Often it can happen that before we open up some technical work that was performed by somebody else, we have one idea about what to find, but that after we do so, we find something quite different. Today, while working on my project, this was the case.
When Electricians connect two leads to a single-pole, single-throw switch, what they are supposed to do is remove the insulation a certain distance from the free end of each lead, loop the bare wires around each terminal of the switch, and tighten the screws of the terminals.
When the switch is ‘open’, no current can flow, and when the switch is ‘closed’, current flows with minimum series resistance.
If one wire is black and the other red, which are both codes for phase-wire, past experience tells me that they have never been connected to supply, 180° out of phase with each other, because the first time the circuit was closed, there would have been fireworks. In this case, the supply-wire was black, and the load-wire to be fed was red.
But this is how the previous design was screwed up: Instead of having a free end of supply (black) wire, the previous Electrician had de-insulated a segment about 1.5cm long along this wire, leaving the rest of the wire insulated. Hence, the black wire came from out of the wall, looped through one of the switch-terminals where it was de-insulated, and went back into the wall in one continuous path, to feed circuits elsewhere, which that switch was not supposed to be able to turn off.
But, the load (red) wire was passed in as one free end, and lodged in so tightly that even after I had completely removed the screw of the terminal, I could not remove this red wire. My only solution was actually to cut the red wire, and to leave some length of it in the terminal, rendering the rest of the switch useless, even if it was to be reassembled – ever.
What this meant, was that the plastic screw-on caps, with the little springs inside, that are normally excellent for this sort of thing, were useless to me, because nowhere did I obtain 3 free leads facing in one direction, to twist together mechanically. All I could do, was to entwine the red (load) wire with the bare section of the black (supply) wire a little bit, and then rely on my soldering job 100% to hold everything together.
Then, I had to apply several layers of professional-grade electrical tape, to prevent this blob of metal from shorting against the inside switch housing.
When we apply any soldering job, a detail which most inexperienced people may not know, is that we never really apply the solder to the tip of the soldering iron or gun. We always use the soldering tip, to heat up the copper wires or terminal, until the copper itself becomes hot enough to melt the solder. If we neglect to do that, liquid solder will fail to bond to the colder parts of the copper, will bead instead, and will yield a faulty connection which we will hear bad news from…
It comes as a secondary fact, that we actually cannot avoid the liquid solder additionally touching the tip of the soldering iron or gun.
The fact that I had chosen the higher-melting solder worked both for and against me in certain ways;
- I needed to heat both wires to an exceptionally high temperature, so that the silversod-like mixture would melt against them.
- If the bonding is good along the available length of bare copper, the fact that this solder is more similar to silversod means, that it will also be less likely to break down later due to mechanical stress, or to overheat as a result of heavy current…
I could not have pulled this off without:
- My high-powered soldering gun.
- My wire-stripper.
- Diagonal pliers.
- Quality electrical tape.
Now the only thing left to do, is wait and see if mechanical fatigue sets in, and if not, put a new faceplate on the former switch-box.
- Oh yes. I needed to inspect the joint with a magnifying lens – and not theatrically – to make sure that the bond between the solder and both wires extended along the bare length. With my naked eyes, I could not have been able to distinguish. According to what I saw with the magnifying lens, the two wires are indeed bonded along the entire bared length, of the one wire.
(Edit 12/02/2016 : ) Certain countries, such as Germany, have gone beyond banning aluminum wire, to banning solid copper wire, thus only allowing braided copper wiring.
In the case of aluminum wire, I think that one existing problem was, fractures.
But solid copper wire also has its issues, the main one being, that when two solid bodies come into contact, they often only do so at one point, or at three points defining a plane. This same fact is true, if one of the solid bodies is a wire.
Thus, those screw-on caps work well if we are twisting together two braided leads, but when twisting together two solid leads, again contact only takes place along very small surfaces. The tiny little spring inside these caps exerts very little force, compared with what 12-gauge wire withstands.
The idea when using screw-terminals, is that we should tighten the screws enough, actually to compress the loop of copper wire, so that contact takes place along the length of the free lead, and not at a few points. In this regard, screw-terminals work well.
Yet, with those plastic electrical caps, an additional problem I would have faced, would have been twisting together 3 leads instead of 2, while the diameter of the little spring inside was calculated for 2 leads…