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Wire Sizing Worksheet TheSolarPlanner.com

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45

0.87

Inverter Model

Check box if system is positive grounded 0

Minimum Wire Gauge for Conductors

Step 2: Size PV Output circuit conductors.

Check here if using a combiner box 0

20

Circuit Isc 0.00 80% Temp Adder 33

Conductors Exiting Box 4 0.00 0.41

Minimum Wire Gauge for Conductors Enter Wire Type:

Project Name: Scroll to the right for Page 2…

Copyright © 2013 TheSolarPlanner.com

Energy Management ServiceSee Instructions.

Residential Wire Sizing Worksheet (Gauges, Lengths & Voltage

Drop)

Use link below to get local high temperature.

Step 1: Size the source circuit conductors.

Max. High Temperature

(Celsius)Solar ABC's

This calculation applies to PV or USE-2 wire between the array and the junction/combiner box. Do not use this step to size wire for microinverters.

2% Avg temp recommended.

Temperature Correction

Factor

Module Brand/Model #

Default Max High Temp = 45. (You can change defaults. Don't leave the box blank.)

Module Isc - short circuit current

Module Ipm - operating current

Worksheet designed for a grid-tied system with one inverter. Use only 90°C rated conductors, minimum gauge 12. Conduit is assumed to

carry wire for this PV system only. Conductor gauges may be changed

in later steps.

Type only in the black outlined boxes

Ampacity Calculation

This calculation applies to THWN-2 or other approved wire that's run through conduit between a junction box/combiner and the inverter.

Number of Array Strings (Default = 2)

Inches btw conduit & roof

Check here if no conduit on roof

Conduit Adjustment Ampacity

Calculation Temp Correction

Factor

Page 2

Scroll right for Page 3.

Check box if inverter will be indoors. 0 35

0Indoor Temp Correction 0.96

Ampacity Calculation 0.00 100% 1

Minimum Gauge for Conductors Wire Type

Step 4: Measure wire lengths.

String 1 2 3 4

0

PV Output Circuit:

Distance of EGC (if different from conductors)

Inverter Out Circuit

Calculations:

Source Positive 0 Neg. 0 EGC 0 All lengths in feet.

PV Output Positive 0 Negative 0 EGC 0

Inverter Out Hot 0 Neutral 0 EGC 0

Residential Wire Sizing Worksheet See Instructions.

Type only in

the black outlined boxes

Step 3: Size Inverter Output conductors.

Inverter AC Output Current - Imax

If indoors, estimate highest Celsius temp. (Default = 35.)

Check box if conduit will carry more than 3 conductors. (Max=6)

Conduit Adjustment

Check here if using a transformerless inverter

An array EGC will be shorter if grounding clips are used on the

modules.Source Circuit: (Use feet only.)

Distance of home run (i.e. from array far end to junction box)

Length for Ground

Wire(EGC)Distance of near-end run to box if not connecting by module cable

Check box if home run is the positive wire When measuring wire runs, be sure to factor in obstacles,

wide turns and an extra foot for wiring inside electrical boxes. Enter one-way travel distances only. No roundtrips. Do not factor in the length of module leads.

Distance between junction box/combiner and inverter Distance of

inverter EGC Wire distance between

inverter and main panel

Page 3

Step 5: Perform voltage drop calculations. Enter the number of modules in the array(s).

48

0.0 A 2

Length ft Ohms per kft

0.0 A NO

Length ft Ohms per kft

0.0 A

Length ft Ohms per kft

Calculations:

Circuit: Source PV Output

Circuit Volts 120 V

Percentage

0 0 0

New size New size New Size

Do not remove these tables.

Residential Wire Sizing Worksheet See Instructions.

Module Operating Volts Vpm

Module Cable Length in inches

Module Count

Source Circuit

Operating Current

Provide length of one cable only. (Default is 48.)

Array Strings

Conductor gauge

PV Output Circuit

Operating Current

Combiner Box?

Selected in Step 2.

Scroll left for Pages 1 & 2.

Conductor gauge

Inverter Out Circuit

AC Maximum Current

Circuit wire gauges were selected in

Steps 1-3.

Type only in the empty or check boxes outlined in

black.

Conductor gauge

Note: Step 5 is optional. It's accepted practice not to allow

the voltage drop to go too much higher than

3%, but the NEC doesn't regulate this

amount.

