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Stranded wire & circuit breakers

canon's picture

Is there a guideline as to the preferred way to connect stranded (#10) wire to a circuit breaker? The breakers in my box have a lug screw that squeezes the wire, and this is great for solid however, stranded wire squishes out a bit. Is this OK? Would it work to solder the strands solid and then attach the bonded wire? How about a short solid pigtail attached to the stranded with a wire nut? This is the kind of thing you don't find in a book so I'm hoping for some divine enlightenment. Thanks


Edited 4/9/2006 5:04 pm ET by canon

(post #71397, reply #1 of 43)

Forget the pigtail in this app. I would opt for exposing 1/2 inch of stranded, solder the exposed wire and insert into breaker. Make absolutly sure the gauge of the wire is sufficient to carry the breaker load. Fifteen amp use 14 gauge or larger , 20 amp use use 12 gauge or larger. Actually, the stranded 12 gauge should carry more current then solid 12 gauge but stay with the above gauges and amp rating and you should be ok. Ten gauge wire your using sounds plenty healthy enough for the small breakers mentioned above. You must be working with 30 amp breaker but the same idea applies. Make sure not to overload the wire. Overload the breaker but not the wire.

Don't be a clown and insert more than one wire in each breaker. I've seen some people do this and it's asking for trouble.

(post #71397, reply #3 of 43)

Actually, the stranded 12 gauge should carry more current then solid 12 gauge


care to explaing that? (other than stranded is typically THHN or better)


 

(post #71397, reply #7 of 43)

It's something of a fiction. At high frequencies all the "juice" is carried in just the "skin" of the wire -- it can be hollow and carry the same current. But the high frequencies we're talking about here are in the GHz range -- not 60Hz.


If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #71397, reply #8 of 43)

Junkhound has got the idea... more surface area when considering multiple wires and current runs around the outside of the wire.

(post #71397, reply #12 of 43)

Just to clarify for some that may get the impression (from your and Dan's post) that stranding help skin effect in 12 AWG stranded, Litz wire needs to have the individual strands insulated to counter skin effect. Beleive that at skin effect frequencies the impedance of 19 strand 12 AWG is actually slightly higher than solid due to proximity effects also.  EDIT PS: Bill beat me to it.


Edited 4/9/2006 9:55 pm ET by junkhound

(post #71397, reply #4 of 43)

Thank you. I am quite conservitive about things like this as I don't want any trouble. The solder technique sounds like a winner to me. Thanks again. Bob

(post #71397, reply #13 of 43)

Is it possible for the soldered strands to heat up and defofm after time to create a loose connection?


TRIGGER

(post #71397, reply #20 of 43)

If you tighten the connection screw in the breaker it shouldn't create any heating at all. On the other hand, any loose connection or dirty connection increases resistance heating and then you have problems. So, if it's clean and tight then no problem.

(post #71397, reply #33 of 43)

It seems that the latest (and slow in arriving) consensus agrees with your  very early assessment.


 Congrats.

(post #71397, reply #34 of 43)

On the other hand, the typical lighting/wall outlet circuit only occasionally sees loads beyond about 1/4 of circuit capacity. The thermal/electrical stresses involved are not likely to result in any of the failures discussed above. You're far more likely to see a failure in an overheated overhead light fixture, due to oversized bulbs.


If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #71397, reply #38 of 43)

I was thinking something along the same lines, Dan. I wouldn't want to condemn all soldered joints after  all the Heathkit stuff I've built over the years! . When I think about it more I realize that  those circuits were not heavily loaded, much like a lighting circuit as you suggest.


The catastrophic failure I have experience with was just the opposite, a heavily loaded industrial application.


I like the idea of a crimped/swaged  ferrule, although after reading John's dissertation I would now think Copper would be a better choice of material than the Aluminum that was  suggested earlier.


The most compelling reason was from Riverman, IIRC. NOT CODE APPROVED INSIDE A PANEL BOX


 


Edited 4/13/2006 9:29 pm ET by STAINLESS

(post #71397, reply #42 of 43)

Thank You!


It was nothing really.


TRIGGER

Stranded wire termination in breaker (post #71397, reply #43 of 43)

I stumbled across this 6 year old post and took the time to register just to repond.

"I would opt for exposing 1/2 inch of stranded, solder the exposed wire and insert into breaker."

 

This is right up there with double dumb.  The solder will crystalize under compression stress and form a weak connection which will get hot , melt remaing solder, get hotter and hotter and hotter the fine strands oxidize and it gets hotter and hotter, you get the drift.

Don't follow lame [JOBSITE WORD] advise on discussion boards when your family's safety is concerned.

 

(post #71397, reply #2 of 43)

twist the strands CCW with Kleins about five or six turns....that will tighten em up

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'Wer ist jetzt der Idiot?'

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(post #71397, reply #5 of 43)

Thank you.

(post #71397, reply #6 of 43)

welcome

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'Wer ist jetzt der Idiot?'

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(post #71397, reply #9 of 43)

I wish 4Lorn would hop in here and give you a full dissertation.


Usually you have 19 strands. You do not have to solder them. There are a couple of common terminals. On, like a grounding bar has a hole you stick the wire into. A screw intersects the hole. You tighten the screw and it squishes the wire in place, making the connection. Breakers usually have a little metal brass plate which is compressed by a screw. For some reason, the screw is the obsolete straight slotted type so it is hard to use a torque wrench on it. The plate often has two pressed in grooves on either side of the screw. I take this to indicate that it is permissible to have two wires to the breaker. There should be some permission printed in 3 point type somewhere on the breaker allowing this.


