Guides, code references, and independent research for contractors, inspectors, and homeowners working through service capacity. Free to use, no account required.
Will the existing service take a heat pump or an EV charger? Plain answers for contractors and homeowners, and a calculator to check.
A quick screening check: will a heat pump, EV charger or other new load fit on the existing electrical service? Uses the NEC 220.87 arithmetic - measured peak at 125 percent plus the new load.
Told your 100-amp panel can't take a heat pump or EV charger? Most homes use far less power than the estimate assumes. Here is how your contractor can check your real usage with smart-meter data, and what to send them.
Usually yes. A heat pump draws less than most people expect, and most 100-amp services have more room than a worst-case calculation shows. Here are the real numbers, what actually causes problems, and how to document it for a permit.
A Level 2 EV charger on a 100-amp panel is often possible without a service upgrade. See how charger size changes the math, how the NEC 220.87 load calculation works, and what to do when it is close.
How to use TrueLoad itself — setup, utility data, and producing a report.
The complete walkthrough: setting up a project, requesting utility data, entering new load, and producing the report you hand to the AHJ.
A one-page summary of what TrueLoad does and who it is for: why AHJs increasingly want a formal calculation before new load goes on an existing service, how measured demand is established from a year of the home's own interval data, and the four steps from utility file to permit-ready report. Print it or leave it with a customer.
What the code actually requires — the primary sources themselves, plus plain-language explanations of them.
A plain-language guide to NEC 220.87, the code section that lets an existing service load be based on what the meter actually recorded. What it requires, how the 125% rule works, and when it beats a traditional load calculation.
The code itself, readable in full at no cost. NFPA publishes every edition of NFPA 70 for free online viewing. TrueLoad implements two of its methods: measured demand from utility interval data, and the traditional calculation for existing dwellings.
Both methods apply to existing dwellings and both are in the code. One models the house from nameplates, the other measures it. A worked example shows why the same 100-amp service can fail 220.83 and pass 220.87.
A measured-demand load calculation gets approved when the reviewer can follow it in two minutes. The eight things an AHJ looks for in a 220.87 submission for a heat pump or EV charger permit, and the questions to settle before your first one.
Adding a heat pump, EV charger or range to an existing service means a load calculation for the permit. The four NEC methods compared, what each one needs, how long it takes, and which to try first.
Getting interval data out of a utility, and knowing what you are looking at once you have it.
An NEC 220.87 load calculation needs a year of smart-meter interval data. Here is where to find it, what to ask the utility for, how to read the file, and the pitfalls that make an inspector push back.
How Vermont contractors and homeowners request 12 months of 15-minute smart-meter data from Green Mountain Power for an NEC 220.87 load calculation, with a copy-and-paste email.
How the customer-initiated download works, and which utilities have been certified to provide it.
The industry-standard format for utility usage data. If your utility offers "Download My Data", this is what you are getting and what it contains.
Independent work on panel capacity, electrification, and what upgrades actually cost.
ACEEE study quantifying how much of the existing housing stock is genuinely capacity-constrained versus how much only appears to be under a worst-case calculation.
A survey of the options available when a panel looks undersized on paper — including establishing actual measured demand before assuming an upgrade is required.
US Department of Energy overview of the panel-constraint problem and the research program addressing it. Good orientation if you are new to the topic.
LBNL technical brief on how service panels have historically been sized, and why the assumptions behind that sizing no longer match how homes actually use electricity.
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Turn a year of utility interval data into an AHJ-ready 220.87 report.