Does coating stranded copper wire with solder and then connecting it to
a standard outlet cause any issues or break any codes?
I have a small project I put together (this is all inside of a big box
... ie: not inside a wall or part of the house ... but I still would
like to make sure it's safe and meets any code requirements as if it
was inside a wall or part of the house) which uses stranded copper wire
(14AWG). I coated the ends with solder and then bend them to shape
before connecting them to standard outlets (screwed on, not the push
in). Will this cause any problems or break any electrical codes (I'm
located in Ontario, Canada in case that matters).
The reason why I'm asking is because I've been doing a whole bunch of
reading about issues with aluminum wire, one of the issues being the
thermal expansion problems caused by the aluminum wire expanding at a
different rate than the screw connector it's connected to on an
outlet/switch/etc. So this made me wonder if the solder will cause any
problems with thermal expansion of it being different than the screw
that it's screwed on to, etc.?
Thanks for any info you share,
back before the advent of 'solid state' and 'Printed circuit boards' all
electronics, even high power devices, used copper wires that were 'tinned'
with solder before being attached to screw terminal strips.
it was the 'professional way of doing it.
as an electronics guy, I still 'tin' all wires I'm going to be soldering.
"tinning" means putting a coating of heated solder over the bare wire PRIOR
to making the final solder connection.
A "tinned" wire that is done that way by the manufacturer is
different than tinning wires at your bench or via a solder pot.
For one thing, the manufactured tinned wire has no lead in the
PLATING (co-valent), and said plating is very uniform and very thin.
A tinned wire at the bench has lead in it, IS susceptible to solder
creep, and the process is intermetallic, but only when done right.
Placing said wire in a PCB, the proper way to prep the wire is the
way you describe. For it to be pre-tinned as it is called. The MAIN
reason is so that one can construct the PCB / wire / solder joint
connection in the fastest time frame, reducing the likelihood for
insulation damage to a minimum. It also increases the odds of
constructing a proper solder joint with the highest reliability and
least amount of leeching of the solder up the wire, in the case of
The discussion, however, is about whether or not a wire inserted
into a crimp type solderless connector should be soldered, and whether
or not such a termination preparation is an accepted practice by the
industry engineers and manufacturers, not necessarily at the assembler
or inspector level.
The only prohibition is against a connection that depends on the solder; you
could not solder the wire to the outlet because the screw fell off. Using
solder for convenience, as you have, is fine.
I usually crimp fittings on stranded wire.
Now, your box project is suspect; but you didn't ask about that.
You should not solder stranded wire prior to putting it into
a screw terminal. Solder creeps under pressure, so the contact
pressure will steadily reduce over time until it forms a bad
contact. Strands which are tinned during the cable manufacture
are OK, as the solder layer thickness is controlled and very thin.
I'm not familiar with your local regulations, but in cases of
stranded wire connecting to terminations which don't work well
with stranded wire, the normal method is to crimp on a bootlace
ferrule or an eyelet, depending on the terminal style.
Andrew Gabriel ( firstname.lastname@example.org) said...
The only place I ever use stranded wire with screw terminals is in
a lamp, and I have on occasion tinned the end first.
I find the creep problem very bad and screws and stranded wire are
a bad mix. I have had a few instances where #14 or #12 stranded wire
was pulled through a conduit, so instead of trying to attach it to
a screw terminal, I would pigtail a short piece of solid wire to it
and attach it to the terminal.
That reminds me of a lecture I once attended. The speaker was telling
of an experience with a company he was working with back in the 1960s
when they got a project related to the space program. They all had to
be "schooled" in procedures such as soldering, which seemed beneath them
at the time.
The thing that stuck out in my mind was part of NASA's standards: when a
stranded wire was tinned or soldered to a terminal, you should still be
able to count how many strands it has.
"Never ascribe to malice what can equally be explained by incompetence."
Reminds me of ET-Maintenance school in the military. Spent literally a
*week* learning/practicing on just how to solder to bi-furcated and turret
We too had to be able to count the strands after tinning. And how much
insulation to strip off so that no more than 2 mm of conductor was exposed
after attaching to terminal. And no melted insulation, and... and... and...
There was something like 14 checks for each soldered terminal connection.
Was bad enough on the bench, but then doing it laying on your back reaching
up inside a cabinet with just a drop-light to see by. Now *that* was fun
Is there any reason to consider tinning the ends when fixing through a screw
terminal? The surface area of contact would be increased at the contact I
suppose, and thereby increase the area of contact for the passage of
electrons, but the cables should never be used *at capacity*. Next thought
is on how the crimped terminals of the wires lose area of contact for
passage of electrons and hence the heat evolved on the lines at the
terminal(s) increases as a proportion borne on each line. Hence
consideration would lead me to increase cable sizes and design cable sizes
for the terminals; the specifications being based upon the surface area made
at the fixing and the heat I would wish to allow there.
