Mechanical Relay "Must Operate/Release Voltage" - Confusion Around Terminology
The numbers are intended to guarantee the operation or non-operation of the relay over variation from unit-to-unit (but not coil temperature). They are intended to guide you in your design, to apply suitable voltages so that their relay will operate reliably.

You can gamble if you like. The manufacturer's guarantee is 1.2VDC at 25°C. At lower temperatures it will not be that high. In practice there is little reason to partially power a coil when it should be off, modern transistors leak negligible current, even at high temperature. Contacts can also get a bit sticky as they wear, so a marginal design can fail in the field, causing immense grief.

You can interpret it that way, however in practice there is a hysteresis between operate and release, as you have observed. They do not specify a &quot;must not operate&quot; voltage, only a &quot;must release&quot; voltage.

You must provide it with at least 18VDC if you want to operate reliably, with the coil temperature 25°C. At higher ambient temperatures you will need more voltage for the same safety margin. That includes self-heating of the coil. At 100°C coil temperature (ambient might be 70°C) you would need to give it about 23.5VDC for the same safety margin, because relays are current-operated and copper has a temperature coefficient of resistivity of about +0.4%/K.


Even if you are sure it will never be operated in a warm environment, it's unwise to operate at the lower end of the range because that sickly &quot;click&quot; you hear means that the contacts are not closing smartly, and unnecessary wear will likely take place. Similarly, the life specs are generally given with no flyback diode and will be degraded by the presence of a simple flyback diode.