You've identified a potential discrepancy, and you're right to question it! Let's break this down and see where the difference lies.

Here's the breakdown

1.

Table C.11

This table is specifically for the number of conductors

of the same size in a conduit. It suggests 4 #3 RHW conductors fit in 1-1/4" PVC Schedule 40.2. Area Calculation

This is where we need to be careful.

#3 RHW Area

You're using 0.1521 sq. in. for the #3 RHW. This is the correct area from Table 5. NOTE: We'll double-check this against a commonly used software calculation below.

4 #3 RHW Total Area

4 0.1521 = 0.6084 sq. in.

1-1/4" PVC Sch 40 Fill Area (40%)

You're using 0.581 sq. in., which is correct from Table 4.
3.

The Problem

Your calculations correctly show that 0.6084 sq. in. (4 #3 RHW) exceeds the 40% fill allowance of 0.581 sq. in. for 1-1/4" PVC Schedule 40.
4.

The Key (Multiple Conductor Sizes)

You cannot use Table C.11 directly because you have multiple conductor sizes (#3 RHW and #8 RHW). Table C.11 only works if all conductors are the same size. Since the #8 is a different size, you must use the area fill calculations.

Correct Calculation Method (Area Method)


#3 RHW Area

0.1521 sq. in. (from Table 5)2.

#8 RHW Area

0.0547 sq. in. (from Table 5)3.

Total Conductor Area

(4 0.1521) + 0.0547 = 0.6084 + 0.0547 = 0.6631 sq. in.
4.

Conduit Sizing

We know we need to exceed 0.6631 sq. in. to fit the wires. Let's look at conduit sizes: 1" PVC Sch 40 = 0.340 sq. in. 1-1/4" PVC Sch 40 = 0.581 sq. in.

1-1/2" PVC Sch 40 = 0.824 sq. in. (This is the next size up and should work)

Conclusion

You are absolutely correct that 4 #3 RHW cannot fit in 1-1/4" PVC Schedule 40 based on area calculations.

The NEC requires you to use the area method (Tables 1, 4, and 5) when you have conductors of different sizes. Table C.11 is ONLY for conductors of the same size. Therefore, 1-1/2" PVC Schedule 40 is the minimum size conduit required.Important Considerations



Derating

You might need to consider derating the ampacity of your conductors based on the number of current-carrying conductors in the raceway. This doesn't affect the conduit size, but it affects the allowable current you can carry.

Software Verification

While your manual calculations are excellent, use a wire fill calculator (many are available online) to double-check your work. These tools often incorporate derating factors as well.

Local Codes

Always check with your local electrical inspector for any specific local code interpretations or requirements.

RHW vs. RHW-2: The area is slightly different for RHW vs RHW-2.I hope this clarifies the situation! Let me know if you have any more questions. Flag for review