Installation of fire suppression detection options. Linear wire and spot sensors, installed on heavy duty equipment.

Fire suppression systems are an organization’s first line of defense against mobile equipment fires so it’s vital that the onboard suppression system be able to detect a fire quickly and accurately. There are two common fire detection methods among fire suppression system manufacturers: linear wire and spot sensors. What’s the difference? Is one more effective than the other? What are the pros and cons of each method? Let’s explore the answers to these questions and more.

Fire Detection Method #1: Linear Wire

One detection method used in fire suppression systems is linear wire. This two-conductor wire is coated with a special heat-sensitive polymer barrier that, when exposed to temperatures of 356°F and greater, melts and creates a short. A control panel in the machine’s cab detects this short and actuates the system to suppress the fire.

What are the pros of using linear wire for fire detection? 

  • Linear wire has a lower upfront cost and is easier and faster to install.
  • Linear wire only has two connection points, reducing overall maintenance and service time.
  • It is easy to identify where the fire originated on the machine by looking at the linear wire, aiding in fire investigation efforts.
  • Vibration has less of an impact on linear wire.
  • Coil guard is available as an added protection for linear wire. It safeguards against abrasion and makes the wire stand out on the machine to deter unnecessary damage or cuts by maintenance personnel.

And some of the cons of using linear wire vs. spot sensors?

  • Linear wire requires a slightly higher temperature to signal a fire than sensors.
  • After a fire event, the complete linear wire detection loop must be replaced.
  • Linear wire is not resettable, meaning if high temperatures quickly lower below the 356°F threshold for system activation, the system will still discharge, and the wire will require total replacement.
  • If damage is found on the linear wire during maintenance and inspections, the entire detection loop requires replacement.

Fire Detection Method #2: Spot Sensors

Another detection method commonly used in fire suppression systems is spot sensors. These sensors are typically comprised of a thermostatic switch mounted to a bracket. And, when exposed to continuous temperatures of 300°F, the sensor’s switch will snap closed to indicate a fire, signaling a control panel in the machine’s cab to initiate a system discharge and suppress the fire.

What are the pros of using spot sensors for fire detection?

  • Sensors offer earlier detection since they require a lower temperature to indicate a fire.
  • Once they detect a fire, sensors without damage can be reused vs. requiring replacement.
  • If sensors need to be replaced due to fire damage or regular wear and tear, they can be replaced individually without the need to replace all sensors on the machine.

What are some of the cons of spot sensors when compared to linear wire?

  • Spot sensors come with a higher upfront cost.
  • Installation can be timely due to necessary splicing and crimping, as well as the need to mount sensors in a specific orientation.
  • Spot sensor inspection takes more time, as each sensor must be examined and heat tested individually.
  • It might be hard to identify which sensor detected a fire.
  • Sensors are less ideal for environments with high amounts of vibration­­.

With all the facts in hand, you can make an informed decision about the best detection method for your heavy equipment’s fire suppression system. And, if there are additional questions, a fire suppression expert is available to assist. Afterall, fast and accurate fire detection – every time – is crucial to protecting your operators, your operation, and your profits.

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