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Troubleshooting Article Archive:  July 2004          
Electric Junction Boxes
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 indeed.

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.