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Before using these tables, some calculations must first be performed by the system designer to insure accurate current ratings and safety factors are used.
For solar modules, the UL-1703 standard requires the short circuit current (isc) rating of the PV module be multiplied by 125% before other factors are applied. This is because the PV module electrical performance can increase above the factory rating, due to the combination of increased operating temperatures and enhanced irradiances over 1000W/M2 (such as edge-of-cloud effect).
The NEC requires the short circuit current rating of the PV module or array be multiplied by 125% before calculating amperage capacities (ampacities) of any cable or over- current device. This is in addition to the UL required 125%! This yields a multiplier of (125% x 125%=156%)1.56. Although this may seem redundant, good design practice dictates both factors should be used when determining wire size from the solar array to the battery.
When calculating wire size from battery to load, multiply the load current by only 125% (1.25).
SAMPLE:
A 24V Solar Array of four Kyocera KC-120 Modules, 2 in series by 2 parallel
Modules located 30 ft. from the battery;
Isc = 7.45A (one module)
7.45 x 2 = 14.9 A (two modules)
14.9 A x 1.56 =23.2 A
Using the 24 volt table, locate a value equal to or greater than 23 amps from the left column, follow a line to the right until a distance at or above 30 ft. is found.
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| Amps | Wattage | #14 | #12 | #10 | #8 | #6 | #4 | #2 | 1/0 | 2/0 | 3/0 |
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27.0 | 45.0 | 73.0 | 115.0 | 145.0 | 183.0 |
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| Amps | Wattage | #14 | #12 | #10 | #8 | #6 | #4 | #2 | 1/0 | 2/0 | 3/0 |
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138.0 | 228.0 | 363.0 | 575.0 | 725.0 | 913.0 |
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Copyright © 1991- 2006; 2007 Enviromart Inc. All rights reserved. Information in this document is subject to change without notice. No text, code, or graphics herein may be copied for any purpose other than for consumer viewing without the express written consent of Enviromart Inc. Other products and companies referred to herein are trademarks or registered trademarks of their respective companies or mark holders. Copyright of individual articles is retained by the individual authors or their assigns. Copyright of the compilation as a whole is held by Enviromart Inc.