The main reason is controling multiple circuits of differing voltages with one single switch. On a single 120V switch circuit you can use contactors to control 277V fixtures without having to opperate the breakers. And for the user, most non electrical people don't feel comfortable going near a breaker panel let alone operating breakers. Also they can be operated in an emergency situation with a single palm switch, connected thru a photocell ar again with a single 120V or 24V DC circuit.
In addition, most circuit breakers are not designed to be operated repeatedly like that. You can get HACR (Heating Air Conditioning Refrigeration) rated breakers that are designed to be turned on and off more often, but still, they are more expensive than a simple switch and a contactor for multiple loads.
"Venditori de oleum-vipera non vigere excordis populi"
Their main application is for groups of fixtures where gang-controlled at one point such as a photocell or time clock, or switched manually from multiple points, using conventional 3-wire control.
Some applications may dictate magnetically latched contactors like
These devices will maintain their last state through a power interruption. An advantage is that as soon as power is restored, the lighting will be powered without need for human interaction.
jraef,
The NEC would require breakers used for switching HID fixtures to be marked HID, not HACR. Most branch circuit breakers of the bolt on type and some of the plug in type are so marked without extra cost of special order.
"240.83 ... (D) Used as Switches. Circuit breakers used as switches in 120-volt and 277-volt fluorescent lighting circuits shall be listed and shall be marked SWD or HID. Circuit breakers used as switches in high-intensity discharge lighting circuits shall be listed and shall be marked as HID."
Of course for the reasons stated in the other posts, the use of a lighting contator is a better installation.
resqcapt19
It has been a while since I had to deal with small CBs, thanks for the update. I still think that breakers are an expensive switch becuse of the cost of replacing them when they wear out. In my mind it is better to let the breaker do it's designated job of protection, leave the switching to switching devices.
"Venditori de oleum-vipera non vigere excordis populi"
