With the main breaker on (which reads 120 volts) I'm only reading 98 volts at the light switch, and light will not turn on. FYI the main breaker is 150ft from the light switch. Is 98 volts enough to operate a 120 volt light?

  • When you're measuring voltage at the switch, where are you putting your probes? What size are the wires? – Tester101 Sep 27 '15 at 16:19

98 volts is a significant drop over 150 ft. This likely indicates a failing connection, possibly arcing. Arcing is fire risk and you should only have a breaker on to help locate the fault, otherwise leave it off until corrected. To locate the fault, check every junction between the breaker and switch for the voltage drop, loose wires, or blackening of the wires.

For the light, 98 volts will usually be enough to see some light on most fixtures, particularly incandescent lights. What's missing is how many amps are moving through the wires. You can read phantom voltage from wiring running in close proximity, or a slight voltage from arcing, but with few amps. Without both, the light will not work.

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  • Thank you for your help BMitch! The light switch being referenced is in an outdoors storage shed so I shouldn't be reading phantom volts from near by lines. A break in the supply line is most probable answer. Dumb question but how do I measure amps? I'm using a basic 6 function digital multimeter. – Charles Brumbelow Sep 27 '15 at 15:09
  • You'd want a current clamp meter for that, e.g. (not a recommendation, just came up at the top of my search): amazon.com/… – BMitch Sep 27 '15 at 15:33
  • Why do you care about amps? – Tester101 Sep 27 '15 at 16:20
  • @Tester101 -- to see what the load is actually pulling. – ThreePhaseEel Sep 28 '15 at 0:02
  • @ThreePhaseEel Still not clear why that matters? – Tester101 Sep 28 '15 at 0:12

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