We need a load calculation to get new load approved.
Before the authority that approves new electrical load reviews it, 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
There are 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
- A calculated method 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
- Where your local code accepts it, existing load is taken from the highest demand the facility recorded, from a year of utility data or 30 days recorded on the panel, with the margin the code requires added on top. The starting point is what the service really carried.
- What the reviewer 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 Uses
- 01
Maximum demand over a full year, from the utility's own records, where the facility has them.
- 02
Where it does not, a 30-day recording 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, with the margin your code requires, becomes the existing load, and the new load is added to it.
What Answers It
From utility records
The Capacity Determination Report 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.
What We Do and Do Not Do
Wattif produces one thing for an application: the load calculation it is drawn against, reviewed and signed by a licensed engineer under their own licence. We do not prepare, assemble or submit applications, and we do not complete the authority's forms. Your designer, your contractor or an agent does that, and the calculation is written so they can use it as it stands.
Whether a signed calculation is required at all is set by the authority that approves the load and by the licensing law where the facility is. The report is always signed, so that question never holds an application up.
Where This Comes Up
A restaurant replacing gas with electric cooking
Electric ranges and a booster heater go on an existing service. The reviewer wants the existing load documented before looking at 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
- Does the code accept a measured calculation?
- Where your local code accepts a method for existing load based on recorded demand, the calculation follows it. Accepting any application is always the reviewer's decision, and we answer any electrical comment raised on the calculation.
- Do you prepare or submit the application?
- No. We provide the calculation of existing and proposed load, signed by a licensed engineer. Drawings, applications and submission stay with your designer, contractor or agent.
- 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.