tapping off a long underground circuit

Status
Not open for further replies.
S

Stevenfyeager

Senior Member
Location
United States, Indiana
Occupation
electrical contractor
Customer wants to tap out of a 465' underground circuit powering a detached building. Wants to install some LED lighting along the way. Above ground J box, splice #12 off of the #2 AL URD 120v, 20 amp run. Any problems with this ?
 
Assuming the URD is protected at 20 amps or less, and the splice is made in a code complaint manner, there is no issue.
 
don_resqcapt19 said:
Assuming the URD is protected at 20 amps or less, and the splice is made in a code complaint manner, there is no issue.
Click to expand...
Either that or use the tap rules and place a panel w/OCPD, and feed the lights from that.

ETA: I actually typed this almost two hours ago but failed to hit post! Sorry Pton!
 
Thanks, the customer is wanting bottom dollar. He wants lights and outlets in the 10x10 building and will use a computer, small air conditioner.
Calculator.net tells me the drop will be 4.68 %. I don't like to push the limits, and would not want to be that close to 5% and would normally go up one more wire size but he doesnt. You know anything about computers needing closer to 120 volts or not ?
 
I get roughly 6.2% VD with a 20 amp load @ 120 volt 465 feet. You will notice voltage drop each time the A/C starts. A 12 amp A/C unit could easily pull 60 amps at start, however briefly. That could give a 22 volt drop. Will the computer need 120? Maybe, probably not. Depends on its power supply. He might want to invest in a UPS to ensure it doesn't drop out. Ignore the issue if its a lap top, he can live with the blinking lights.

I have very little sympathy for someone that can build a He/She shed, then wants to pinch pennies on what will make the building usable.
 
Rule of thumb used to be 10 watts of heat per sq ft. Roughly 8.3 amps.
Resistive PF is 1. Motor load is less, hence the .8.

8.3 amps would be about 2.6% vd.
Start up of an 8.3 motor load could be 49. 15.5%

Neither includes the lighting load that he wants to include somewhere in between.
 
Stevenfyeager said:
Thanks, the customer is wanting bottom dollar. He wants lights and outlets in the 10x10 building and will use a computer, small air conditioner.
Calculator.net tells me the drop will be 4.68 %. I don't like to push the limits, and would not want to be that close to 5% and would normally go up one more wire size but he doesnt. You know anything about computers needing closer to 120 volts or not ?
Click to expand...
Both laptop power supplies I have here say 100-240 volts.
 
Stevenfyeager said:
Thanks, the customer is wanting bottom dollar. He wants lights and outlets in the 10x10 building and will use a computer, small air conditioner.
Calculator.net tells me the drop will be 4.68 %. I don't like to push the limits, and would not want to be that close to 5% and would normally go up one more wire size but he doesnt. You know anything about computers needing closer to 120 volts or not ?
Click to expand...
Computers like newer tvs are DC now days.
they convert AC to DC.
*Generally speaking*, the voltage ranges are 90-135V
 
If you run # 2AL underground and the current will not exceed 15A over 3 hours the wire temperature will not exceed 30°C
so there is no need to calculate voltage drop using 75°C resistance.
I am getting these results:
Voltage = 120 V, 1 Phase
Current = 15 Amp
Power = 1,620 W @ PF = 0.9
Voltage Drop = 3.68 V / 3.06 % of the supply voltage.
For 465 FT long, single run of #2 AWG Aluminium installed in PVC conduit.
Estimated circuit operating temperature (continuous load) is 28.3°C
Conductor parameters used in calculation:
AC resistance = 0.271 Ohm/1000ft for conductor temperature of 30°C
XL reactance = 0.046 Ohm/1000ft
Calculated for RHH, RHW, RHW-2 wires types with insulation rated at 75°C (167°F).
 

Attachments

  • VD Calc.JPG
    VD Calc.JPG
    137.8 KB · Views: 4
Status
Not open for further replies.
Top