contactors and relays

[stillp]

Only in the genitive tense.

 

[bernardgreen]

In Germany a normally-open switch is called a "closer" and normally-closed is called an "opener".

Arbeitskontakt = working contact = normally open

Ruhekontakt = rest contact = normally closed

AK and RK were used in days of old but NO and NC are commonly used in mpdern documentation.

 

[stillp]

I'm more familiar with 'offner' and 'schliesser'. Then again I'm thinking of solid-state switches, from when I used to sell proximity switches for a living.

 

[ban-all-sheds]

Only in the genitive tense.

I had heard that the Germans are well known for making training videos for opening and closing genitives.

 

[matt1e]

A good discussion here
I've worked with these all my working life, I'll give some of my views

I, personally distinguish between the two as follows

If it looks like this

I'd call that a contactor

If it looks like this

or this

then I'd call them Relays

If you were to ask me what they are used for I'd say

Contactors are primarily used to switch heavier loads
Relays are used in control circuits for logic switching and to switch on small loads

If you were to ask me how they differ physically/mechanically then

Contactors usually can be fitted with auxiliary devices and double disconnect their poles
Relays usually can not and only disconnect one pole

Well works for me

Matt

 

[JohnW2]

I, personally distinguish between the two as follows ... If it looks like this ... I'd call that a contactor ... If it looks like this ... then I'd call them Relays

I would imagine that nearly all of our minds think essentially like that, in terms of the fairly ‘clear-cut’ ones. However, harping back to what I wrote on page 1, what would you think about something which looked like:

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• JohnW2
• 28 Jan 2013
• 1

If you were to ask me what they are used for I'd say ... Contactors are primarily used to switch heavier loads ... Relays are used in control circuits for logic switching and to switch on small loads

Again, as already discussed, I think most would agree with that as a working generalisation. However, as you can see here, the one pictured above is rated at 1000A (albeit DC) – and you don’t have to look far to find things called ‘contactors’ rated at 5A, 3A or even lower.

If you were to ask me how they differ physically/mechanically then ... Contactors usually can be fitted with auxiliary devices and double disconnect their poles. ... Relays usually can not and only disconnect one pole

I mentioned auxillary contacts at the start, and have to agree that I haven’t seen relays with such a facility (or ‘interlock’ facilities) - so I'd certainly agree with that bit. I’m not sure what you mean by ‘double disconnection’ – you presumably aren’t denying the existence of 2-pole and 3-pole relays? Are you perhaps talking about the actually mechanics of the disconnecting? (I have a feeling that, in many contactors, neither of the functional contacts actually move – instead, they are both fixed a ‘connecting bar’ joins them in the ‘on’ condition. Mind you, I’ve also seen that in some ‘plug in relays’, including at least one available from Maplin)

Kind Regards, John

 

[matt1e]

I’m not sure what you mean by ‘double disconnection

Hi John I mean that there are two contacts per pole mate,
if you look at the contact arrangement below its a typical relay, the switch part is permanently connected to the common

Now below is a contactor, and its associated circuit diagram, you will see that it is pretty much indistinguishable from the relay diagram,ie it shows one side of the switch tied to one of the poles, a quick goggle will yield many more such diagrams

But if you actually opened it up and looked at the contacts you would see that in reality there are actually two fixed contacts per pole

the above diagram attached to that contactor should really look like this (but with an extra pole)

Matt

 

[JohnW2]

Hi John I mean that there are two contacts per pole mate, ... Now below is a contactor, and its associated circuit diagram, you will see that it is pretty much indistinguishable from the relay diagram ... But if you actually opened it up and looked at the contacts you would see that in reality there are actually two fixed contacts per pole

the above diagram attached to that contactor should really look like this

Indeed - what you are describing is exactly what I was referring to when I wrote:

I have a feeling that, in many contactors, neither of the functional contacts actually move – instead, they are both fixed a ‘connecting bar’ joins them in the ‘on’ condition.

However, as I went on to say ....

Mind you, I’ve also seen that in some ‘plug in relays’, including at least one available from Maplin)

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• JohnW2
• 28 Jan 2013
• 1

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• JohnW2
• 28 Jan 2013
• 1

It looks like, smells like and is called a 'relay', but it has the contact arrangement (albeit a '2-way' version thereof) which you describe as identifying it as a contactor (and it also has a contact rating of 30A, which goes a bit against one of your other distinguishing features of relay vs. contactor).

Kind Regards, John

 

[matt1e]

Mind you, I’ve also seen that in some ‘plug in relays’, including at least one available from Maplin)

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• JohnW2
• 28 Jan 2013
• 1

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• JohnW2
• 28 Jan 2013
• 1

It looks like, smells like and is called a 'relay', but it has the contact arrangement (albeit a '2-way' version thereof) which you describe as identifying it as a contactor (and it also has a contact rating of 30A, which goes a bit against one of your other distinguishing features of relay vs. contactor).

Kind Regards, John

No it doesn't John, it might switch 30A but you can't fit auxiliary devices to it

That drawing does not exactly match that relay either, I guarantee it

I'm visiting a few plant rooms today I'll take some pics of a few control panels and post them later

Matt

 

[JohnW2]

It looks like, smells like and is called a 'relay', but it has the contact arrangement (albeit a '2-way' version thereof) which you describe as identifying it as a contactor (and it also has a contact rating of 30A, which goes a bit against one of your other distinguishing features of relay vs. contactor).

