Limiting Conductor Length (Distance) to Minimize Voltage Drop 8.10 Elect. Exam Prep.

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Hello,
I am reading a statement note from the answer sheet 8 10, question 47. It states...

Don’t confuse distance (D) with length (L). This formula give you distance between two points, not length of conductors in the circuit.

As I would understand this statement... if D=149 then this is as the crow flies from point A to point B. In practice, I would not want the wire between the two point to be more than 149 feet. If I had vertical runs of 5 ft on both sides then the distance between the two points would be 139 feet. Making the wire length still not more than 149 feet.

Can anyone provide any further explanation that I may be missing?
 
ptonsparky said:
I thought I knew what you meant but changed my mind. What is question 47. Can you supply a bit of detail?
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What's the approximate distance that a 240v, 31a, single-phase load can be located from a panelboard so the voltage drop doesn't exceed three percent? The load is wired with 8 awg copper.
 
It also makes a difference whether the circuit is single phase or three phase and if the loads are balanced, but yes, conductor length is what matters, not physical distance. The NEC has not always gotten this right; for example 705.31 used to say that a disconnect for a supply side interconnected power source had to be within 10 feet of the point of interconnection whereas the restriction should have been expressed as conductor length. Most of us interpreted it as conductor length anyway even though the code did not say that.

As for voltage drop I always revert to Ohm's Law with appropriate values.
 
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ggunn said:
It also makes a difference whether the circuit is single phase or three phase and if the loads are balanced, but yes, conductor length is what matters, not physical distance. The NEC has not always gotten this right; for example 705.31 used to say that a disconnect for a supply side interconnected power source had to be within 10 feet of the point of interconnection whereas the restriction should have been expressed as conductor length. Most of us interpreted it as conductor length anyway even though the code did not say that.

As for voltage drop I always revert to Ohm's Law with appropriate values.
Click to expand...

Ohms Law is for DC.

The advanced version is FAR more complicated. Irrespective of voltage drop and NEC for that matter there are other limitations on length. Read the two technical papers linked with the software.

steeltubeinstitute.org

GEMI Analysis Software | Steel Tube Institute

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Voltage drop calculation (finding distance of existing circuit)

I know this is quite simple but have never really done it before until today, and while it might not be spot on I believe it should be relatively close. Any thoughts? So anyhow bored on a Friday no work got a cold or allergies can’t go around anyone for respect with all the stuff going around...
forums.mikeholt.com


OP trying reading this old thread of mine and see if it helps any. I tried an experiment at the house one day trying to use ohms law to find a round about distance of a circuit.
 
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