The NEC and NM-B Romex Cable Gauge for 48 Amp EVSE Circuits

Mon 22 Jan 16:10:00 EST 2024

If using NM-B (Romex) cable, the 2020 National Electrical Code (NEC) requires minimum 4 gauge conductors for a 48 Amp EVSE. A 48 Amp EVSE such as the Tesla Wall Connector is a continuous load and therefore the circuit conductors and devices must be rated for 125% of the 48 Amp continuous load. NM-B 6 gauge cannot be used because NM cable ampacity is only 55 Amps at 60C and the 60C column must be used.

Ryan Jackson has published Electric vehicle circuit sizing (NM Cable) YouTube video explaining the code requirements that make NM-B 6 gauge non-complient.

New Jersey has published a 2020 Construction Code Communicator Volume 35, Number 3 stating that NM-B 6 gauge is ok. This is contrary to the NEC.

Soneone in a Rivian forum summarized the issue like this: In a nutshell, it’s the “continuous load” rule 215.2(A)(1) that trumps the “next size up” rule 240.4(B). The maximum ampacity of #6 Romex is 55amps. Since an EVSE is “continuous load”, rule says you must multiply 48A load by 125%=60amps, too much for 55ampacity #6 Romex.

References

• Argument to allow NM-B 6/2
• Diagram for 210.19(A)(1) Exception (2)
• EV Charger Circuits - NM Cable Size?
• Heat in Adjacent Components
• #6 NM-B on 60 amp breaker for 48A EVSE