Agency Approvals & Self Certifications UL Listed, UL 486D Standard, File E102356 CSA Certification, File LR86335 Voltage Rating 600 V Direct burial and Submersible For use with Listed, Crimp-type, Splice Connectors All other product claims are made by 3M and not covered by the UL Listing
Also, not that i believe you wouldn't be able to direct burial this splice but my thoughts on the application are in instances where you would use a compression butt splice, or maybe a junction block, all inside enclosures.Thanks for the point on the insulation though, I've only exothermic welded grounding and bonding conductors but i don't remember any kind of damage to the local insulation, definitely gonna look closer next time.
Yes, if done properly twisting is a type of cold weld and very reliable but even back in the day not everyone managed to get that right. The same technique was used extensively in Japanese audio equipment back in the 60s and 70s, it's known as "wire wrap" in that field. In audio it was typically used to connect wires to a post soldered into a PCB rather than joining wires but the physics are the same.
The worst splice method I've personally encountered is looping several small wires around an M3 screw with nut and washer, tightening the screw and taping the whole lot. It was tremendously popular from the early days of electricity into the early 1960s in Austria and these splices fail by the dozen! I've never been to a place with that type of splice that didn't have at least a few loose ones! My first experience with them was pulling a few splices from a box just to get an idea of what goes where, then turning the circuit back on, only to hear a highly ominous crackle and fizzle from that box! Just moving the splices had loosened the connection enough to make it arc! Needless to say I always disconnected all power when leaving from that point until the full rewire was completed!
Wire wrap was also used in industrial equipment of the day. When I worked at GE I 'fondly' recall making up control systems for VFDs using the wire wrap method. I even have my old wire wrap tool in my box of mementoes...along with my slide rule and drafting triangles.
Wire wrap depends on the sharp edges of the pins biting into the wire as you wrap it. That is not like simply twisting 2 round conductors together. As for the shrink tube, I still wonder how many of the characteristics of the wire insulation are "equivalent to that of the conductors". What is the temperature rating? 60c? 75c? 90c?
1.3 These requirements apply to sealed wire connector systems intended for use with 30 AWG (0.05 mm2) through 2,000 kcmil (1,012 mm2) conductors with currents not exceeding the ampacity of insulated conductors rated either 75°C (167°F) or 90°C (194°F) and intended for use at 1500 V or less.
I know there is some junk shrink tubing out there, but your statement has me curious because not that i work with a lot of hard line standard followers but i have never heard of a problem code wise or in practicality of using shrink tubing for splices. have you heard of problems either standard wise or in actual use? /inspector issues? do you think it is a poor application?