NEC Requirements for Solar — Part 2 – Electrical Construction & Maintenance (EC&M)

Install a permanent, readily visible label indicating this voltage at one of these locations [Sec. 690.7(D)], as shown in Fig. 1:

(1) PV system DC disconnect

(2) PV system electronic power converters

(3) Distribution equipment associated with the PV system

If the PV system is rated below 100kW, the maximum PV system circuit current is 125% of the sum of the short-circuit current ratings of the PV modules connected in parallel [Sec. 690.8(A)(1)(a)(1)].

If it’s rated 100kW or more, the requirements are considerably greater [Sec. 690.8(A)(1)(a)(2)]. Among other things, it must be based on the highest three-hour current average resulting from the simulated local irradiance on the array accounting for elevation and orientation. In no case is the PV source circuit DC current permitted to be less than 70% of the PV source circuit DC current as calculated in Sec. 690.8(A)(1)(a)(1).

Where a circuit is protected with an overcurrent protective device (OCPD) not exceeding the conductor ampacity, the maximum current is permitted to be the rated input current of the inverter to which it is connected [Sec. 690.8(A)(2)].

PV circuit conductors must have an ampacity of at least the largest of Sec. 690.8(B)(1) or (B)(2):

(1)  Conductor Sizing. PV circuit conductors must have an ampacity of at least 125% of the current as determined by Sec. 690.8(A).

Exception: Where the assembly, including the OCPDs protecting the circuit(s), is listed for operation at 100% of its rating, the ampere rating of the OCPD can be sized to 100% of the continuous and noncontinuous loads.

(2) Conductor Sizing, With Ampacity Correction and/or Adjustment. PV circuit conductors must have an ampacity of at least 100% of the current as determined by Sec. 690.8(A) after conductor ampacity correction [Table 310.15(B)(1)(1)] and adjustment [Table 310.15(C)(1)].

Where overcurrent is provided for parallel-connected PV string circuits, the conductor ampacity must be at least [Sec. 690.8(D)]:

(1) The rating of the overcurrent device.

(2) The sum of the currents as calculated in Sec. 690.8(A)(1)(a) for the other parallel-connected PV string circuits protected by an overcurrent device.

Overcurrent protection

PV system DC circuit and inverter output conductors and equipment must be protected against overcurrent [Sec. 690.9(A)]. But OCPDs are not required where these two conditions are met [Sec. 690.9(A)(1)]:

(1) The PV system DC circuit conductors have an ampacity of at least the DC current per Sec. 690.8(B).

(2) Where the currents from all PV sources do not exceed the OCPD rating specified by the manufacturer for the PV module or electronic power converters (inverters and DC-to-DC converters).

OCPDs are required for PV system circuit conductors connected at one end to a current-limited supply and also connected to sources having an available circuit current greater than the ampacity of the conductor at the point of connection to the higher current source [Sec. 690.9(A)(2)].

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