In a proper connection, the heat rise is only a few degrees more
than that produced in the conductor itself. If there is an excessive
differential between the heat in a conductor, and the heat generated
at a connection node, then the connection either has a problem, or is
not of a sufficient capacity for the current in the circuit.
: > Does coating stranded copper wire with solder and then
connecting it to
: > a standard outlet cause any issues or break any codes?
: > I have a small project I put together (this is all inside of
a big box
: > ... ie: not inside a wall or part of the house ... but I
: > like to make sure it's safe and meets any code requirements
as if it
: > was inside a wall or part of the house) which uses stranded
: > (14AWG). I coated the ends with solder and then bend them to
: > before connecting them to standard outlets (screwed on, not
: > in). Will this cause any problems or break any electrical
: > located in Ontario, Canada in case that matters).
: > The reason why I'm asking is because I've been doing a whole
: > reading about issues with aluminum wire, one of the issues
: > thermal expansion problems caused by the aluminum wire
expanding at a
: > different rate than the screw connector it's connected to on
: > outlet/switch/etc. So this made me wonder if the solder will
: > problems with thermal expansion of it being different than
: > that it's screwed on to, etc.?
: You should not solder stranded wire prior to putting it into
: a screw terminal. Solder creeps under pressure, so the contact
: pressure will steadily reduce over time until it forms a bad
: contact. Strands which are tinned during the cable manufacture
: are OK, as the solder layer thickness is controlled and very
: I'm not familiar with your local regulations, but in cases of
: stranded wire connecting to terminations which don't work well
: with stranded wire, the normal method is to crimp on a bootlace
: ferrule or an eyelet, depending on the terminal style.
: Andrew Gabriel
I know that, at least on Ottawa, and I imagine most places, you
cannot tin wires to be used where an electrical inspecation is
necessary. Same in the states. No, I cannot cite NEC, so no
The reasons are exactly as Andrew pointed out. Solder
compresses and deforms to whatever force is applied to it and as
soon as air creeps in, there is corrosion, moisture, etc etc
etc., not to mention the affects of vibrations, etc..
How do I know? I got to see a connection that failed, then
started to heat (high currents) and the solder dripped out of the
connection onto the wireing below it. No, it's not a horror
story, but the melted solder wasn't too cute inside the box.
Whoever installed it didn't know the first thing about tinning,
besides it not being acceptable to do; he had the wiring well
"blobbed" with sodler<g>.
I think I understand why you want to tin it, but properly
dressed stranded wire will work perfectly under appropriate screw
heads. If it's a permanent install, I'd modify it accordingly,
again along the lines of Andrew's suggestions. He's right on.
I like a mechanical crimp to a terminal, but then followed up by soldering
My father used crimped connections on all his wiring on his house, then
soldered and taped (no wire nuts, was done in 1970) All still works
great. At time when having to replace an outlet or light switch,
everthing was still pretty solid, but do intend on doing a preety
thorough inspection soon including junction boxes in the attic.
I am in the industrial controls business and work with
stranded wire extensively, especially finely stranded wire in
challenging environments. It is almost pervasively common
that manufacturers supply equipment with the wire ends dipped
in solder, I have never seen those loosen to any degree more
than non soldered ends,
the soldered ends seem to be much more reliable and preferred.
Thats after 40 years in the business across a broad spectrum
of industrial applications, nuclear, petrochemical,
semiconductor, food and marine applications.... including DDC
Crimp connectors also work. they are less reliable than
factory or field soldered ends under a screw in marine or
industrial corrosive environments however.
The code says you can't make a connection that depends entirely on solder.
It has to be a compression connection. Screws, bolting, clamping crimping
etc. It's O.K. to solder after it's tight. I have heard of failed
inspections because someone tinned stranded wire, then secured it in a
solderless lug. The reasoning being that if it gets hot, the solder flows
out, and it is then loose.That may be debatable, but I lean toward agreement
The NEC says "electrically and mechanically secure". My understanding is
that solid wires can stil be twisted then soldered as was the practice
before wirenuts appeared.
If tightly twisted wire was minimally tinned I would think the solder
would hold the strands in place and the stress of clamping would be
borne almost entirely by the copper. Do you still get cold flow?
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