After experimenting with the Zooz ZEN51 Relay with the sense line decoupled from the relay, I offer the following analysis. Please let me know if it contains errors.
Zooz ZEN51: Notes & Analysis
Version 1.90 firmware. Driver: Zooz ZEN17 Universal Relay Advanced, Ver 1.3.2
Sense Line decoupled from relay via parameter 13 (ZEN51) or 28 (ZEN52)
Sense Line (S for short), Hardware Characteristics:
The Sense line (S) is an edge-triggered device that only changes value (ON/OFF) when it detects a transition to or from a floating state. S only responds to transitions; it is not level sensitive.
When connected to either line or neutral, S is not considered floating. Therefore, the three possible physical states of S (LINE, NEUTRAL, FLOATING) are compressed into a simple ON/OFF status for the software to see.
Sense Line Truth Table:
TRANSITION (L, N, F) | RESULTING STATE
F>L | | ON
F>N | | ON
N>F | | OFF
L>F | | OFF
L>N or N>L | | No Change
No Transition | | No Change
Practical implications:
There is no way to distinguish if S is connected to neutral or line.
A transition that occurs while the unit is powered off will not be detected. Therefore, immediately after power up, there is no certainty about the physical state of S. -See more below*
You cannot connect S to the high side of a load as a way of detecting power to the load. For a typical load, such a connection causes S to always report ON. This is because S will always see a connection (current flow) to neutral through the load.
A high impedance voltmeter connected to a “floating” S will read about 95 volts.
*More about possible issues after power up:
Let’s say S is floating (Reporting OFF) when power fails but, during the power failure, S is physically connected to line (120V). When power returns, S will continue to (incorrectly) report OFF because it missed the transition to floating state. Furthermore, after power up, when S first goes floating, this (L to F) transition is never reported.
