16.2 Energy Storage and EV Charging (Articles 706, 625)
Key Takeaways
- ESS OCPDs must be rated at least 125% of the ESS nameplate current per 706.30(A), and output conductors sized at 125% of the ESS current rating per 706.31.
- ESS disconnecting means per 706.15 must be readily accessible, marked ENERGY STORAGE SYSTEM DISCONNECT, and include emergency shutdown in one- and two-family dwellings.
- EVSE requires an individual branch circuit (no other outlets) per 625.40 and is a continuous load per 625.41; the branch-circuit load = 125% of the EVSE rated maximum continuous load per 625.42.
- A 40 A EVSE requires a 50 A OCPD (40 × 1.25 = 50 A) and a conductor with ampacity ≥ 50 A — 6 AWG copper at 75°C (65 A per Table 310.16) is a common selection.
- 220.57 sets the EVSE dwelling load at 7200 VA minimum (new in 2023 NEC); EVSE is excluded from the 220.53 fastened-in-place 75% demand factor.
Why Articles 706 and 625 Matter for the TX Journeyman Exam
Content-outline area 10 (Renewable Energy Technologies) extends beyond solar to include energy storage systems (ESS) and electric vehicle charging. The exam tests these primarily on the NEC Knowledge part — scope, disconnecting means, labeling, and continuous-load classification — with EVSE branch-circuit sizing also appearing on the Calculations part.
These systems are increasingly common in Texas residential and commercial work, and the 2023 NEC reorganized both articles significantly from prior editions.
Energy Storage Systems — Article 706
Scope (706.1)
Article 706 applies to all ESS with a capacity greater than 1 kWh (3.6 MJ) that operate stand-alone or interactive with other power sources. This covers most modern battery systems (lithium-ion, flow batteries, etc.). Legacy standby-only battery systems regulated under Article 480 are separate.
Key Provisions
| Section | Topic | Core Rule |
|---|---|---|
| 706.4 | Nameplate | Each ESS must be listed with nameplate data |
| 706.7 | Commissioning | ESS must be commissioned upon installation (non-dwelling); written maintenance records kept |
| 706.15 | Disconnecting means | Must disconnect ESS from all wiring systems; readily accessible; marked "ENERGY STORAGE SYSTEM DISCONNECT" |
| 706.30(A) | Circuit current / OCPD | OCPD rated ≥ 125% of ESS nameplate current (exception: 100% if listed for continuous operation at 100%) |
| 706.31 | Conductor sizing | Output circuit conductor ampacity ≥ 125% of ESS current rating or the OCPD rating |
| Article 250 | Grounding & bonding | ESS grounding and bonding per Article 250; equipment grounding conductors sized per Table 250.122 |
ESS Disconnecting Means — 706.15 Details
706.15(B) requires the disconnect to be readily accessible and comply with one of:
- Located within the ESS
- Within sight and within 10 ft of the ESS
- If not within sight, capable of being locked in the open position per 110.25
706.15(B) Emergency Shutdown (one- and two-family dwellings): must include an emergency shutdown function to cease power export, with the initiation device located readily accessible outside the building.
706.15(C) marking: must plainly indicate open/closed position and be marked "ENERGY STORAGE SYSTEM DISCONNECT." For non-dwelling installations, marking must include nominal battery voltage, available fault current, arc-flash label, and date of calculation.
ESS Grounding
ESS grounding and bonding comply with Article 250. Key applications:
- Equipment grounding conductors sized per Table 250.122 based on the OCPD rating
- Connection to the building's grounding electrode system
- Bonding jumpers between metallic ESS enclosures, racking, and conduit
- For DC battery systems with ungrounded (floating) circuits, a ground-fault detection device is essential
Electric Vehicle Supply Equipment — Article 625
Scope (625.1)
Article 625 covers the electric vehicle charging system: the EVSE (supply equipment), the connector, and the cable between them. It applies to wired-in (fixed) and cord-and-plug-connected equipment in residential, commercial, and public locations.
