Am I crazy or correct?

[Dsg319]

Question is asking minimum size RMC nipple less than 24” so obviously 60% fill is allowed.

3-3/0THWN=0.8037
1-#1awg THWN=0.1562
1-#6awg THWN=0.0507
TOTAL= 1.0106sq inches.
1.0106/60%=1.6843 sq in.

so I need to select a RMC trade size of that or larger I selected 2”. Next available size up coming in at 2.045sq in.

Went to check myself in an answer key and it says
1 1/2” should be selected at 60%fill at 1.243sq in.

Either I’ve lost it or this book is wacky.
To me what they have selected brings there fill up to 81%!

 

[david luchini]

1.25" RMC has an area of 1.526sqin.
1.5" RMC has an area of 2.071sqin.

Your calculation says you need a raceway with an area of 1.6843sqin.

1.25" RMC is too small. 1.5" RMC would be the next size up.

Or put another way: 1.243sqin (available) is greater than 1.011sqin. (needed.)

Edit: Or put another way, you are applying the 60% twice. Once to the conductor area and once to the raceway area.

 

[infinity]

I agree, 1.5" is the minimum size. Chapter 9 Table for RMC says at 60% 1.25" has an area of .916 square inches, 1.5" is 1.243.
According to the numbers in the OP:
"TOTAL= 1.0106sq inches" so 1.25" RMC is too small and 1.5" RMC is large enough.

 

[Dsg319]

So 1.5” RMC could fit those given conductors and be within the 60%fill?

I think I just had my moment, and realized my mess up. I did not need to try to find that 1.0106 is 60% of such number. I just needed to use that number and find equal too or larger (next available size). Guess it wasn’t my day for studying lol. Thanks guys.

 

[david luchini]

So 1.5” RMC could fit those given conductors and be within the 60%fill?

Yes. 1.243sqin (60% raceway area) is larger than 1.0106sqin (conductor area.)

 

[Dsg319]

Yes. 1.243sqin (60% raceway area) is larger than 1.0106sqin (conductor area.)

Yes for some reason I was trying to take 1.0106sqin and figure out what it was 60% of get my answer. Idk where I pulled that one out of this evening.

 

[LarryFine]

Remember: the ID of a conduit may never exceed the OD.

 

[Dsg319]

Conclusion—— I’m crazy today, was not my day for book work. Thanks guys for correcting me.

 

[don_resqcapt19]

So 1.5” RMC could fit those given conductors and be within the 60%fill?

I think I just had my moment, and realized my mess up. I did not need to try to find that 1.0106 is 60% of such number. I just needed to use that number and find equal too or larger (next available size). Guess it wasn’t my day for studying lol. Thanks guys.

You are just fine doing it that way, but you have to look at the 100% column in Chapter 9, Table 4 for type of conduit you are using.

 

[Dsg319]

You are just fine doing it that way, but you have to look at the 100% column in Chapter 9, Table 4 for type of conduit you are using.

Your exactly right, I was trying to figure out how to explain what I’d done. The way I done it I needed to look at 100% not 60% column.

 

[Dsg319]

Remember: the ID of a conduit may never exceed the OD.

Except for Monday’s.....

 

[gadfly56]

You need to remember that RMC is not EMT. It's essentially Schedule 40 pipe, which as we all know isn't its nominal size in any dimension. I learned this lesson as a senior in college, where I was supposed to be building onto a previous senior project. Sadly, there were no plumbers in the family.

 

[Little Bill]

Remember: the ID of a conduit may never exceed the OD.

Unless you turn it inside-out!

 

[augie47]

In regard to your original question:
Am I crazy or correct
Keep in mind, you could be BOTH

 

[Dsg319]

In regard to your original question:
Am I crazy or correct
Keep in mind, you could be BOTH

I know there’s deffintly days that’s true lol.

 

[kwired]

So 1.5” RMC could fit those given conductors and be within the 60%fill?

I think I just had my moment, and realized my mess up. I did not need to try to find that 1.0106 is 60% of such number. I just needed to use that number and find equal too or larger (next available size). Guess it wasn’t my day for studying lol. Thanks guys.

I think your method would work but you need to calculate the extra free space that needs to be available so you would be calculating the conductor area plus the remaining 40% that needs to be free space in the raceway. Then select any raceway that is larger than your result.

 

[kwired]

I think your method would work but you need to calculate the extra free space that needs to be available so you would be calculating the conductor area plus the remaining 40% that needs to be free space in the raceway. Then select any raceway that is larger than your result.

The fact there is already table column for 60% fill means all you really need to calculate is the conductor area though, but this should work if all you know upfront is 100% of raceway area.