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Electrical Puzzle


Jim Katen
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Here's a good puzzle.

This is a 1978 house with copper wiring and no other significant electrical problems.

When I turn on the heatilator motor, it runs fine and no odd things happen.

When I turn off the heatilator motor, three things happen simultaneously: the heatilator motor shuts off; the nearby dining room light fixture flickers briefly; and a halogen floor lamp in the living room turns itself on for just a brief instant. The floor lamp's switch is in the "off" position.

Why do these things happen?

- Jim Katen, Oregon

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Heatlilator motor equals gas fireplace blower, correct?

I have no idea if this is possible, but could the blower motor be acting as a dynamo as it slows down and put some weird current into the neutral wiring? I can see the nearby lights flickering from that...maybe. The floor lamp coming on is more puzzling. Even with the weird current in the neutral creating some type of reverse polarity and therefore able to reach the lamp despite the switch being off, it would still seem you need a circuit for it to actually light up. Hmmm...(going deeper into WAG territory)...neon lamps can do some strange things in electrical fields. It was definitely halogen?

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Jim,

This is an odd one. What you described is what usually happens when the fan motor turns on. The motor has "inrush current" when it's first turned on, which causes a voltage drop. The voltage change could be causing the lights to flicker. I think the NEC allows up to a 5% voltage drop. If you have a Ideal Suretest, you can measure the voltage drop.

http://www.valuetesters.com/Ideal-Indus ... alyzer.php

It could also be a loose or poor connection somewhere on the circuit path (neutral).

Kevin

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I would guess that current is somehow shunted to ground at the heatilator. I have described here before how a heatilator switch energized an entire house through the flue strapping and foil faced WRB. I would concentrate on the blower motor or switch.

Tom

Added:

The heatilator and the ceiling light fixture should both be equiped with EGCs, but floor lamps generally aren't. It makes sense that stray current traveling on the GC and EGC could breifly energize the ceiling light but the floor lamp would need another ground path to complete the circuit, was it sitting on or touching a heat register? If not then the stray current is traveling on the neutrals and it breifly arcs past the switch.

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Thanks everyone.

The lamp is not on a touch-me switch.

Nothing strange happens when I turn on the heatilator, so I don't believe that inrush current is responsible.

None of the lights is fluorescent.

Zombies are a distinct possibility and I might have been deceived about the age of the house. It could be a 1981 zombie hideout.

I didn't actually see the heatilator motor. Those things are usually simple shaded pole motors but I suppose that this older one could be a capacitor start motor. If so, there might be a fault that's causing the capacitor to discharge when the motor is switched off. That would energize the circuit with a high voltage pulse that might actually be strong enough to jump the cheesy switch on the halogen lamp.

I didn't have time to investigate properly. The seller was home with the flu and she insisted on hobnobbing with us, hacking, coughing, and spreading contagion with every breath. In fact, come to think of it, she did look kind of zombie-ish. I just wanted to get the heck out of there.

- Jim in Oregon

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. . . Added:

The heatilator and the ceiling light fixture should both be equiped with EGCs, but floor lamps generally aren't. It makes sense that stray current traveling on the GC and EGC could breifly energize the ceiling light but the floor lamp would need another ground path to complete the circuit, was it sitting on or touching a heat register? If not then the stray current is traveling on the neutrals and it breifly arcs past the switch.

Yes, the floor lamp wasn't grounded. Whatever was happening had to be jumping the switch.

- Jim in Oregon

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