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I have 50'of Romex 6/3 wire, 50 amp Square D breaker and a Hubbell 50 amp receptacle - that I want to install with metal conduit on the inside of my garage on wall by car. The 100 amp sub panel box is on outside of garage in stucco wall about 35' (total run) from where I want to place the receptacle - so I will have to go up outside wall with conduit into attic - which is accessible by pull down ladder - and run 6/3 wire above insulation on rafters to where it will go through finished ceiling in garage, and down the wall with metal conduit into metal receptacle box. Do I have to protect that 6/3 Romex copper wire with some kind of oversized conduit like 1" flexible metal conduit or liquid tight 1" flexible conduit??? Thank you

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  • In conduit, (becasue it's normal to have devices that have 75°C terminals at this size class, and you are not limited to 60°C by using (most) cable) this can be #6 aluminum wires and save a lot of money .vs. knee-jerking to copper. Or you can go to #4 aluminum wires and still save a lot of money. Enough to buy the conduit and then some, most likely.
    – Ecnerwal
    Sep 20, 2022 at 22:41

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NM-B cable is not allowed outdoors, not even in conduit. UF-B cable is, but it requires enormous conduit - 6/3 requires 2” conduit for Pete's sake. If conduit is continuous between panel and interior box, you can run THWN individual wires which are easy to wire and easy to change. Neutral is wasted on an EVSE but an RV socket requires it.


Review Technology Connections' excellent video on this topic. I've cued it up to the part about sizing your charging circuit.

Please consider two critical things:

  • hard-wiring the EVSE (i.e. using a Tesla Wall Connector instead of the granny/travel charger)
  • Thinking carefully about the ampacity of the charging circuit, particularly relative to what your house is capable of, vs what you actually need.

When they sell you an EV, they typically "throw in" what's called a "granny charger". That name is wrong. It is actually a travel charger intended for "opportunity charging" on road trips or unexpected situations. And they give you the 2 plugs you're most likely to find on the road -- the common 120V plug, and also, the common RV (Recreational Vehicle) plug found at RV campgrounds. That's what it's for and nothing else. The travel EVSE belongs in your trunk for use in a pinch.

But this has created a number of misconceptions: That NEMA 14-30 is the standard EV socket (no: it's the standard RV socket). That EVSE's should use enormous plugs (no, hardwired is better). That your car "needs" to charge at "50A" (LOL no, that is gross overkill for almost any car, but especially for a Tesla).

In fact, trying to charge that high is dangerous in many homes. The house's service is not ready for the load. And since cars don't actually need it, why do it?

A common 20A circuit, bumped to 240V, will give you 4KW charge rate or 120 miles restored in a conservative 10-hour overnight. Think about it. That's plenty. Even if it wasn't, literally 5 minutes at a Supercharger will get you the rest of the way.

So you don't need a 50A circuit or probably, even a 30A circuit. Feel this getting easier?

Ampacity / available service at the house

You must begin by doing a Load Calculation on the service, per NEC Article 220. Many city governments have a worksheet to help you do this. Many commercial websites also have fake articles on this topic; a proper Load Calculation starts with "3 VA per square foot" and 1500VA for kitchen and laundry circuits, and then looks at 240V appliances.

Once you have a Load Calculation, you can compare that to your service size (the size the power company has sized their delivery wires for; typically same as the main breaker) ... and that will tell you the max for the EV breaker. (note that EVs actually charge at 80% of breaker trip, so 32A on a 40A circuit).

How do you tell the charger what amps it can safely pull from the house? With the Tesla Wall Connector, you dial it to anything as part of the Commissioning Procedure. With the travel EVSE, they sell 8 different dongle plugs, and the plug actually contains a microchip which tells the car the ampacity of the plug. (e.g. 20A for a NEMA 6-20 plug).

If you just use the travel charger with 50A socket as you plan, that socket is also used on 40A circuits, so the EVSE assumes 40A and charges at 32A actual. So you don't even get "50A" (40A actual) out of it.

What keeps you from overloading the house? On old Rule of Six "6 main breakers" panels, nothing but the Load Calculation. Really. On panels with a single main breaker, that helps, but really the Load Calculation should be reviewed as part of pulling the permit.

Remember the part where I said EVs can charge very comfortably on a 20A/240V circuit? Yeah, that's a lot easier to get by the inspector, since it wires exactly like a normal household circuit with normal #12 Romex.

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240V at 15 or 20 amps is just that easy.

EV charging does not require neutral. BUT: If you install a receptacle that does have neutral, such as a NEMA 14-50, 14-30 or (outlawed) 10-30 -- then you must run neutral to the receptacle. It will be wasted, but it's necessary in case somebody plugs something else into that receptacle. Plugging an RV into a 14-50 that didn't have neutral would fry every electrical appliance on it.

