Normally Open or Normally Closed Switching

[bages]

Hi all,

Thanks for reading.

I am using momentary press switches with the Pro Dimmer 2PM.

The switches have two contact options: normally open and normally closed.

I think both can work with the shelly, but which one should I use and why?

Thank you

 

[thgoebel]

To ensure a proper function, you should use the normally open (NO) contact. 

[bages]

4 hours ago, thgoebel said:

To ensure a proper function, you should use the normally open (NO) contact. 

Hi thank you so much for joining the discussion.

Could I please trouble you to explain why N.O. should be used?

[thgoebel]

Usually, a single or two push buttons are use in order to enable the dimming function with manual buttons. To differentiate between on and off command and dim command, short pushes are switching the device on or off, long pulses enable the dimming. This needs NO contacts, cause NC contacts would impede thIs functionality.

NC contacts can only be used with switches which enable on/off function only. Dimming isn’t possible with these switches.

Edited September 14, 2024 by thgoebel

[bages]

I thought the Shelly was simply looking for a change in state in order to make a decision... if the state is NC but it goes NO when pressed isn't this 'just as good' as being NO then going NC when pressed?

[thgoebel]

You have to set „Invert“ the button/switch in switch configuration menu to enable NC. And please be aware that dimming needs button, as I mentioned before.

Wondering where the issue is hidden: This seems to me a rather ‚academic‘ question…

[bages]

Yes you are 100% correct; this is an academic question.

I am having a discussion with my friend about this topic and, apart from best practice being that these things are usually NO, we are wondering if there is any 'harm' or loss of features if the Shelly is wired NC and then the "Invert" setting is adjusted.

Thank you

[thgoebel]

Power consumption is slightly higher with NC contacts: You may figure out this by yourself: When a Shelly‘s input is activated, a DC current of approximately 35μA is flowing from terminal SW to L. Driving voltage is 3V DC. Excess power consumption can now be determined…

Edited September 16, 2024 by thgoebel

[bages]

Thank you for your reply and information!