Voltage Drop Calculations Data Entry Window Printable View

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1 120 No 9

Select voltage Maximum voltage drop allowed

2 5% 10

Select the max desired voltage drop (0%-5%) Minimum voltage allowed at load

3 Single Phase

11

Select phase type Multiplier

4 Stranded Copper Uncoated 12

Select the type of wire Resistance/1000' of wire

250 kcmil 5 * 13

Select the size of wire if known Wire Size

6 50 * 14

Enter the length of wire (0-5000') if known Distance

7 1000 *

15

Enter Amps (0-6000) if known Maximum Amps

8 1 16

Minimum number of parallel wires

Enter data into these cells Calculated information

Formulas used:

9. Maximum voltage drop allowed = Circuit Voltage(Cell 1) X Maximum voltage drop 17. Actual voltage drop = Resistance(Cell 20) x Amps(Cell 15) % allowed(Cell2). x Distance(Cell 14) x Multiplier(Cell 11)

10. Minimum Voltage drop allowed at load = Voltage(Cell 1) - Max vd allowed (Cell 9) 18. Acutal Voltage with load = Voltage(Cell1) - Acutal Voltage drop(Cell17)

11. Multiplier = 1 (if cell 3 is single phase) 19. Voltage Difference = Actual Voltage(Cell 18) - Min. voltage(Cell 10)Multiplier = square root of 3 or 1.732050808 (if cell 3 is three phase) If ok then this cell turns green, if not then it turns red

12. Resistance/1000' of wire = resistance of the type wire in cell 14 and 20. Total Resistance per foot = Res. in table 8 of Cell 4 and Cell 13 sized per cell 13 from Table 8 1000 x number of parallel wires (Cell 16)

13. Size wire =Cell 5 (if known and entered in cell 5) 21. Minimum wire size = the wire that has low enough resistance to carry

The following voltage drop calculations were all based on the resistance values in Table 8 of Chapter 9 of the 2011 NEC. This spreadsheet only considers voltage drop. Many other factors affect wire size. Refer to the entire NEC when sizing wire.

The NEC indicates in a FPN that a 3% voltage drop on branch or feeder circuits provides reasonable efficiency of operation.

Note: If only one of cells 5,6 and 7 is left blank, then a calculated value will appear to the left of the cell.

If the wire is smaller than AWG 1/0 then parallel wires are not allowed except per 310.4 exceptions.Select the number of parallel wires

(1 is non-parallel) or 2-25 pairs

Directions: Fill in blank cells 1-8. If you leave only one entry blank in cells 5, 6 or 7, then a recommended maximum will appear to the left of the cell. The Ampacity of the wire in cell 13 is given in cell 23. If this cell turns red, the wire size in cell 13 is not large enough to carry even the minimum load. This ampacity is calculated in Table 310.16 as per 110.14(c). This number does not consider any other factors such as insulation type, continuous load, correction factors or adjustment factors.

Size wire =Cell 21 (if unknown and cell 5 is left blank) the load without more than the max voltage drop.

14. Distance=Cell 6 (if known and entered in cell 5)Distance =Cell 22 (if unknown and cell 6 is left blank)

15. Maximum Amps= Cell 7 (if known and entered in cell 7) 22.Maximum Amps= see below (if cell 7 is left blank) Amps(Cell 15) x Resistance(Cell 20) x Multiplier(Cell 11)

Max voltage drop(Cell 9) x Number of parallel wires(Cell 8)Resistance/foot(Cell 20) x Distance(Cell 14) x Multiplier(Cell 11) 23. Max Ampacity of the selected wire in Cell13 =

16. Number of sets of parallel wires=Cell 8 (if known and entered in cell 8)Number of sets of parallel wires=1 (if unknown and cell 8 is left blank)

The calculations above were based on the following equations: 24. Amps above or below load = Ampacity of Cell 23 - Ampacity of Cell 15

Vd= I x R x L x M Where: Vd= Maximum Voltage Drop in volts Disclaimer: Voltage drop calculations and Table 310.16 are not theP only considerations when sizing conductors. Many other factors

I= Current in Amps must be considered, such as: the type of load, the ambient temp,I= Vd x P the type of insulation, the association with other conductors,

R x L x M R= Resistance in ohms per foot the temperature rating of the equipment, the type of environment,the size of the breaker, the type of circuit (branch, feeder, service,

R= Vd x P L= Length of wire one way in feet grounding, or control), continuous load, etc. Use this spreadsheetI x L x M to check voltage drop. See the NEC to size wires.

