Surfing the Internet a
few months ago, I came across an article about a small passenger airline
in Canada's Northwest Territories that flies a fleet of Douglas DC-3
aircraft. The last DC-3 made rolled off the assembly line in 1944,
making these planes at least 60 years old.
Yet far from being some museum
reenactment, this airline flies these planes every day, on a for-profit
commercial basis, in temperatures well below zero. The article
reminded me that when you maintain and design equipment to endure the
effects of the passage of time, it can remain usable for a very long time
You don't have to expend a lot of
effort or money to design equipment for the ages, instead of for next
week. Consider the electrical junction box, for example, in the bed
of your tow truck. The box contains several threaded studs onto
which the manufacturer installed electrical terminals and single retaining
nuts. On some junction boxes, the studs come anchored in the plastic
body of the junction box with only the threads sticking out. When
new, the studs hold the electrical terminals tightly, between the nut and
the plastic body of the junction box.
Over years of seasonal
temperature changes, however, the plastic expands and contracts, slightly
loosening the electrical terminals. The looseness causes the
terminals to heat up when you use the lights, and the heating further
melts the plastic, which further loosens the connection, in a repetitive
cycle. Sometimes the whole stud will come unanchored inside the
junction box like a tooth coming loose in one's mouth.
The solution: install two
nuts on the stud, install all the electrical terminals between the two
nuts, and tighten one nut against the other. You will thereby
eliminate the plastic of the junction box as anything but an anchoring
device. Most junction boxes use either 10-32 or 10-24 nuts, which
cost only cents.