You've hit on a common area of confusion with electrical load calculations, specifically around Article 220. Let's break down each point

1. Heat vs. A/C and Omitting the Lessor Load:
You're right that in dwelling units, you typically omit the smaller of the heating and air conditioning load when calculating the feeder or service load. This is based on the assumption that heating and cooling won't operate simultaneously to their maximum capacity. This is based on 220.82(C).2. 220.60 and Motor Loads: The 125% vs. 25% Confusion You are absolutely correct! 220.60 deals with Noncoincident Loads. It addresses situations where you have loads that are unlikely to be used at the same time. It does NOT mention adding 25% of the motor load. It only states that you don't need to account for the loads that are unlikely to be utilized at the same time. 125% is for CONTINUOUS loads. This percentage is for continuous loads. This is in 210.19(A)(1), 215.2(A)(1), and 230.42(A)(1). The 25% rule you are referencing applies to calculations for the FLA on single motor-compressors, when calculating the branch-circuit selection current. This is found in 440.6. 440.32 is for conductors supplying one or more motor-compressors.3. Mike Holt's Book and Example Problems

It's possible there's an error in the Mike Holt book or the explanation of that specific question (Unit 7, 7.12, question 49). Without seeing the exact question and the provided solution, it's difficult to say definitively. The context of the question is important. Is it asking about:

Service or feeder load calculation for a dwelling unit (220.82)? In that case, omitting the smaller of heating/AC is often appropriate, and the 125% rule typically applies to continuous loads (like general lighting/receptacles). Branch circuit sizing for a specific motor-compressor (Article 440)? That's where you'd use the 25% rule for the branch-circuit selection current.

Here's a general approach to these calculations


Identify the Type of Load Calculation

Is it for:

A service or feeder? (Article 220) A branch circuit? (Article 210) Specifically dealing with motor-compressors? (Article 440)2. Determine Continuous vs. Noncontinuous Loads

Continuous loads (operate for 3 hours or more) need the 125% factor.3.

Apply the Appropriate NEC Sections

Dwelling Unit Service Calculations: Follow 220.82. Omitting smaller of heating/AC is common. Motor-Compressor Branch Circuits: 440.6 for branch-circuit selection current.

Recommendations1. Provide the Exact Question from Mike Holt's Book

If you can share the exact wording of the question and the provided solution from Unit 7, 7.12, question 49, I can analyze it and point out the potential error or explain the logic behind it.
2.

Double-Check the NEC

Always refer directly to the National Electrical Code (NEC) to confirm the correct calculation methods and requirements. The NEC is the ultimate authority.3.

Practice with Varied Examples: Work through different types of load calculation problems to solidify your understanding. Pay attention to the specific scenario in each question.The NEC can be tricky, and these kinds of nuances can easily cause confusion. By focusing on the specific scenario and consulting the appropriate sections of the code, you'll become more confident in your load calculation abilities. Good luck with your exam! Flag for review