Ceramic PTC Thermistor for Telecom High Voltage Current Surge Protection

Why Ceramic PTC Thermistor Is Chosen for Telecom High Voltage Current Surge Protection?

PTC Thermistor High Voltage Telecom Protect

PTC Thermistor High Voltage Telecom Protect

Ceramic positive temperature coefficient PTC thermistor help provide protection against power cross, power induction surges and lighting surge defined in ITU, Telcordia, UL.

Available in chip, radial-leaded coated and non-coated configuration.

This thermally sensitive semiconductor resistor provides reversible, self-resetting fuse protection against over-currents short circuit for telecommunication line protector units, improve the reliability of custom premises and network equipment.

PTC Thermistor Current Limiting Protection Device can be found providing resettable line protection at the exchange, monitoring hot spots and protecting ringers, battery feeds, transformers, switches and relay circuits. Also used extensively to protect the mobile phone’s battery pack against overcharging in land-based and radio mobile communications.

For PTC Thermistor for general circuit overcurrnt protecion, transformers, switches, power supply, battery feeds, meter , instrument overload protection, please refer to AMWEI PTC Thermistor Current Protect Resettable Fuse Page.

This page is focus on PTC thermistor for ITU-T K20 K21 K45 standard requested high volage current surge protection.

Advanced developments in telecom equipment in recent years have radically altered the protection requirements of both exchange and subscriber equipment. PTC Thermistor Current Protector must protect the telephone line circuit against overcurrent, which may be caused by the following examples:

  • Surges due to lighting strikes on or near to the line plant.
  • Short-term induction of alternating voltage from adjacent power lines or railway systems, usually caused when these lines or systems develop faults.
  • Direct contact between telephone lines and power lines.

To provide good protection under such conditions, a PTC thermistor is connected in series with each line, usually as secondary protection; However, even with primary line protection (usually a gas discharge tube), the PTC thermistor must fulfill severe requirements.

Surge pulses of upto 2KV can occur and in order to withstand short term power induction, the PTC thermistor must withstand high voltages.
If the line has primary protection, a 220V to 300V PTC thermistor is adequate.
Without primary protection, 600V PTC device is necessary.
We can manufacture a series of PTC thermistor fulfilling both requirements.

PTC Thermistor Replacement Idea for a Current Fuse

PTC thermistor Replacement Benefits

  • Automatic reset from protective trip up to 265V AC line contact
  • Compatible with the 600V over voltage test by UL60950
  • High resistance to the lighting surge  (A surge absorber is still required to protect SLIC)

 PTC Thermistor Application in Telecommunication Equipment

  • Central Office Switching Equipment (C.O): analog and digital line cards, POTS, T1/E1 equipment, xDSL modems and splitters, multiplexers, CSU/DSU, servers.
  • Primary Protection Modules: MDF (main distribution frame) modules, network interface devices (NIC).
  • Custom Premises Equipment, also known as subscriber terminal equipment (T.E.), IT equipment: Modem, phone sets, fax machines, phone wall outlet (plugs), alarm systems, answering machine, PBX systems, ADSL Splitters, internet appliance, POS terminals.
  • Access Network hardware, LAN WAN equipment, Powered Ethernet systems, VoIP (voice over IP equipment), integrated voice data (IVD), Set-top box (S.B), etc.
  • Landline telephones or FAX machines
  • Telephone interface of STB, VoIP equipment
  • Any other equipment of communication facility having a phone line interface

PTC Thermistors Telecom Application Features:

  • Compliant with ITU-T K20 K21 K45
    –Basic level lightning surges (10/700μs)
    –Basic level power Induction (600V,1A,0.2S)
    –Power contact criteria A/B (230V,15min.)
  • Suitable for continuous connection to main voltage 110/230 VAC in tripped (high ohmic) condition.
  • Round leadless disk thermistor available for combined usage of PTC and primary protection, e.g gas arrestor.
  • Thermistor disk coated non-coated construction, diameter 5mm to 10mm.
  • Typical Resistance @25C (R25) 10 ohm, 12 ohm, 18 ohm, 20 ohm, 25 ohm, 50 ohm, 55 ohm.
  • Matching available with narrow resistance tolerance.
  • Tight resistance tolerance maintained after switching.
  • Negligible resistance drift after soldering or switching.

Telecom PTC Thermistor Performances

Rated Zero-power Resistance (R25)

Operating temperature range: 25±2℃,  Within the allowable tolerance.

Non-operating Characteristic

Operating temperature range: 40±2℃.
In static air for 30min.
Max. voltage: 60VDC.
Non-operating current.
Energized time: 60min.
(R-R25)/R25≤50%

Over-current operating characteristic

Operating temperature range: 25±2℃,
Max. voltage of power supply: 220Vrms.
Test the time for the current decrease to limited value. See the spec. Table.

