Contactors and relays

[Electron1]

I understand that! Thanks! But can u explain the cable sizes? Would 25mmm come from the mcb or mccb trgen to a switch - contactor 25mm out of that and then in to the machine ect?

---------- Post Auto-Merged at 00:57 ---------- Previous post was made at 00:55 ----------

Or this

Mcb 1mm to the small switch , then 25mm out of the small switch and then to the contactor also in 25mm

 

[Sidewinder]

Electron,

A contactor has 2 "sides" with "basically" separated supplies.

You have the low current control side which operates the coil to switch the contactor "on & off".

This would normally be fused very low, single Amps typically.

This could have all sorts of control devices in series with the coil to only operate the coil at the appropriate time.

The control side could & often would be electrically separate from the power side.

Here you could have a high current supply switched to a high current load with its own different circuit protection from the control side, often at a different voltage even.

This is not an exhaustive explanation but does this help at all?

 

[Electron1]

I think the best way to explain it is to try and five me a diagram in paint or some thing then I could see how and why it works? Where u get the supply from and then the out going current very confused now lol

 

[steptoe]

how about you do some searching?

google some manufacturers data on contactors

 

[Doc Hudson]

Relays Relay - Wikipedia, the free encyclopedia

Contactor Contactor - Wikipedia, the free encyclopedia

Doc H.

 

[Electron1]

I understand what they do! It's just the cabling I don't understand! How can u have a small cable operation a small switch then from there in to a contactor with a larger cable feeding the lights/ motor ect?

 

[Evans Electric]

As I said , Electron , have a look at one and all will become clear.

 

[SPECIAL LOCATION]

:C

I understand what they do! It's just the cabling I don't understand! How can u have a small cable operation a small switch then from there in to a contactor with a larger cable feeding the lights/ motor ect?

The above statement is a contradiction in terms me thinks?????

Do you understand magnetism?????

12v supply through a coil wound around a metal slug that becomes magnetically charged when a current goes through the wire...

the magnetic force pulls a bit of spring loaded metal nearer to it..

the metal bar physically moves two other metal contacts together making a switch..

just like a mechanical switch makes two contacts...

230v is joined onto these two contacts..

so low voltage low current can operate a higher voltage and higher current..

if you can't grasp this best go to a NON-electrical forum??

:C opcorn

so two wires onto coil..

two wires onto switch contacts..

SIMPLES!!

 

[Technician]

Relays can be of the electro-mechanical type, or solid state. Transistors can be used as relays to switch large loads when biased to class C. According to the regs these devices cannot be used to isolate and can only be used for functional switching (Page 117 regs).

Transistors can switch large currents upon extremely small base currents of a few micro-amps. When connected as super-alpha devices the switched current can be massive. These are known as Darlington Pairs.

The beauty of transistors is that they do not generate too much heat, but when controlling a relay with an inductive element in it, a diode must be connected across the relay so that the collapsing field in the inductive element does not blow the collector/base junction. The diode is forward biased when the magnetic field collapses, caused by the transistor turning off.

Hope this informs.

 

[ProDave]

I understand what they do! It's just the cabling I don't understand! How can u have a small cable operation a small switch then from there in to a contactor with a larger cable feeding the lights/ motor ect?

That question shows you DON'T understand what they do.

So lets try again.

The small switch with it's small wires turns on the power to a "coil" feed inside the contactor. This supplies power to an electromagnet inside the contactor. This only takes a relatively small current so the switch and it's cables don't pass much current so can be small.

The electromagnet pulls some BIG switch contacts together.

It's these BIG switch contacts that switch the main load and this can be a big load hence it needs bigger cables. The maximum load is determined by the construction of the switch contacts and their size.

 

[Technician]

Like it, Pro Dave.

 

[M107]

Darlington Pairs

Takes me back to college

 

[pickleye]

https://www.youtube.com/embed/RjYyAPcr_7k?feature=oembedmaybe these will help a little

 

[lkayelectrical]

Example I've just used customer needed a last man switch wanting to turn 40+ lighting circuits off from a few switches

Put them through a contactor and used a normal switch to switch to contactors

 

[M107]

I understand that! Thanks! But can u explain the cable sizes? Would 25mmm come from the mcb or mccb trgen to a switch - contactor 25mm out of that and then in to the machine ect?---------- Post Auto-Merged at 00:57 ---------- Previous post was made at 00:55 ----------

Or this

Mcb 1mm to the small switch , then 25mm out of the small switch and then to the contactor also in 25mm

Ok a very basic in laymans terms quick picture... ( I do hope this isnt your homework)

http://i83.photobucket.com/albums/j293/gazjothomas/contactor023.jpg

Edit to say: the cable to A2 is 1.5mm

 

[Electron1]

I understand now thanks to the diagram! So u will still need a larger cable going in to the contactor from the CU and then another mcb suppling the switch to then turn the contactor on in order to power the load ??

 

[lkayelectrical]

from what i remember we had some quite good hand outs regarding contactors at college didnt do alot of practical on them though but very simple when you "get it"

 

[Electron1]

Can u plz do a diagram of a singe phase contactor that is suppling lighting!

For example

15 400w high bay lights

Would u take a 1.5mm cable to the 10a switch then a 1.5mm from the switch to the contactor?

But would u need to run another larger cable to the contactor (incoming to cope with the demand) say 4mm for example

And then 4mm to the lights ?

So the 1.5mm to the switch is only to turn the contactor on! Not to carry the load, so there for u will need to install a larger cable!

Is this correct

 

[M107]

Look at the three phase diagram,Now imagine the contactor is the same size as an mcb, with only terminals A1 & A2for the coil & terminal 1 / 2 for the load with 3/ 4 for the supply.

The size of the conductors to terminals 1234 are dependant on your circuit calculations.

The size of the conductors to A1 & A2 can be 1.5mm or smaller if you wish but must be protected by a correctly rated ocpd for the cable csa.

This is starting to look like homework,

 

[Electron1]

No it's not I understand now how it's done!

I got confused with the bit when some one said 1.5mm to turn it on and then 25mm out! That's why I didn't think the cable for the 1.5 could handle such a current