Inverter Out

Voltage Drop

Check box to use the next beefier wire

gauge for this circuit.

Scroll right for Overcurrent

Protection Ampacity Check and EGC Sizing

Conductor Gauge

You can change gauges again in Step 6.

New Voltage Drop/%

Gauge

1 0.1542 0.1943 0.2454 0.3086 0.4918 0.778

10 1.2412 1.98

Voltage Drop Resistance for Stranded Wire

Ohms per kft

Page 4

Circuit

PV Source 0.0 A Data Missing

PV Output 0.0 A Data Missing

Inverter Out 0.0 A Data Missing

Enter final conductor gauges after reading the red instructions above.PV Source PV Output Inverter Out

Step 7: Choose a ground wire and gauge for each circui

NEC Table 250.122

AWG Max Amps

12 = 20

PV Source PV Output Inverter Out 10 E 30

Minimum EGC Gauge 10 G 40

Wire Type: 0 0 10 C 60

8 = 100

Do not remove these tables.

Wire Sizing Worksheet

After completing this page, click on the Report tab below to view your results.

Step 6: Compare wire gauge ampacities to any overcurrent device ratings.Note: Overcurrent protection in the PV Source and PV Output circuits may be optional when you use less than 3 strings. Check the NEC or ask a qualified expert for guidance.

Overcurrent Ampacity

CalculationEnter O.C.

Rating (if any)Conductor

GaugeDerated Wire

AmpacityIs the wire ampacity equal to or greater

than the O.C. rating?

Fill in each box if you plan to use O.C. protection for that circuit. An O.C. device is rated in amps. Use the size nearest to, but not less than, the Overcurrent Ampacity Calculation. Click the Resources tab below for links to O.C. device sizes. NOTE: Per NEC 690.8(B)(1)(c), for any O.C. device subject to an ambient temperature more than 40˚C, you must implement the fuse or breaker's manufacturer temp correction factors when selecting a size. Once you've selected O.C. devices, enter values in all three boxes below.

If the last column above reads "check wire gauge", the circuit may require a beefier conductor. However, if the O.C. Rating is the next available size for the Derated Wire Ampacity value, you can stick with the gauge that's listed.

Conductor Gauges

Transformerless inverter selected.

See Step 3

If a transformerless inverter is used, the EGC (ground wire) for each circuit must be rated to carry twice the Overcurrent Ampacity Calc. For a normal inverter: If an O.C. device is used, pick a gauge that corresponds to the Max Amps in NEC Table 250.122 (e.g. a 30-amp breaker requires Gauge 10 wire). If no O.C. device is used, pick the same gauge as the conductors, or beefier. For bare copper, the minimum gauge is usually 6.

Click Resources tab or NEC Tables for help.

The most commonly used wire type in the Source circuit is Bare Copper - AWG 6. PV and Inverter Output wire types were picked in Steps 2-3.

Gauge Ampacity Ampacity Gauge1 220 40 122 190 55 103 165 80 84 140 105 66 105 140 48 80 165 3

10 55 190 212 40 220 1

Gauge Ampacity Ampacity Gauge1 150 30 122 130 40 103 110 55 84 95 75 66 75 95 48 55 110 3

10 40 130 212 30 150 1

Free Air Conductor Ampacities for PV Wire, USE-2 and THWN-2 Copper at 30 degrees Celsius

In Conduit Conductor Ampacities for PV Wire, USE-2 and THWN-2 Copper at 30 degrees Celsius

Residential Wire Sizing Report Worksheet Checklist Calculations Notes Do not fill in any blanks.

Step 1 Data Missing Transformerless inverter selected.

Step 2 Data MissingStep 3 Data MissingStep 4 Data Missing Wire lengths must be entered.

Step 5 Data Missing Voltage drop calculation is optional.

Step 6 Data Missing Conductor gauges or O.C. rating must be entered.

Step 7 Data Missing Ground wire, gauges or wire types must be entered.

Array Source Circuit ResultsMinimum Conductor Gauge

Conductor Wire TypePV Wire or USE-2 0 0 0

Wire Length Pos. ft. Neg. ft. EGC ft.

PV Output Circuit ResultsMinimum Conductor GaugeConductor Wire Type

0 0 0 0Wire Length Pos. ft. Neg. ft. EGC ft.

Note: PV Output/Inverter Out calculations assume the same conductor type and gauge.

