Why do timers that do not requie neutral have minimum load current

[katwalatapan]

Hello,

I found few timers where their wiring diagram did not require a neutral wire connection. I also found that such timers had a minimum requirement for total load current such as minimum 0.3A up to 3A. Why would there be a requirement for minimum load current in a timer switch?

Thank you.

Regards,

 

[davidbeach]

Probably is self powered from a CT on the line, need enough line current to power the timer.

 

[katwalatapan]

Thank you David. But the same timer with a neutral wire connection has lower minimum amperage requirement such as 5W or 0.04A for 120V circuit whereas without neutral wire connection the minimum required amperage is 0.3A. So why the considerable change in minimum amperage for with/without neutral wire connection.

 

[davidbeach]

With a neutral the timer is powered line-neutral.

 

[Mobius44]

The 2-wire timer "leaks" a small current into the load rather than using a neutral. The load current needs to be much larger than this leakage current to ensure the leakage current has neglible effect on the load, and that's why I think the minimum load current rating's higher for a 2-wire timer.

Once we tried a 2-wire timer with a small relay as the only load, and the timer's leakage current (~10mA IIRC) energized the relay coil enough for the relay contacts to pull in.

 

[OperaHouse]

Often a few small RC snubber networkss or capacitor of about .47uF as a load will supply enough current to operate these two wire devices without creating heat like a resistor.