Volt Free Contacts on Boiler (UK)

http://www.bing.com/search?q=volt-free+contact&qs=n&form=QBRE&pq=volt-free+contact&sc=2-17&sp=-1&sk=

Go to Maplins and pick up a normally open momentary action pushbutton switch. You will be holding an example of a volt-free contact. That's all there is to it. Any mention of "internal power" or whatever is a contradiction of terms.

The volt free contacts are exactly what they say they are. A relay on the circuit board operates and drives a pair of contacts.

In some circuits the contacts might pick up 24VDC or 230VAC to switch on a device, lamp, relay etc so they would be 24V or 230V switched.

The advantage of voltfree is that within the parameters of the relay you decide the operating voltage. If you need to operate a water pump then you will put 230V live to one side of your volt free contact. The switched live then goes to the pump and the other side of the pump to neutral.

If you were switching a 24V relay you would introduce 24V to one side of your contacts etc.

Do you ever read back what you wrote? It is garbled rubbish and misleading at best.

As I commented just before:

Your first paragraph works well with me. The thermostat will need to have a volt free contact that closes or open depending on the temperature settings, to signal to the board that a set point was reached or exceeded ... BUT the thermostat does not rely on the supply from the board, via THIS particular contact, to operate.

Your last paragraph has nothing to do with "Volt free Contact" in the normal jargon of the control circuit Industry. It is an auxiliary relay (or transistor) contact point that is attached (figuratively) to a particular function of the board: remote Alarm , remote indicator of some status like Normal run, Standby, High water level, low water level etc that the user can use to trigger his own designed action based on these sontacts being closed or opened by the board circuitry.

If the manufacturer of the board has confused the meaning of 'Volt Free Cntact' then you will have a nasty surprise. Check carefully.

the thermostat is volt free. There needs to be a voltage from somewhere and this somewhere is the circuit board. The boiler is asking for a volt free input. Without volts from somewhere it won't work.

The last part has everything to do with control circuits. The last thing you would want is for the boiler to push a signal that was biased to say 230V to a DCS system that wasn't expecting it.

Agree completely you need to check the wiring diagram and more so when it has been translated from something that involves symbols and squiggles rather than letters.

Un-assigned, unused, "spare" contacts that can be used when needed for the purpose of interlocking permissives and/or other control logic required to make the control circuit and/or machine operate.

In order to understand what voltage source is controlling the operation of the contact (make or break) you must consult the wiring or schematic diagrams to determine which control circuit or power circuit is providing power to the operating coil.

Example: Spare "voltage-free" contacts on a "sudden-pressure" transformer protective trip relay can/could be used to trip (de-energize) an auxillary breaker/contactor when the transformer trips to ensure the transformer is completely unloaded before re-energizing it.

Volt free (or potential free) contacts have no voltage on them from the device that is controlling them.

It will usually be a relay where the coil is being activated and deactivated by something like a controller or other machine, but no voltages are being applied to the contacts themselves from that machine.

It could even be the contacts from a push button that you are pressing with your finger......

Its just a pair of contacts opening and closing.....nothing more, nothing less......

If a voltmeter shows a DC voltage across them, either the voltmeter is defective or its simply not "volt-free".........

There is a very faint chance of an induced voltage when the contacts are closed, this will be an AC voltage, very tiny in level, so using the DC part of the meter will allow you to totally ignore it.

Andy, I am sorry to disagree and also you have a contradiction in your comment:

"It could even be the contacts from a push button that you are pressing with your finger......"

This sentence resumes it clearly! The others are contradictory.

IF The contacts, which are from the interna board, have no voltage at all (0.00), then when you connect a push button and press, the contact will close (Short the contacts) on nothing, and nothing will happen!

Ex: If you have a PLC (programmable logical Controller) with Digital Inputs (DI). You can use these DIs to indicate that a push button was pressed ON. this DI is Volt FREE because you are closing the contact to send back a 24V DC from the PLC Common point: i.e. DI1 -- P/B -- Com of the 24VDC from the PLC internal circuit etc

The DOs (Digital outputs) are also volt free from the PLC, being relay contacts or Solid State contacts, and are used to operate external devices, BUT these are not Volt Free contacts since you have an external power source connected via these contacts.

If you use a "volt Free " Labelled contact like if it was an internal relay contact, then good luck! {In any case you will apply a certain voltage accross it to operate anything(!!?) }

this just isn't right. If you have a contact in the boiler circuit and an external contact you have 2 contacts in parallel.

The input to the boiler isn't a contact it is part of a circuit that needs a voltfree switch or contact to operate it.

A voltfree DO from a PLC is voltfree - it has no voltage. You bring an external voltage to the contact and then switch your circuit.

