electricalwiring
I found this mystery wire while changing out a plug In my home. It doesn't look like anything I've ever seen. I can't identify it by memory or google. I'm curious what it is commonly used for. Was it ever acceptable as house wiring in the United states?
Almost every thermostat installation manual I've read always says something along the lines of "Make sure to mark you wires based on the currently connected thermostat. Do not rely on the wire coloring".
The colors are really just a guideline, there is no requirement to adhere to them.
Looking at the controller board of your furnace should confirm how they are connected. It's possible that the blue wire isn't even connected to anything on the furnace side. Perhaps the furnace was replaced at some point and the thermostat wasn't re-wired.
It's not uncommon to not have a C wire as older thermostats were either unpowered or powered by batteries. New thermostats (especially the ones with LCD screens, Wifi, etc.) have larger power requirements and rely on the C wire to provide a return path for power coming from the R terminal.
In the 2011 version of the National Electrical Code, there was Table 310.15(B)(7). This table was quite handy for determining the service conductor size. In the 2014 version, it looks like they've done away with this table. However, the long code trail that has replaced it, seems to basically say the same thing.
National Electrical Code 2011
Article 310 - Conductors for General Wiring
II. Installation
Typical services (in the US) are 100, 150, or 200 ampere (though 60 is common for older dwellings). Which means you'll be dealing with a possible range from 4 AWG copper to 2/0 copper (2 AWG al to 4/0 al). Which means you'll want a device that can accommodate conductors from about 0.3 in. diameter to about 0.7 in. diameter, if you want to cover the whole spectrum of possibilities.
Best Answer
The wire turned out to be a cable with three conductors. The insulation was melted almost 3/8ths of inch up under the white sheath. the receptacle was indeed spliced 6 inches inside the wall. I removed the spliced section and remounted the box at 40 inches for ADA compliance. Thanks to everyone who participated.