We need a load calculation for a permit.
Before a permit office reviews new electrical load, it wants to know what the existing service already carries. We calculate it deterministically from the demand the facility actually recorded. The application itself stays with your designer or contractor.
Why the Method Matters
The code allows two ways to establish the load a service already carries. They start from the same panel and can reach very different answers, because one adds up what is connected and the other reads what the facility actually drew.
- The standard calculation
- Article 220 adds up the connected loads and applies the demand factors the code sets. It has to assume a good deal of equipment runs at once, so on a full service it can put a modest addition over the rating.
- The measured method
- NEC 220.87 takes the highest demand the facility recorded, from a year of utility data or a recording of at least 30 days, and multiplies it by 125%. The margin is written into the code, and the starting point is what the service really carried.
- What the plan checker reads
- Either way the reviewer wants the same things: the existing load, the new load, and a total within the rating, with every figure traceable to its source.
What the Measured Method Asks For
- 01
Maximum demand over a full year, from the utility's own records, where the facility has them.
- 02
Where it does not, a recording of at least 30 days on the service or feeder, taken while the facility runs as it normally does. Heating load is recorded in winter.
- 03
The highest demand in that record, multiplied by 125%, becomes the existing load, and the new load is added to it.
What Answers It
Preliminary Capacity Report
The same analysis and the same numbers, engineer-reviewed and unsealed. It tells you whether the load fits before anyone draws a design. It is not submittable to an AHJ.
From utility records
The Determination of Load Capacity from 12 months of utility demand data. It is the document your electrical plans cite for existing load.
From 30 days on the panel
Where the utility cannot see the panel in question, or the facility has no usable records. Loggers record the exact service or feeder for 30 days, and come off again when the window closes.
The $500 Preliminary Capacity Report comes off whatever determination follows on the same panel. No seal, so it is not submittable to an AHJ.
What We Do and Do Not Do
Wattif produces one thing for a permit: the P.E.-signed load calculation the application is drawn against. We do not prepare, assemble or file permits, and we do not complete jurisdiction forms. Your designer, your contractor or an expediter does that, and the calculation is written so they can use it as it stands.
If plan check raises an electrical comment on the determination, we answer it. Whether a sealed calculation is required at all is set by your jurisdiction and your state's licensing law, since NEC 220.87 itself asks for no stamp. Both signed studies carry the seal, so that question never holds a submittal up.
Where This Comes Up
A restaurant replacing gas with electric cooking
Electric ranges and a booster heater go on an existing service. The plan checker wants the existing load documented before reviewing the new circuits.
A suite fit-out in a multi-tenant center
The landlord's service feeds several suites, and the question is the feeder to one of them. A utility bill cannot see one feeder, so it is metered.
Heat pumps replacing a boiler plant
Heating load lives in winter. Last winter is read from the utility record, or a 30-day recording is scheduled for the heating season.
Questions Owners and Designers Ask
- Is a measured calculation part of the code?
- Yes. NEC 220.87 is part of the National Electrical Code and establishes existing load from recorded demand. Accepting any submittal is always the reviewer's decision, and we answer any electrical comment raised on the calculation.
- Can I submit the $500 report?
- No. It carries no seal, so it is not submittable to an AHJ. It is for deciding whether you have a project, and all $500 of it comes off the sealed determination on the same panel.
- Do you prepare or file the permit?
- No. We provide the P.E.-signed calculation of existing and proposed load. Drawings, applications and filing stay with your designer, contractor or expediter.
- What happens if the load does not fit?
- The determination says so plainly and states the measured headroom. From there you can add less, recover capacity from the service, or design an upgrade against a measured basis.