Why is 1/2 inch pipe called that when nothing about it is 1/2 inch?

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K8MHZ

K8MHZ

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Michigan. It's a beautiful peninsula, I've looked
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Electrician
I learned something today.

OK, so I have an old Chicago bender (a real one, made in Chicago) that someone cut the wheels off. I also have a newer one, the next size up, and am using it for a pattern to make the old one moveable again and have them both look the same.

So, I get a couple wheels that take a 1/2" axle. An off the rack 1/2" steel rod fit perfectly.

Next, I needed a piece of pipe to slide the axle into. That pipe would be welded to the bender. A trip down to the hardware and all they had was 1/2" black pipe and it was sloppy. I bought it anyway, but started to look for a better fit.

Here are some specs. 1/2" black pipe .622" I.D.

1/2" RMC, .632" I.D. , which is larger than 5/8"

With a bit of research, I found out why.

Oddly, there is nothing about a ?" pipe that is ?", be it copper, iron, or PVC. The outside diameter of copper is 5/8", and the inner diameter is either 0.527", 0.545", or 0.569", depending on the series. So-called ?" iron pipe is 0.840" outside diameter and 0.622" inside. PVC is the same outside as cast iron, but it is 0.608", 0.528", or 0.480" inside.

If no dimension is ?", why call it ?" pipe?

Well, it seems that back in the beginning of time - copper pipe was introduced in the 1930's - copper pipe was indeed standardized at the nominal diameter inside with a 1/16" wall, making it 1/8" bigger on the outside. As the metallurgy improved, allowing manufacturers to use thinner metal (and thus increase profits), they increased the inner diameter rather than decrease the outer diameter simply to allow the pipe fit existing fittings.

As the manufacturers began to make bigger and bigger pipe, they found that 1/16" wall thickness was insufficient. Thus, the inner diameter of larger pipes is smaller than the nominal size, while smaller pipes are larger.

Wrought iron pipe has a similar history, though I don't know the details. When PVC was developed, it inherited it's outside diameter from iron pipe.
Click to expand...

http://www.gizmology.net/pipe.htm
 
OD vs ID, rigid vs EMT and the desire to make KOs uniform size.


What's in a name anyway, go get me a '2x4'. :).


And yes, I know the origin of that. :cool:
 
Strathead said:
What is the difference between a 3/8 and 1/2 MC connector?
Click to expand...

Is there a difference other than labeling?

OK, another mystery solved:

3/8" fitting:

"Fits 1/2 inch knockout, non-metallic cable numbers 14/2, 12/2, 12/3 AWG or 2 number 14/2 AWG or flex cord .300 to .560 inches diameter."

1/2" fitting:

"Non-metallic cable size: 2 #14, 2 #10, 3 #14 or 3 #12
with or without ground"
 
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Dennis Alwon said:
I always wondered where the 3/8" came from. I know that make some connectors for the undercabinet lights that have a 3/8" throat but why call the 1/2" nm connector 3/8"???? I don't know.
Click to expand...

I think it is because many 'NM connectors' are dual rated for use with 3/8" FMC. (Which of course is not really 3/8")
 
Where did 4160v 3ph4w come from? As I understand it a 2400v 1ph distribution system came first. May it be why was 4160v selected for a wye distribution system to increase the 2300v 1ph systems capacity with out the need to change the L-G voltage?
And what about 7200? Would it be 7200/1.73= 4160V nominal. And 12470/1.73=7200v nominal. And what about 13,200, and 13,800?

And why was 480v selected as basis for a LV dist sysem?
 
1/2"

1/2"

What sounds better or easier to remember 3/8; 5/8; OR 1/2. The same in guns, would you rather say 429 caliber (actual size) gun/rifle OR 44 caliber ????????????:happyyes:
 
inside/outside

inside/outside

PIPE is measureds as INSIDE dia........


TUBEING is measures as OUTSIDE dia.............

A 2" Tubeing should fit inside a 2" pipe
 
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