Thermal Lo Limiter

Austdac Thermal Io Limiter FWT1


  • IECEx certified
  • Wide selection of Io currents
  • Wide operating temperature range
  • DIN rail mounting
  • Wide operating voltage range Compact size

The thermal Io limiter type FWT1 is an intrinsically safe Io current limiter that may be used to match a load maximum input current (Ii) to a power supply maximum output current (Io). The Io limiter is particularly useful when constructing panels or systems with multiple intrinsically safe loads powered from the same intrinsically safe power source.

Occasionally one or several of the loads may have an Ii entity parameter that is lower than the Io entity parameter of the power supply, making the connection of the load to the power source unsafe.

The thermal Io limiter type FWT1 solves this problem by providing an Ii parameter that is suitable for the power source and an Io parameter that is suitable for the load.

The FWT1 is simply wired in series with the positive supply lead from the power source to the load with the low Ii parameter. Other loads connected directly to the power source are unaffected by the FWT1.

The Uo parameter of the power source and the Ui parameter of the load are unaffected by the Io thermal limiter type FWT1 and still require assessment in accordance with IEC/AS/NZS 60079-25.

The FWT1 has two identical output circuits each with a separate fuse, these two circuits can be used to power individual loads or one circuit can be kept in reserve in case the first circuit fuse is ruptured due to a high load.

Never connect the two individual output circuits together to obtain higher output currents.

The FWT1 has a Ui entity parameter of 16.0 volts making it suitable for most installations encountered in coal mining applications.

The FWT1 is available with maximum Io output currents ranging from 85mA to 1700mA.

The thermal Io limiter is housed in a small IP20 (NEMA Type 1) DIN rail mounting enclosure measuring 75mm (H) x 17mm (W) x 52.5mm (D) (2.95" (H) x 0.67" (W) x 2.07" (D)) making it suitable for mounting in panels or enclosures where space is at a premium. The FWT1 must be housed within an enclosure having a minimum ingress protection rating of IP54 (NEMA Type 3).