THHN in Conduit vs NM-B Cable for an EV Circuit
Short answer
NM-B is the familiar sheathed cable used inside walls, and where code permits it for the location it is quicker and cheaper to install. THHN individual conductors pulled through conduit is required in many locations, including most exposed runs and anywhere subject to damage, and it allows conductors to be replaced or upsized later without opening the wall.
At a glance
| 6 AWG THHN stranded copper, 100 ft | 6/3 NM-B cable with ground, 50 ft | |
|---|---|---|
| Physical protection | Conduit protects the conductors | Sheath only |
| Permitted exposed | Yes, in conduit | Generally not |
| Permitted outdoors or underground | With the right conduit and conductor type | No |
| Future upsizing | Pull new conductors through | Replace the cable |
| Installation time | Longer | Shorter |
| Who decides which is permitted | Code and your inspector | Code and your inspector |
Choose the 6 AWG THHN stranded copper, 100 ft if…
Conduit is the choice for exposed runs, garage walls where the cable could be damaged, outdoor sections and anywhere the code requires it. It also leaves you able to pull larger conductors later if you upgrade the charger, which is worth real money on a long run. The conduit type and fill are code matters your electrician handles.
Check 6 AWG THHN stranded copper, 100 ft on Amazon
Choose the 6/3 NM-B cable with ground, 50 ft if…
NM-B is quicker and cheaper where it is permitted, which usually means concealed inside finished walls in a dry location. It cannot be used in the situations conduit covers, so this is not a preference so much as a question of where the run goes. Your electrician will choose the wiring method that suits the route and satisfies the inspector.
Check 6/3 NM-B cable with ground, 50 ft on Amazon
Related
Comparison based on published manufacturer specifications and the general consensus of owner reports. We have not tested these products side by side. Confirm current specifications and prices before buying. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you.
Common questions
Which method is actually required?
It depends on the route, the location and the code edition adopted where you live. Exposed runs, outdoor sections, wet locations and areas subject to physical damage all have specific requirements. This is exactly the sort of thing a permit and an inspection exist to confirm, and it is why the wiring method is chosen by the electrician rather than the homeowner.
Can conduit be run outdoors?
With the correct conduit type and conductors rated for wet locations, yes, and the requirements are specific. Underground runs have their own rules about burial depth and conduit type. The conduit guide on this site covers the concepts; the actual specification for your installation comes from your electrician and your inspector.
Is it cheaper to oversize the conduit now?
Often, yes, and it is one of the few genuinely useful pieces of future proofing. A slightly larger conduit costs very little extra during the original installation and makes a later upgrade to a higher amperage charger a pull rather than a demolition. Raise it with your electrician when the job is quoted.
Does the wiring method affect ampacity?
Yes. Conductors bundled in a cable or in a conduit with other current carrying conductors are derated, and ambient temperature affects it too. That is another reason the conductor size is calculated rather than picked from a chart in isolation. The wire gauge calculator on this site shows the general relationship.
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How this page was researched
Specifications come from manufacturer documentation, listed safety certifications and verified owner reviews. We do not perform hands-on product testing and never claim to. Figures are researched planning information, not professional electrical advice. Last reviewed 2026-08-17.