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TWW (Electrical)
24 Jun 03 18:56
For constant current regulated 6.6A airport lighting circuits, what is the determining factor one must consider in sizing the cable, ie. allowable voltage drop. I have one run here that is 51,000 ft!

Thankyou in advance.
jeffs01879 (Electrical)
25 Jun 03 13:54
Voltage drop per se is not an issue.  The major factor is the that the total load on the regulator, both lamps and cable losses, not exceed the rating of the regulator.  Basically what would be a voltage drop in a conventional parallel circuit turns into an increase in the voltage which the regulator must deliver to the circuit to provide for the loss in the cable.  51,000 feet of cable on a 6.6A circuit seems like a lot, but check the total load and size the regulator accordingly.
wilber (Electrical)
25 Jun 03 14:11
A good article on airport lighting cable can be found

http://ecmweb.com/ar/electric_series_lighting_circuitry/index.htm


TWW (Electrical)
25 Jun 03 16:29
Thanks for the information, The only argument I could come up with is the cable loss effecting the system efficiency and regulator loading as you have discussed. And Yes the actual cable is only half the 52000 stated.
busbar (Electrical)
25 Jun 03 18:47

51- or 52-k∙ft would very likely be the length for voltage-drop calculations—it is a series loop regardless of cable route.

I'll bet that it's far more a regulatory than an engineering issue.

Some text states, "...8 AWG, 5,000-volt cable will satisfy most operational requirements. No. 6 AWG, 5,000-volt cable should be used for long “homeruns” or with 20 ampere circuits."  BUT I HAVE ABSOLUTELY NO CLUE IF THAT APPLIES TO YOUR INSTALLATION.  WHAT DOES THE DESIGNING REGISTERED PROFESSIONAL ENGINEER SAY?
  
TWW (Electrical)
25 Jun 03 19:27
That would be me, are you impressed?
jbartos (Electrical)
26 Jun 03 13:20
Suggestion: Check federal and military standards for airports.
E.g. Visit
http://assist.daps.dla.mil/quicksearch/
for military documents available to public.
jcai (Aerospace)
27 Jun 03 1:00
HI GUYS - JUST A WORD OF CAUTION AS THE MAN SAYS - TALK TO F.A.A. IN THE U.S.A. BEFORE YOU DO ANYTHING ON AIRPORT RUNWAY TYPE LIGHTING .  THEY HAVE ALL THE SPECS SET IN CONCRETE YEARS AGO .    ALSO DO NOT USE DIFFERENT CROSS SECTION TYPE CABLE WHICH IS DIFFERENT TO THE CABLE ENTRY GLAND IN THE INSET CENTER LINE RUNWAY LIGHT FITTINGS - THAT CAUSES US LOTS OF LEAKS - THIS IS NOT FIXABLE WITH SILICONE GOOP ETC ! DO NOT USE THICKER 'O'RINGS - DO NOT OVER TORQUE BOLTS . J.C.
markac (Electrical)
27 Jun 03 11:10
See FAA advisory circular No. AC 150/5340. Advisory circulars can be found on FAA website. Fifure 14 has some criteria for load calculations, but refer to accompanying text to fully follow this figure.

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