Alternatives to a Service Upgrade

Why this matters

When the load numbers come up short, the reflex answer is a bigger service. Sometimes that is right. Often it is the answer that adds weeks of utility scheduling and a large line item to a job that could have fit with a device, a different appliance or a smaller backup heater. The opposite mistake is just as real: a shop that sells a load-management box to a house that genuinely needed capacity has built a house that sheds its own heat on the coldest night of the year. This card covers the tools that let a house fit, how the code counts each one, and the gate that says when none of them is the answer.

The measured-load method itself belongs to Measuring Existing Load Before You Sell a Service Upgrade. This card starts from its result.

The tools, and how the code counts each

An energy management system (EMS). A system that monitors the service or feeder current and reduces or switches off controlled loads to hold the total under a setpoint. The NEC treats it in Article 750, and in the 2023 edition 220.70 lets the load calculation use a single value equal to the EMS's maximum ampere setpoint for the service it limits, as adopted by your jurisdiction. In code terms that is the big lever: the house is counted at the setpoint, not at the sum of its nameplates. Earlier editions handled the EV case through 625.42(A), which allows an EMS to set the charger's load for the calculation. The EMS has to be listed and installed as an energy management system; the inspector will want to see that.

An adjustable charger setting. Most chargers can be set below their maximum, and 625.42(B) lets the calculation use the setting rather than the maximum when the adjustment is restricted to qualified persons. Do not expect it to go below 30 amps on paper. 220.57 counts an EV charger at the larger of 7,200 watts or its nameplate, and 7,200 watts at 240 volts is 30 amps. A 16-amp setting still counts as 30 in the calculation. That floor surprises people who expected a low setting to make a charger disappear from the arithmetic.

A circuit-sharing device. A listed device that feeds two loads from one circuit and locks one out while the other runs, for example a dryer and an EV charger sharing the dryer's 30-amp circuit, with the dryer taking priority. Because the two cannot run together, the calculation can treat them as noncoincident and count the larger (220.60, as adopted by your jurisdiction), and the device solves a panel-space problem at the same time. Ask the inspector how they treat the specific device's listing before you build a quote on it.

A smart panel. A panel or breaker set with remotely controlled breakers. It is an EMS in the code's sense only if it is listed and configured as one. A panel that reports usage to an app and lets the owner switch circuits by hand is a monitoring tool, and it counts for nothing in the calculation.

A 120-volt appliance. Plug-in heat pump water heaters, 120-volt heat pump dryers and some lower-power induction ranges run on ordinary circuits. They take a smaller share of the service and often avoid a new 240-volt circuit and its two breaker spaces. Each trades something, usually recovery time or power. See related: Plug-In 120-Volt Heat Pump Water Heaters.

Right-sizing. The largest single lever on most conversions is resistance backup heat, at about 4.2 amps per kilowatt at 240 volts. Envelope work that lets 10 kilowatts of strips become 5 removes about 21 amps; choosing a cold-climate heat pump that needs less backup removes more. A heat pump in place of a resistance heater for the same heat draws a fraction of the current. See related: Heat Pump Versus Electric Resistance, Explained, and Sizing a Heat Pump for a Cold Climate.

What shedding costs the household

Every load-management tool works by making something wait. The design question is what waits, and when.

• Shed the car first. An EV that charges slower on a cold evening is an inconvenience the owner rarely notices if it charges overnight.
• Shed the water heater second. A tank is stored energy. Delaying recovery for an hour costs little unless the household is mid-shower.
• Do not shed the heat on a design day. An EMS that holds the setpoint by switching off backup strips or the heat pump in the coldest hour has turned a capacity shortage into a comfort failure, and in a hard freeze into a frozen-pipe risk.

So an EMS is a good answer where the flexible loads are large enough to absorb the excess and a bad one where the excess can only come out of the heating. That is the gate below.

The gate

Run the house's worst realistic hour, not just its code calculation: the measured existing peak at its actual value (not multiplied), plus every new fixed load running at once, the heat pump and its backup on a design night, the water heater recovering. Call that the fixed demand.

An alternative is the answer when the fixed demand sits under the service rating with room left, and the overage in the code calculation comes from loads that can wait. An upgrade is the answer when the fixed demand alone approaches or passes the rating, because then the only thing an EMS can shed to hold the line is heat.

