I was told today by a Sun System rep..

[rives]

12/4 is overkill, but 16/4 is marginal. 75' is the maximum ballast-to-lamp distance for #16 that I've seen ballast manufacturer's recommend. While the current levels are fine, the voltage drop can become a factor. If the OP is figuring this length cord as the overall length it should be fine. However, if there is additional length at each end from the hood to a junction box and the ballast to a junction box, it could become problematic. And yes, if the ignitor is left at that ballast, the increased capacitance of the larger wire can attenuate the starting pulse.

 

[Avenger]

How much voltage drop do you expect with 415 volt open circuit voltage, 7 amps current and 75' of 16AWG conductor?

I calculated it at about 1-1.5%

If thats correct, do you think this is acceptable?

 

[rives]

That voltage drop would be completely acceptable - the problem that I saw was that open circuit voltage is entirely different than what you would see when the lamp was in the circuit. I couldn't find any information on what the running voltage was, and don't recall the figure if I've ever checked it. I know that I've never had a scope and current gun on an HID lamp when it ignited, but I would think that it would have a very dynamic impact on the voltage/current that it was being fed with - while a poor comparison, tungsten lamps go from almost a direct short to a very high resistance almost instantly. From years in an industrial setting with HID lighting, I know that even direct-coupled fixtures are extremely sensitive to short-duration voltage sags. Older lamps in particular are very prone to shutting down and re-igniting when a momentary sag hits, so it might not be that big of a factor with the re-lamping practices that most growers use.

I tend to try and err on the conservative side of things.

 

[Avenger]

good point regarding the difference in OCV and lamp operating voltage.

I believe the rated voltage for the 1000 watt HPS lamp is 250 volts.

and the calculated voltage drop for that voltage at 75' on 16AWG with 8 amps is still slightly less than 2%.

Still acceptable I think, but in order to err on the side of caution, I'll change my recomendation to 14 AWG SO cord for ballast to lamp distances over 50 feet.



cheers.

 

[rives]

Using those parameters, I calc the drop at 2.4% on #16.

14 gauge would certainly work well. I confess that I tend to completely overlook that size wire - I've installed probably hundreds of miles of both #16 and #12, and I doubt that I've ever used a full spool of #14. In the plants that I worked in, #16 was used for control circuitry and power wiring started with #12. With the current cost of copper, I need to change my way of thinking.