What Every Electrician Should Know for the Exam and the Job
Load calculations are one of the most important — and sometimes most frustrating — parts of preparing for your electrician licensing exam.
Whether you’re working on a residential service or a large commercial panelboard, calculating electrical loads correctly is essential to getting the job done safely and up to code.
Exams often include multiple questions on load calculations, and it’s one area where even experienced electricians can get tripped up. If you’re serious about passing your exam and becoming a confident, well-rounded electrician, you need to get comfortable with this topic.
In this post, we’ll walk through what load calculations are, how demand factors affect them, and how to approach these problems on the exam and in the field.
What Are Load Calculations?
Load calculations determine the amount of electrical power (in watts or volt-amperes) that a circuit, feeder, or service must supply. This process ensures that the system can safely carry the electrical load without overheating, causing voltage drops, or tripping breakers.
There are many different types of loads you may be asked to calculate:
- General lighting loads
- Receptacle loads
- Appliance loads
- HVAC and motor loads
- Fixed equipment
- Demand loads for services or feeders
Each type follows specific rules found in the National Electrical Code, often under Article 220, which deals with branch circuit, feeder, and service calculations.
Why Demand Factors Matter
Demand factors allow you to reduce the total calculated load because not all connected loads will operate at the same time. The NEC provides specific tables and guidelines that tell you when and how to apply demand factors.
For example, when calculating the load for a residential service, the NEC allows a reduced calculation for the general lighting and receptacle load based on the total connected wattage. This helps prevent overbuilding the electrical system.
Using demand factors properly is key to sizing services and feeders efficiently — not just to pass the exam but also to keep projects cost-effective.
Common Load Calculation Scenarios
Here are a few examples of the types of questions and scenarios you may run into on the exam.
1. General Lighting Load for a Dwelling Unit
The NEC requires you to calculate general lighting at 3 VA per square foot. So, for a 2,000 sq. ft. home:
Load = 2,000 sq. ft. × 3 VA = 6,000 VA
Then, using NEC Table 220.42, you can apply a demand factor based on the total load.
2. Small Appliance and Laundry Circuits
A dwelling unit must include at least two small-appliance branch circuits and one laundry circuit, each calculated at 1,500 VA.
Load = 3 × 1,500 VA = 4,500 VA
These values are then added to the general lighting load before applying any demand factors.
3. Kitchen Equipment
If you’re calculating for commercial kitchens or fixed cooking appliances in a home, you’ll refer to NEC Table 220.55, which includes demand factors for multiple cooking appliances.
Example: For three electric ranges rated at 12 kW each, Table 220.55 allows you to apply a demand factor of 65%:
Load = 3 × 12,000 W = 36,000 W
Demand load = 36,000 W × 0.65 = 23,400 W
4. Motor Loads
Motor calculations involve determining the largest motor and applying demand factors to the others per NEC Article 430. Typically, you add 125% of the largest motor’s full-load current and 100% of all others.
Study Tips for Mastering Load Calculations
- Memorize key values: Know common VA values like 3 VA per square foot for lighting or 1,500 VA for small appliances.
- Understand the NEC tables: Tables 220.42, 220.55, and others are critical. Learn how to read and apply them.
- Practice word problems: Load calculation questions are often written as scenarios. Practice interpreting and breaking down what is being asked.
- Use a step-by-step method: Always write out each step — it reduces careless errors and makes it easier to spot where you went wrong if you miss the answer.
- Don’t guess demand factors: They vary by situation. Double-check whether the load is continuous, non-coincident, or requires 125% adjustments.
On the Job
Once you’re licensed, load calculations don’t go away. You’ll use them to design circuits, size panels, and verify compliance during inspections. Doing this right protects both people and property, and it reflects your professionalism as an electrician.
For example, when adding a new HVAC unit to a building, you’ll need to evaluate the existing panel’s load capacity and confirm that the new load won’t exceed the limits — and that requires precise calculation.
Load calculations and demand factors may feel like a puzzle at first, but once you understand the rules and practice applying them, they become a powerful tool in your electrician skillset.
They show up regularly on licensing exams because they’re essential in real life. Master them now, and you’ll be better prepared both for the test and the job site.
