I have a question that seems to baffle electricians that I've spoken to. I'm running a 115V Fan off a TRIAC controller that utilizes a 0-10VDC control signal. When I power the DC control signal down, the fan stops running as expected. However, when I take voltage readings at the fan terminal box I get 120V readings from Line/Ground and 120V from Neutral/Ground but zero volts from Line/Neutral. Can somebody explain this to me?
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4\$\begingroup\$ I'd guess that your controller is switching the Neutral line and therefore Live is always connected. Whether or not this is a good idea is a different question ... \$\endgroup\$– brhansCommented Jun 9, 2015 at 17:21
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2 Answers
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Assuming there is a neutral to ground connection somewhere between your supply transformer and your building ...
simulate this circuit – Schematic created using CircuitLab
Figure 1. Switched neutral.
It sounds as though the triac controller is in the neutral line.
when I take voltage readings at the fan terminal box I get 120V readings from Line/Ground
That's the VM1 reading.
and 120V from Neutral/Ground
That's VM3. The live feed is coming through the lamp filament.
but zero volts from Line/Neutral.
That's VM2. The lamp is off and there is no voltage drop across it.
answered Mar 20, 2016 at 10:35
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- pl. check the earthing (ground)..perhaps it is floating
- Instead of checking voltage by voltmeter, pl. check the voltage by 240 V filament bulb..vtingole