If the whole lot is voltfree then you need to get volts from somewhere and the PLC common 24V bus is usually a good place.

I think you are getting mixed up with a volt free contact and a circuit that needs a volt free contact to operate.

GA.

Every technical discipline has its own jargon.

For me the term Volt Free Contact is a confusing as we all know that a contact is of no value if it cannot switch a voltage or current.

In the discipline of controls, the term just means that the terminals are not connected and are available to connect to what every you wish. This is important distinction to the controls guys as frequently in a control system contacts have one of the terminals pre-connected to voltage bus.

The computer world would use the term "Isolated Contact". A device with a "Volt Free Contact" and a device with an "isolated contact" may be physically identical and manufactured on the same production line. They just have a different name because of the industry that uses them. The names of the same thing also change from country to country.

Confusing, you bet.

I think in USA we use expression "Dry Contact". Think of it like a central heat/air cond system. The thermostat in my house is electronic, powered by 2 AA batteries. When the electronics senses the house is colder than the set point it energizes a relay in the thermostat. This closes a set of "Dry" or "Volt free" contacts. The thermostat does not send its 3 volt DC to the furnace. The furnace, on the other hand, does not know why the contact is closed. It just knows that when wire "A" is connected to wire "B" it should start into its heating mode. This could be because a manual switch has be closed, a relay activated or direct acting thermostat changed position. Your boiler seems to have everything in it to operate when told to by simply connecting one terminal to another, again, by a simple hand operated switch or more a complicated control system that closes a set of contacts.

All this said, don't think that there is no consideration of the voltage/current needed. Very small current at low voltage will require different contacts than a line voltage control system. Also, the wiring method (Conduit or just wire) will change.

Hope this helps. -- JHF

http://wiki.answers.com/Q/What_is_a_volt_free_contact

Joshi - This is a repeat of one of the links that Andy pointed out in his post #18 which is the best answer so far. (Of course, I think that post #17 is pretty good too.)

It is not a repeat exactly. Please compare letter to letter in both the links, you will, I am sure, find the difference. Both the links may open the same web page, that is entirely a different matter.

Sorry - you are correct.

The minor difference is because one is for "voltage free" contact and the other is for "potential free" contact, which as we all here know are one and the same thing.

Minor wording changes only between the two entries....

Do remember that a "dry contact" is also the same thing. There may even be other names for such contacts that we have not even heard of up to now!!!!

Just all different words for the same thing.

You need to understand that, but if you still think that there is a difference, you may not understand correctly what it is!!!!!

We will see what you know and understand the next time you post....but do not get upset by my post, even if your understanding is at fault, you are certainly not alone here!!

Have a great day....

I do understand that Volt Free Contact is same as "dry contact" & rest assured, I will remember all that you said.

"We will see what you know and understand the next time you post...."

Who is "We", by the way?

What a simple question to answer! Thanks!

"We" are the people on CR4 who follow such blogs as these, see that the blog is "going in the right direction & accurately" and feel no need to chime in and add to the general furor discussion themselves. CR4 is not a war zone.....

I even get private emails from some saying "well done" or similar. Sometimes even criticizing a particularly obtuse opponent!!!

I am sure that I am both not alone in receiving such email posts, as well as being one who also sits back and occasionally sends such personal posts when I see the need to support a CR4 colleague....

I would like to just add, in case it was not apparent to you, that your recent comment:-

I do understand that Volt Free Contact is same as "dry contact" & rest assured, I will remember all that you said.

Could possibly be taken (maybe wrongly) to mean that a "potential free" contact is not included. My apologies if I misunderstood your post in this manner.

Just in case that is so, please remember that a voltage can also be described as a "Potential difference".....so "Potential free" is the same as "volt free".

Do you feel the need for any further information on this subject? I will do my best to help.

Thank you kind Sir!!!

Post #17 was pretty good....

At least since Posts # 17 & 18 "our friend" has not posted anymore of his daft, inaccurate, dangerous and misleading explanations......he knows who he is, as we do too!

Now if he is basically clever, he will not post here again....we will see!

Come on Andy, don't take it to heart. Live & let live.

Live and let live

As such contacts can carry high voltages, start and stop heating systems or heavy plant, a wrong explanation could cause injury or worse......which is why I take it so seriously......

Now its all sorted lets hope no ones spoils it with a question about contact wetting which is very different and does not involve water!

Awww! Come on, why spoil the fun? -- JHF

LOL!!!!

....as against "dry" contacts?

Dry contacts can often be cleaned with wet'n'dry, unlike wetted contacts. (Methinks this line of thought has some potential !).

Good humor!

Great!!!

(Methinks this line of thought has some potential !).

Only if it is current! -- JHF