id, aliases, title, tags, author, dg-publish, year
| id |
aliases |
title |
tags |
author |
dg-publish |
year |
|
|
Voltage Drop Calculations |
| authorship/other |
| destiny/permanent |
| status/incomplete |
| topic/construction/electrical |
| type/media/article |
|
David A. Snyder, PE |
false |
2020 |
Voltage Drop Calculations
%%
E426_Voltage_Drop_Tables.pdf
retrieved from pdhonline.com "Voltage Drop Calculations"
PDHonline Course E426 (3 PDH)
Local copy saved as snyder_2020_voltage-drop-calculations.pdf
%%
Introduction
Table 1 --- Quick Guide to Voltage Drop Formulas
Voltage Drop and the National Electrical Code
Branch Circuits
Feeders
Sensitive Electronic Equipment
Other Considerations
Common Formulas for Voltage Drop Calculations
Single-Phase Approximate Voltage Drop Formulas
Figure 1 --- Single-Phase, Two-Wire Voltage-Drop Circuit Diagram
Figure 2 --- Distributed Resistance in Conductors
Table 2 --- Derivation of the Value of K for Copper Conductors
Figure 3 --- Single-Phase, Three-Wire Voltage-Drop Circuit Diagram
Three-Phase Approximate Voltage Drop Formulas
Figure 4 --- Three-Phase Wye-Connected with Neutral Voltage-Drop Circuit Diagram
No Neutral Current in a Balanced Three-Phase System?
Figure 5 --- Balanced, Wye-Connected, Three-Phase, Resistance Load, with Neutral Connection
Figure 6 --- Balanced, Wye-Connected, Three-Phase 10 KW Load at 480 V
√3 Relationship of Three-Phase Voltages
Figure 7 --- 480Y/277V Wye-Delta Voltage Relationship
Figure 8 --Wye-Delta Voltage Relationship --- Right Triangle Geometry
Figure 9 --- 208Y/120V Wye-Delta Voltage Relationship
Why the √3 Is Used in Balanced, Three-Phase Voltage Drop Calculations
Figure 10 --- The Square Root of Three in Three-Phase Voltage-Drop Calculations
Table 9 in the NEC
Which Columns Are Applicable?
XL (Reactance)
Alternating-Current Resistance
Effective Z at 0.85 PF
Table 3 --- Selected Effective Z Calculations at 0.85 PF (Ohms-to-Neutral per 1,000 feet) . 21
Effective Z at Any Power Factor: Note 2 to Table 9 in the NEC
Table 4 --- Effective Z Calculations for Selected Wire Sizes at Various Power Factors (Ohms-to-Neutral per 1,000 feet)
Note 2 to Table 8 in the NEC
Phasor Diagrams of Resistance, Reactance, and Impedance for Conductors
Figure 11 --- Phasor Diagram of Resistance, Reactance, and Impedance for 12 AWG Copper Conductors in Steel Conduit at 0.85 PF
Figure 12 --- Phasor Diagram of Resistance, Reactance, and Impedance for 12 AWG Copper Conductors in Steel Conduit at Selected Power Factor Values
Figure 13 --- Phasor Diagram of Resistance, Reactance, and Impedance for 250 KCMIL Copper Conductors in Steel Conduit at 0.85 PF
Figure 14 --- Phasor Diagram of Resistance, Reactance, and Impedance for 500 KCMIL Copper Conductors in Steel Conduit at 0.85 PF
Figure 15 --- Phasor Diagram of Resistance, Reactance, and Impedance for 500 KCMIL Copper Conductors in Steel Conduit at Selected Power Factor Values
Estimated Vdrop Derived from Impedance Phasor Diagrams
Figure 16 --- Applying 300 Amps to the Impedance Phasor Diagram for 500 KCMIL Copper Conductors in Steel Conduit at Selected Power Factor Values
Estimated Vdrop, Single-Phase:
Estimated Vdrop, Three-Phase:
Voltage Drop Phasor Diagram in IEEE Standard 141 (Red Book)
Figure 17 --- IEEE Phasor Diagram of Voltage Drop
Figure 18 --- Vertical Components of Phasor Diagram of Voltage Drop
Figure 19 --- Triangle Formed by Vs, Vr + Estimated Vdrop, and IXcosΦ-IRsinΦ
Figure 20 --- When the Vector I * Z Really Is the Actual Vdrop
Figure 21 --- If Conductor X > R, the Error Increases as Power Factor Increases
Calculating the Error Shown in the IEEE Phasor Diagram
Figure 22 --- Finding the Height h of a Circular Segment
Single-Phase Formulas for Error and Actual Vdrop:
Three-Phase Formulas for Error and Actual Vdrop:
Table 5 --- Error Voltage Drop Calculations for Real-World Examples in Next Section
Real-World Examples
Table 6 --- Real-World Examples
10 Hp Motor at 480V/3Φ with 12 AWG Conductors
Figure 23 --- Line-to-Neutral Voltage Drop for 10 Hp Motor at 480V/3Φ with 200' of 12 AWG Conductors
Table 7 --- Line-to-Line Voltage Drop for 10 Hp Motor at 480V/3Φ with 200' of 12 AWG Conductors
15 KW Heater at 480V/3Φ with 10 AWG Conductors
Figure 24 --- Line-to-Neutral Voltage Drop for 15 KW Load at 480V/3Φ with 200' of 10 AWG Conductors
Table 8 --- Line-to-Line Voltage Drop for 15 KW Load at 480V/3Φ with 200' of 10 AWG Conductors
250 Hp Motor at 480V/3Φ with 500 KCMIL Conductors
Figure 25 --- Line-to-Neutral Voltage Drop for 250 Hp Motor at 480V/3Φ with 200' of 500 KCMIL Conductors
Table 9 --- Line-to-Line Voltage Drop for 250 Hp Motor at 480V/3Φ with 200' of 500 KCMIL Conductors
Rearranging the Formulas Used for Approximate Vdrop
Single-Phase Voltage Drop Formulas --- Rearranged
Table 10 --- Voltage Drop for 10 A Load at 120V/1Φ with 100' of 10 AWG Conductors
Three-Phase Voltage Drop Formulas --- Rearranged
Other Considerations
Increase Equipment Grounding Conductor Size
Increase Grounded (Neutral) Conductor Size
Verify Wire Size and Quantity Capacity of Terminations at Both Ends
Verify Conduit Size
Rule-of-Thumb
Converting Formulas from Single-Phase to Three-Phase
Table 11 --- Voltage Drop for 10 A Load at 120V/1Φ with 120' of 12 AWG Conductors
Table 12 --- Voltage Drop for 10 A Load at 208V/3Φ with 208' of 12 AWG Conductors
Table 13 --- Voltage Drop for 10 A Load at 277V/1Φ with 277' of 12 AWG Conductors
Table 14 --- Voltage Drop for 10 A Load at 480V/3Φ with 480' of 12 AWG Conductors
In Closing
Abbreviations
Additional Reading
