NJ has a code assistance unit within the department that regulates the Uniform Construction Code, they produce a newsletter periodically, the recent edition had an article regarding the size of NM cable permitted for a 48-amp EV charger.
Let me know your thoughts on this, as my understanding on this does not align with what is being permitted.
"One of the more frequent questions we get in the Code Assistance Unit relates to the use of Non-metallic sheath (NM) cable for EV chargers. Specifically, the use of #6 CU on a 48-amp load.
There appears to be a significant portion of code officials with a difference in opinions on how we should apply the requirements found in Article 625 of the National Electrical Code (NEC), with continuous load designation and NM cable.
First let’s start with Article 625; Article 625.41 requires the overcurrent protection device (OCPD) to be sized for “continuous duty,” thus applying a factor of 125% to the full load of the equipment. “Continuous Duty” is a term used to alert installers that considerations must be made to help dissipate excessive heat when a substantially constant load is present for an indefinitely long period of time. This increase is a “cushion” to help the circuit components deal with this heat. There is NO additional current on this circuit.
Article 625.42, however, states: “Electric vehicle charging loads shall be considered to be continuous loads for the purpose of this article." A review of the Code Making Panel notes shows their primary intent is that this continuous load designation is limited to this article and shall not extend to service calculations (Review 220.83. There is no 125% factor for continuous load).
Neither article requires the conductors to adhere to this increase. This may be because the “continuous load” or “continuous duty” designation is intended for the protection of devices and not conductors. Exception #1 to Article 210.19A(1), appears to support this, but because Article 625.41 explicitly requires us to apply the 125% factor, this exception cannot be applied.
So, let’s assume for the sake of this article that we interpret the code to read that the conditions for continuous loads apply to the conductors as well. Table 310.16 of the 2020 NEC shows 6 AWG having an ampacity of 55 amps at 60°C (See 334.80 for ampacity limitations). "Ampacity," as defined by the NEC, is “The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.” Based upon table #6, NM can safely carry 55 amps WITHOUT exceeding the temperature rating of the conductor at 60°C. Considering most devices and OCPD’s have dual rated lugs with temperature limitations of 60°C/75°C, limiting the ampacity to 55 amps or less will inherently limit the temperature of any device to be well within its listed operating temperature. Which means, applying the 125% to a conductor which is already limited by 60°C does nothing more to protect the equipment or the conductors in the circuit.
In the 2020 NEC, a change to Article 334.80 was made from “allowable ampacity” to just “ampacity." This change seems to imply that the ampacity safely carried by NM cable is dictated by the actual load and not OCPD. Furthermore, the provisions of Article 240.4 for applications under 800 amps do not exclude NM cable.
Therefore, the opinion of the Code Assistance Unit is that #6 NM cable should be permitted to be utilized for EV chargers with loads not exceeding 48 amps"
Let me know your thoughts on this, as my understanding on this does not align with what is being permitted.
"One of the more frequent questions we get in the Code Assistance Unit relates to the use of Non-metallic sheath (NM) cable for EV chargers. Specifically, the use of #6 CU on a 48-amp load.
There appears to be a significant portion of code officials with a difference in opinions on how we should apply the requirements found in Article 625 of the National Electrical Code (NEC), with continuous load designation and NM cable.
First let’s start with Article 625; Article 625.41 requires the overcurrent protection device (OCPD) to be sized for “continuous duty,” thus applying a factor of 125% to the full load of the equipment. “Continuous Duty” is a term used to alert installers that considerations must be made to help dissipate excessive heat when a substantially constant load is present for an indefinitely long period of time. This increase is a “cushion” to help the circuit components deal with this heat. There is NO additional current on this circuit.
Article 625.42, however, states: “Electric vehicle charging loads shall be considered to be continuous loads for the purpose of this article." A review of the Code Making Panel notes shows their primary intent is that this continuous load designation is limited to this article and shall not extend to service calculations (Review 220.83. There is no 125% factor for continuous load).
Neither article requires the conductors to adhere to this increase. This may be because the “continuous load” or “continuous duty” designation is intended for the protection of devices and not conductors. Exception #1 to Article 210.19A(1), appears to support this, but because Article 625.41 explicitly requires us to apply the 125% factor, this exception cannot be applied.
So, let’s assume for the sake of this article that we interpret the code to read that the conditions for continuous loads apply to the conductors as well. Table 310.16 of the 2020 NEC shows 6 AWG having an ampacity of 55 amps at 60°C (See 334.80 for ampacity limitations). "Ampacity," as defined by the NEC, is “The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.” Based upon table #6, NM can safely carry 55 amps WITHOUT exceeding the temperature rating of the conductor at 60°C. Considering most devices and OCPD’s have dual rated lugs with temperature limitations of 60°C/75°C, limiting the ampacity to 55 amps or less will inherently limit the temperature of any device to be well within its listed operating temperature. Which means, applying the 125% to a conductor which is already limited by 60°C does nothing more to protect the equipment or the conductors in the circuit.
In the 2020 NEC, a change to Article 334.80 was made from “allowable ampacity” to just “ampacity." This change seems to imply that the ampacity safely carried by NM cable is dictated by the actual load and not OCPD. Furthermore, the provisions of Article 240.4 for applications under 800 amps do not exclude NM cable.
Therefore, the opinion of the Code Assistance Unit is that #6 NM cable should be permitted to be utilized for EV chargers with loads not exceeding 48 amps"
