When things are “neutral” it typically means things are not going anywhere. Like a car for example.
There might be “potential” for it to be going somewhere–as in the engine idling waiting for the driver to shift it into gear. The car could also just be sitting on a hill waiting for the driver to take their foot off the brake so the car could coast to the gas station hopefully somewhere off in the distance. The later condition is a type of neutral that can still be dangerous, while often when we think of “neutral” we liken it to some sort of state of rest.
It older houses, back when we first started wiring houses, it was common practice to “switch” the neutral wire to a light fixture instead of switching the hot wire as is now required. Sometimes the hot and neutral wires were inadvertently reversed, resulting in the same thing.
Of course in either scenario, when we turn the switch off, and the light goes out, there will still be power to the light and down to the switch, waiting for anyone working on the fixture or the switch to come in contact with the hot wire and something grounded.
By switching the hot wire, we are likely to be somewhat safer working on the fixture—however, there can still be scenarios where there might be energy at the fixture, for example if the light is part of a Multi-wire Circuit. This later example is why most homeowners may not be knowledgeable enough to know how to change a light fixture safely.
At a recent inspection I found a light fixture that had a switched neutral. As you can see in the picture above, the light is on. While not shown, the switch is also on, but notice that the tick tester is not glowing at either wire to the box.
When I have Knob & Tube wiring systems such as this one, I like to check the wires with a voltage indicator (when I have access to the wires) to see if the house has switched neutrals or not. Taking the switch cover plates off to check is another way.
While this condition in the all-wood-covered closet on the second floor it is not likely to represent much of a safety hazard, the same installation in a bathroom or basement, with proximity to grounded surfaces, might be a real safety concern–and a person could be shocked.
Another issue, anyone using these inexpensive voltage indicators should be aware of, is just because they do not glow does not mean there isn’t any voltage present. For example the one pictured above is a 90-1000 volt indicator. In other words there could be voltage up to 89 volts and the tester would “see” nothing. That “nothing” could easily result in serious shock. In the picture above there is going to be a small amount of current flowing back to the electrical source but because it is the “grounded conductor” the voltage detector cannot see it. A 40 watt light bulb will result in .33 amps on the neutral wire at 125 volts–certainly enough to light up your day given that as low as .1 to .2 can kill you.
By Charles Buell, Real Estate Inspections in Seattle
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