No Volt contacts ??

[madmatt]

Forgive me for being clueless here but I am hearing a lot at the moment at work about no volt contacts and wiring them ! mainly for air con equipment, such as chillers pcb's and sometimes contacts for shutting down air conditioning in the event of a fire for obvious reasons from the fire panel.

Stupidly I always assumed that you need volts to switch otherwise what is signalling ?? air ?

 

[Phil Mumford]

Think of a control thermostat.

It COULD (when turned up) generate a 240V signal to, say, the boiler (or A/C).

I could also close a contact so that a supply from elsewhere is sent back as a signal. This is a no-volt contact - one that would not have voltage on it unless connected to a source of voltage.

 

[madmatt]

Thanks Phil, I am still somewhat confused but you have left me slightly less baffled than I was earlier !

 

[Yooj]

Just think of a standard light switch...this is a no-volt contact. So, this switch, will switch any voltage (up to its max. rating), I.e, it could be 12v, 24v, 24v, etc...The thing is, a standard light switch generally needs someone to switch it.

Now, when someone talks about a no-volt contact, what they mean is basically a switch, which can be wired with any voltage to be switched (up to its max. rating) which is switched in an automated fashion...the way to think about it is for the light switch above which is switched by an external force...the external force could be a solenoid valve, it could be a contactor, relay, PLC, air-switch even...therefore, the 'no-volt' part is basically the switch-contacts.

Yooj

 

[ian.settle1]

A no volt contact is a switch which is supplied via one piece of equipment to operate another piece but does not supply a voltage to it as voltage is supplied via equipment using it.

As you said about a fire panel, it will have a set of contact on the PCB so that when it is all normal the contacts are closed but when a fire is detected and the alarm is sounded these contacts will open thus shutting down Air Con system, for this to happen you take a feed and switch wire from the control side off the air con.

When doing this then the shuold be a label on panel stating there are 2 sources of supply within the panel.

 

[Had8Lives]

It think this is reffered to genrally as Volt-Free contacts. As described, you use one piece of equipment to switch antoher but there is no electrical connection bewteen the two.