MTL TP48 Range

Brand: MTL Instruments

The TP48 range of surge protection devices uniquely provide a level of protection for 2, 3 and 4 wire field-mounted transmitters that is far in excess of the optional transient protection facilities available from the transmitter manufacturers - without involving any additional wiring, conduit modifications or other expensive extras.

The TP48 range protection network consists of high-power, solid-state electronics and a gas-filled discharge tube capable of diverting 20kA impulses. The whole unit is encased in a 316 stainless steel housing, threaded for the common conduit entries used on process transmitters. Versions are available for 1/2” NPT, 20mm ISO, and G1/2” (BSP 1/2 inch) threaded entries.

Installation can easily be carried out retrospectively to existing installations. The TP48 is screwed into any unused conduit entry on the transmitter case and flying leads are connected to the terminal block (+ve, -ve) and the internal earth stud. The 3 wire TP protects +ve, -ve and signal. The 4 wire TP48 protects +ve, -ve, signal +ve and -ve. The TPs operate without in any way affecting normal operation - passing ac or dc signals without attenuation while diverting surge currents safely to earth and clamping output voltages to specific levels.

The all-important earthing connection is made to the local casing of the transmitter with no separate earth connection or ground stake at the transmitter being needed. In operation, the TP48 makes sure that the transmitter electronics are never exposed to damaging transients between lines or between lines and casing/earth.

Any surge current appearing as a series-mode or common-mode transient is converted into a common-mode voltage - whereupon the transmitter electronics are temporarily raised to some higher voltage level before ‘floating’ down automatically (and without damage) to resume normal operation.

For hazardous area use, approvals for both intrinsically safe and flameproof (explosion-proof) operation are available in all gas groups and apparatus temperature classification up to T4 for the TP48 3 & 4 wire and T6 for the TP48. Where transmitters are used in circuits suitable for Div 2/Zone 2 installations, the TP can be added without adversely affecting the level of safety.

For fieldbus applications, use the TP32 which meets the requirements of IEC61158-2:2004 and ANSI/ISA-50.02-2 1992 for 31.25kbit/s systems as used by Foundation™ fieldbus, PROFIBUS-PA and WorldFIP
  • Protects 2, 3 and 4 wire transmitters
  • Easy and direct mounting — screws into spare conduit entry
  • Intrinsically safe and flameproof to CENELEC standards
  • Parallel connection avoids introduction of any resistance into loop
  • ATEX approved
  • 10 year product warranty

MTL 48V 1/2" NPT thread - Non-Certified
1 - 3 weeks
$192.00USD / ea
$30.00 Shipping
MTL 48V 1/2" NPT thread - Certified
1 - 3 weeks
$228.00USD / ea
$30.00 Shipping


Maximum Surge Currrent

  • 20 kA peak Current (8/20 μs waveform)

Leakage Current

  • Less than 10 μA at max. working Voltage

Working Voltage

  • 35 V dc maximum


  • 1 MHz


  • No resistance introduced into loop

Ambient Temperature Limits

  • -40° C to +85° C (-40° F to +185° F) (Storage)
  • -40° C to +85° C (-40° F to +185° F) (Working)


  • 5 % to 95 % Relative Humidity, Non-Condensing

Electrical Connections

  • Lead length: 250 mm (Minimum)
  • Wire size: 32/0.2 (1.0 mm², 18 AWG)
  • TP48 3 Wire 4 flying leads (+ve, -ve, signal & earth)
  • TP48 3 flying leads (Line1, line 2 & earth)
  • TP48 4 Wire 5 flying leads (+ve, -ve, signal +ve, signal -ve, earth)


  • 316 Stainless Steel suitable for harsh environments


  • TP48-3-G & TP48-4-G - G 1/2" (BSP 1/2")
  • TP48-3-I & TP48-4-1 - 20 mm ISO ) (M20×1.5)
  • TP48-3-N & TP48-4-N - 1/2" NPT


  • 175 g (6.2 oz.)

EMC Compliance

  • BS EN 61326-1: 2013 for industrial environments
  • To Generic Immunity Standards

Hazardous Area

  • Ex ia IIC T4, Ceq=O, Leq=0, the unit can be connected without further certification into any intrinsically safe loop with open Circuit Voltage < 60 V and Input Power < 1.2W
  • Ex d IIC T4, the unit is apparatus approved to flameproof (explosion-proof) Standards, and can be Fitted into a similarly approved housing

Electrical Safety

  • To BS EN 61643-21: 2001 for surge Protection devices


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