M= Multiplier L= Vd x P 2 for single phase or Wirelab Services

I x R x M or 1.732050808 for three phase Please report any errors to:Bill Bamford

P= I x R x L x M P= Number of parallel runs Albany, GeorgiaVd

Resistance =

Distance =

Bill_Bamford@Yahoo.comDate of last revision or correction:

Resistance value of 1 wire per 2002 NEC

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Yes###

6 7 5.15 volts (ok) Maximum voltage drop allowed Actual voltage drop

114.00 18 114.85 volts (ok) Minimum voltage allowed at load Actual voltage with load

2 19 0.85 volts (ok) Multiplier Voltage difference

0.0515 20 0.0000515 ohms Resistance/1000' of wire Total resistance per foot

250 kcmil 21 250 kcmil recommended Wire Size Minimum wire size for voltage drop

50.00 22 58 feet Distance Maximum distance with this load

1000 23 255 amps@ 75°F Maximum Amps

1 24 -745.00 amps (Failed) Minimum number of parallel wires Ampacity above or below load

Good data Bad data

Actual voltage drop = Resistance(Cell 20) x Amps(Cell 15) x Distance(Cell 14) x Multiplier(Cell 11)

Acutal Voltage with load = Voltage(Cell1) - Acutal Voltage drop(Cell17) ###

Voltage Difference = Actual Voltage(Cell 18) - Min. voltage(Cell 10)If ok then this cell turns green, if not then it turns red

###Total Resistance per foot = Res. in table 8 of Cell 4 and Cell 13 1000 x number of parallel wires (Cell 16)

###Minimum wire size = the wire that has low enough resistance to carry 0

The following voltage drop calculations were all based on the resistance values in Table 8 of Chapter 9 of the 2011 NEC. This spreadsheet only considers voltage drop. Many other factors affect wire size. Refer to the entire NEC when sizing wire.

Max ampacity of the wire in Cell 13 per Table 310.16 of the 2011 NEC

Directions: Fill in blank cells 1-8. If you leave only one entry blank in cells 5, 6 or 7, then a recommended maximum will appear to the left of the cell. The Ampacity of the wire in cell 13 is given in cell 23. If this cell turns red, the wire size in cell 13 is not large enough to carry even the minimum load. This ampacity is calculated in Table 310.16 as per 110.14(c). This number does not consider any other factors such as insulation type, continuous load, correction factors or adjustment factors.

the load without more than the max voltage drop.

### Amps(Cell 15) x Length(Cell 14) x Multiplier(Cell 11)

Amps(Cell 15) x Resistance(Cell 20) x Multiplier(Cell 11)

Max Ampacity of the selected wire in Cell13 =

The ampacity of the conductor listed in Cell 4 and Cell 13 per Article 110.14(C) and Table 310.16. Note: This is the maximumampacity allowed under ideal conditions.

Amps above or below load = Ampacity of Cell 23 - Ampacity of Cell 15

Disclaimer: Voltage drop calculations and Table 310.16 are not theonly considerations when sizing conductors. Many other factors must be considered, such as: the type of load, the ambient temp,the type of insulation, the association with other conductors,the temperature rating of the equipment, the type of environment,the size of the breaker, the type of circuit (branch, feeder, service,grounding, or control), continuous load, etc. Use this spreadsheetto check voltage drop. See the NEC to size wires.

Wirelab ServicesPlease report any errors to:Bill BamfordAlbany, Georgia

Resistance = Max voltage drop((Cell 9) x parallel wires(Cell 16)

Distance = Max voltage drop(Cell 9) x parallel wires (Cell 16)

Bill_Bamford@Yahoo.comDate of last revision or correction: July 2011

software was written in Visual Basic by Bobby Bamford, an electrical engineer in Orlando, Fla. The text book was written by his twin brother Bill Bamford, a state licensed electrician in Albany, Ga, who taught electrical classes in a Technical College for 8 years.

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Panels must be wired, with proper breaker selection Sample trim-out inspection All receptacles, switches, lights, and appliances must be wired

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I. IntroductionI. Roughing-in the house 1. Installing Service and Panel Enclosures 2. Installing Receptacle Boxes 3. Installing Swtich and Lighting Fixture Boxes 4. Installing Appliance Enclosures 5. Installing Service and Feeder Cables 6. Installing Branch Circuit Cables 7. Installing Cables for Restricted Branch Circuits 8. Installing Cables for Switches and Fixtures 9. Installing Cables for Appliances10. Finishing up the Rough-inII. Trimming-Out the House 11. Wiring Receptacles 12. Wiring Single Pole Switches 13. Wiring 3-Way and 4-Way Switches 14. Wiring Fixtures and Ceiling Fans 15. Wiring Appliances 16. Wiring Services and Subpanels 17. Finishing up the Trim-outIII Appendix A. Voltage and Current B. Grounding Equipment and Buildings C. Wire Sizing D. Box Sizing (Box Fill Calculations) E. Tools of the Trade The illustration above shows a branch circuit that has all lights wired hot. F. International Building Codes on Drilling and Notching Wood The 2011 NEC requires the use of four conductor cables for 3-way and G. The Functioning of GFCI 4-way switches wired this way in order to meet the new code requiring H. The Functioning of AFCI a neutral conductor in every switch box for future use [NEC 404.2 (C)]. I. Wirlab's Rough-in and Trim-out Inspections This illustration is in Chapter 13 for wiring 3-way and 4-way switches. J. Definitions and Abbreviations K. NEC Residential Code Changes in a jurisdiction that does not adopt this new code. L House 1 Assignments

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