EMS Load CalculatorService capacity planning with energy management NEC 2023
What this tool checks: Determine whether an existing electrical service may accommodate new major loads—such as EV chargers, electric water heaters, heat pumps, and HVAC equipment—using energy management instead of a service upgrade. Relevant NEC 2023 provisions include §§220.70 and 750.30 for EMS-controlled loads, §625.42(A) for EV charging, and §220.82 for the dwelling optional load calculation. Final feasibility depends on the applicable load calculation, compatible listed equipment, verified controls, and AHJ approval.
1Service & existing loads
2New loads
3EMS configuration
4Evaluation
1. Existing Electrical Service
Enter the calculated demand or 125% of the qualifying peak demand from 12-month data or a 30-day recording (NEC 2023 §220.87).
NEC 2023 §220.82 — Single Dwelling Optional Method. Existing or new dwelling; enter EMS-managed loads in Step 2. General loads (3 VA/sf, small-appliance and laundry circuits, appliances and motors at nameplate): first 10 kVA at 100%, remainder at 40%. Heating/cooling: larger of the §220.82(C) options. EV charger: 100%.
Unit Details
Use the dwelling floor area applicable under NEC 220.5(C).
Existing/New Fixed Appliances — Nameplate VA
Dwelling EV charger (nameplate). Add EMS-managed chargers in Step 2. Counted at 100% (no demand factor), as in the Single Dwelling Unit calculator.
Existing/New Heating and Cooling
The larger of heating or cooling is used (NEC §220.82(C)).
Condensing unit or heat pump. 0 if none.
AHU/FCU fan motor only (excludes supplemental heat).
Total nameplate kW.
4 or more: 40%. Fewer: 65%.
Existing/New Demand (§220.82 optional method)
General load (connected)–
General load after demand factor First 10 kVA at 100%, remainder at 40%–
Heating / cooling Larger of heating or cooling, §220.82(C)–
Existing/New EV charger (100%)–
Existing/New calculated demand–
Engineering check: This is a simplified §220.82 worksheet. Confirm the qualifying optional-method conditions, load classifications, heating/cooling percentages, largest motor, EVSE treatment, and actual nameplates before relying on results. Heating and cooling follow §220.82(C), the same as the Single Dwelling Unit optional-method calculator.
2. Proposed New Electrical Loads
Add multiple EV chargers, water heaters, HVAC equipment or other new loads. Input actual operating nameplate current, not just the breaker size.
Load
Type
Qty
Voltage
Operating A (each)
EMS controlled?
Load Calculation Without EMS
Review the existing demand plus all new loads before selecting an EMS configuration.
Existing/New demand
—
New loads
—
Total demand without EMS
—
Existing service capacity
—
3. ZigTech EMS Configuration
A
19.2 kVA80% of 100 A service
Maximum: 80A (80% of the 100A service rating).
NEC 2023 §220.70: the EMS setpoint is treated as a continuous load in the load calculation, so the service must be rated at least 125% of the setpoint. The setpoint therefore may not exceed 80% of the service rating.
NEC 2026: §120.7 keeps the same limit: a power control system setpoint used for load calculations may not exceed 80% of the rating of the overcurrent device it monitors. Confirm which NEC edition your AHJ has adopted.
AHJ Approval: The proposed ZigTech EMS installation and load-management approach must comply with applicable NEC 2023 requirements and are subject to review and approval by the Authority Having Jurisdiction (AHJ).
