Should I use solid or stranded 14 AWG wire in conduit for lighting?
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The last time I used 14 gauge wire in lighting, I was installing runway lights. Can you be a bit more specific about what you want to use it for and where? Not just the rules, but also the grid voltage varies in different countries, validating some arguments in some places, while making them irrelevant. elsewhere.– user136947Commented Feb 12, 2022 at 12:22
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1I would not say it’s an opinion. the industry standard is stranded in conduit. Why just try to pull solid not only as it doesn't uncoil as easy and going around bends it tougher. Stranded is much easier and well there is no solid wire above 10Awg. So stranded is not an opinion it is an industry standard.– Ed BealCommented Apr 12, 2022 at 20:02
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5 Answers
Whichever you find more convenient.
It doesn't matter to the wires. Stranded is certainly more pleasant to work with, it pulls easier and is more resistant to kinking or snagging.
However, stranded wire is not allowed in "backstab" connections (which we strongly recommend you not use anyway). It is allowed on side screws but is quite a challenge to keep from unraveling and "birdcaging" when you tighten the screw - not allowed and you'd have to comb it out, re-twist and refine your technique. It works best on "screw-and-clamp" as found on spec-grade receptacles and switches, but those are more money.
However, it works absolutely great in wire-nuts and even better in Wago Lever-nuts. So you can always "pigtail" to screw terminals with solid wire. Extend the stranded wire a little bit taller when joining the wires, so they come out even when twisted.
answered Feb 10, 2022 at 6:45
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4For screw-and-clamp if you have stranded coming in you should use stranded for everything. Don’t mix stranded and solid in a single clamp (most clamps allow two wires) because the stranded will work its way out. If you want to transition, do it with a lever nut as described above for screw-only.– jay613Commented Feb 10, 2022 at 13:42
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Could you tin solder the ends of stranded #14 and #12? Commented Feb 10, 2022 at 18:12
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@Jim I suppose you could. Solder doesn't have nearly the conductivity of copper, but the proper screw torque is going to make the solder spread (more contact) and squish mostly out of the way. Commented Feb 10, 2022 at 19:36
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Whichever one you're competent in making the connections for; I hate working with stranded but the best splice and connection I've ever seen in my life was. The connections were done as if in-line; they stripped the insulation but didn't pull it all the way off which keeps the strands together. And there was 6" of completely twisted together wires, obviously done with a linesmen once the nut came off, which on a connection that well done, did little more than provide insulation.– MazuraCommented Feb 11, 2022 at 4:30
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How do I properly prepare stranded wire for a screw down connection?– MazuraCommented Feb 11, 2022 at 4:32
You should check your local code.
Problem with stranded wire in screw connections is that the screw will usually not clamp the whole wire, only whatever strands it happens to catch, which makes a worse connection. Also stranded wire is much more flexible (that's the point) so sometimes it can wiggle out, leaving only a few strands to make contact, which means high resistance and therefore localized overheating and fire.
Best connectors are Wago 221.
If you use stranded, I would strongly recommend getting an hexagonal crimper (about €20 off the internet):
And some non-isolated crimp ferrules:
These are very easy to apply and you get a neat termination on your wire, without any stray strands making a mess. That works wonders with any type of termination that uses screws. It will also work with backstabs, but only the ones with a lever to open the jaws. If there is no lever to open the jaws, you won't be able to insert it, and even if you do, you'll never be able to pull it out if needed.
Also available with insulation (below) but I find these less useful because the extra thickness gets in the way when trying to fit two wires in the same screw terminal.
Note
Being French I am specifically referring to euro-style screw terminals where the tip of the screw squeezes the wire directly. These have fallen out of fashion due to unreliability, especially with stranded wires. They've been obsoleted by wagos. Also there is no way to look into the thing to make sure it is properly connected, and mixing solid with stranded in the same hole is a recipe for disaster. These terminals used to be common in sockets, with the same problems. Pic source.