No it doesn't John, it might switch 30A but you can't fit auxiliary devices to it

I conceded that it does not fullfil the 'auxillary devices' criterion (which is, in fact, not possible with many a small 'contactor') but I don't really understand what you're saying. It certainly looks like a relay and, as you say, cannot have auxillary devices (hence tending to make it a 'relay'), but it has a fairly high switching capacity and has the sort of double disconenction that you said was usually present in contactors, but never in relays. It therefore seems to me that, by your criteria, that product is about 50:50 relay and contactor!

That drawing does not exactly match that relay either, I guarantee it

What do you mean? I have the relay in my hand, and phographed it and drew the diagram (well, by modification of yours ) myself this morning. In what way do you feel you can guarantee that my diagram does not exactly match the relay? There are 4 (fixed) contacts. A large lump of copper or brass attached to the armature joins either one pair of contacts or the other pair. As I see it, the only thing 'wrong' with my diagram is that I have shown the 'moving contact' in a mid-position that would never normally occur - but I did that deliberately, because I thought some people may have misunderstood had I shown it in contact with one of the pairs of (fixed) contacts (i.e the true resting state).

Kind Regards, John

 

[matt1e]

That drawing does not exactly match that relay either, I guarantee it

What do you mean? I have the relay in my hand, and phographed it and drew the diagram (well, by modification of yours ) myself this morning. In what way do you feel you can guarantee that my diagram does not exactly match the relay? There are 4 (fixed) contacts. A large lump of copper or brass attached to the armature joins either one pair of contacts or the other pair. As I see it, the only thing 'wrong' with my diagram is that I have shown the 'moving contact' in a mid-position

Kind Regards, John

That's what I was getting at John I thought that the diagram had come with the relay, didn't realise you had drawn it your self

Matt

 

[JohnW2]

As I see it, the only thing 'wrong' with my diagram is that I have shown the 'moving contact' in a mid-position...

That's what I was getting at John I thought that the diagram had come with the relay, didn't realise you had drawn it your self

Fair enough - but,as I went on to explain, I did that deliberately for what I (seemingly misguidedly!) thought would be better clarity for some people! If it makes you more comfortable:

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• JohnW2
• 28 Jan 2013
• 1

The fact remains, however, that, per your criteria, that product does seem to be about 50% relay and about 50% contactor!

Kind Regards, John

 

[matt1e]

I conceded that it does not fullfil the 'auxillary devices' criterion (which is, in fact, not possible with many a small 'contactor') but I don't really understand what you're saying. It certainly looks like a relay and, as you say, cannot have auxillary devices (hence tending to make it a 'relay'), but it has a fairly high switching capacity and has the sort of double disconenction that you said was usually present in contactors, but never in relays. It therefore seems to me that, by your criteria, that product is about 50:50 relay and contactor!

I am glad you noticed my use of the word 'usually' when referring to contactors John
I'm sure that I also applied the same word when referring to relays
Don't recall using the word 'never'
Listen as I said earlier in my first post This is how I personally distinguish between the two, I'm not arguing the toss between whether its right or wrong, as I said It seems to work in the field for me

View media item 55925
In the panel abovethere are contactors, plant control relays and bms relays
And I know they're similar animals
But if I were to ask you to check say all of the plant control relays then I'd expect you to go straight to them without arguing the toss that technically the BMS ones are the same
I haven't got the time mate

Matt

 

[JohnW2]

I am glad you noticed my use of the word 'usually' when referring to contactors John
I'm sure that I also applied the same word when referring to relays Don't recall using the word 'never'

Yes, that's all correct - you used the word 'usually' in both cases and did not use the word 'never'.

Listen as I said earlier in my first post This is how I personally distinguish between the two, I'm not arguing the toss between whether its right or wrong, as I said It seems to work in the field for me

I realise that, and I'm not arguing, either. I was merely trying to underline what I and others have been saying all along about the fact that there are 'grey areas', and I think your description of how you personally make the distinction makes that as true of your view as any other. The product I've been discussing seems to tick two of your relay boxes (looks like a relay and can't have auxillary contacts etc.) but also one or two of your contactor boxes ('double disconnection' and fairly high current rating). I've merely been underlining that the disctinction is not always all that clear-cut.

But if I were to ask you to check say all of the plant control relays then I'd expect you to go straight to them without arguing the toss that technically the BMS ones are the same

Indeed - in many, but not all, cases, there would probably be general consensus.

Kind Regards, John

 

[Simon35]

I conceded that it does not fullfil the 'auxillary devices' criterion (which is, in fact, not possible with many a small 'contactor') but I don't really understand what you're saying. It certainly looks like a relay and, as you say, cannot have auxillary devices (hence tending to make it a 'relay'), but it has a fairly high switching capacity and has the sort of double disconenction that you said was usually present in contactors, but never in relays. It therefore seems to me that, by your criteria, that product is about 50:50 relay and contactor!

I am glad you noticed my use of the word 'usually' when referring to contactors John
I'm sure that I also applied the same word when referring to relays
Don't recall using the word 'never'
Listen as I said earlier in my first post This is how I personally distinguish between the two, I'm not arguing the toss between whether its right or wrong, as I said It seems to work in the field for me

View media item 55912
Sorry the image is upside down (on IPad) I will spin it round later
But in that panel there are contractors, plant control relays and bms relays
And I know they're similar animals
But if I were to ask you to check say all of the plant control relays then I'd expect you to go straight to them without arguing the toss that technically the BMS ones are the same
I haven't got the time mate

Matt

[/b]

Doesnt seem very fair, keeping your contractors locked in the panel, just in case...