question about contactors

assegayer · Jun 27, 2015

hi guys just a newbie question,

i know that a contactor functions when it recieves a current from a switch wire then closing the contactor...

however does the switch line current have to be constantly flowing in order to keep the contactors closed?

also why use contactors? i mean a simple switch should do it shoudnt it?

could you give me some examples where they may use contactors and why if a switch doesnt suffice?

telectrix · Jun 27, 2015

deleted.

assegayer · Jun 27, 2015

telectrix said:
deleted.

may i ask why?

telectrix · Jun 27, 2015

deleted because it's not a simple answer, and i'm half asleep.

assegayer · Jun 27, 2015

telectrix said:
deleted because it's not a simple answer, and i'm half asleep.

lol will have to wait till morning then aye

telectrix · Jun 27, 2015

for starters, you might use a contactor to switch 2 or 3 loads with a single switch, or to switch a 3 phase load with a single switch. also, the switch current can be much lower than the load current.

ElectroChem · Jun 27, 2015

You can also use a different voltage for the control and load circuits, like using 24V DC switches/contactors to control 230V AC motors.

Darkwood · Jun 27, 2015

Why use a contactor?

Contactors give us many advantages like controlling a large load with a small control circuit, so you could have say a 100amp load running through a contactor that can be operated at 12v through a switch or other control device, it allows selv/pelv to operate LV or higher systems this is good for ensuring the safety of the operater and also limits the current going through any switching device to that of the control circuit.

In machinery controls they become an essential part of the set-up, domestic see's little call for them except for the likes of switching big loads like storage heaters through the lower rated contacts of a timer.

Your wiring configeration of the control side can make the setup latch when energised by having a retaining circuit so for example a pushbutton could pull the contactor in but remain in when you let the button out, then another button could drop out the contactor - like a start/start arrangement for a motor.

Another advantage would be switching multiple circuits from one switch point and not having loads of switches.

This is a compressed explanation and using contactors and relays gives many more advantages but we start going into areas you probably will not encounter.

assegayer · Jun 27, 2015

thanks all for the explanations very very useful and i have a much better understanding now. so are contactors that noise you hear when they turn on flood lights in a stadium and they are slowly turning on like 'don don don don'

Darkwood · Jun 27, 2015

assegayer said:
thanks all for the explanations very very useful and i have a much better understanding now. so are contactors that noise you hear when they turn on flood lights in a stadium and they are slowly turning on like 'don don don don'

Couldn't say high wattage induction lamps can give a thump when energised as their ballast become magnetic and send a little shock wave out and as for Don ... never met him!