I have an example where an Electrical Contractor wired Modbus and other low voltage comms systems as a "home run" style and then when told the bus portion of the job was an incorrect way to assemble a bus topology, they proceeded to splice the wires back together, solder the splices, and then also add wire nuts to the same splices.
(As an aside, the same contractor also ran the shielded 18-2 wires thru pre-existing conduit and junction boxes which also contained various unrelated line votage circuits).
I'm aware under NEC article 300 there isn't technically a problem as the low volt wire is rated to 300 volts and the maximun applied voltage in the shared conduit is either 120, 240, or 277 depending on the building and example (multiple buildings). I am also aware that under articles 725 and 800 it is pretty clear the wires should not be combined in shared conduit.
It's also pretty clear from a signal noise point of view its just plain wrong. IEEE / TIA and other standards and best practices for insturmentation jobs don't seem like rocket science to me.
I've been studying NEC2005, and apparently NEC2002 may have been in effect at the time of the work. I'm told they are more or less the same in the areas of interest, but I also need to know where they may differ.
In numerous observed examples, the wire nuts fall out when opening the junction boxess for inspection, and in some cases the wire splices were found to be snapped when the wire nut was applied.
Question is, where in the NEC Code should I look to pin down the issues with the solder joints being not code compliant?
Thanks guys. I just got back from the local Law Library (my source for reference of these codes, short of buying them).
It appears after reviewing both the 2002NEC and 2005NEC, there is very little to mention about the solder issue except what's mentioned in the above comments RE the "mechnically joined" and being "insulated equivalent to..." criteria. There is no mention of whether a wire nut is or is not considered "identified for the purpose of use" as also mentioned, and I suppose a wire nut counts as insulation referencing 110.14 opening paragraph and section (B) splices.
The section seems to be more concerned with the issues of dissimilar metals such as copper and aluminum, which is understandable given the nature of potential connection failures.
I suppose twisting 18-2 standed wire counts as "mechancially joined" in this context.
Any other ideas or suggestions?
#186644 - 05/22/0904:02 PMRe: Question about NEC Code and Solder for connections
Twisted tight and soldered is fine and a wirenut is adequate insulation so you are good to go. It is a whole lot more than most low voltage guys do. I see twisted and a dab of tape as often as anything (landscape guys), little blue wirenuts if they have them handy (HVAC and gate guys). These days most datacom is on punch blocks of some kind. Nobody solders.
#186645 - 05/22/0904:04 PMRe: Question about NEC Code and Solder for connections