Long residential feeder [RE-wrenches]

[Steve Johnson]

Comments on long feeder runs.

Typically when you get around 250 to 300 feet or so you want to add an 
underground pullbox in a conduit run.  A Quazite or CDR box can be used, 
without a bottom, resting in a bed of gravel for drainage.  This cuts 
down on the friction of a long pull and provides many benefits for 
unknown developments in the future.

I would design for 80% of system ampacity in a situation where loads 
could be added.  Of course that is easy to say, harder to do.  Another 
way would be to estimate maximum current load, add 20% for growth, and 
spell that out to the cutomer.

The URD cable is a good application, 2 feet deep typical for 240 volts.  
Around here we call it "Pump Wire" because it is used on farms to drop 
down to a submersible pump.  The insulation is very tough. Watch for 
rocks on back fill though.  I've had 300 feet of it in my front yard for 
16 years so far.  Aluminum connections should be retorqued after one 
year to allow for 'flow' as the relatively soft aluminum will flow into 
the corners of the lugs after warming up and over time.  This 
retightening the connection is good maintenace if you are in a panel 
with aluminum feeders.  Once it has been retorqued after 'flow' it is 
good to go as it has taken up all available room.


Steve Johnson
LightWave Electric
Nashville, Tennessee


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