A very common problem encountered in crawl spaces is for the
toggle switch used as a furnace disconnect to die. Often you turn it off, and
it will never turn on again. They can also fail on their own over time. Toggle
switches are not really made for the environment found in most crawl spaces. The
contacts and the switch mechanism get corroded. The contact corrosion causes
voltage drop and heat, further degrading the switch.
The picture shows what is
left of the toggle switch that was serving as a furnace disconnect. The switch
had failed, keeping power from reaching the furnace. It was relatively easy to diagnose:
nothing happening with any thermostat setting, no transformer hum, and no LEDs
glowing. My non-contact voltage detector showed power entering the switch but
not leaving it. When I started to remove it so I could check it, it just fell
apart.
To avoid similar problems, toggle switches in crawl spaces
should be installed inside a weather proof switch box. I also recommend spending
a few extra dollars to get a commercial, heavy duty toggle switch instead of
the normal light duty residential toggle switch. In fact, the NEC requires the
weatherproof box, but it is often overlooked. The relevant NEC sections are
listed below. These are from the 2017 edition, but I do not think these
particular sections have changed from previous code versions.
“404.4 Damp or Wet
Locations
(A) Surface-Mounted Switch or Circuit Breaker. A surface
mounted switch or circuit breaker shall be enclosed in a weatherproof enclosure
or cabinet that complies with 312.2.
312.2 Damp and Wet
Locations.
In damp or wet locations, surface-type enclosures within the
scope of this article shall be placed or equipped so as to prevent moisture or
water from entering and accumulating within the cabinet or cutout box, and
shall be mounted so there is at least 6-mm (1∕4-in.) airspace between the
enclosure and the wall or other supporting surface. Enclosures installed in wet
locations shall be weatherproof. For enclosures in wet locations, raceways or
cables entering above the level of uninsulated live parts shall use fittings listed
for wet locations.
Exception: Nonmetallic enclosures shall be permitted to be
installed without the airspace on a concrete, masonry, tile, or similar
surface.”
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