DIY EVSE Installation
Most people hire an electrician to install their EVSE, but if you are at this site, chances are you are more of a DIYer. You can indeed install your own EVSE, but there are some common things people, including electricians(!) get wrong, so here are some tips to point you in the right direction.
Disclaimers apply, I'm not going to talk about your particular local electrical code (these specification apply to the National Electric Code), nor about permitting.
Hardwired Recommended
Unless you have a good reason, I would recommend hard wiring your EVSE. It results in less connections meaning less chance of something degrading over time, and it allows you to install an EVSE with faster charging speeds. Plug in EVSEs max out at 40A, whereas common hardwired EVSEs allow 48A charging, but can go all the way to 80A if your EV supports it (Eg. the Ford F150 Lightning).
Note that you do not need a nearby disconnect box/mechanism if your EVSE is connected to a 60A breaker or less. If you do use/have a disconnect, make sure it is specified for continuous use, like a blade/handle type disconnect. Pull out disconnects, which are often used for air conditioners, are not recommended.
Receptacle Considerations
You can buy a EVSE that has a short plug that can be plugged into a receptacle. This can be useful if you plan on moving soon and would like to take your EVSE with you, or if you are renting a house.
By code, all new garage receptacles (including high amperage 50A ones) should be protected by a GFCI circuit breaker. If installing a new receptacle, buy the most robust one you can find since EV charging is major load. For 50A receptacles, stay away from the standard big box store Leviton, and look for one made by Hubbell or Bryant. The cheaper ones only have half height steel blade grips and can cause overheating over time.
High powered plug in EVSEs will come with a NEMA 14-50 plug (more common) or a NEMA 6-50 plug. A 14-50 receptacle requires an extra wire to be pulled (the neutral wire) during receptacle installation, but the EVSE doesn't use it. If the receptacle is only going to be used for the EVSE, then a 6-50 receptacle is preferred since it uses one less wire. However note that the 14-50 is a standard receptacle for plugging in an RV into shore power so if you want the receptacle to occasionally be used for that, then the 14-50 is a better choice.
Wire/Cable Sizing
Please stick with the more expensive copper wire/cable. Aluminum wire is not recommended for EVSE installation.
There are four popular wire/cable types people normally use when installing EVSEs and/or receptacles:
- NM-B often called Romex, has a vinyl outer sheath with conductors inside.
- UF-B, Underground Feeder cable has a tough outer jacket suitable for direct burial.
- MC, Metal Clad cable has a flexible metal outer sheath containing THHN conductors inside.
- THHN conductors in either PVC (a type of polymer) or EMT (metal) conduit.
A hardwired EVSE and a NEMA 6-50 receptacle will only need two conductors plus a ground, whereas a NEMA 14-50 receptacle will require three conductors plus a ground. When buying a bundled cable, the ground conductor is ignored in the description, so a 6 gauge two conductor plus ground cable would be referred to as a 6/2 cable. When buying individual wires for a conduit, just buy THHN wire in the correct gauge (buy black for both hots, white for neutral if you need it, and green for the ground).
Some cable types can be used in wet locations, some in dry only.
Following is a chart that shows what gauge cable/wire (for COPPER conductors!) can be used with your EVSE's charge rate, and whether each type is suitable for wet or only dry environments. In some cases, your ground wire can be a smaller gauge and that is shown in (parenthesis). A more complete chart can be found here.
| EVSE | Wire Gauge (Ground Gauge) | |||||
|---|---|---|---|---|---|---|
| Charge Amps |
Breaker Size |
NM-B (US) |
NMC90 (Canada) |
UF-B | MC | THHN/ Conduit |
| 24A | 30A | 10 | 10 | 10 | 10 | 10 |
| 32A | 40A | 8 | 8 | 8 | 8 | 8 (10) |
| 40A | 50A | 6** | 8 | 6 | 8 | 8 (10) |
| 48A | 60A | 4** | 6 | 4 | 6 | 6 (10) |
| 80A | 100A | N/A | N/A | N/A | N/A | 3 (8) |
| Environment: | Dry | Dry | Wet | Dry | Wet* | |
Note that if your wire run is long (like more than 75'), you should check this Voltage Drop Calculator and make sure the wire gauges in the above table are sufficient. For long runs, you might need to use a bigger gauge. Aim for less than 3% voltage drop in the calculator.
* - PVC can be used in wet conditions, and EMT only when using wet couplers and fittings (for instance, screw type EMT couplers are
not rated for wet conditions).
** - Certain states, like MA, allow NM-B to use smaller gauge (the MC column) when not installed in insulation.
Sourcing
The big box stores normally stock NM-B and UF-B down to 6/2, but not 4 gauge. They typically don't stock MC cable at the required gauges. So this is fine if you are installing a 40A or lower charge rate EVSE. For a 48A or higher charge rate, you have to either use PVC or EMT conduit with THHN wire (which the big box stores do carry at all required gauges), or order online for your cable (or visit your local electrical supply house, call ahead to make sure they have what you want in inventory).
I've used this supplier to purchase 6/2 MC cable for 48A charge rate chargers, and Amazon has this supplier. For 80A charge rates, use PVC or EMT conduit.
Make sure to strap whatever cable/conduit you are using/building. Use proper couplers and strapping appropriate to the particular cable or conduit you are using.
MC Cable Tradecraft
MC cable is easy to work with since it is a flexible conduit that you can string wherever you want, no need for junction boxes along the way for wire pulls. But it is a bit finicky when it comes to terminating the cable at the electrical boxes. I would recommend checking out this YouTube video to learn how to install it. Note that even though the video recommends it, anti-short bushings aren't actually a code requirement for MC cable.
Use 1/2" box connectors for 6/2 MC cable. Make sure you get use a box connector that is made for MC (usually they are listed for flex, MC and AC cable).
PVC Conduit Tradecraft
PVC conduit is relatively easy to work with, but just takes time assembling a completed conduit. Use a conduit fill table like this one to determine your conduit size. Don't forget to include the ground wire, so for a hardwired EVSE, you would be pulling 3 wires, while a NEMA 14-50 would require 4 wires of whatever gauge you need.
Electrical code calls for a maximum of 360 degrees of bends in your conduit between pull points. So that's the equivalent of four 90 degree sweeps. If your run has more than that, then you'll have to install a junction box part way (and remember, don't bury junction boxes, the cover must be accessible in an attic or on a wall). DO NOT exceed this 360 degree rule or else you'll be cursing yourself when it comes time to pull wire through your crazy routing.
Build the conduit all the way from the EVSE to the breaker box first, making sure you solvent glue all connections. Once the conduit is built, you have two options to pull the wires through. You can use a flexible metal fish tape which you shove through the conduit and use that as a pulling line coming back. Or you can use electrician's nylon pulling string attached to a little plastig bag "parachute" which you feed into the conduit on one end while you have a shop vac sucking the air out of the conduit on the other end.