It is ok if the stranded wires get squashed a little bit. It is important to get all [19] strands in the hole -- that is no loose strands sticking out which could cause an unintentional short or shock. As to strip length, there may me a strip guage molded into the side of the breaker. Otherwise make a test and bottom the stripped wire in the hole and I like to leave about 1/16" of bare copper exposed to show that insulation is not trapped inside the connection.


As for the ampacity of stranded versus solid, the stranded wire is slightly larger in diameter than the solid to account for the air spaces between the strands. This is why you must use special strippers for stranded wire.


the breaked is the easy part of a stranded wire connection. What about the other end? My current practice [since we are too cheap to get the push in the back and tighten the screw type receptacles] is to cut the insulation with the strippers ~5/8" from the end and pull that piece off. Make a second cut of the insulation ~1/2" further on. Carefully pull this piece to the end of the wire and slightly beyond. This will hold the strands together. Then twist the strands counter-clockwise [opposite of the way they were]. You should have ~3/4" of bare wire and then the bit of insulation showing. Wrap the bare part around the clockwise and tighten.


If you can afford the time and expense, wrap the receptacle with a layer of black phase tape.


~Peter M of PM Electric

(post #71397, reply #11 of 43)

Actually for power wiring you don't get up to 19 strands until you hit AWG 1, at least according to the NEC tables. Now fixture wiring and other applications is different.

Everything smaller than #1 is 7 strand.

Now about the resistance, WOULD YOU BELIEVE (How can I do Get Smart in a written message) that stranded actually has more.

1.24 ohms/1000 ft for stranded vs 1.21 for solid #10.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #71397, reply #14 of 43)

Thanks for the great message. I have a Cutler Hammer service and use CH breakers. In the square D breaker, the screw bears down on a grooved plate to grip the wire that you mentioned, but in the CH breaker the screw itself actually presses on the wire. I think that the square D type is a better connecting method but not what I have. To be clear, all the wires are properly stripped and all the strands in the hole. The last post addresses the possibility of the soldered end piece working loose due to heating and cooling and causing a high resistance and a hot connection. It doesn't seem to me that it would be any more prone to this than a solid wire,if tightened securly upon installation. Is this correct? I knew that I was going to get some great advice and I appreciate everyones input. Thanks

(post #71397, reply #15 of 43)

The soldered wire would only be prone to the described problem if the initial connection wasn't solid. You need to use enough pressure to deform the wire significantly (but not enough to break it, of course).


If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #71397, reply #16 of 43)

Dan, Thats what I suspected and thanks for the confirmation. Bob

(post #71397, reply #18 of 43)

Oh, a Cutler Hammer panel. Well, I use these all the time, and you just twist the strands and put them in the hole and tighten the screw. Easier than the Square D plate. Square D users will have a diffent opinion! No need to solder. That went out with knob and tube wiring methods except for some odd repair work.

Frank DuVal

You can never make something foolproof because fools are so ingenious.

Frank DuVal

(post #71397, reply #19 of 43)

Frank, I really appreciate your input tonight as well as that from the others. You know the breakers I'm using and what works. Thanks

(post #71397, reply #10 of 43)

I have seen incidences where a small piece of thin wall aluminum tube is fitted to the end of the multi-stranded wire. It is then swaged and fitted into the breaker and held in place with the fixing screw. 

(post #71397, reply #17 of 43)

Thank You for the input. Bob

(post #71397, reply #21 of 43)

Although soldering the stranded seems like a good idea, I would advise against it.


As a service tech. for a machine tool co. about 18 years ago I remember a common failure that ocurred on a power supply for a 60 Amp Servo drive. The fuse blocks on numerous machines were burning up at the point where the conductors were entering the screw clamp connectors. The funny thing was that the fuses were not blowing! The conductors were stranded and (you guessed it ) were soldered into a solid wire by the manufacturer before tightening in the connectors.


 We went nuts trying to tighten the connections to prevent the failures until it was figured out that soldering the wire was the problem. Some engineer finally read the mfg. data on the fuse block which advised against soldering stranded conductors. I can't explain all the reasoning behind it, but I remember a term called THERMAL RATCHETING.


This is not my general condemnation of stranded conductors however, just a heads up to check with the breaker manufacturer as to what they suggest you do when installing their stuff.


Be safe.

(post #71397, reply #22 of 43)

Yeah, with solder there's a chance of "creep" as the solder cycles thermally and crystalizes, and this can allow the strands to move relative to each other and loosen. Plus the solder is a lot softer than the copper, once again allowing the strands to move relative to each other as the connection cycles thermally.

In practice I don't think this should be a major issue, IF the connection is tightened enough to essentially displace the solder and smash the copper a bit, but the theory is there.

A lot depends on the properties of the solder, of course, and that unfortunately a big variable. Not just the composition of the solder, but the soldering temp/time come into play. You can have what seems to be a perfectly good solder joint, yet it will come apart looking like a "cold solder joint" years later, due to thermally-driven crystalization.

I think a ferrule would probably be a better solution if one needs to control stray strands. However, I don't know of a source for appropriate ferrules.


If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #71397, reply #24 of 43)

like these ??????
http://www.panduit.com/search/search_results.asp?N=5000001+129&Ne=1&region=USA&Nu=P_RollupKey

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'Wer ist jetzt der Idiot?'

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(post #71397, reply #25 of 43)

Those appear to be crimp-on pin ends, not ferrules.


If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #71397, reply #26 of 43)

More like this:

http://www.panduit.com/search/product_details.asp?Ntt=ferrule&N=5000001+3001359+5000013&Nty=1&region=USA&Ntx=mode+matchallpartial&recName=F83%2D25%2DD&Ntk=All


If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville