Pressure switch NO and NC

[MikeHolm]

Is there a trend at all towards using either normally open or closed HP an LP switches amongst different manufacturers or from different parts of the world? Just curious.

[Grizzly]

Logically a safety circuit would be NC failing to NO on a rise above the HP setpoint.
Likewise NC failing to NO on drop in pressure below the LP setpoint.
The NO circuit can be wired up to a alarm, be it a fault lamp or software imput.

Or to put it another way HP switches break the circuit on rise in pressure and LP switches break the circuit on a drop in pressure.

I cannot think of any that work the other way around?
Grizzly

[MikeHolm]

I ask the question because i use a lot of temperature controls where either NO or NC can be used and I wondered if the same was true for refrigeration,

Thanks Grizzly

[chillerman2006]

Unless some wotsit wires it the other way and I spend hours trying to work out why it keep going off on lp.... but dont tell no-one they may laugh

Regards Chillerman (http://www.refrigeration-engineer.com/forums/member.php?4978-chillerman2006)

[install monkey]

on ranco pressure switches there a diagram for the correct connections-normally closed under normal operation 1,3
2 and 4 for high,low pressure-(based on a dualtype) once connected to a system test for continuity before wiring

[chillerman2006]

have posted a few links to help you Mike ;)

heres the link you want https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B35a42p6LY0AZTEyNzU5MTEtNmE2NC00ODIxLWIyZDgtNzA1ZjQwZmYyNDBh&hl=en_GB

and heres the others

http://www.refrigeration-engineer.com/forums/showthread.php?32957-Danfoss-Tips&highlight=

http://www.refrigeration-engineer.com/forums/showthread.php?32958-Tips-Hints-Bulletins&highlight=

Hope that helps mate ;)
Regards Chillerman (http://www.refrigeration-engineer.com/forums/member.php?4978-chillerman2006)

[MikeHolm]

I have no idea how you manage to find all these references so quickly.................takes me forever

[NoNickName]

It is a good practice to wire all digital inputs close on go, and open on no-go.
This is especially true when DI are status contacts fed back from relays. When the coil falls (e.g. power failure), the digital input opens.

[chillerman2006]

I have no idea how you manage to find all these references so quickly.................takes me forever

there all tagged on

www.myhard-drive.com (http://www.myhard-drive.com)

Regards Chillerman (http://www.refrigeration-engineer.com/forums/member.php?4978-chillerman2006)

[chillerman2006]

It is a good practice to wire all digital inputs close on go, and open on no-go.
This is especially true when DI are status contacts fed back from relays. When the coil falls (e.g. power failure), the digital input opens.

Yeah your right mate

its just when someone wires them wrong and trys to set up the switch

you get breakdown or commissioning...cutting out lp

you put gauges on... think...thats not set right

you dont expect wires wrong way round and just keep thinking, why cant I make it work :o

[al]

CM

"there all tagged on

www.myhard-drive.com"

Can't seem to locate that drive, is it close to mydocuments.com?

al

[chillerman2006]

CM

"there all tagged on

www.myhard-drive.com"

Can't seem to locate that drive, is it close to mydocuments.com?

al

Yeah thats it mate, my docs on my hard drive :D

[MikeHolm]

sneaky guy, ya had him searching for it.................:D

[SeanB]

Most thermostats are configured so that the contacts close to enable the action, either heating or cooling. This makes the system fail safer, as a fault that disables the controller will stop the action ( no cooking of the baby chicks or freezing the room into a block of ice) and fail to room temperature. Safety circuits are wired in series with the wire to the contactor, so that any of those faults result in the same action.

[MikeHolm]

Most thermostats are configured so that the contacts close to enable the action, either heating or cooling. This makes the system fail safer, as a fault that disables the controller will stop the action ( no cooking of the baby chicks or freezing the room into a block of ice) and fail to room temperature. Safety circuits are wired in series with the wire to the contactor, so that any of those faults result in the same action.

Yes, I know they are in series, same for all heating systems I work on but in a lot of control circuits we can have the switch one pump on while another turns off, for example, so it is not guaranteed to be NO, same as any relay. The pressure switches I am thinking of are 2 wire so it is hard to screw it up when wiring it.

[chillerman2006]

Yes, I know they are in series, same for all heating systems I work on but in a lot of control circuits we can have the switch one pump on while another turns off, for example, so it is not guaranteed to be NO, same as any relay. The pressure switches I am thinking of are 2 wire so it is hard to screw it up when wiring it.
Hi Mike Agreed as when pressure switches are used for staging condensor fan control
switchs are normaly open & close upon head pressure reaching the setting
it all depends on the application, they are being used for
R's chillerman