How should I interpret “N/100mm” in the parameter table? How much pressure can it withstand?
In the technical specifications for fiber optic cables and fiber optic patch cords, N/100mm (Newtons per 100 millimeters) is the standard engineering unit used to measure the Crush Resistance of optical cables.
I. Physical Definition and Test Principle
According to the international standard IEC 60794-1-21 Method E3 (and national standard GB/T 7424.21):
- Test Method: The testing machine uses two flat, rigid pressing plates (standard plate length is typically 100\text{ mm}) to place the optical fiber patch cord or cable to be tested between them, applying a uniform normal force perpendicular to the cable’s axis.
- Parameter Meaning: N/100mm represents the maximum lateral compressive force (unit: Newtons, \text{N}) that the optical cable can withstand over a 100\text{ mm} (i.e., 10\text{ cm}) compressed length without causing fiber breakage or irreversible excessive attenuation.
II. How to Convert to “Weight-Bearing Capacity”?
Under Earth’s gravitational acceleration (taking g \approx 9.8\ \text{m/s}^2), force (\text{N}) can be directly converted to the equivalent weight mass (\text{kg}) it can bear:
\text{Equivalent Mass } m = \frac{F}{g} \approx \frac{F}{9.8}
Common Parameter Conversion Examples:
-
Standard Indoor Patch Cords / Flexible Patch Cords (e.g., 300\ \text{N/100mm})
- Equivalent Weight Bearing: Withstands approximately 30.6\ \text{kg} of static weight on a 10\text{ cm} contact surface.
- Engineering Significance: Can only withstand slight stepping or minor external squeezing; cannot withstand heavy object rolling or prolonged stacking pressure.
-
Regular Armored Patch Cords (e.g., 1000\ \text{N/100mm})
- Equivalent Weight Bearing: Withstands 102\ \text{kg} of weight on a 10\text{ cm} contact surface.
- Engineering Significance: Can withstand normal stepping by adults and impacts such as cabinet door pinching during installation.
-
Heavy-Duty / Industrial Grade Armored Optical Cables (e.g., 3000\ \text{N/100mm} to 5000\ \text{N/100mm})
- Equivalent Weight Bearing: Withstands a load of approximately 306\ \text{kg} to 510\ \text{kg} on a 10\text{ cm} contact surface.
- Engineering Significance: Can withstand short-term crushing by tires of industrial vehicles (such as forklifts, light vehicles).
III. Key Engineering Considerations When Viewing Parameter Tables
- Short-term vs. Long-term Crush Resistance:
- Short-term: Refers to the pressure limit during installation, setup, or brief occasional squeezing (e.g., from a few minutes to several hours).
- Long-term: Refers to the allowable pressure value for cables that are permanently buried, stacked in conduits, or subjected to soil weight pressure. Typically, the long-term index is only 30\%\sim 50\% of the short-term index.
- Difference Between “Linear Load” and “Point Pressure”:
- \text{N/100mm} is a linear load (distributed flat contact surface).
- When encountering sharp edges (point contact, such as sharp stones or metal edges), the extremely small contact area causes the local pressure (\text{MPa}) to amplify exponentially. In such cases, the optical fibers within the cable may experience micro-bending loss or even fracture at a total force far below the rated \text{N/100mm}.
- Strength Expression for Metal Tube Armored Optical Fibers:
- For some high-protection-grade micro seamless steel tube/elastic alloy armored patch cords (e.g., OFSCN® Armored Series), due to the extremely high ring stiffness and yield strength of the metal tube itself, the anti-pressure parameters are sometimes directly specified as material-level compressive strength (e.g., > 150\ \text{MPa} or > 200\ \text{MPa}).