Strange Voltage Drop When Light Bulb is Installed

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Molo

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Hello,
I am very confused by a situation where the voltage drops from 120 to 103 when a lightbulb is installed in a light circuit.
Some Info:
-Brand new installation, new wiring, new fixtures (6 in total, and all identical). Each light takes a 60 watt bulb max.
-There are 6 ceiling lights on the circuit, and when a 60 Watt bulb is installed in any of the lights the voltage on the circuit drops from 120 to 103-104.

Thanks in Advance!
 

Molo

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Is there a dimmer control in the circuit?

- Yes there is a dimmer.

-Another discovery: There is another lighting sub-circuit on the same breaker that is doing the same thing (reading at 103 with a bulb installed and lit and 120 with no bulb). It also has a dimmer....

-More info: There is a third lighting sub-circuit on this breaker that DOES NOT have a dimmer, and it is not doing this.

Thanks again
 

Jadnashua

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Many electronic dimmers cannot pass 100% of the voltage through to the bulbs. I do not know if any do unless they have an actual switch at 'max' to bypass the dimmer, but turning the thing on/off may then shorten its life. Many of the rheostat types do have a bypass at 'max'. Whatever they are using for dimming would never be perfect, but a simple diode nominally would only account for maybe 1.4v (0.7 or so on each peak)...a triac (sp?) may have a bit more, maybe double that, but a transistor based design might have less. Anyway, from my limited experience, what you're seeing is normal and corresponds to those I've got in my place (I compensate by using slightly bigger wattage bulbs, but rarely run any of the circuits at max anyways - it's nice to have it for those rare occasions when you need an operating room, though!). Interested to hear other experiences and maybe a better explanation - always ready to learn.
 

Molo

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Electrician checked voltage at the dimmer switch and confirmed it is the dimmer causing the voltage drop.
 
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