The nominal size of copper tubing, in the North American plumbing industry, refers to a size that is approximately 1/8th of an inch less than the actual outside diameter (OD) of the tube.
Understanding Nominal Size
While the outside diameter of copper tubing is consistent, the inside diameter varies depending on the wall thickness (Type K, L, or M). The "nominal size" helps plumbers and engineers identify the tube size for fittings and applications, even though it doesn't directly represent the inside or outside diameter. It is a trade size.
How Nominal Size Works
Here's how the nominal size relates to the outside diameter:
- Nominal Size = Outside Diameter - 1/8 inch
For example, a copper tube with a nominal size of 1 inch will have an outside diameter of approximately 1 1/8 inches.
Copper Tubing Types and Wall Thickness
It's crucial to note that different types of copper tubing (K, L, and M) have different wall thicknesses, even when the nominal size is the same. This influences the inside diameter and pressure rating. Type K is the thickest, followed by Type L, and then Type M.
| Nominal Size (inches) | Approximate Outside Diameter (inches) | Common Applications |
|---|---|---|
| 1/2 | 5/8 | Water lines, drainage, vent systems |
| 3/4 | 7/8 | Water lines, heating systems |
| 1 | 1 1/8 | Main water lines, commercial plumbing |
| 1 1/4 | 1 3/8 | Larger water systems, industrial applications |
Why Use Nominal Size?
Using nominal size simplifies the process of specifying and ordering copper tubing and fittings. It provides a common reference point, even with varying wall thicknesses. This standardization is crucial for ensuring compatibility and proper fit in plumbing and HVAC systems.
In conclusion, the nominal size of copper tubing is a convention used in the plumbing industry, representing a value approximately 1/8 inch less than the actual outside diameter of the tube. This convention helps ensure compatibility between tubing and fittings.