Then add the customer's next five years: a second car, a hot tub, a workshop, solar with a battery. A device that fits today's house and fails next year's is a deferral, and the customer should hear it called that.

One gate, two houses

Both houses have a 100-amp, 120/240-volt service, bus and conductors confirmed at 100 amps, and twelve months of 15-minute utility data. Nameplates are illustrative.

House A. Gas heat today. Measured peak 7.2 kilowatts, which is 7,200 divided by 240, 30 amps; at 125 percent, 37.5 amps. New loads: heat pump 20 amps, 5 kilowatts of backup at 20.8 amps, a 240-volt heat pump water heater at 18.8 amps. Calculated total 97.1 amps, which passes. The charger, at its 220.57 value of 32 amps, takes the total to 129.1 and fails.

The gate. The fixed demand on a design night is the actual peak of 30 amps plus 20, 20.8 and 18.8 amps of new load: 89.6 amps, under 100. The calculation's overage is entirely the car. An EMS with a 100-amp setpoint brings the calculated load to 100 and passes. On the worst winter hour the charger gets 100 minus 89.6, about 10.4 amps instead of 32, and on almost every other hour of the year it gets all of it. Alternative wins. The design note says the EMS sheds the charger first and the water heater second, and never the heat.

A second route for House A: swap the 240-volt water heater for a 120-volt plug-in unit and leave the charger at its full setting. Whether that fits depends on the 120-volt unit's nameplate and how the calculation counts it; run it, do not assume it.

House B. Electric range and dryer already, a hot tub, gas heat. Measured peak 14.4 kilowatts: 14,400 divided by 240 is 60 amps, 75 amps at 125 percent. The owner wants a heat pump at 20 amps with 10 kilowatts of backup at 41.7 amps, because the house has not had envelope work. Calculated total 136.7 amps before any car.

The gate. Fixed demand on a design night: 60 plus 20 plus 41.7, about 121.7 amps, over the rating with no car in the picture. An EMS could hold 100 amps only by switching off heat in the coldest hour. The owner also plans a second vehicle. Upgrade wins, and the envelope work becomes a way to shrink the backup on the new service, not a way to avoid it.

What flips each answer. House A tips toward an upgrade if the owner adds a hot tub or a second car, because the fixed demand rises toward the rating and the flexible slack shrinks. House B tips toward an alternative if air sealing and a cold-climate unit cut the backup to 5 kilowatts: fixed demand becomes 60 plus 20 plus 20.8, 100.8 amps, still at the rating, so it does not tip far enough on that alone. Run the gate on the real numbers every time; the direction of the answer is not obvious from the description of the house.

When an upgrade is the answer for reasons the arithmetic does not show

• The equipment is the problem. An obsolete or damaged panel, a meter base that is failing, aluminum service conductors with damaged terminations, or a panel type with a known failure history. Capacity is not the question; the service needs replacing anyway.
• There is no room. A panel with no spaces and no allowance for tandem breakers cannot take a new circuit regardless of amps. See related: Panel Space Versus Panel Capacity.
• Solar and storage are coming. Interconnecting a solar system on the load side is limited by the panel bus rating (NEC 705.12, as adopted by your jurisdiction). A larger bus can be the cheapest path for a customer whose plan includes it. See related: Solar and Batteries in a Conversion Plan.
• The utility side is already undersized. Sometimes the drop or the transformer is the constraint, and the utility will tell you that only after you ask. See related: The Utility Service Upgrade and Its Timeline.

How the bad version shows up later

Three field signatures of an alternative that should have been an upgrade: the customer reports a cold house on the coldest nights and the EMS log shows heat being shed; the charger app shows sessions that never finish on winter evenings; and a main breaker that trips anyway because the device was configured to shed only the car and the fixed demand alone exceeded the rating. When you inherit a house with any of these, pull the EMS configuration and re-run the gate on today's loads.

References

• NFPA 70, National Electrical Code, Article 750, 220.57, 220.60, 220.70, 625.42 and 705.12 (2023 edition numbering), as adopted by your jurisdiction
• See related: Measuring Existing Load Before You Sell a Service Upgrade
• See related: EV Charger Load Management Reference
• See related: Electrical Panel Upgrades for Electrification Reference
• See related: The Whole-House Electrification Sequence