Photocell and HID Ballast

[Tomko]

Colleagues: I have a Metal Halide ballast that I need to control with a photocell.

The wiring diagram from Advance, the ballast manufacturer, directs the installation of the photocell on the output of the ballast, just before the bulb. It does not direct the installation of the photocell on the 120V supply to the ballast.

I know that not all photocells are created equally. But Advance makes no comment on photocell design or specification.

My questions:

1) Why would advance direct the photocell on the ballast’s output - and not its supply?

2) Would not the ballast be functioning and drawing power 24/7 with the photocell only controlling its output to the bulb?

3) What would happen if I installed the photocell on the supply to the ballast?

The ballast is an Advance postline model 74P5104011P driving a 50W MH.

https://www.1000bulbs.com/pdf/advance-74p5104011p-specs.pdf

Many thanks,

Tomko

 

[dw1]

Power into fixture goes to black on photo cell, red on photo cell goes to input on ballast, if you have a multi tap ballast, make sure you use the correct wire, tie incoming neutral (White wire) to photo cell white and fixture common

 

[Bert_]

That diagram does NOT show the photo cell wired to the ballast output. That is a postline ballast so the black wire passes though the ballast can but goes directly to the photo cell. The red wire is the power input to the ballast.

 

[Norcal]

Wire it as shown, since it's a Postline ballast all wiring has to go through the ballast case because of no space between the outside of the case & the inside of the post, & even if there were, conductor insulation damage could occur.

 

[Tomko]

Thank you kind gentlemen. I am in your debt.

With the benefit of your explanation I’m coming to understand that the photocell is intended to be mounted above the ballast.

I am intending to use this ballast to retrofit an HPS lamp to MH. In the existing HPS installation the ballast is configured above the photocell. I can see how I can use a chain to drop this postline ballast below the photocell that is mounted 16” below the lamp.