Contents
1. What a Temperature Rating Means
A fusible link temperature rating is the nominal temperature at which the link is designed to separate. The rating is tied to the fusible alloy used to join the link’s plates or straps. When the alloy reaches its rated melting point, the link separates and releases the connected mechanical action.
Key point: The rating is about the temperature at the link, not the temperature elsewhere in a room or duct. Installation location, airflow, and heat transfer can affect how quickly the link reaches its rated temperature.
2. How Ratings Are Determined
Manufacturers produce links using alloys with controlled melting points and test performance under recognised standards. A rating typically represents a nominal activation temperature for the alloy and design. In practice, activation depends on:
- Alloy formulation and manufacturing tolerances
- Thermal mass of the link (how quickly it heats)
- Airflow and heat transfer in the installation environment
- Contamination (dust, grease, coatings) that can change heat transfer
3. Common Ratings and Typical Use
Typical ratings vary by system design and jurisdiction. The table below is a practical reference for common installations.
| Nominal rating (°C) | Nominal rating (°F) | Typical use case | Notes |
|---|---|---|---|
| 57 | 135 | Low‑temperature environments | Use only where ambient temperatures remain well below rating. |
| 68 | 155 | General fire safety applications | Common across many systems. |
| 74 | 165 | HVAC fire dampers | Frequently specified for duct and damper assemblies. |
| 93 | 200 | Warmer mechanical spaces | Consider where ambient temperatures are elevated. |
| 141 | 286 | High‑heat industrial environments | Use only where code and equipment design permit. |
4. How to Select the Correct Rating
Selecting the right rating is about balancing false activation risk versus timely activation in a fire. A practical selection process:
- Start with the equipment or system specification (damper, door, suppression system).
- Confirm applicable code requirements for your jurisdiction and installation.
- Check ambient temperature conditions where the link will be installed (duct, ceiling void, plant room).
- Account for normal heat sources (sun exposure, ovens, heaters, industrial processes).
- Use the manufacturer datasheet to confirm ratings, approvals, and compatibility.
Selection note: Do not choose a higher rating simply to avoid nuisance activations. If ambient temperatures are approaching the rating, the correct fix is usually repositioning the link, addressing heat sources, or following the system’s specified rating.
5. Placement and Airflow Considerations
In HVAC systems, links may be installed in ductwork where airflow can cool the link during normal operation. Placement matters because it affects:
- Heat transfer from hot gases to the link during a fire
- Response time (how quickly the link reaches rated temperature)
- Exposure to dust, grease, or contaminants
Install links exactly as specified for the damper or system assembly. When in doubt, refer to the damper manufacturer’s installation instructions.
6. Common Mistakes
- Using colour alone instead of the product’s marked rating and datasheet.
- Installing the wrong rating for the equipment or code requirement.
- Painting or coating links, which can slow heat transfer.
- Allowing contamination (dust, grease) to build up on the link.
- Ignoring ambient heat sources in plant rooms or near process equipment.
- Reusing a link after activation (links are single-use devices).
7. Frequently Asked Questions
What does a fusible link temperature rating mean?
It is the nominal temperature at which the fusible alloy is designed to melt, allowing the link to separate and release a mechanical fire protection action.
Are temperature ratings exact?
They are engineered and tested to a standard, but real activation depends on heat transfer, airflow, contamination, and installation conditions.
Are fusible link colour codes universal?
No. Colour codes can vary by manufacturer and product line. Confirm the rating using markings and datasheets.
Can I install a higher rating to avoid nuisance activations?
Only if permitted by the system specification and applicable codes. Often the correct solution is to address ambient heat sources or placement rather than increasing the rating.
