General Demand Factors for Whole House Load Calculations – NEC Table 120.45

Where the Demand Factor Finally Comes In

If you have been working through a whole house load calculation, you have already met two building blocks. The first is 2 VA per square foot — take the square footage of the dwelling and multiply it by two, and that gives you the volt-amperes required for your general lighting and general receptacle outlets. The second is the 4,500 VA that accounts for the two small appliance branch circuits and the one laundry branch circuit.

What you probably did not do at that stage was apply a demand factor. There is a good reason for holding it back: a demand factor is a concept you need to be comfortable with in its own right before you start stacking it onto a multi-step calculation. As the Electrical Code Coach puts it in lesson 4.2:

“The reason I didn’t show you earlier in the program is because there’s several key steps. And at that beginning portion, you didn’t even know what a demand factor was.”

By the time you reach this point, you have applied demand factors to ranges, dryers, and other loads. You are a pro at them. So now let’s look at the one that governs the general lighting load itself: Table 120.45.

How Table 120.45 Is Organised

Open your NEC to Table 120.45 and you will see three columns. Understanding the layout is half the battle:

• Left column — Type of Occupancy. You will recognise some familiar entries here. The one that matters most for our purposes is “All other locations” right at the bottom. That is the row a dwelling unit falls under.
• Middle column — Portion of Load. This is where the VA gets broken into slices. Each slice gets its own treatment.
• Right column — Demand Factor (Percent). These percentages are simply your multipliers. Nothing more mysterious than that.

For the “all other locations” row, the slices break down like this:

1. First 3,000 VA at 100%
2. Next 117,000 VA (i.e. from 3,001 VA to 120,000 VA) at 35%
3. Remainder over 120,000 VA at 25%

The Three-Step Process

Here is the process to commit to memory. It works every single time, no matter the square footage:

1. Find your total connected load. Square footage × 2 VA per sq ft, then add 4,500 VA for the two small appliance circuits and one laundry circuit.
2. Set aside the first 3,000 VA at 100%. Subtract 3,000 from your total and hold that remainder.
3. Multiply the remainder by 0.35, then add the 3,000 back in. That sum is your general lighting load after demand factors.

That third step is where people lose marks. It is easy to apply the 35% and then forget to add the original 3,000 VA back on. Don’t be that candidate.

Worked Example One — 1,600 Square Foot Dwelling

Question: What is the total general lighting load you would calculate for a 1,600 square foot home, including the small appliance circuits and the laundry circuit in a dwelling unit, after demand factors?

Step 1 — Total connected load:

• 1,600 sq ft × 2 VA/sq ft = 3,200 VA
• 3,200 VA + 4,500 VA = 7,700 VA

Step 2 — First 3,000 VA at 100%:

• 7,700 − 3,000 = 4,700 VA remainder

Step 3 — Remainder at 35%, then add back:

• 4,700 × 0.35 = 1,645 VA
• 1,645 + 3,000 = 4,645 VA

Your answer is 4,645 VA.

Notice how the demand factor took a 7,700 VA connected load down to 4,645 VA — a substantial reduction, and exactly why the NEC allows it. Not every lamp, receptacle, and appliance in a house draws at the same moment.

Worked Example Two — 1,200 Square Foot Dwelling

Question: What is the total general lighting load for a 1,200 square foot dwelling unit?

Step 1 — Total connected load:

• 1,200 sq ft × 2 VA/sq ft = 2,400 VA
• 2,400 VA + 4,500 VA = 6,900 VA

Step 2 — First 3,000 VA at 100%:

• 6,900 − 3,000 = 3,900 VA remainder

Step 3 — Remainder at 35%, then add back:

• 3,900 × 0.35 = 1,365 VA
• 1,365 + 3,000 = 4,365 VA

Your answer is 4,365 VA.

Note something important about that question wording: it did not mention the small appliance or laundry circuits. That is exactly how it will appear on your exam.

“When you’re taking your exam, they’re not going to mention that. You just have to know that when you’re doing a full general lighting calculation that you have to include the 4,500 VA for the two small appliance and one laundry.”

If you skip the 4,500 VA, you will produce a clean, confident, completely wrong answer — and the exam writers will almost certainly have that wrong answer sitting there as a distractor.

The 25% Tier — Master and Contractor Level

You may have noticed that neither worked example used the third slice of the table. That is deliberate. You only need the remainder-at-25% portion if you are sitting a master electrician exam or higher, which includes the electrical contractor’s exam. Dwelling unit general lighting loads rarely climb past 120,000 VA.

That said, the process is simple enough that there is no reason to avoid it. Let’s walk a 130,000 VA general lighting load through the table:

1. First 3,000 VA at 100% — subtract it right off the top. That leaves 127,000 VA.
2. Next 117,000 VA at 35% — you are only allowed to apply the 35% factor to 117,000 VA of that remainder. So subtract: 127,000 − 117,000 = 10,000 VA left over.
   • 117,000 × 0.35 = 40,950 VA
3. Remainder at 25% — that leftover 10,000 VA gets the 25% factor.
   • 10,000 × 0.25 = 2,500 VA
4. Add all three portions together:
   • 3,000 + 40,950 + 2,500 = 46,450 VA

Same three-step rhythm as before, just with one extra slice in the middle. Set aside, factor, add back.

Common Traps to Watch For

• Forgetting the 4,500 VA. The single most common error. Two small appliance circuits plus one laundry circuit is a fixed 4,500 VA addition to every dwelling unit general lighting calculation.
• Forgetting to add the 3,000 VA back. Applying the 35% and stopping there will land you on a wrong-answer choice every time.
• Applying 35% to everything. The 3,000 VA at 100% is not part of the 35% slice. Keep them separate.
• Using the wrong occupancy row. Dwelling units live under “All other locations”. Don’t get pulled into a different row because the wording sounds vaguer.
• Rounding too early. Carry your VA figures through the calculation and round only at the end, or your answer will drift off the listed options.

The Bottom Line

Table 120.45 is one of those code tables that looks intimidating on first read and turns out to be a three-line recipe once you have practised it:

1. Total it up — square footage × 2 VA/sq ft, plus 4,500 VA
2. First 3,000 VA at 100%, set aside
3. Remainder at 35% (and above 120,000 VA, that last slice at 25%), then add everything back together

As the coach says at the end of the lesson: “this is going to seem complicated at first, but with practice, time, and patience, I know you can do it.” That is not empty encouragement — it is genuinely a mechanical process. The only thing standing between you and getting it right under exam pressure is repetition.

How NEC Mastery Fits Into This

Demand factor questions are pure repetition territory. You do not need to understand anything new after reading this article — you need to run the process enough times that it becomes automatic when a load calculation appears on your exam paper.

• 8,000+ exam-style questions include a deep bank of dwelling unit load calculations, so you can work Table 120.45 problems at every square footage until the three-step process is muscle memory
• Detailed explanations referencing specific NEC articles walk you through each step of the calculation and point you straight back to Article 120 and Table 120.45, so you learn where the rule lives as well as how to apply it
• Timed mock exams weighted to your exam type matter enormously here — calculation questions eat clock time, and practising them under a timer is the only way to know whether you can finish with room to review
• Master and contractor level content covers the 25% remainder tier as well, so if you are sitting a higher-level exam you will not be seeing that third slice of the table for the first time on exam day

Pair the app with your codebook, work the load calculation questions until the arithmetic stops slowing you down, and Table 120.45 becomes free marks rather than the question you dread.