LED

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 SKEPRat (October 21, 2017, 14:51:22 PM):
Hi Tweefo. What needs to be remembered is that all plugs or lights in a house have two power wires connected to them. The live and neutral. When the live is connected via the switch the light or plug is "On". When it is disconnected via the switch the power is "Off". What many fail to remember is that the return conductor, the neutral, always has a voltage of 220V. An electrician will easily measure which is the neutral in a plug by measuring the earth contact to the power contacts. When off the voltage will register if the neutral and earth are measured. This is how the light "knows" that there is still power in the system and there is not a power failure. During a failure the voltage between the neutral and earth will be zero.
 Mefiante (October 21, 2017, 17:03:20 PM):
What many fail to remember is that the return conductor, the neutral, always has a voltage of 220V. An electrician will easily measure which is the neutral in a plug by measuring the earth contact to the power contacts. When off the voltage will register if the neutral and earth are measured.
I’m afraid the above is incorrect. If you were to measure the voltage between earth/ground and neutral, you will measure only a small potential difference of less than 3V, which is due to stray self-induction from AC current flow in other parts of the house. With shielded cables throughout, you’d measure 0V. Measuring between the mains live and neutral terminals, or live and ground/earth, you’ll measure around 220V. You can confirm this yourself with a suitable multimeter that can handle AC.

In fact, except for earth leakage detection, the neutral plug connection is actually redundant in single-phase mains electrical supply because you could run any AC appliance by connecting it to live and earth, rather than live and neutral (try this only if your house doesn’t have earth leakage protection because it’ll trip immediately). At the power station’s generators themselves, neutral and earth are identical: A giant electrode sunk into the ground. Again, with a suitable multimeter, you’ll measure around 220V between the mains live terminal and something grounded, such as a water tap fed by steel or copper piping. (The resistance of the multimeter when measuring potential differences is so high that only the tiniest current will flow, and hence the earth leakage won’t trip.)

Also, if the passage cited above were correct, the single-bulb restriction wouldn’t be necessary.

While this stray self-induction may indeed present a possible mechanism for differentiating between being switched off and a power failure, it’s far too unreliable. With no other appliances drawing any power in the house, it’s likely to misidentify such a situation as a power failure.

'Luthon64
 Faerie (October 22, 2017, 05:33:36 AM):
My guess would be capacitive sensing of the circuit it's connected to. It can probably baseline on what the capacitance of the wires are when the switch is in the off position vs. what it is in the "on" position.
Instead of a simple explanation, we get this. Never even heard the word, nevermind understanding what it means. Think it's maybe time to go back to my cave now. ; ???
The occupational hazard of associating with clever peiple!! Did you understand Mefi's post?
 brianvds (October 22, 2017, 06:37:05 AM):
The occupational hazard of associating with clever peiple!! Did you understand Mefi's post?

It's every bit as simple and straightforward as the specifications for the turboencabulator...

https://en.wikipedia.org/wiki/Turboencabulator

:-)
 Tweefo (October 22, 2017, 11:42:12 AM):
My guess would be capacitive sensing of the circuit it's connected to. It can probably baseline on what the capacitance of the wires are when the switch is in the off position vs. what it is in the "on" position.
Instead of a simple explanation, we get this. Never even heard the word, nevermind understanding what it means. Think it's maybe time to go back to my cave now. ; ???
The occupational hazard of associating with clever peiple!! Did you understand Mefi's post?
It's a tough word out there. Way back when, if a guy walks on water or changes water into wine, you just assume he was a god. Now we want explanations for everything but first, you have to go to school and all that, to understand said explanations. Better to just call her (Mefi) god, cut off a chicken's head in her name, and pray to her if the light does not go on. However, if she can walk on wine I will have to spell god with a capital G.