Why You Cant Use 6 AWG Romex for a Hardwired EV Car Charger Installation

When homeowners plan to install a wall-mounted electric vehicle (EV) charger, one of the first questions that comes up is: Can I use 6 AWG Romex cable (NM-B) for my charger circuit?

The short answer is no : not for a hardwired EV charger delivering 48 amps. While 6 AWG Romex can be used for a NEMA 14-50 outlet, it doesn't meet the code or manufacturer requirements for a 48-amp continuous-load hardwired charger such as a Tesla Wall Connector, Emporia, or ChargePoint Home Flex. Let's break down why.

Romex (NM-B) Cable and Its Temperature Limitations

Romex, technically known as NM-B cable, is rated at 60°C (140°F) under the National Electrical Code (NEC) Table 310.16. That rating is the key limitation when it comes to EV charging installations.

When you install a hardwired EV charger that outputs 48 amps continuous, you must size the conductors to 125% of the continuous load under NEC Article 625.42 and 210.19(A)(1).

48 A × 1.25 = 60 amps minimum conductor ampacity required.

A 6 AWG NM-B conductor is only rated for 55 amps at 60°C, which is undersized for this application. That's why NM-B cannot be used for this type of installation : even though the wire size "sounds" large enough. The insulation temperature rating is what disqualifies it.

This is a common misconception we encounter with homeowners throughout Ashburn, Aldie, and South Riding. Many DIY-minded folks assume that bigger wire gauge automatically means it can handle more current, but temperature ratings are equally important for safety and code compliance.

When 6 AWG Romex Is Acceptable : NEMA 14-50 Outlets

For a NEMA 14-50 receptacle, the maximum continuous load is limited to 40 amps per NEC 210.21(B)(1) and 210.23(A). At that current level, 6 AWG NM-B is acceptable on a 50-amp breaker, because 55 amps (NM-B rating) covers 40 amps continuous with the 125% rule.

That's why you'll commonly see 6 AWG Romex used for 14-50 outlets in garages throughout Northern Virginia : but not for hardwired chargers at 48 amps continuous. The outlet option gives you flexibility to plug in different chargers, but you're limited to slower charging speeds.

If you're considering a plug-in vs. hardwired setup for your home near me in Leesburg or Sterling, understanding this distinction can help you make the right choice for your charging needs.

The Ground Wire Issue : Why Size Matters

Inside 6-2 NM-B, the bare ground wire is only 10 AWG. That's a problem, because many EV charger manufacturers (Tesla, Emporia, Rivian, etc.) specify a minimum 8 AWG equipment grounding conductor for 48-amp units.

A smaller ground wire has higher resistance and less fault-current carrying capability, increasing the risk of improper breaker tripping or delayed fault clearing. In the event of a ground fault or short circuit, that undersized ground wire might not be able to safely carry the fault current back to the panel, potentially creating dangerous conditions.

In short: even if the hot conductors were acceptable (which they aren't), the undersized ground wire in NM-B fails to meet both manufacturer and best-practice requirements. This is particularly important for high-current applications like EV charging, where safety margins matter most.

The Correct Cable Type : 6 AWG SER Copper

For professional, code-compliant installations, the best choice is 6 AWG SER copper cable (Service-Entrance Rated). Here's why SER wins every time for EV chargers:

✅ Higher Temperature Rating – Typically 90°C XHHW-2 insulation, allowing full 65 amp ampacity per NEC Table 310.16 : perfect for a 48 amp continuous charger.

✅ Proper Ground Size – Includes a 6 AWG ground conductor, meeting or exceeding manufacturer specs.

✅ Stronger & Better Insulated – The XHHW-2 insulation resists heat, abrasion, and moisture better than the soft PVC insulation of NM-B.

✅ Safer to Pull Through Walls and Ceilings – SER cable has a smoother jacket and tougher insulation, making it far less likely to nick or damage during wire-fishing.

When we install chargers in homes throughout Stone Ridge, Chantilly, and Haymarket, we exclusively use SER copper cable for these reasons. It's simply the right tool for the job.

Durability and Safety in Real-World Installs

When fishing wire through joist cavities, drywall, or existing finished ceilings, Romex is much more prone to jacket tearing or insulation nicks. Those small damages can expose copper and create a point of failure or arcing later on.

This is especially relevant in Northern Virginia homes, where we often encounter tight spaces, existing insulation, and complex routing paths from electrical panels to garages. The homes we work on in Gainesville and Fairfax frequently require running wire through finished areas, making cable durability crucial.

By contrast, 6 AWG SER copper maintains its integrity even after multiple bends and pulls, giving a far more durable and professional result : especially critical for high-current EV circuits that will be in service for decades.

Cost Considerations and Long-Term Value

While SER cable typically costs more upfront than Romex, the difference becomes negligible when you consider the total installation cost. More importantly, using the right cable from the start prevents costly rework, failed inspections, and potential safety issues down the road.

We've seen too many DIY installations near me that used improper wiring and had to be completely redone to pass inspection. That's not just expensive : it's frustrating and delays getting your EV charger up and running.

The Bottom Line

If you're installing a hardwired 48 amp EV charger, skip the Romex. It simply isn't rated for the heat, load, or grounding requirements of modern EV charging systems.

Use 6 AWG SER copper cable : it provides:

• Full 90°C ampacity for continuous loads

• Proper grounding size

• Superior insulation and mechanical strength

• Long-term reliability that meets both NEC 2020 standards and manufacturer requirements

The electrical code exists for good reasons, and EV charger installations represent some of the highest continuous loads in residential settings. Taking shortcuts with wire type isn't worth the risk to your home, your vehicle, or your family's safety.

Pro Tip from Auto Charge Pros

Every home and panel setup is different. Before choosing wire type or breaker size, always consult with an experienced electrician familiar with NEC Article 625 and local inspection requirements.

At Auto Charge Pros, we install every EV car charger circuit using SER copper conductors, with all drywall patched and finished after inspection : ensuring your installation is both safe and code-compliant from start to finish.

We've completed hundreds of successful installations across our service area, and we stand behind every job with a one-year warranty. Whether you're in Reston, Centreville, or anywhere else in Loudoun County, we bring the same attention to detail and commitment to quality.

Ready to get your EV charger installed the right way? Call or text 571-293-0373 for a free estimate, or visit our website to learn more about our EV car charger installation services across Northern Virginia.