Contactor

[michael_brooke]

Hi all
Im struggling to understand why we use contactors i know hoe they are wired and i know how they work, take a lighting circuit controlled by a contactor that needs more amps than a 6amp switch surely wudnt this trip the 6 amp mcb or am i lost all together

 

[Lighthouse Phil]

To put it simply ---- most switches can not handle the starting current used by some appliances. The contactor can....they are rated at different values of output/switching current......

 

[kingeri]

The MCB is selected according to the inrush current expected on the circuit as well as the operating current, that's why we have type C and D MCBs.

 

[michael_brooke]

So for example a bank of flourescents that need more than 6 amp to start up would i need to just upgrade mcb to 10amp

 

[kingeri]

So for example a bank of flourescents that need more than 6 amp to start up would i need to just upgrade mcb to 10amp

Not necessarily....if the total operating load is less than 6a you could use a type C 6a MCB in most cases, this can handle the startup current no problem.

 

[michael_brooke]

Thank you

 

[kingeri]

Thank you

Hint....please use the thanks button

 

[Deleted member 26818]

Contactors and relays are used to switch greater currents than a standard switch would handle.
This can have a cost benefit, as the cabeling and control gear for the low current switching would in many cases be cheaper than cabeling and control gear designed to handle the larger current.
With the starter motor on a car for instance low current is switched via the ignition to a relay which then switches a large current to from the battery to the starter.
If a relay was not used, extra large diameter cable would have to be run from the battery to the ignition switch and then to the starter, and the ignition switch would have to be designed to handle the extra current.
The most common use of contactors is to switch currents used to stat and run motors.
However they are often used where there are lots of lights and where the lights are on different phases.
A single single phase switch is used to switch a 3phase contactor, rather than having a 3phase switch, or three single phase switches.
This also saves on cabeling, as only a single phase needs to be wired to the switch rather than wiring three individual phase conductors.

 

[MDJ]

theres so many times when using one is beneficial I can't imagine how we would get on at times without them.