I bet that the 40V measurement is likely a "ghost voltage," which is a misleading reading that can show up as a side effect of using a digital voltmeter on a dead wire. The misleading measurement happens because there is capacitive coupling when you have an un-energized wire running next to an energized one. The impedance of the voltmeter itself causes the high voltage to register, though the current it is capable of delivering would be miniscule. In this case, it would be from the switched wire running next to the hot wire.
To determine whether or not the voltage is actually present and being fed from a true voltage source, rather than being a misleading reading of an induced voltage from an adjacent wire, you need a low-impedance voltmeter. Fluke makes several.
Given that this is the only time I am likely ever going to need this test, I'm not going to purchase a dedicated low-impedance tester. Instead of doing that I'm going to do a few brute-force tests.
We're going to start with the assumption that the red wire is likely connected to nothing other than the outlet. Today, when the switch is closed, it sends connects the black wire to the red one and sends hot down the red wire.
As far as we know, no other devices are connected to this switch. If we shut off the circuit breaker, connect both ends of the red wire to ground, then turn it back on, the circuit breaker shouldn't trip. If this is the case, measure the current from the red wire to ground on each side, and from the red wire to neutral and hot. There shouldn't be any current flowing into or out of a dead wire, period.
Obviously, this was done at my own risk. Current to ground came up with .001 mA. Tied the red wire to neutral at the outlet, connected the smart switch, and works like a charm.
I concur with your guesses. (I must say I've never seen anyone conduct a circuit discrimination by manipulating the neutral wires!) The cable with [2,7] supplies power to everything else.
Questionwise:
If the white bundle were ground, where would the neutral be? It looks like you have no fault ground available in that junction box.
There's no fault ground now, so installing the switch without using the fault ground terminal will not make things worse.
Since you can't provide fault grounding without rewiring the apartment, consider replacing the outlet (or all the outlets) with GFCI-protected outlets. They usually come with a "No Equipment Ground" sticky label, which you would use. But that may be a project for another time.
Uncouple the white bundle and use a wire nut to tie them together, including a short pigtail to the neutral connection on the GE 12724.
Yes, you should. Use a wire nut to tie together the line hot, the load to the outlet, and a pigtail to the line terminal of each switch. Don't leave any connections just wrapped in tape; that's very unsafe.
How deep is the junction box? You want to know if you're exceeding the volume capacity of the box.
You have 8 conductors entering the box, and two device yokes which count as 2 conductors each. You have no internal clamps, no support hardware, and no ground screw, so your total conductor count is 12. If you wires are 12-guage, as they appear to be, each conductor requires 2.25 cubic inches. This gives a total requirement of 27 cubic inches.
You can find the capacity of the box with a ruler; just multiply width X height X depth. Two-gang boxes are typically about 4" square, so at 2.5" deep the capacity would be 40 cubic inches. Even if your box is a little smaller, if it's 3.75" X 3.75" X 2.25" that's still big enough at 31.6 cubic inches.
- Yes, strictly speaking, it's bad. Electricians really do not like to put outlets and lights on the same circuit. Perhaps a licensed electrician will chime in here and tell us what the NEC has to say about this.
Best Answer
You may only use wire which is legal for wiring in your country (I am presuming USA and thus National Electrical Code). The NEC allows many types of wire, but as a practical thing, it boils down to two types: Multi-conductor cable, typically NM aka Romex; and single-conductor wire used in conduit, typically THWN.
You are dealing with solid wire, which is stiff. For a much more flexible wire, stranded wire is available. However, Romex is not available in stranded. Each of your devices must be rated for the strandedness of your wire. (for instance "back stab" connections found on very cheap components are rated for solid wire only).
Neutral must be in the same multi-conductor cable, or the same conduit/raceway, as the other conductors. You cannot retrofit a neutral to a multi-conductor cable.
If those boxes are connected by conduit, then each of the wires is a single conductor. You can simply pull (or shove) an additional neutral wire through the conduit.
If those boxes are connected by flexible cable, then you will need to pull an entire, additional multiconductor cable between the two boxes. You have two ways to go.
- Pull a 12/3 or 14/3 cable to replace the existing cable. This will include hot, switched hot, and neutral.
- Pull an additional 12/2 or 14/2 cable alongside the existing cable. Cable A will carry always-hot and neutral for the switch and lamp. Cable B will carry switched-hot and neutral for the lamp. This means when the switch is on, neutral will make a seemingly redundant round-trip between the boxes. This is required by Code, and for good reason.
You don't need a plumbing snake. They make "fishing tape" specifically for electricians, used for a variety of hat-tricks to route flexible cable through existing finished work in residences. Generally in commercial work, everything is in metallic conduit, so any conduit they plan to use must be installed before walls are finished.
If you are starting into electrical work and plan to stay awhile, I'd encourage you early to get acquainted with your local Electrical Supply House. This is the sort of place that's open from 7am to 6pm and at 7am, the parking lot is full of electricians' trucks. Electricians are smart people and are perfectly capable of finding the local Home Depot; they buy from electrical supply houses because the pricing is roughly equal and the support and selection is a LOT better.