I picked off 120v from an outlet (parallel) to power a dual switch that inturn will switch on a light and the other to switch on a bathrom fan using a 3/12 with grnd. The circuit is connected through the dual switch by providing the black "hot" wire to the "com" terminal of the dual switch. The other side of one switch will go to the light (wht) and the other side of the second switch will go to the fan (red) and all the grounds and nuetrals are continuously connected respectively. The open wires are waiting to be connected to their respective fixture. With my multimeter on the open wires I turn the switch on and I get 120volts but when I turn the switch off I get a 15volt reading. Is this normal because I am reading through a switch that doesn't have a load on it?
Is this normal
It is most likely a capacitatively coupled voltage from "hot"/"live" wires running adjacent to the wire being measured using a high-impedance multimeter. If your meter has a "low-Z" setting, try that. If the voltage is zero using a low-Z setting, there is nothing to be concerned about.
Due to the high impedance of measuring instruments, a voltage reading may be detected on open conductors where there is no hard electrical connection to a voltage source. Conductors that are installed in close proximity to one another, and are capacitively coupled to each other, can cause this a.c. voltage reading. Such a reading could be 2 or 3 volts, or it may be as high as the voltage on the adjacent conductors. This is what is referred to as a “phantom” voltage. ... NEMA recommends the use of a Listed low impedance multimeter in place of a high impedance multimeter or other high impedance measuring device for testing on open conductors where there is no hard electrical connection. Without a low 2 impedance measuring device, a high voltage reading is an inconclusive indication of possible faults in the cable