The terminals where the screw uses a washer to squeeze the wire have much less problems. Code still mandates a ferrule, though.
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2This answer seems to have a somewhat Euopean perspective, while the asker appearsto be American. Americans don't tend to use the types of terminals where ferrules are appropriate much. Also ferrules are really designed for fine stranded flexible conductors, so using them on coarse-stranded conduit wires is somewhat controversial. Commented Feb 10, 2022 at 15:48
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If the wire squishes out under a screw connection, and less than all wires make contact, that is incompetent installation and must be re-done. An installer who declares this to be the normal state of affairs has a falsely high self-opinion, effectively "blaming the equipment" and refusing to refine their technique. If the screw wiggles out, that is a torque setting problem, which causes bad connections, and is why North America now requires torque drivers. Spec torques are rather higher than you'd expect. Commented Feb 10, 2022 at 16:37
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2TBF, this answer does start with "You should check your local code". This probably does not apply to the US, while it does apply to many (most? all?) places in the EU.– FreeManCommented Feb 10, 2022 at 17:20
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So is it the case that most local electrical permitting authorities in the US don't allow these ferrules? Can these be used to terminate aluminum, either solid or stranded? I have stranded aluminum for a clothes dryer (30 A breaker) and electric range (50 A breaker). Commented Feb 10, 2022 at 18:24
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1Not just European, for all the internet only electricians many industrial panels have ferrules and are required by FM without insurance doors would close, why not use solid ? It tends to break at the insulation strip point even if the wire was not nicked. Stranded in a ferrule no problem.– Ed BealCommented Apr 12, 2022 at 20:16
Stranded: it's easier to pull, easier to remove, does not break if bent. Here (Italy) you can't even find solid wire on the market since, I think at least 30 years (the only exception is telecommunication wire)
Also many electricians tend to replace it when found (understandably, given it's 40years old or more) even if it's still in safe conditions.
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So in Italy do they use ferrules to terminate the stranded wire or do they clamp the stranded wire ends as is? Commented Feb 10, 2022 at 18:43
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It depends on the fitting: if it's designed for stranded often usually it is connected as is, ferrules are used if the connection requires it and sometimes just to keep the wiring better-looking.– DDSCommented Feb 11, 2022 at 11:06
Stranded is flexible, solid is not; It does not need to be flexible in conduit so stranded is not necessary. Stranded is used for appliances, extension cords, etc, where flexibility is needed. The finer the wire, the more flexible. Welding cables have (many) fine wires to make them more flexible for the operators comfort.
answered Feb 10, 2022 at 15:46
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The flexibility isn't needed in conduit, but it does make pulling easier.– FreeManCommented Feb 10, 2022 at 16:16
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I have never seen an oven element connected with solid wire, no flexibility there but as far as I know high temp fixture wire only comes in stranded.– Ed BealCommented Apr 12, 2022 at 20:08
Electric connections design has suffered massively under the stress of economy over the years, making them minimalistically engineered calculation designed components, rather than the reliably dimensioned product of hands-on practice. Properly screwed in wire connections demand forcing the wire out of shape, which is harder to do on solid wire than on stranded wire. That is why in lamps stranded wire is to be preferred over solid wire. The screw connections in modern lamps, more often than not, simply can't handle the required force.
The way I learned to prepare for and execute stranded wire screw connections some fifty years ago, goes as follows:
Turn up the screw so it no longer obstructs any part of the wire hole.
Strip the wire to twice the length of the depth of the hole.
Twist the strands to form a single firm cable.
Bend the cable until the top half points backwards towards the isolation and squeeze it to a sharp tight turn.
Slide the cable turn into the hole without deforming it at all, until no more blank metal is visible.
Tighten the screw as tight as the connection allows and Bob's your uncle.
I frequently lift my hand tools by the cable. I pull straight plugs out of wall sockets by the cable. I even whip them out if necessary, but I have never had a screwed-in stranded wire connection fail on me. Then again, I don't go for cheap, I don't go for easy and I don't go for fast.