Heads Waterproof caps, also called weatherheads, entrance caps, or rain caps, which are placed at the upper part of an electrical mast at the point where the wires are run to the inside electrical meter. Wires hang from the pole to the entrance cap so that the entrance cap is not the low point in the downhill run from the pole because water will run to the low point before dripping to the ground.
Wires enter the entrance cap at an upward angle through a tight insulator.
Water is further stopped from getting through the entrance cap because of this entrance angle. Master Antenna Television System Central television antenna serving an apartment or other multi-family complex. Master Deed Deed filed by the developer or converter of a condominium for the purposes of recording all of the individual condominium units owned within a condominium complex. Master Lease A controlling lease in an apartment or office building that controls subleases. Master Limited Partnership Unincorporated combination of limited partnerships in real estate together as a group.