wire resistance,temp,soil cond

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stev11

Member
Location
india
Hello!

I am trying to calculate the voltage drop for my case and I need to know the necessary factors that will change wire dc resistance ???as follows

I have 48v dc solenoid valve,6 watt,the wire length is 600m(from the solenoid to the controller) and the cable is installed inside pvc conduit and then the pvc conduit is installed in the ground at depth 60cm(soil).

View attachment 10638
 

Sahib

Senior Member
Location
India
Why not just measure the voltages at the controller and valve and compute the difference at noon and evening?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Once you complete the install the only thing that will change the conductor resistance is a change in the conductor temperature.
 

Julius Right

Senior Member
Occupation
Electrical Engineer Power Station Physical Design Retired
The minimum conductor you have to run is 1.5 sqr.mm copper.
The resistance of one conductor at 20oC will be Rdc@20= 1/58*600/1.5=6.9 ohm.
The current will be 6w/48V=0.125 A.
The voltage drop will be 2*Rdc*I=2*6.9*0.125=1.725 V[1.725/48*100=3.6%
The wire temperature for 1 A load will be 0.2 oC above the earth temperature [the raise of the wire temperature is negligible].
The temperature of the wire will be the surrounding earth temperature [not more than 30oC-in my opinion].
The resistance at 30oC will be Rdc@30= 6.9*(1+0.00393*10)=7.17 ohm
Then the voltage drop will be 1.725*1.04=1.794V [3.74%].
If we'll take 2.5 mm^2 copper the voltage drop will be 1.794*1.5/2.5=1.076 V[2.24%].:D
 

stev11

Member
Location
india
thanks for Sahib and don_resqcapt19,,and special thanks for Julius Right

but how can I choose
the surrounding earth temperature(20c?30c??50c) for this cable??? because we choose the 50 c ambient temp for the air cable(gulf temp)??
 

Smart $

Esteemed Member
Location
Ohio
IDK for India, but here in the States we can access historical and current climate conditions, including soil temperature at various depths, on the web through national agencies. Perhaps India may have something similar.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
thanks for Sahib and don_resqcapt19,,and special thanks for Julius Right

but how can I choose
the surrounding earth temperature(20c?30c??50c) for this cable??? because we choose the 50 c ambient temp for the air cable(gulf temp)??
If you choose a conductor with an acceptable voltage drop at the worst case, that is the maximum possible temperature, you are good to go.
Using this calculator and #12 wire, there is only a 0.2% change in the voltage drop between an ambient of 30?C and one of 60?C
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
And except in a thermal hot springs area, the ground temperature will be less than the air temperature in the summer.
The cooling effect on the wires will be almost as good as free air.
 

stev11

Member
Location
india
IDK for India, but here in the States we can access historical and current climate conditions, including soil temperature at various depths, on the web through national agencies. Perhaps India may have something similar.

thank you very good idea.
 

Julius Right

Senior Member
Occupation
Electrical Engineer Power Station Physical Design Retired
i am waiting your help ???
The study of air and shallow underground for US Military in Saudi the soil temperature was 2-3 degrees less than the Arizona.See:
http://www.kau.edu.sa/files/155/researches/177erid.pdf
According to
http://www.builditsolar.com/Projects/Cooling/EarthTemperatures.htm
the maximum average temperature in US [including Arizona] does not over 90 F [32 C].
So, in any case 30 dgr.C it should be the maximum temperature considered for 2-3 ft. depth.:)
 

stev11

Member
Location
india
The study of air and shallow underground for US Military in Saudi the soil temperature was 2-3 degrees less than the Arizona.See:
http://www.kau.edu.sa/files/155/researches/177erid.pdf
According to
http://www.builditsolar.com/Projects/Cooling/EarthTemperatures.htm
the maximum average temperature in US [including Arizona] does not over 90 F [32 C].
So, in any case 30 dgr.C it should be the maximum temperature considered for 2-3 ft. depth.:)
thank you,i tested it at site and it was 32c in the day at 2 ft.thank you again
 
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