contactors

[jonny1]

could somebody explain why contactors are sometimes used for switching lights pls????

 

[Spark123]

A few reasons that immediately spring to mind:
small switch circuit for example a photocell controlling a large lighting circuit,
volt drop,
switches not designed to switch highly inductive loads.

 

[breezer]

warehouse with lots of lights (big load)

 

[Steve]

convenience - for example in a shop, you can have a "last man out" key switch by the front door which operates every light in the store, and with a few more contactors, all the non-essential circuits too. Instead of a switch, you could use a timer.

In a house, you could use a contactor to apply power to a fan on the lighting circuit, when the shower switch is pulled.

Contactors are sometimes used on large fridge projects, where a small LCD temperature controller is required to bring online several 3 phase compressors and the like.

 

[sm1thson]

three phase: so 400v stickers arent needed on the light switches (dont know if anybody uses them like that, but i would as stickers look poo)

 

[jonny1]

if you were to use contactors for a warehouse with lots of lights for example, how would it be wired?????

 

[ricicle]

If the lights were spread over 3 phases then the feed from the protective device(s) would come straight into the top of the contactor.From the bottom of the contactor the phases would go out to the lights (neutral(s) straight out from the DB)
From one of the phases a control phase is taken to a switch.This switch then switches on the small load of the contactor coil rather than the lights.The contactor will require a direct different phase to the other side of the coil if 400V or a neutral.
The disadvantage of this system is that if you lose the control phase you lose the lot.If any emergency lighting is required then it should be off the control phase.

 

[Steve]

If the lights were spread over 3 phases then the feed from the protective device(s) would come straight into the top of the contactor.From the bottom of the contactor the phases would go out to the lights (neutral(s) straight out from the DB)
From one of the phases a control phase is taken to a switch.This switch then switches on the small load of the contactor coil rather than the lights.The contactor will require a direct different phase to the other side of the coil if 400V or a neutral.
The disadvantage of this system is that if you lose the control phase you lose the lot.If any emergency lighting is required then it should be off the control phase.

Good point that. Our shop lost a phase all night a week or so ago. a few rows of lights went out, control phase for the contactors was still online. However, the emergency lights discharged themselves within 3 hours, and when all the power was cut the next day, no EM lights

Is this a reg or just a suggestion then, re. the EM lights?