operating a fan from a thermostat and a humdistat at once

[garygaz]

I have a thermostat that is wired to an extractor fan. Id like to also add a humidistat controller as well to operate the fan.
If I wire them up in parraell fan will operate from the thermostat so there is power going to the fan but as soon as the humidistat goes live then there will be power also going to the fan at the same time which I think cant be good.
I thought having a switch/relay of some sort that knows which one is workling could be the answer because if I wire them up in series and the thermostat operates then the power wont get to switch the fan on if the humidistat is not operating.

I think one side needs to know what the other is doing so it can switch on/off accordingly

I hope someone can help and let me know how its possible to wire this up and also to point me in the direction of buying a switch/relay if necessary or if someone has a dual system already and wants to sell it let me know but it would appear that a dual system is not available, unless you know better?

 

[Lectrician]

Nothing wrong with having them in parallel.

But why do you want both?

 

[ban-all-sheds]

I hope someone can help and let me know how its possible to wire this up and also to point me in the direction of buying a switch/relay if necessary or if someone has a dual system already and wants to sell it let me know but it would appear that a dual system is not available, unless you know better?

TBH, given your lack of basic knowledge and understanding of electrics I really don't think you should be trying to implement a non-standard self-designed system like this.

Also, what sort of room is this fan in?

 

[garygaz]

Ive actually asked 5 local qualified electricians and all were stumped (honestly) which is why Im asking this question. I even offered to pay them!
As for the room and use, well its a bigish vivarium so I need to control the temp and humidity.The higher the temp the more humid the air which is not desirable but not enough temp is also not good. The fan is situated on the outside wall
As for my lack of knowledge, its improving as we speak!

I wont be installing the system myself but I obviously need the knowledge to be sure its achieveable and to understand it so I know its working and to pass the info on if needed.

Just to be sure what you are saying (please excuse my lack of knowledge), you are saying its ok for the thermostat to power the fan and then when the humidistat comes on it will also send more 240 supply to the fan and this is ok?

 

[Spark123]

I don't see any reason why wiring them in parallel wont work, if either switch is made then the circuit is complete and the fan runs. If both are open circuit the fan will stop. Are both the humidistat and thermostat 2 wire connections?

 

[garygaz]

yes the thermostat and humidistat are 2 wire connections.
you are saying that "If both are open circuit the fan will stop" but this is not desirable because if they both switch on then the fan needs to operate, or am I missing something.

 

[vsynth]

If you want the fan to run when the thermostat says the room is too hot and also when the humidistat says there's moisture in the air then yes all you do is wire them in parallel.

This means that when the thermostat says the room is not hot and the humidistat says the room is not humid then the fan will stop, also what you want.

 

[Lectrician]

Rocket science?

 

[333rocky333]

Just to be sure what you are saying (please excuse my lack of knowledge), you are saying its ok for the thermostat to power the fan and then when the humidistat comes on it will also send more 240 supply to the fan and this is ok?

From a safety view, I personally would take the supply to both thermostat and humidistat from the same source or sfcu (spur) to ensure total isolation of the fan set up for maintenance etc,

 

[Lectrician]

Just to be sure what you are saying (please excuse my lack of knowledge), you are saying its ok for the thermostat to power the fan and then when the humidistat comes on it will also send more 240 supply to the fan and this is ok?

From a safety view, I personally would take the supply to both thermostat and humidistat from the same source or sfcu (spur) to ensure total isolation of the fan set up for maintenance etc,

I think that was naturally assumed!

 

[garygaz]

thanks guys and Ill let you know how much of my freinds house burns down!
As for rocket science, well if you know you know and if you dont then you ask questions on the net because Im not stupid and want to find out and we cant all know about everything can we.
In my world there are no stupid questions only stupid answers, assume nothing then you can make less mistakes.
cheers

 

[Lectrician]

Very true, and I wasn't really trying to be rude - more of a nudge nudge laugh laugh

I ask more questions that you may realise.....just not to do with lecky

 

[briwire]

There's nothing wrong with that electrically, although what you are doing in the room might be questionable is your "friend" into growing things?

 

[garygaz]

what, anyway the vivarium is still not working as the thermostat is switching off at high temps when it should be switching on. Im not sure what to do about this. In fact I think I was right (although not sure) as there is a potential cross feed from the thermostat to the humidistat through the fan but installing a small relay cures this problem although the system still doesnt work. Is all this hassel worth the trouble, hardly!

 

[333rocky333]

There will be a voltage coming back to the other stat from the closed stat, but that should not be a problem as that contact is either open (isolated) or closed and connected to the same supply

Think of a socket ring circuit that is fed from two ways both at 240 volt , but as they are from the same source mcb there is still the same 240v and is not a problem

Have you got N/O and N/C contacts on the stat for switching on at high temp, I think you may need to use common/live and the N/O contact