I don't know about electrical regs in the USA, but in the UK I think I am right in saying the max. No of lights allowed on one circuit is 15.
On this basis, you would need 6 separate circuits, each individually protected.
You would then need a seven way distribution board, 6 for the lights and one for the timer/photocell cct.
The timer/photocell would then need to control a contactor, say 15 kW, to put power to the distribution board, but only needs to be capable of switching power to coil of contactor.
You also need protection devise for power to contactor.
This would be fine if all your lamps are incandescent. However, if they are tungsten halogen, then you may need to stagger the switching on of the circuits, by individual delay-on timers.
Tungsten halogen lamps have an extremely low resistance when cold and draw more current at switching on, than when running hot.
This can cause circuit breakers to trip!
The economics depend on the length of the lighting string, and
whether the controls and wiring are indoors or outdoors.
Assuming simultaneous operation is desired, only a single timer
can be used to actuate multiple relays. In this case the timer
can be pilot duty (low voltage and current). It's not clear why
a timer and photocell are required, but if both are needed, the photo
cell would be used in series with the timer's output.
The signal voltage from the timer would be brought to the
branch relays where the power for the branch is distributed.
The number or branches would be determined by convenience
of bringing power to the relays.
For a simple solution;
90 100 Watt lamps will draw 75 Amperes at 120 Volts.
Make 6 branches of 1,500 Watts each.
The timer required depends on the type of lighting.
For 15 100 Watt incandescent bulbs, you will need
a 1500 Watt tungsten rated timer,and AWG#12 wire.
1500 Watt timers (for indoor mounting) are reasonable in cost.
This arrangement doesn't permit a photocell or
synchronized operation.
Ultimately it depends on the wiring for the lights. 9000 WATTS at 120v is about 75 amps or at 220v about 40 amps. I would use the photocell and timer to actuate a contactor (or 2) that the lights are connected to IF the wires for the lights can be brought back to a single junction box. If the wiring is extensive, it might be better to use localized timers and photocells. If you use the contactors make sure the FLA rating is somewhat in excess of the total load.
if each light pulls 10W then you are looking at 9kW. Depending on your supply (110vac or 240) your current draw will be about 40 A or 80 A. (You should double this for inrush current.) This is a lot to pull from a single domestic circuit!!
If it is a commercial/industrial installation most likely you will have 3 phase power so you will need to use a 3 phase contactor & drive its coil with the output of your timer.
Since you dont seem to know much about it I very strongly recommend you get an electrician to do it for you.
I have to control 90 External lights with the use of timer and photocell.. one light is 100 watts. how many timer i have to fix? i need in economic way. Please help. i heard 1 timer can be connected to maximum of 10 lights, if so i need 9 timers??? any better contactor or relay i have to use.? Suggest a better economic way... thank you
