The system taps on the line/supply side of the 200 A main breaker of the 120/240 V service. If this was a connection on the load side of the main breaker, the conductors would be 3 AWG and rated at 100 A. I need clarification on the conductor size for a line-side tap. I read that they need to be sized as service-entrance conductors, but what would that be? Would the ground need to be the same size?
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9 years 10 months ago
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Hello MG,
These are great questions. The size of the conductors for line side taps are based on the inverter's continuous output current. If you have more than one inverter, it is the sum of all continuous output currents of all inverters.
The conductor's ampacity is calculated as 125% of the inverter's continuous output current - NEC 690.8(B)(1). In your case, 79A * 1.25 = 98.75A. Choose a conductor that will handle this ampacity at a minimum using NEC Table 310.15(B)(16). The 75 degC column presents #3 AWG with a 100A current rating which would be sufficient for this application (assuming no correction factors apply).
The grounded conductor would be sized per NEC Table 250.102(C)(1). If the largest ungrounded conductor is sized #2 AWG or smaller a #8 grounded conductor would be sufficient.
The overcurrent protection device is determined based on the conductor chosen in the previous step. In this specific case a 100A, 2-pole fused AC disconnect rated for service entrance would be appropriate.