320 feet underground circuit

S

Stevenfyeager

Senior Member
Location
United States, Indiana
Occupation
electrical contractor
According to on line calculator, #2 AL would be needed for 320' underground 20 amps, 120 volts. (4% drop) Does this sound right? I've read that some people have trouble with gfi outlets feeding a long run tripping. They advised installing the gfi outlet at the end instead of feeding from one. Is that true ? I would rather feed from one to allow me to trench more shallow. Thank you.
 
2 x 21.2 x 320' x 20a divided by 66360(cm of #2 AL) = 4.09 volts dropped 3% vd on branch ckts is recommended. I would say you are correct.
If the load is not a full 20a, you may be able to go smaller.
 
2-2-4, or 2-2-2 if you want to want to follow that stupid proportional sizing rule, triplex is pretty cheap, relatively speaking. I'd still put it in conduit though.

But for some landscape lights, they aren't going wide open at 20 amps, so I'd probably just use some #10.
 
can always put some concrete over it-
I’d get a transformer at the start get voltage higher and then transition back at the load. Be a wash probably for parts and save on labor. Maybe- but smaller conductors are my go to
 
Stevenfyeager said:
customer wants a landscape transformer with lights at his driveway entrance
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So load is probably only an amp or even less? I wouldn't increase conductor size for that alone. If there is other temporary load to consider I might run 10 AWG just because but that's probably the most I would do for this install with no other regular loading.
 
it’s landscape lights anyway, would the transformer not really care about the drop in voltage just output less and might not get as many landscapes on a long run?
 
AC\DC said:
it’s landscape lights anyway, would the transformer not really care about the drop in voltage just output less and might not get as many landscapes on a long run?
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Presuming these are low level light output luminaires you can get an awful lot of these on a 20 amp 120 volt circuit. A majority of the transformers utilized are probably 100 watt or less with LED lighting that is now common. Even non LED still tends to be 100 watt or less though for this sort of lighting. If there is much for flood type lighting to light up structures, statues, shrubbery, flagpoles, etc then that may increase the load.
 
Maybe the customer wants this at the end of their driveway:
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kwired said:
Presuming these are low level light output luminaires you can get an awful lot of these on a 20 amp 120 volt circuit. A majority of the transformers utilized are probably 100 watt or less with LED lighting that is now common. Even non LED still tends to be 100 watt or less though for this sort of lighting. If there is much for flood type lighting to light up structures, statues, shrubbery, flagpoles, etc then that may increase the load.
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Not to mention that all the landscape lighting transformers I've seen have a tap to select up to 14 volts. Set the tap on the highest voltage and run #10 to the receptacle.
 
kwired said:
So load is probably only an amp or even less? I wouldn't increase conductor size for that alone. If there is other temporary load to consider I might run 10 AWG just because but that's probably the most I would do for this install with no other regular loading.
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a small landscape transformer is one to two amps input, so I should be fine with a #10 Cu, right ?
 
Stevenfyeager said:
a small landscape transformer is one to two amps input, so I should be fine with a #10 Cu, right ?
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I didn't do calculation but for voltage drop on 2 amps you possibly still fine with 14 AWG. The less voltage drop you wish to tolerate the more chance you may need a larger conductor.
 
I haven't heard back yet from the customer. Thank you. I'm thinking on suggesting my #2 Al anyway to give him the option of a gate opener later down the road instead of just a couple of landscape lights like his wife asked me for.
 
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