Over voltage withstanding (Power line contact)

Voltage of power supply: 250VAC,
Initial current: 3A,
Energized time: 30min .
Restore time in room temperature 4 hours,
then test the R25. ΔR/R25≤20%.

Over current withstanding

Max. voltage of supply: 220VAC,
Initial current: 3A.
ON 60S, OFF 600S ,
Cycle:30 times,
Restore time in room temperature is 4 hours,
then re-test the Rn.  ΔR/Rn≤20%.

Surge current withstanding

Current waves: 10/1000μS,
Minimum opening circuit voltage: 1.0kv,
Peak current: 25A,
Interval: 3min,
Cycle:30 times,
Restore time in room temperature is 4 hours,
then re-test the R25. ΔR/R25≤20%.

Induction voltage current withstanding (Only for maximum voltage more than 600V)

Max. voltage of supply: 650VAC,
Initial current: 1.1A,
ON 60S, OFF 600S,
Cycle:10 times,
Restore time in room temperature 4 hours,
then re-test the R25. ΔR/R25≤20%.

Fail Model

I. Voltage of power supply: 250VAC. Initial current: 10Arms,
II. Voltage of power supply: 600VAC. Initial current: 15Arms.
III. Voltage of power supply: 650VAC. Initial current: 10Arms.
Energized time: 30min.

High resistance or open circuit is allowable. Low resistance state or firing is not allowed.

Restore time

The necessary time of a PTC to return to twice of R25. ≤60S.

Telecom PTC Thermistor Outline and Dimensions (unit:mm)

PTC Thermistors Drawing Chip Radial Part

PTC Thermistor for Telecom Line Card Protection Data

AMWEI Part Number Resistance
@25C
R25
(Ohm)
Non-trip current
Int
(mA)
Trip
current
@25C
It
(mA)
Tripping
time
@ max
current
(Seconds)
Max.
current
Imax
(A)
Max.
voltage
Vmax
(V)
Fail model Dimension
(mm)
 @25C  @40C  Dmax  Tmax  Φd
AMZ23-10RM130 10 ohm 130mA 100mA 260mA <0.2s  2.0A 250V 250V/10A  7.5  4.0 0.6
AMZ23-10RM150 10 ohm 150mA 100mA 260mA <0.3s  2.0A 250V 250V/10A  9.0  5.0 0.6
AMZ23-12RM130 12 ohm 130mA 100mA 260mA <0.3s  2.0A 250V 250V/10A  9.0  5.0 0.6
AMZ23-12RM090 12 ohm 90mA 60mA 160mA <0.2s  2.0A 250V 250V/10A  9.0  5.0 0.6
AMZ23-20RM100 20 ohm 100mA 80mA 200mA <0.2s  3.0A 250V 250V/10A  9.0  4.0 0.6
AMZ23-35RM090 35 ohm 90mA 75mA 180mA <0.2s  3.0A 250V 250V/5A  9.0  5.0 0.6
AMZ23-40RM080 40 ohm 80mA 70mA 160mA <0.2s  3.0A 250V 250V/5A  9.0  5.0 0.6
AMZ23-50RM070 50 ohm 70mA 60mA 150mA <0.2s  3.0A 250V 250V/5A  9.5  5.0 0.6
AMZ23-50RM075 50 ohm 75mA 60mA 150mA <0.2s  3.0A 650V 650V/10A  9.5  5.0 0.6
AMZ23-55RM070 55 ohm 70mA 60mA 150mA <0.2s  3.0A 650V 650V/10A  9.5  5.0 0.6
AMZ25-9RM160 9 ohm 160mA 130mA 330mA <0.8s  3.0A 250V 250V/10A  10.5  4.5 0.6
AMZ25-25RM100 25 ohm 100mA 80mA 220mA <0.2s  3.0A 250V 250V/10A  6.6  4.0 0.6
AMZ25-25RM120 25 ohm 120mA 100mA 300mA <0.4s  3.0A 250V 250V/10A  8.2  4.0 0.6
AMZ26-35RM080SMD 35 ohm 80mA 60mA 180mA <0.2s  2.5A 250V 250V/10A / / /

Note: Standard Resistance @25C (R25) allowable tolerance +/-20%, if not specified.