About hard-wiring

NEC 2020 requires that 240V circuits that go to a socket be GFCI protected, and the only way to GFCI-protect a 240V circuit is with a costly 240V GFCI circuit breaker. Which notably, takes 2 full spaces in the panel. So stepping away from the socket can save you some coin. It also removes true stupidity, since all EVSEs already contain a "smart GFCI" capable of resetting itself, and some can signal you that they're having problems. Putting a dumb GFCI on an EVSE breaks those abilities.

Also, flimsy $10 30-50A sockets are just not designed for repeated insertions, and the better $50-60 30-50A sockets are strongly recommended. That's not a problem with 20A sockets, since they are just normal sockets with a twist!

Also, using the travel charger as your daily EVSE gets old real fast and people want a wall-mount unit. The Tesla Wall Connector is an absolute bargain at $400 (contrast with ClipperCreek or Siemens units, and contrast with the cost of GFCI+expensive socket+special dongles), supports hardwiring, and supports any ampacity so you can Definitely use it safely regardless of what your house can support.

The only rub is that hardwired things require a disconnect switch reasonably nearby and definitely in line-of-sight. Your panel breaker won't do because it's on the wrong side of the wall.

I really want to march forward with 50A, though

Well actually, your 6/3 NM-B cable is rated for 55A and can be breakered at 60A. But you can only plan to use 55A.

OK, if your house is ready for it! I would still recommend a wall unit and I'd still recommend hard-wiring. Especially because 50A, with wall units, prepares you for having two EVs.

Hard-wired, you'll have a disconnect switch. For two EVs, swap that out for a 4-space subpanel which serves as a disconnect for both wall units. Then, put two 60A breakers in there. Say whaaaaa???

Really. The Wall Connector 2.0 and 3.0 have a feature that others call "Share2". It allows 2 Wall Connectors to share one power allocation. You commission (or re-commission) the units and set up one as the Master and the other as Remote, linked to the Master. You tell the master "You share 55A" or whatever you have available. The two units will then dynamically split the power between any EVs plugged in. If only one EV is plugged in, it gets the works. Otherwise they split. If one is tailing off at end of charge and pulling only 10A, the other gets 45A. Etc. It does this on the fly.

Pretty clever, if not embarrassing that it uses basically mid-1980s technology to do it LOL. I could have coded this functionality on an Apple II (or Arduino today).

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You've got a few different issues:

  • Protecting Wire/Cables (what you actually asked about)

Generally speaking, wires need to be in conduit and cables don't. But cables in certain locations outside of walls need to be protected. That can be large conduit or it can be wood or something else placed around it to protect it.

  • Cable Outside

Only certain types of cable are allowed outside, because outside is considered a wet location. When we use the brand name "Romex", that normally refers to cables designed for inside use. If you are using that as a generic term for "any cable" and the cable you have is rated for outside/wet use then you are OK. If not then you can't use it outside, even if it is physically protected.

If you have to get new cable, you should seriously consider individual wires and using conduit for the entire distance.

  • Receptacle

Generally speaking you do not need to use a plug and receptacle with an EV charger. A hardwired connection:

  • Saves the cost of a receptacle and plug/cord. (OK, not necessarily a savings because if not near the breaker panel you will need a disconnect.)
  • Avoids the requirement of separate GFCI protection. That protection, practically speaking, has to be at the breaker. You don't generally have the easy (and inexpensive) option of GFCI/receptacle that you have for 120V 15A and 20A receptacles. This is not a requirement everywhere yet, but it is, I believe, a requirement in NEC 2020. My electrician can tell you a horror story he had recently with one customer who insisted on an EV receptacle and he couldn't just hardwire it because the customer has not yet selected the EV equipment. He came very close to having to physically modify a breaker to make it fit or install a subpanel (right next to the main panel) in order to use a different brand of breaker. In the end he found a just-released newer GFCI breaker for the panel. But the point is that hardwiring avoids the issue as (a) the requirement does not apply and (b) EV equipment includes GFCI protection.
  • Provides a neater, simpler installation.
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New code requires garage receptacles to be GFCI protected, either at the breaker or receptacle.

Most/all EV chargers can be hard wired to the panel and eliminate the need for having GFCI protection, besides what the chargers provide.

By code cables need protection below 8 feet from floor. in conduit or inside walls.

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    There is no such thing as a 240V GFCI receptacle. Oh wait. A wall-mount EVSE is a GFCI receptacle. However that only satisfies the requirement if it's hard-wired. Sep 20, 2022 at 22:51
  • It will be interesting to see, once NEC 2020 gets more traction, whether some of the most common 240V receptacles start being available in GFCI versions - particularly 14-30. On the one hand, it should be cheaper than a GFCI breaker. On the other hand, most people who would bother would be when doing major renovation to a house or a heavy-up - and in those cases the breaker would just be one of many. Sep 21, 2022 at 3:03

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