Posted by Sherman in Idaho [108.162.245.181] on Thursday, December 15, 2016 at 15:54:55 :
In Reply to: Re: Two things about connectors in general posted by Willy-N [172.68.58.165] on Thursday, December 15, 2016 at 15:07:26 :
All good points. Knob and tube was a great system because it was based on the assumption that things would go wrong. They didn't trust the insulation to last forever so they kept the wires far apart and used ceramic knobs and tubes for extra insulation. In the oldest installations they fused BOTH wires just in case one fuse didn't blow or the not and neutral were swapped. Splices were done with a special pattern of twist, then soldered, then wrapped with friction (not vinyl) tape. Electrical boxes were made on-site of wood lined with thick asbestos paper. There was no aluminum. There was much soldering. Nobody trusted a hollow rivet to maintain a connection. it was assumed that things would get hot.
It was slow work, and probably very expensive by today's standards. Like you say, the problems have all come with the add-ons. Someone strips the knob-and-tube wires in the attic and twists some romex around it and calls it good. The 15 amp fuses keep blowing so they put in 20s and then 30s, when the branch circuit wiring is almost always 14 gauge. My favorite add-ons so far have been an 30-amp #10 dryer outlet with the hot end of the wires stuck into the feed lugs of the main breaker (no room in the panel to add an extra breaker), and a "grounded" outlet added to a knob-and-tube circuit with the aforementioned attic "splice", and the ground wire securely fastened to a large nail driven into a stud. Like we say, "Invent a fool-proof device and someone will invent a smarter fool".
But connectors and connections are the vast majority of problems with everything electrical. The military and aerospace industries have studied the problem exhaustively and their conclusions are all expensive -- avoid crimps, and avoid connectors entirely if possible, use gold-on-gold for small signal connections and silver-on-silver for power connections (never use gold on tin under any circumstances). Strain-relieve the wires, and use a positive mechanical connection between the connector halves. Make sure everything is gasketed and sealed for environmental protection.
We can't build trucks like they were ICBMs or fighter jets, but we need to at least be humble and be wary of "cheap" or "easy" connectors. Anything with self-piercing prongs on it is particularly treacherous because they have a way of just barely touching so that it appears to work until it gets wiggled slightly or goes through a few thermal cycles.
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