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I a have a house with 3x20A grid connection. With the usual big loads like washing machines, kitchen. For each socket in the house (many...) I want to determine the phase a wall socket is connected to in a digital way using a microcontroller telling me what phase it is on relative to another device connected to another socket (with known phase number). The result on a display could be e.g. ‘same phase’ or ‘other phase’ or even ‘lagging phase’.

I know how I would do this in an ‘analog’ way: measure current of the three grid connection phases using CT’s and switch on a significant load on the target socket and see which one responds.

But as a thought experiment I wanted to explore if there is something you can measure on the device, receive something TCP/UDP from the reference device with known phase and determine wheter it is the same phase or not. My engineering mind tells me it cannot be done since I cannot think further than a zero crossing detector with 100 crossings/s at 50Hz comparing which are only shifted >60 or <-60 degrees at 50Hz compared to the other phases, resulting in 20/6ms time difference. I then believe that is too short to receive a TCP (or UDP) reference signal to compare it to.

This is in my head as impossible for quite some time now. Just want to explore with you if you have ideas.

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  • \$\begingroup\$ A house will generally only have the lighting circuit on 1 phase, will probably be easier to have an optocoupler for the circuit your plugged in to and a light sensor to detect the light pulses of the ceiling light for that room, that way your in reference to that phase, you can see if its leading or lagging by ~7ms and know what relative phase your on. \$\endgroup\$ – Reroute Aug 28 at 11:48
  • \$\begingroup\$ @Chu, that is out of my box I was thinking in. Clever!! \$\endgroup\$ – JeromeBu1982 Aug 28 at 20:25
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If the devices share a time standard by some other method than Ethernet, then all they need to do is measure the phase relative to that time standard, and communicate the result by Ethernet.

There's a couple of ways the devices could share that time signal. Probably the simplest is to give each one a GPS receiver, though they may need pretty good antennae for indoor use. Another way would be to put a low-drift clock in each, and connect them together directly to synchronise them before you start. Alternatively, if you have ethernet cables running directly between the devices (no switches etc) you could transmit a time signal down the cable using a protocol with a lower overhead than TCP or UDP.

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  • \$\begingroup\$ Yes! Using good enough time. GPS is hard indeed. But there must be ways to sync clocks using wired Ethernet, keep time with RTC for a couple of minutes. Would NTP be suitable? \$\endgroup\$ – JeromeBu1982 Aug 28 at 20:29

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