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Protecting Temperature Sensor Lead Wires
Protecting Temperature Sensor Lead Wires
September 10, 2019

Temperature sensor lead wires often live in pretty tough environments. Physically, they may ecounter tight corners, sharp edges, vibration, and impacts of various sorts. Electrically, they may be surrounded by all sorts of components and wiring operating at significantly higher voltages than the temperature sensors. If the temperature sensors are to perform effectively, they need to be protected from both physical and electrical challenges. Knowing what protection your temperature sensor leads will require will help you order temperature sensors with appropriate leads. 

The biggest mechanical risk to temperature sensor leads often occurs during installation . Wires can be struck, compressed, or bent when a system is being assembled, weakening or breaking the leads. Risk can be reduced using path control and minding bend radius, particularly around corners and through holes. After installation the biggest risk is generally vibration that, over time, can wear through lead wire insulation and produce breaks or shorts. The most common form of mechanical protection is rugged stainless steel braid (SSB). It can be configured with or without a flexible polymer jacket, typically made of fluorinated ethylene propylene (FEP or Teflon™). Basic mechanical protection can be provided by an FEP jacket alone, while the highest level of mechanical protection is armor, a thin, flexible, solid metal conduit completely enclosing the lead wires. 

Electrical protection of lead wires can be more challenging. The temperatuure sensors themselves, along with terminations can be designed for low- or non-inductance operations. Lead wires, however, can act as antennas and must be protected from ambient electrical fields that can induce noise in the sensor wires. Temperature sensors operate with low current and are considered passive devices. For this reason, it takes very little induced current to throw off their readings, and that induced current can be generated by a variety of devices from motors and generators to servos and relays.  

Twisting the lead wires helps cancel the effect of an electrical field and is the first small step in resisting induction of current. If more protection is needed, metal braid is again a popular solution, but in this case silver-plated copper braid (SPC), always coupled with a polymer outer jacket, is more effective at blocking induced current than stainless steel braid. Coverage by silver-plated braid can vary, but more complete coverage will increase resistance to induced current. Coverage may not be listed among a lead wire’s specs, but our minimum braid coverage is 90 percent. 

If more complete coverage is required, aluminum foil shield offers 100 percent coverage, but provides less mechanical protection than braid. In choosing lead wire configuration, keep in mind that stainless steel braid provides better mechanical protection, while copper braid is softer and provides less mechanical protection but more prevention of induced current. If you need both mechanical and electrical protection, SPC braid with a polymer jacket provides a good balanced level of protection.  

If the proper choice of protection schemes isn’t obvious, at we’re always available to help with your lead wire protection decisions. 

Learn more about our temperature sensors here 

We look forward to hearing how how we can help with your next project!


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Mod Tronic Instruments Limited
1 Delta Park Blvd #12
Brampton, ON L6T 5G1
Phone: 905-457-6322 or 1-800-794-5883
Fax: 905-457-4716 or 1-800-830-7122