Core EVSE Rules
| Section | Rule |
|---|---|
| 625.40 | Individual branch circuit required for EVSE rated above 16 A or 120 V; no other outlets permitted on the circuit |
| 625.41 | EVSE is a continuous load |
| 625.42 | Branch-circuit load = 125% of the EVSE rated maximum continuous load |
| 625.43 | Disconnecting means required for EVSE/WPTE rated >60 A or >150 V to ground; must be readily accessible and lockable in the open position per 110.25; if installed remote from the equipment, a plaque denoting the disconnect location is required |
Worked Example — Size the Branch Circuit and OCPD for a 40 A EVSE
Given: A hardwired EVSE rated 40 A maximum continuous load, installed in a garage. Copper conductors, 75°C terminations, no more than 3 current-carrying conductors in the raceway.
Step 1 — Continuous-load adjusted current (625.41/625.42):
Formula: Branch-circuit load = EVSE rated max continuous load × 1.25
Substitution: 40 A × 1.25 = 50 A
Step 2 — OCPD selection:
The calculated load is 50 A. Per 240.6(A), standard ratings include 50 A. So the OCPD = 50 A.
Step 3 — Conductor selection (Table 310.16, 75°C column, copper):
The conductor ampacity must be ≥ 50 A (the continuous-load value the OCPD protects).
| Conductor Size | 75°C Ampacity (Cu) |
|---|---|
| 8 AWG | 50 A |
| 6 AWG | 65 A |
8 AWG copper at 75°C gives exactly 50 A, which meets the requirement. In practice, many installers use 6 AWG (65 A) to provide margin and accommodate voltage drop on longer runs.
Trap: Do not forget that 625.40 requires an individual branch circuit. You cannot share this circuit with a receptacle, lighting, or any other load.
Load Calculation Cross-References — 220.57 and 240.6(A)
220.57 — EVSE Dwelling Unit Load
New in the 2023 NEC, 220.57 establishes a minimum EVSE load of 7200 VA for dwelling unit feeder/service calculations.
| Rule | Detail |
|---|---|
| Minimum EVSE load | 7200 VA per EVSE (dwelling) |
| Demand factor | EVSE is excluded from the 220.53 fastened-in-place 75% demand factor |
| Application | Use the larger of the actual EVSE rating or 7200 VA |
240.6(A) — Standard Ampere Ratings
When selecting an OCPD, use a standard rating from 240.6(A). The full run includes:
15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, 6000
Note: 25 A and 35 A are in the standard list. If your calculation yields 28 A, the next standard rating is 30 A. If it yields 36 A, use 40 A.
Comparing ESS and EVSE Requirements
| Feature | ESS (Art. 706) | EVSE (Art. 625) |
|---|---|---|
| Continuous load? | Not explicitly; sized via 706.30/706.31 | Yes — 625.41 |
| OCPD sizing | ≥ 125% of nameplate current (706.30) | ≥ 125% of rated max load (625.42) |
| Conductor sizing | ≥ 125% of ESS current (706.31) | ≥ 125% of rated max load (625.42) |
| Individual branch circuit? | Not required by 706 specifically | Required — 625.40 |
| Disconnect marking | "ENERGY STORAGE SYSTEM DISCONNECT" (706.15(C)) | Not specified by 625.43 (must be lockable open per 110.25) |
| Grounding | Article 250 | Article 250 |
Key Takeaways
- ESS: Remember the 125% multiplier for both OCPD (706.30) and conductors (706.31), and know the disconnect marking text.
- EVSE: Three rules to memorize — individual branch circuit (625.40), continuous load (625.41), 125% sizing (625.42).
- 220.57: The 7200 VA dwelling minimum is new in 2023 and very testable.
- 240.6(A): Always round up to a standard rating; 25 A and 35 A are standard sizes candidates often forget.
Per 625.42, what is the minimum branch-circuit load for an EVSE rated 32 A maximum continuous load?
Which section of the 2023 NEC requires an individual branch circuit for EVSE rated above 16 A or 120 V, with no other outlets permitted?
What is the minimum EVSE load for a dwelling unit feeder/service calculation per 220.57 (new in the 2023 NEC)?
Per 706.15, the ESS disconnecting means must be marked with which of the following?