Inverter Out Circuit Results

Conductor Wire Type Minimum Conductor Gauge Ground Wire Gauge/Type0 Transformerless = Ungrounded. 0 0 0

Wire Length Hot ft. Neu. ft. EGC ft.Wire Totals Use the list below when preparing a purchase order.PV Wire or USE-2 Pos./Neg. feet Gauge 00 EGC/Ground feet Gauge 00 Pos./Hot ft. Neg./Neutral ft. Gauge 0

Hot Neutral Gauge0 Ground/EGC 1 ft. Gauge 0

Ground/EGC 2 GaugeModules: 0 Inverter: 0

Project Name: 0

Copyright © 2013 TheSolarPlanner.com

Energy Management

ServiceSee Instructions.

Ground Wire (EGC) Minimum Gauge/TypeUse PV

Wire only.

Ground Wire (EGC) Minimum Gauge/Type

Ask a PV contractor, electrician, or inspector to verify your wire sizes and types before buying any material.

Do not use grounded conductors.

Wire Sizing Calculators Online Resource LinksElectrician2.comConduit Fill CalculatorSouthwire.com

Search for Inverter SpecsElectrician.com

Energy Development Cooperative

Electrician.com

NoOutage.comSearch for Module Specs

BuildMyOwnCabin.com

Electricians Toolbox

Solar ABCs

TutorialsOvercurrent Protection Rating

TheSolarPlanner.comTypical Sizes - DC fuses (+ 240 volts) 1, 4, 6, 8, 10, 12, 15, 20, 30 amps

TheSolarPlanner.comTypical Sizes - AC/DC breakers

EHow.com

CivicSolar.com

MikeHolt.com

15, 20, 30, 40, 50, 60, 70, 80 amps

By John Wiles Search O.C. Device Sizes OnliHomePower.com

Hardwarestore.comSolarProfessional.com

Northern Arizona Wind & SunSolar Pro Magazine

SolarProfessional.com

Raceway/Conduit Fill Calculator

Vist the TheSolarPlanner.com Worksheets Page for instructions and other info.

Wire Size Calculator

DC Cable Sizing Calculator AltE Store

Voltage Drop Calculator Civic Solar

Voltage Drop Calculator Wholesale Solar

Conductor Properties Chart

More Calculators AltE Store

Low/High Temp Data for U.S. Cities Civic Solar

Wholesale Solar

Wire Sizing & Voltage Drop

Understanding Electrical Devices, Wire & Conduit in a Home PV System

Electrical Wire Types & Uses10, 15, 20, 25, 30, 40, 45, 50, 60, 70, 80 ampsTransformerless Inverters

Wiring Methods and Materials Typical Sizes - Dual-Pole Backfeed Breakers (for Main Service Panel)

Counductor Sizing and Overcurrent Device Ratings

Grounding and Bonding PV SystemsGeneral Purpose Fuses and Breakers

NEC Rules for Ungrounded PV SystemsPV Fuses and Breakers

Code-Compliant O.C. Device SizingLowes - Fuses and Breakers

Grounding PV Systems (Note: Not all brands are compatible with any electrical component. Always check component specs before purchasing.)

Table and Chart Info Extracted from 2011 NEC

Temp CelsiusAWG In Conduit and Free Air14 25 10 or less 1.1512 30 11-15 1.1210 40 16-20 1.088 55 21-25 1.046 75 26-30 1.004 95 31-35 0.963 110 36-40 0.912 130 41-45 0.871 150 46-50 0.82

1/0 170 51-55 0.762/0 195 56-60 0.713/0 225 61-65 0.65

66-70 0.5871-75 0.5076-80 0.4181-85 0.29

To research local temps, visit:

AWG

14 3512 4010 558 806 105 Scroll down for more tables…4 1403 1652 1901 220

1/0 2602/0 3003/0 350

NEC Tables and Charts cont…

Maximum Conductor Ampacities per Gauge (run inside conduit) - from NEC Table 310.15 (B)(16) (formerly Table 310.16)

Ambient Temperature Correction Factor for Conductors - from NEC 310.15 (B)(2)(a)

USE-2, PV Wire, THWN-2 Copper 90° CelsiusUSE-2, PV Wire, THWN-2

Copper 90° Celsius

Also applies to these wire types: TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, XHH, XHHW, XHHW-2, ZW-2

Also applies to these wire types: TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, XHH, XHHW, XHHW-2, ZW-2