PTC Thermistor for Telecom MDF (Main Distribution Frame) Protection Data

AMWEI Part Number Resistance
@25C
R25
(Ohm)
Non-trip current
Int
(mA)
Trip
current
@25C
It
(mA)
Tripping
time
@ max
current
(Seconds)
Max.
current
Imax
(A)
Max.
voltage
Vmax
(V)
Dimension
(mm)
 @25C  @40C  Dmax  Tmax  Φd
AMZ21-10RM150  10 ohm 150mA 130mA 350mA  <4.0s  3A 230V  7.2  1.5 /
AMZ21-18RM110  18 ohm 110mA 90mA 220mA  <0.15s  3A 250V  5.5  1.5 /
AMZ21-18RM125  18 ohm 125mA 110mA 250mA  <0.18s  3A 250V  5.5  2.0 /
AMZ21-18RM130  18 ohm 130mA 110mA 260mA  <0.18s  3A 250V  6.2  2.0 /
AMZ21-18RM135  18 ohm 135mA 110mA 270mA  <0.2s  3A 250V  6.6  2.0 /
AMZ21-20RM085  20 ohm 85mA 70mA 170mA  <0.18s  3A 250V  6.2  2.0 /
AMZ21-25RM055  25 ohm 55mA 45mA 110mA  <0.4s  2A 230V  5.3  2.0 /
AMZ21-25RM060  25 ohm 60mA 50mA 120mA  <0.4s  2A 230V  5.3  2.0 /
AMZ21-25RM085  25 ohm 85mA 75mA 170mA  <0.7s  2A 230V  5.3  2.0 /
AMZ25-25RM055  25 ohm 55mA 45mA 110mA  <0.4s  1A 230V  5.3  4.0 0.6
AMZ25-25RM060  25 ohm 60mA 50mA 120mA  <0.4s  1A 230V  5.3  4.0 0.6
AMZ25-20RM145  20 ohm 145mA 100mA 250mA  <0.2s  3A 250V  6.6  4.0 0.6
AMZ25-10RM130  10 ohm 130mA 110mA 260mA  <4.0s  1A 230V  6.6  4.0 0.6
AMZ25-10RM150  10 ohm 150mA 135mA 300mA  <7.0s  1A 230V  8.2  4.0 0.6
AMZ25-18RM125  18 ohm 125mA 110mA 250mA  <1.0s  1A 230V  5.5  4.0 0.6
AMZ23-18RM135  18 ohm 135mA 110mA 270mA  <0.2s  3A 250V  7.5  4.5 0.6
AMZ23-18RM110  18 ohm 110mA 90mA 220mA  <0.2s  3A 250V  9.0  4.5 0.6
AMZ23-20RM100  20 ohm 100mA 80mA 200mA  <0.2s  3A 250V  9.0  4.5 0.6
AMZ23-25RM085  25 ohm 85mA 75mA 170mA  <0.7s  1A 230V  6.5  5.0 0.6
AMZ23-25RM090  25 ohm 90mA 70mA 180mA  <0.2s  3A 250V  9.0  4.5 0.6

Note: Standard Resistance @25C (R25) allowable tolerance +/-20%, if not specified.

Circuit Diagram Examples of PTC thermistors for Telecom Protection

An example of PTC Thermistor for telecom circuit protection

An example of PTC Thermistor for telecom circuit protection

Telephone line PTC thermistors used for overcurrent protection

Telephone line PTC thermistors used for overcurrent protection

PTC Thermistor Telecom Application

PTC Thermistor Telecom Application

How to choose PTC thermistor for telecom applications? Consideration Factors

Rated current and temperature

The PTC thermistor is primarily used to protect the switching equipment against fault current through direct contact with a power line (power contact) or an induced surge of short duration and low voltage from a neighboring line (power induction).

For obvious reasons, the rated current of the PTC thermistor should be kept as low as possible so that the protection responds quickly to overcurrents. The rated current should typically be slightly higher than the operating current of the system to be protected at the normal operating temperature.

Here the dependence of the rated current on the temperature of the ambient must be considered.

Duration of disturbance — voltage classes

An aspect that is too often neglected is the duration of the power contact. Such disturbances can go undetected for many hours, meaning that the PTC thermistor could be held in the high resistance condition exposed to the line voltage for an indefinite period.

AMWEI PTC thermistors for telecommunication applications have a maximum switching voltage of at least 265 V AC and can withstand this condition indefinitely.

Imbalance on the line — resistance of PTC thermistor

For most telecom applications the balance between the tip and ring (often referred to as longitudinal balance) is essential. A figure must be assigned to the balance between the line resistances that must apply initially and, after a short cooling period, after operation.

Typically 1 Ω is demanded on delivery, which should also apply throughout the service life of a system.

As opposed to PTC thermistor made of plastic materials, ceramic PTC thermistor always return to their initial resistance value, even after frequent heating/cooling cycles.

Other AMWEI Thermistors Products for Current Protection

PTC Thermistors for Transformer Equipment Overload Short Circuit Protection

PTC Thermistors for Transformer Equipment Overload Short Circuit Protection

NTC Thermistor for Inrush Current Limit Surge Suppression in Power Supply Transformer Motor Circuit Turn-on Stage

NTC Thermistors for Inrush Current Limit Surge Suppression in Power Supply Motor  Transformer Circuit Turn-on Stage

Content Headline

Technical Information