Blue wiring

Inspected a condo built in 1972 today. The light switch had only 2 blue wires. No ground. What type of wiring is this and what are the troubles with it.


More than likely the reason no ground is visible is because there is a conduit system and the conduit itself is providing the ground. When conduit is used, wires of many colors can be pulled. While I am surprised they are both the same color (usually the switch leg has an alternate color), there should be no issues at all.

The light switches in my place are yellow (sw. leg) and blue (power). The reason for the blue is likely that the power comes from a 3ph service and that circuit happens to be on the “blue” leg. The apartment may have full 3ph service or much more likely, 2 legs (1ph) from a 3 phase service.

Usually in 3 phase wire the conductor color is kept consistent with the leg of power that it comes from. For example my apartment has either black or blue hot wires, and no red, because I don’t get the red phase.

No problems I can think of with this approach; it is very common in high rise buildings.

Thank you. That was a new one for me. You guys are the best.

It also should have had metal box for switch. Probably THHN wiring. Was it solid, or stranded. Color doesn’t matter necessarily. There was probably a light in the ceiling where the circuit come into the box, and the 2 blues went to the switch. Doesn’t matter which one brings power, or which is the switch leg. In strict commercial applications it may though.