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Let me rattle your brains and if you can you give us a brief desciption on how they actually work with the windings n that? why we use them? drawing would be nice :)
 
R

rumrunner

Hi Luke,
the only winding a contactor has is the coil ,this is fed with a set voltage via the control circuit,most coils are marked with the opperating voltage and can be ac or dc,24volt ,110 volt ,240 volt ,or 415 volt, upon completion of the control circuit the coil is energised and operates as a solinoid and attracts an armature which makes the conection between the contacts, most contactors have three main contacts for the phases and various auxillary contacts for the control circuit ,these can be normally open or normally closed ,for motor control the contactor is often "held in"by taking the coil feed via a n/o contact, hope this helps a bit ,its difficult to explain in words and i cant upload a picture at present
atvbitwww
 
W

wayne

i tried to figure out the difference between contactors and relays the only real answer i came up with is size and purpose, nothing definitive
both are used so a smaller circuit can energise a larger circuit
 
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  • #5
whats the main reason for using a contactor, rather than connecting direct to the board? large currents?

when I helped wire one up, the contactor were feeding outside lights, and had 2 cables coming into the contactor from the board, one to close (i'd say trigger) the contactor, and one fed the lights. would it have been possible to just have one cable incoming from the board to the contactor, and using that to close the contactor and feed to the lights, rather than having 2 cables, get me??? :S cheers
 
R

rumrunner

i presume the cable to "trigger", as you say ,i would say" bring in" ,the contactor went to the coil and was switched in some way
 
L

Lofty

Hi,
We've fitted one at a hotel to monitor freezers that are in an remote building.
If the supply to the freezers failed then an external light would come on to alert the staff.

Best regards,
Lofty
 
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  • #8
is there some sort of light on the contactor? or are there external lights wired to the contactor, which become lit when power to the freezers is lost?
 
S

Shakey

is there some sort of light on the contactor? or are there external lights wired to the contactor, which become lit when power to the freezers is lost?
luke, contactors are absolutely vital for industrial circuits.

lets say you have a circuit carrying, say, 1000A at 1000V, by using a contactor you could control that circuit using 12V dc at 100mA. From miles away if you wish.

imagine a 3 phase motor. If you strapped it accross the supply, it would just run continously. By using a contactor (or a configuration of them) you can start it and stop it at will, and again, remotely.

Regarding the light, a contactor will frequently have 'normally open' (N/O) contacts and 'normally closed' (N/C) contacts. 'Normally' relates to its de-energised state.

So take the circuit mentioned above, by using a set of N/C contacts, when the contactor de-energises (loss of power to the freezer) the N/C contacts will close and complete a circuit to the warning light. The N/C contacts could even be in the 'pull in' circuit for a seperate contactor which will feed the lights.

and so on, and so on

You can use the same principle to bring in a stand-by generator, for, say, a hospital, when the mains fails.

And imagine connecting a circuit to a generator that was off. the genny would be at zero hertz and volts. By the time it got to 50Hz and 230/400V the circuits connected to it would be fried. So we put in a contactor which wont connect the output until its at correct V and Hz. And the same contactor will 'drop out' if it drops to say, 45Hz (when the diesel runs out and its stopping), for example

PLC's are just banks of 'electronic contactors', and without them, most industrial machinery would be buggered.

Many many uses.

hope this helps:)
 
W

wayne

lscotty did you mean how do contractors work because thats a mystery to everyone:D
 
M

markthespark

Ive installed them in schools for lighting controls where lights in a room had 2 circuits, so i ran it through a contactor to switch them on and off at the same time through a PIR, also ive used them for switching a large load through a time clock.
 
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  • #12
so , i could impliment a switch into the contactor, which could power some lights?
 
S

Shakey

Luke

Not quite sure what you mean?

you could use a switch to operate the contactor, and the contactor could control the lights

do you have specific circuit in mind?
 
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  • #14
am unsure how contactors work, and hardly installed them. but basically with what you've said I sort of understand. so I could put a switch on the contactor, which would trigger the coil for the contactor to control (allow power to) the lights???
 
S

Shakey

Yup, thats it

the contactor is just a coil, with an armature connected to it. When you energise the coil, the magnetic field around it attracts the armature, this pulls in the sets of contacts

it is normal practice to have a N/O on (or start) switch in series with a N/C off (or stop switch), in series with the coil

you then wire a set of N/O auxilliary contacts on the contactor in parralel with the on switch, which act as the hold on.

So when you press on, the coil energises and closes the contactor, the N/O contacts close and short out the on push, keeping the contactor energised. The contacts can be used for any circuit, within their current rating

This system is used because if you were to lose power, the contactor would drop out, and would not re-energise until the 'on' push is pressed again.

If you were to use a straightforward toggle switch, for example, the contactor would re-energise when power was restored. And the person working on the motor (for example) which would suddenly restart would NOT be impressed!!!!
 
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  • #16
righty, could we possibly explain how to wire this up, bare with me please cus I don't do this everyday, lets imagine that I'm doing one next week (most unlikely) anyways

this is the contactor http://www.mkelectric.co.uk/images/products/6420S.JPG

lets pretend we've got 2 circuits, one for the contactor and one for alot of high powered lights

am guessing A1 and A2 energise the coil ? so.... line to a1, neutral to a2 ?

whats next, and wiring the lights to - from and via the contactor :)

regards
 
M

MacSparky

Nice;) cant wait for the explanation on that one.........:eek:....lol
 
W

wayne

oh f**k here we go
two circuits one to energise the coil one to power the lights
1st circuit ,wire from your mcb(control circuit ) to your light switch (normal everyday thing)then back to your a1 terminal .neutral of this circuit is taken straight to the a2 terminal
2nd circuit (power circuit ) is taken through the terminals of the contactor (l1,l2,l3...t1,t2,t3)and back out to your lights .neutral is taken straight to the lights
dont forget the relevant earths and make sure the contactor is correctly sized ,also check the control voltage info
this is the most simple way of doing things it gets fun when you add pir sensors ,timers photocells................
have i missed anything?
 
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  • #19
how is the neutral jointed through, connector block (through crimp?) within the contactor? if ran in armoured cable??

cheers wayne,
 
W

wayne

a contactor is a self contained item , if you are talking about the enclosure then lets continue
you have two circuits ,that is two feeds two neutrals two earths
if you are junctioning the neutral through the enclosure via a teminal block or crimp,for the power circuit either is fine i prefer terminal block
 
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  • #21
is joining the neutral via the contactor acceptable? like a double pole one or something?
 
S

Shakey

Yes Luke, this is done as well.

I have used large contactors where there are fixed terminals for the neutral in and out, or an additional set of contacts for the neutral

The contactor you have shown is 3 pole, so could be used for three phase (L1, L2 and L3)
or single phase using two of the three contacts to switch line and neutral


- i dont know if you are aware, but a lot of industrial three phase systems (particularly those supplying motors) dont use the neutral anyway!
 
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  • #24
what about contactors with a2 at the top and a2 at the bottom of the contactor, are they linked in some way, so it doesn't matter which one you put the neutral in??
 
M

MacSparky

Nice find rumrunner:D
 
  • Thread Starter Thread Starter
  • #29
spot on cheers,
 
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