Panel load and service capacity
How This Calculation Works
This planning tool adds an estimated existing demand to selected future loads and compares the total with the service rating and a chosen headroom factor. It is designed to answer “should I start a service-upgrade conversation?” rather than produce a permit-ready demand calculation. Real demand is not simply the sum of every breaker handle: dwelling calculations apply code demand factors, while heating, motors, EVSE, cooking, and other equipment have specific rules. Treat the output as a conservative screening number and keep the nameplate data for a professional review.
Applicable Code Rules & Standards
Ontario service and feeder sizing is governed by the current OESC and CEC Section 8, with utility requirements and ESA notification for service changes. NEC projects use Article 220 and local amendments. The service rating, panel busbar rating, feeder conductors, meter equipment, grounding electrode system, and utility connection must all be compatible. A 200-amp main breaker does not prove that a panel busbar, feeder, or service conductors are rated for every planned addition. Pair this screen with the Service Size Calculator and a full load review.
Common DIY/Installation Errors
- Adding breaker ratings together and calling that the dwelling load.
- Assuming empty spaces mean spare service capacity.
- Installing a larger main breaker without checking busbar, conductors, meter, and utility limits.
- Ignoring future EVs, heat pumps, electric water heating, or solar backfeed.
- Working inside the panel or at the service without a permit and qualified supervision.
Capacity also includes physical and operational realities. A panel may have open spaces but no approved breaker type, insufficient busbar rating, poor working clearance, or no route for a new feeder. Service upgrades can affect the meter base, overhead or underground conductors, grounding electrode system, utility transformer, and enclosure location. Ask for a written scope that identifies what is being upgraded and what remains unchanged so the inspection and future maintenance records are clear.
Keep copies of the completed load calculation, permit, inspection result, panel schedule, and equipment labels. These records help a future electrician understand which assumptions were used and prevent repeated guesswork when another major load is added.
When to Hire a Licensed Professional
Always hire a Licensed Electrical Contractor for panel changes, service upgrades, feeders, load management, generator interconnection, or solar interconnection. The contractor can complete the formal calculation, coordinate utility disconnects, obtain ESA approval, verify fault ratings, and test grounding and bonding. If the panel is hot, corroded, damaged, crowded, or contains incompatible breakers, keep the cover closed and request an inspection.