Luke

[Nightmare1308]

I'm an Electrican and do alot of testing and fault finding what I enjoy the only problem is its not as busy as it used to be so ive been doing heating systems only problem is i can do them but don't understand the fundamentals ie volt free contacts and NO NC ? Can anyone help thanks

 

[loop3]

Normally opened , normally closed? Is that what you mean?

 

[Nightmare1308]

Yes it's like why is it normally open and normally closed dont see why u get a choice in the programmer when I always connect the heating systems the same ? Thanks

 

[telectrix]

NO is normally open. NC is normally closed. voltage free means that there's no voltage applied to a relay until you apply one.

 

[MDJ]

hello fella, do you understand how NO and NC works bud, I mean how the contacts from the common terminal work when energised or unenergised? how one is energised whilst dead and the other becomes live when juice is put onto it and then the other becomes dead etc?

 

[Nightmare1308]

Yh but the wireless room stat i put a 5 core 2 live neutral earth and switch common and switch NO but it has voltage at them so how can it be volt free how would I no if the boiler is volt free when I connect to allocated terminals? At what point would it be voltage and not volt free if that makes sense ?

 

[Nightmare1308]

MDJ
I'm not sure 100% what a room stat would be or a valve but I kind of get NC is like a light switch being on and the light on then when the light switch is off its NO as the lights off or is that nothin to compare with ?

 

[MDJ]

is the stat electronic?

 

[Nightmare1308]

It's a wireless RF stat as they company dont want to put in wires so its all wireles stats

 

[MDJ]

hmm I'm confused now, if the room stat is wireless where did you connect the 5 core cable? I assume into a reciever near the boiler, I am lost now.

 

[Nightmare1308]

Yh sorry i don't make alot of sense
5 core from boiler PCB board
Live - brown
Neutral - blue
Earth - green yellow
NO - Grey (in boiler terminal 5) with brown sleeving
Common - black with brown sleeving (on boiler terminal 28)
But what I don't get is the NO and NC part what do they mean can u give examples of them so I can understand it i can wire and do them but when a boiler dont work I can work it out I'm lost
Is there easy ways of knowing what the faults could be l?
Sorry for being thick lol

 

[MDJ]

depends on the type of heating system, some systems have a heating on and heating off terminal, so hot water can be prioritised, the heating can be running, but when the householder starts to run hot water the central heating valve gets changed over to the water so it takes priority, this works by NO and NC contacts in the programmer which switches the valve, no idea about the wireless stat though, I assume the electronics in it do the same job via radio links to the receiver which has the wires in it and in turn do the switching.

 

[Nightmare1308]

Is it possible to explain NO and NC as in what's a room stat NO or NC and what's HW NO/NC etc just dont get the make on rise and some people and and break on rise what's that about ?

 

[MDJ]

were talking electronics now, but the principle of NO and NC, which as you know as you have stated that already, a coil on a relay when activated will make the contact between NO and common connect and the connection between NC and common will be broken on energisation, when no electricity is evident on a coil the connection between NC and common is there, but not between NO and common, the same is apparent on central heating, it is just a matter of knowing what system your dealing with and how the valve is supposed to work, once you know how the valve works to make either water or heating or both work you can work out the NO or NC connections surely. the programmer will be NO on all connections until one is switched on, however on some systems once the water is energised the heating will switch off and water will take priority.

 

[Marvo]

Normally open or normally closed refers to the state of the contacts in their normal position ie when there's no power applied to the relay. If a NC contact is operated it will open causing a device or component it's supplying to turn off. If a NO contact is operated it closes causing the thing it's supplying to start running.

As an example, if a pump is supplied via a NC relay contact on a PCB or control board, the pump's normal condition will be to run. Only when the relay operates (energises) will the pump stop. If the same pump was wired through a NO contact on the same relay then it would be off normally and only run when the relay was operated.