ECN Forum Forums General Topics of the Trade General Discussion Area Photocell facing north?

I have lurked here for awhile and decided to finally participate.

I have both a masters and Jmans in the area I work with about 12 years mostly commerical experince. At this time I am employed by a large county jail in Texas.

On to my question, my helper asked me why the instructions on the intermatic photocell we use state "face north"? It also states "do not face directly in the midday sun".

I spent quite a bit on time on google trying to find out WHY they say to face it north with no luck.

So, does anyone here know why it says that?

Last but not least, I cannot face this photocell north in the installation we are doing. So which way should I face it?

Many thanks.

Sunlight, perhaps UV, tends to deteriorate the "electric eye" in certain types of photocells. Here in the Northern Hemisphere, facing them North exposes them to the least amount of sunlight.

Do the photocells "down under" in New Zealand, Australia, etc. have "...face South..." on them?

Here, in the the Northern hemisphere of the planet Earth, the least observed seasonal variation of the primary luminary, the Sun, is to the North. The great god Ohm instructs us to always point our PE cell in that direction. Though our bible, the NEC, is mute on this point, we are urged by other docterines to follow the unwritten text, common sense, to dictate our actions.
I.E. Pointi North and you'll never go wrong.

[This message has been edited by elecbob (edited 03-24-2003).]

If you cannot point it exactly towards North (Mag. &/or True North), then point it either Northeast or Northwest. Either of these will be better than directly pointing East, West, or the worst, South!

Pointing it Northeast will respond to "Dawn Conditions" ("Off" state will be more precise when the Sun rises, and the "On" state will be less precise to when the Sun sets - causing the "On" state to occur more earlier than actual Sunset).

Pointing it Northwest has the opposite affect.

Pointing it directly East exposes it to full AM Sunlight,
Pointing it directly West exposes it to full PM Sunlight,
Pointing it directly South exposes it to near full AM and PM Sunlight.
These directions may cause premature failure.

Scott35

Thanks.

I thought it might have something to do with the seasons. I never thought that the photocell would fail or be damanged.

Now some photocell stories.
Some existing photocells are located under the roof eaves. They work, but they sure take a long time to turn off.

There are also some photocells on lights facing each other seperated by about 20 feet. Only one ever works because the other one shuts it off. I am going to fix this by moving the photocells some day.

As an aside, this being a jail, the lights coming on early or turning off late is much prefered to the opposite.

For municipal street lighting, because the arc of the sun is primarily in the south, they are optimized/”calibrated” for north pointing. Over a year's time, the yields an average "on" time is ~10 hours/day.

Maybe it’s the opposite in the south hemisphere, and illegal on the equator?

Before cheap photoelectric controls, there were older-design time clocks available with “astronomic” dials; that automatically adjust as the days grow shorter or longer. When buying them, they had the instruction to Indicate City and State nearest installation when ordering.”