#6 NM-B on 60 amp breaker for 48A EVSE

[Bill Turax]

I have been asked to connect an EVSE to an existing piece of 6/2 NM-B (ROMEX) in a new home that was installed by the home builder.
the EVSE has a draw of 48 amps, so the breaker needs to be 60 amp (48 x 1.25 = 60).

My understanding is that a continues load (the charger will be drawing maximum current for over 3 hours) is that the over current protection AND the conductors need to be rated at 125% of the maximum draw. so in this case the conductors and the over current device need to be rated for 60 amps.

I told the home builder that the conductors need to be replaced since 6/3 NM-B is only rated for 55 amps. I suggested he replace the circuit with 6/2 MC as that has actual THHN conductors rated for 65 amps at 75deg.

the home builders electrician is stating that he does not need to replace the conductors since the NM-B is rated for 55 amps and the load is 48 amps he can use the next size up rule, 240.4(B).
I do not agree with this since 215.2(A)(1) states that a the conductors of a continuous load needs to be rated for 125% of the maximum load.

Please let me know if I am correct or if I overlooking something that would allow the 55 amp rated conductor to used in this situation.

 

[augie47]

IMO, you are correct. 625.42 states EV equipment shall be considered a continuous load so a 48 amp load would require a circuit (and conductor) with a 60 amp ampacity.
You can direct the "electrician" to Art 210.19

 

[kwired]

I second that you were correct.

It is possible to put #6 NM on a 60 amp breaker, but the load (with any necessary adjustments) can't exceed 55 amps, so the conductor is too small or needs to be one with 75C rating.

 

[Bill Turax]

Perfect, thanks all!

 

[jksmith82]

Hi,
For what ever it’s worth you can also direct him to this This as well.

334.80 Ampacity. The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The allowable ampacity shall not exceed that of a 60°C (140°F) rated conductor. The 90°C (194°F) rating shall be permitted to be used for ampacity adjustment and correction calculations, provided the final derated ampacity does not exceed that of a 60°C (140°F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.80(A). Where more than two NM cables containing two or more current-carrying conductors are installed, without maintaining spacing between the cables, through the same opening in wood framing that is to be sealed with thermal insulation, caulk, or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(3)(a) and the provisions of 310.15(A)(2), Exception, shall not apply.
Where more than two NM cables containing two or more current-carrying conductors are installed in contact with thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(3)(a).