Difference between revisions of "Voltage drop"
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All wires have a certain amount of resistance that corresponds to their diameter which will cause a certain amount of voltage in the circuit to be lost when current is flowing. High voltage drop in a circuit will cause a lower-than-expected voltage which can create performances issues but does not represent a safety hazard in itself. If a wire is improperly sized it can lead to significant loses in voltage that can cause [[Special:MyLanguage/Energy efficient loads|loads]] to stop functioning or improper battery charging. Voltage drop must be examined for all circuits in an off-grid PV system. | All wires have a certain amount of resistance that corresponds to their diameter which will cause a certain amount of voltage in the circuit to be lost when current is flowing. High voltage drop in a circuit will cause a lower-than-expected voltage which can create performances issues but does not represent a safety hazard in itself. If a wire is improperly sized it can lead to significant loses in voltage that can cause [[Special:MyLanguage/Energy efficient loads|loads]] to stop functioning or improper battery charging. Voltage drop must be examined for all circuits in an off-grid PV system. | ||
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The calculation can be performed easily by hand, but there are many different free calculators available online that are much quicker - see [[Special:MyLanguage/Resources]]. The factors that determine voltage drop in an off-grid PV system are: | The calculation can be performed easily by hand, but there are many different free calculators available online that are much quicker - see [[Special:MyLanguage/Resources]]. The factors that determine voltage drop in an off-grid PV system are: | ||
:*The maximum circuit current. | :*The maximum circuit current. | ||
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:*The operating voltage of the circuit. | :*The operating voltage of the circuit. | ||
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The formula for calculating voltage drop is: | The formula for calculating voltage drop is: | ||
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The most important value is the percentage voltage drop for the circuit. This is calculated using the formula: | The most important value is the percentage voltage drop for the circuit. This is calculated using the formula: | ||
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See [[Wire, overcurrent protection, and disconnect sizing and selection#Phase 4: Voltage drop|Wire, overcurrent protection, and disconnect sizing and selection - Phase 4: Voltage drop]] for recommended voltage drop values for circuits in an off-grid PV system. | See [[Wire, overcurrent protection, and disconnect sizing and selection#Phase 4: Voltage drop|Wire, overcurrent protection, and disconnect sizing and selection - Phase 4: Voltage drop]] for recommended voltage drop values for circuits in an off-grid PV system. | ||
− | ==Conductor resistance values== | + | ==Conductor resistance values== <!--T:8--> |
A simplified chart with resistances for copper wires.<ref name="NEC4"> NFPA 70 - National Electrical Code 2017: Chapter 9, Table 8 </ref> | A simplified chart with resistances for copper wires.<ref name="NEC4"> NFPA 70 - National Electrical Code 2017: Chapter 9, Table 8 </ref> | ||
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Revision as of 17:05, 15 March 2021
All wires have a certain amount of resistance that corresponds to their diameter which will cause a certain amount of voltage in the circuit to be lost when current is flowing. High voltage drop in a circuit will cause a lower-than-expected voltage which can create performances issues but does not represent a safety hazard in itself. If a wire is improperly sized it can lead to significant loses in voltage that can cause loads to stop functioning or improper battery charging. Voltage drop must be examined for all circuits in an off-grid PV system.
The calculation can be performed easily by hand, but there are many different free calculators available online that are much quicker - see Special:MyLanguage/Resources. The factors that determine voltage drop in an off-grid PV system are:
- The maximum circuit current.
- The resistance of the conductor (wire) based upon its size.
- The length of the circuit.
- The operating voltage of the circuit.
The formula for calculating voltage drop is:
Voltage drop | = 2 x Circuit current x One-way circuit length (m) x Resistance (Ω/Km) ÷ 1000 |
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The most important value is the percentage voltage drop for the circuit. This is calculated using the formula:
Percentage voltage drop | = Voltage drop ÷ Circuit operating voltage x 100 |
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See Wire, overcurrent protection, and disconnect sizing and selection - Phase 4: Voltage drop for recommended voltage drop values for circuits in an off-grid PV system.
Conductor resistance values
A simplified chart with resistances for copper wires.[1]
Copper resistance at 75°C | |||
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Size AWG | Area | Metric equivalent | Ω/km |
18 | 0.823 mm² | 1 mm² | 26.5 Ω |
16 | 1.31 mm² | 1.5 mm² | 17.3 Ω |
14 | 2.08 mm² | 2.5 mm² | 10.7 Ω |
12 | 3.31 mm² | 4 mm² | 6.73 Ω |
10 | 5.261 mm² | 6 mm² | 4.226 Ω |
8 | 8.367 mm² | 10 mm² | 2.653 Ω |
6 | 13.30 mm² | 16 mm² | 1.671 Ω |
4 | 21.15 mm² | 25 mm² | 1.053 Ω |
3 | 26.67 mm² | — | 0.833 Ω |
2 | 33.62 mm² | 35 mm² | 0.661 Ω |
1 | 42.41 mm² | 50 mm² | 0.524 Ω |
1/0 | 53.49 mm² | — | 0.415 Ω |
2/0 | 67.43 mm² | 70 mm² | 0.329 Ω |
3/0 | 85.01 mm² | 95 mm² | 0.2610 Ω |
4/0 | 107.2 mm² | 120 mm² | 0.2050 Ω |
Notes/references
- ↑ NFPA 70 - National Electrical Code 2017: Chapter 9, Table 8