How To Check If You Have Neutral Wiring 

Most INSTEON-compatible wall switches and dimmers require a neutral wire connection to operate. While all houses have a neutral wire, the real question is "Do I have neutrals in my switch boxes?"

To answer this question, here are some guidelines:
-If your house was built in the mid-1980s or later, there is an excellent chance that you have neutrals everywhere in your home
-If there is an outlet (wall receptacle) near the switch, most likely that switch box has a neutral
-Switches that are ganged together have a much higher likelihood of having neutrals, no matter what year

Checking the Switch Box
If you are unsure whether or not you have neutrals, look in your switch box. Please observe all safety precautions before handling the electrical wiring in your switch boxes.
-Turn off your breaker box
-Take off the trim plate over the switch
-Remove the screws from your switch and pull out the existing switch to look at the wires
-If you see a white wire (or group of them), it is VERY likely that you have a neutral in that switch box

The only way to be absolutely sure that you have found a neutral wire is to check the voltage (110V/120V) between the white wire and the "hot" (usually black in color) wire in the box. In a standard switch/dimmer, the "hot" is using one of the two wires connected to the switch.

If you do not have a neutral wire, you can use a 2-wire dimmer in many cases.
edited by ccicchitelli on 8/6/2013