394.56 Splices and Taps.
Splices shall be soldered unless approved splicing devices are used. In-line or strain splices shall not be used.
That counts out butt splices, or Wago type connectors....
This is a little
article about crimp failures in appliances , but for this type of crimp connector used in a wall, the results would be about the same = not 100% reliable, and dangerous IMO. Sure you are allowed, and in a few situations required to have irreversable connections in a few locations like in grounding, but those connections and conductors are much large, and to be done right require tons of pressure to mash the connector and wire together. I haven't seen any made well enough to trust in the wall of a home for wire sizes 14-10. Most are made for automotive and appliance purposes.
Some places/inspectors would allow you to use a wire-nut type connector. Others wont... But they too have moderate failure rates, and methods of failure (arching) that would make me think twice of using one concealed inside a wall. As it would be inaccessible behind a finish. If I use one on K&T, it'll be in a box...
But mechanical splices done right, with
clean metal to metal contact, and sealed in solder, and cleaned again, have been able to last without abuse or failure for over one hundred years! The only times I have seen ones that have failed, failed for reasons: dirty conductors, poorly or unsoldered connections, left over flux, or long term over-load of the circuit.
You can find more of my opinion on the matter here:
http://www.markhellerelectric.com/wusplice.pdf Some more here:
https://www.electrical-contractor.net/ubb/Forum1/HTML/007216.html Do a search in the general discussion area and you'll find many more.
[This message has been edited by e57 (edited 10-22-2006).]