Always pick a gauge whose ampacity (second column) is equal to or exceeds the value you calculate. Maximum Conductor Ampacities per Gauge (in free air) - from NEC Table 310.15 (B)(17) (formerly Table 310.17)

USE-2, PV Wire, THWN-2 Copper 90° Celsius Solar ABC's

Also applies to these wire types: TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, XHH, XHHW, XHHW-2, ZW-2

Percentage Divider

Less than 3 100% 0 to 1/2 inch 334-6 80% Above 1/2" to 3 1/2" 227-9 70% Above 3 1/2" to 12" 1710-20 50% Above 12" to 36" 14

AWG AWG

14 solid 3.07 14 2.714 stranded 3.14 12 1.712 solid 1.93 10 1.112 stranded 1.98 8 0.6910 solid 1.21 6 0.4410 stranded 1.24 4 0.298 solid 0.764 3 0.238 stranded 0.778 2 0.196 stranded 0.491 1 0.164 stranded 0.308 1/0 0.133 stranded 0.245 2/0 0.112 stranded 0.194 3/0 0.0921 stranded 0.154

1/0 stranded 0.122

Scroll down for more tables…

C = (F - 32) * 5 / 9

Conduit Adjustment Factor for Multiple Conductors Inside Raceway - from NEC Table 310.15 (B)(3)(a)

Ambient Temperature Adder for Raceways on or Above Rooftops - from NEC Table 310.15 (B)(2)(C)

Number of Conductors

Distance Between Roof and Conduit

Celsius Temp Adder

"Number of Conductors" does not include the ground wire/EGC, which must also be run through the conduit. (Since current doesn't normally flow through it, the EGC contributes no heat inside the raceway.) In addition, the use of a combiner in the PV output circuit reduces the number of conductors entering the conduit.

Installers use what's called a "lift" to elevate conduit running across a roof. The height of the lift will give you the data you need to use this table. If you place your junction box below the roof, you can skip this calculation, so long as the conduit doesn't cross the roof.

DC Conductor Properties for Voltage Drop Calculation - from NEC Chapter 9 Table 8

AC Conductor Properties for Voltage Drop Calculation - from NEC Chapter 9 Table 9

stranded or solid?

ohms per kilofoot

Effective Impedance per kilofoot

Minimum Equipment Grounding Conductor (EGC) Size Based on Overcurrent Devices - from NEC Table 250.122

Temperature Conversion Formulas: Fahrenheit/Celsius

Overcurrent Device Rating

(amps)

Minimum Gauge (AWG) Copper Wire

Note: Table does not apply when using a transformerless inverter

C = (F - 32) * 5 / 915 14 F = (C * 9 / 5) + 3220 1230 1040 1060 10100 8200 6300 4

Temperature Conversion TableCelsius F Celsius F Celsius F

0 32 19 66.2 38 100.41 33.8 20 68 39 102.22 35.6 21 69.8 40 1043 37.4 22 71.6 41 105.84 39.2 23 73.4 42 107.65 41 24 75.2 43 109.46 42.8 25 77 44 111.27 44.6 26 78.8 45 1138 46.4 27 80.6 46 114.89 48.2 28 82.4 47 116.6

10 50 29 84.2 48 118.411 51.8 30 86 49 120.212 53.6 31 87.8 50 12213 55.4 32 89.6 51 123.814 57.2 33 91.4 52 125.615 59 34 93.2 53 127.416 60.8 35 95 54 129.217 62.6 36 96.8 55 13118 64.4 37 98.6 56 132.8

(amps) Copper WireNote: Table does not apply when using a transformerless inverter

For an inverter 3800 watts or less, your breakers will be 15-20 amps on the AC side, and the EGC minimum gauge will be 12. For a 4,000-10,000 watt inverter, your breakers should be 30-60 amps on the AC side with an EGC minimum of 10 gauge. Many AHJ's, meanwhile, insist on Bare Copper gauge 6 for the array EGC. (After the junction box/combiner, you must switch to something else, since bare copper can't be run inside conduit.) Transformerless inverters require that all ground wires be rated for twice the largest upstream circuit ampacity.

An O.C. device (aka fuse or circuit breaker) may be located inside the inverter, AC Disconnect, DC Disconnect, Combiner Box and/or the main panel. Normally, for less than three array strings, you don't need overcurrent protection on the DC side, but there are exceptions. This chart is generally used to size breakers in the inverter output circuit (on the AC side).