As the solar industry evolves, so do the electrical codes that govern how we design and interconnect photovoltaic systems.
The 2020 and 2023 NEC updates introduced a powerful new concept — the Energy Management System (EMS) — under NEC 705.13.
For installers and designers, understanding how EMS can expand interconnection options, reduce costs, and improve compliance is becoming a must-have skill.
In this article, we’ll break down what NEC 705.13 means, when it applies, and how to design compliant systems using it.
What is an Energy Management System (EMS)?
An Energy Management System (EMS) is a listed control device or software-based system that can monitor and limit power flow from distributed energy resources — such as solar PV, battery storage, or generators — to prevent the overloading of busbars, feeders, or conductors.
In simple terms:
An EMS is a smart gatekeeper that ensures your system never exceeds the limits defined by the National Electrical Code (NEC).
By dynamically controlling current flow, EMS allows for larger PV systems without physically upgrading panels or service equipment.
Why EMS Exists: The Problem with the 120% Rule
Before EMS, designers were limited by the NEC 705.12(B)(2) “120% rule,” which states:
The sum of the main breaker and PV breaker cannot exceed 120% of the busbar rating.
For example:
A 200A panel could only host up to 40A of backfed PV (≈9.6 kW at 240V).
To add more capacity, you’d have to derate the main breaker or upgrade the service — both expensive options.
NEC 705.13 solves this problem by introducing a dynamic way to manage power flow without hardware upgrades.
How NEC 705.13 Works
Under NEC 705.13, an EMS can control:
- PV inverter output
- Energy storage discharge
- Combined system export
to ensure the busbar rating, feeder ampacity, or service capacity is never exceeded — even under full solar production and grid load.
The EMS must:
- Continuously monitor system output.
- Automatically limit current flow when approaching maximum limits.
- Be listed and recognized for use in energy management.
Designing with EMS: Key Scenarios
Let’s look at how solar contractors can use NEC 705.13 to their advantage:
1. Oversized PV on Limited Service Panels
If you have a 200A service panel but want to install 15kW or 20kW of solar, a listed EMS can actively cap the system export so that combined current never exceeds the safe busbar limit.
- No service upgrade needed.
- No main breaker derating.
- Full compliance with NEC 705.13.
2. Hybrid Systems (Solar + Storage)
When combining solar and storage, the total exportable current can exceed the busbar’s ampacity.
An EMS monitors both sources and prevents overload dynamically.
Example:
- PV Inverter: 60A
- Battery Inverter: 40A
- Busbar: 100A max
The EMS ensures combined current never exceeds 100A, by throttling PV output or limiting discharge.
3. Multi-Inverter or Microgrid Applications
Commercial systems often use multiple inverters across feeders.
EMS can coordinate all generation sources to maintain safe system limits, enabling flexible interconnections under a single service.
Compliance Requirements for EMS (Per NEC 705.13)
To qualify under NEC 705.13, the Energy Management System must:
- Be listed and identified for power control.
- Prevent overloads of busbars, conductors, and overcurrent devices.
- Maintain safe operation under all load and generation conditions.
- Fail-safe: in case of failure, it must default to a non-export or shutoff condition.
This means you can’t just use a programmable logic controller (PLC) or a smart inverter setting — it must be a certified EMS product approved by the AHJ.
Common EMS Solutions on the Market
Some early adopters include:
- SolarEdge Energy Hub EMS
- Enphase IQ Gateway with Export Limiting
- Tesla Powerwall+ Gateway (Dynamic Export Control)
- SMA Data Manager M with Export Control Module
- Eguana or Generac PWRcell EMS Integrations
Always confirm product listings and certifications per UL 1741 SB or UL 916 for compliance.
Key Documentation for Permitting
When using an EMS in your design, your permit package should include:
- Single-line diagram showing control architecture.
- Manufacturer spec sheet stating EMS listing and functionality.
- Load calculations showing controlled limits.
- System operation notes referencing NEC 705.13 compliance.
Many AHJs now specifically ask for:
“Provide documentation showing EMS functionality per NEC 705.13.”
Including these details upfront ensures faster permit approvals.
Field Tips for Installers
- Always verify that the EMS is properly configured before final inspection.
- Label system disconnects clearly to reflect EMS integration.
- Coordinate with utility interconnection teams — some utilities require export-limiting verification during PTO.
- Keep screenshots or commissioning reports showing export limits and real-time monitoring.
Why EMS Matters for the Future
As distributed generation grows, grid export control will become a requirement in many jurisdictions.
NEC 705.13 gives contractors the flexibility to build larger, smarter, and safer systems — without waiting for service upgrades or expensive hardware changes.
This is the bridge between traditional PV design and the future of smart grid-ready solar.
Final Thoughts
Understanding and applying NEC 705.13 can be a game-changer for solar installers and designers.
With EMS, you can:
- Increase PV system capacity
- Avoid panel upgrades
- Ensure NEC and AHJ compliance
- Deliver smarter, safer installations
The key is using listed equipment, proper documentation, and well-defined operational limits.
Need help integrating EMS into your PV designs?
Vishtik’s engineering experts specialize in NEC 705.13-compliant designs that satisfy AHJs and utilities nationwide.
We’ll help you scale your projects safely, efficiently, and code-correct — every time.
Start your next EMS-based permit design with Vishtik today.
