The wire-solder interface should be
completely isolated from the air, hence preventing corrosion.
Yes it SHOULD be. I saw a lot of this type of corrosion in my 7 years in US
Naval Aviation. Some of it was structural and it corroded from the inside
out! When the corrosion started to become visible on the exterior of the
metal, the inside was found to be completely shot. I can't remember for
sure, but I think that dissimilar metal corrosion maybe don't need air. Or
was it that some oxidizers are trapped during the forming process? Help?
Also, if what you say is the case, then
why is solder used for high current wiring in some applications (12v power
supply cords, etc.)?
It works just fine for a while....
It seems to me that this would actually
be MORE prone to corrosion
I personally have seen a number of wire screw terminal (on 5V and 12V
applications) that rusted right through at the contact point. I don't think
these can possibly be very long lived. I would guess that regulatory laws
re: their use may be more related to relatives of legislators who make them
than valid safety arguments. They ARE the best for ensuring a good, strong,
won't-work-free connection, for a while; but house wiring should last for a
long time...
But, isn't the metal inside the twist
cap something other than copper? If so,how do they avoid dissimilar
metals?
1. The cap insert to wire contact may corrode, but the connection between
the wires (as they are pressed together) does not.
2. Twisting the cap sufficiently (as per usage direction) also twists the
wires together so if all else fails, you still have a (poor) mechanical
connection between the wires, and the plastic part of the cap insulating it.
3. Since the wires are twisted together, if they get hot enough, they will
weld to other together (I've seen this) and the plastic cap will melt at a
much lower temp than the solder so its not much of a fire hazard. You still
get a nice fire if the junction is setting near a flammable object though!
That why hi temp junction boxes and "goof rings" around the hole in the
paneling are required now.
3. Recently all the screw caps I have seen have been completely plastic,
including the interior threads. IMHO this type of screw cap, combined with
electrical tape (as Mark suggested) or a blob of SRS in the bottom of the
cap around the wires is the overall best solution.
James Newton, webmaster http://get.to/techref
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mailto:jamesnewton@geocities.com
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