Continuity Tester

[mc2software]

I'm trying to figure out a way to test continuity over a long distance with two ESP32s or ESP8266s (there's no wifi/bt involved, so either board with work and I have a bunch of both). This is not testing the continuity of the ESP circuit, but rather external circuits. The environment is a new garage and addition that I'm wiring. I want to test continuity for all the hot, neutral and ground wires between dozens of circuits and over 100 outlets, and I want to do this before line voltage is applied to the structures. My idea is to connect 2 ESPs to a 3-prong plugand by inserting the plug into two outlets, the ESP will show me (via 3 LEDs?) that there is continuity on the hot, neutral and ground. It should also test for any hot/ground/neutral shorts. The plan would be to power the ESPs with batteries. I have some ideas on how to create this, but was wondering if anyone has ever tried this or seen it done.

[jimmo]

Insert usual disclaimer here about messing with mains!! It would obviously be very dangerous to plug this into a hot socket.

My first thought would be to have the "transmitter" board send a very low bit rate unique pattern on the three pins. Simplest example would be just to do varying length pulses (e.g. 200ms, 400ms , 600ms). You could also use a low speed UART to send a unique message on each.
Then the receiver can do machine.time_pulse_us to measure this and see whether each pin has the expected pulse length (over a series of N samples).

[mc2software]

None of the lines are hot. No power connected as yet. Concern with UART is that I think you need two lines: RCV and TRX receive and transmit. This would require that I have confirmed ground line continuity. I'm trying to send a signal down one line and confirm reception at the other end. I'm trying to figure out how to test the lines before I go hot.

[jimmo]

None of the lines are hot.

That's what my friend said right before he was electrocuted. (He's fine though).

Concern with UART is that I think you need two lines: RCV and TRX receive and transmit.

No you can do UART in one direction. In which case one end transmits (TX) and the other end receives (RX).

What you _do_ need is a common ground though. (Either have an additional cable, or use the cable earth as the ground and then test active and neutral. if you've mismatched the ground then you'll get the wrong result still).

[mc2software]

There's no service line coming into the panel yet.

I was hoping to use UART to test the ground, since once I have that tested, I can use it to test continuity by putting a low voltage pulse on the hot. Can I have one board with TX on one port and another board with RX on one of its port? Do the two boards need to share a ground?

I have some runs that are over 50' long and about 50 outlets, and that's just in the garage. I have a new addition too.

[karfas]

Do the two boards need to share a ground?

Both need to share a common (signal) ground. This is the way a simple UART or RS232 works. For longer distances (hundreds of meters) this doesn't work well. You can use a current loop or a RS485 connection there.

May I suggest another approach ? Do it like an electrician.
Create a device connecting your three cables to each other in a known connect/time pattern.
Detect the pattern with another device.

As long as at least two of the wires are connected, you will be able to find out:
- which wire is not connected
- maybe find some weak connections by measuring the resistance between your devices.

[MasterOfGizmo]

Do the two boards need to share a ground?

Uhm ... yes, since electricity flows in a closed loop. You cannot power something using a single wire only.

Are you sure you are the right person to setup and test mains?