33
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Examples of Express 250 Paired
Wire Sizing
The required DC wire gauge varies based on the specific site. Use these example scenarios to help
you determine the correct wire gauge for your site.
DC Interconnection, Example Calculation: Newark, NJ
Assumptions:
• Breaker and equipment terminal rating minimum 75°C
• Electric Vehicle Charging Equipment rated for continuous duty per Article 625.41
• Maximum 50°C ambient rating
• Installation location: Newark, NJ, USA
• 90°C rated wire required
• Maximum station DC output/input current: 160 A
• Four conductors in conduit, only two current carrying conductors
The continuous duty derating per 625.41 is 160 x 1.25, or 200 A.
From the Appendix D ASHRAE, the table summer design temperature is 91°F for Newark, NJ.
Temperature derating from 2017 NEC Table 310.15(B)(2)(a) based on 30°C the derating factor for
91°F and 90°C rated wire is 0.96 (87-95˚F row).
From the 90°C column of NEC Table 310.15(B)(16), a 3/0 copper conductor has an ampacity of 225 A.
Applying the temperature derating factor, 225*0.96 = 216 A
200 A is the minimum rated ampacity this conductor must have per the NEC to prevent potential
insulation damage and provide the ability of the conductor to dissipate heat caused by the current
flow. After the temperature derating calculation, the resulting 216 A is greater than the 200 A
required.
Important: These scenarios are only examples, and are not intended to replace an
assessment by a local electrician. Always follow all applicable local and national codes and
requirements. A site drawing should be engineered for your specific site to reduce
installation costs and ensure compliance with local codes.
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