Home > PRODUCTS > PTC Thermistors > PTC thermistor for telecom apparatus circuit protection-MZ2 series > PTC thermistor for telecom main distribution frame (MDF)protection-MZ21 series

  • Functional characteristics
  • PTC thermistor for circuit protection of telecom main distribution frame (MDF) MZ21 series
    Brief Introduction of PTC thermistor for circuit protection of telecom apparatus:
    Advanced developments in telecom equipment in rencent years have radically altered the protection requirements for both exchange and subscriber
    equipment.The PTC thermistor must protect telephone line circuit against overcurrent,which mainly caused by the following examples:
    1)surges due to lighting strikes on or near to the line plant;
    2)short-term induction of alternating voltage from adjacent power lines of railway systems,usually caused when these lines or systems occur faults;
    3)direct contact between telephone lines and power lines.

    Product Application of PTC thermistor for circuit protection of telecom apparatus:
    1. Main distribution frame (MDF)
    2. Telecom equipment
    3. Telephone

    Working principle of PTC thermistor for circuit protection of telecom apparatus:
    To provide good protection under such conditions a PTC thermistor is connnected in series with eachline.Usually as secondary protection;However,even with primary circuit protection(usually a gas discharge tube),the PTC thermistor must fulfill severe requirements.Surge pulses of up to 2 KV can occur and in order to withstand short-term power induction the PTC thermistor withstand high voltage.If the line has primary protection,a 220V to 300V PTC thermistor is adequate.Without primary protection,600V PTC thermistor is necessary.The restricting overload protection PTC Thermistor is connected in series in the overloading circuit. when the circuit is in the normal working state , the current flowing through the PTC Thermistor is not high enough to make the temperature exceed the Curie temperature for circuit protection ,and the PTC Thermistor is always in the low resistance state. When the circuit breaks down and the circuit current increases a lot,the resistance of restricting overload protection PTC Thermistor heating sharply until the circuit is “cut off” relatively to achieve circuit protection purpose. After clearing the circuit trouble, the PTC Thermistor begins to cool and come back to the state of low resistance,and then the circuit enters normal working condition. When the circuit breaks down next time, the PTC Thermistor can enter the state of circuit
    protection again.

    PTC thermistor application for MDF protection

    Advantages of PTC thermistor for circuit protection of telecom apparatus:
    1. Automatic circuit protection,can resume steadily;do not need to be reset after circuit protection
    2. Contactless,noiseless and flameless;
    3. Reacts fast;
    4. With a better performance of overvoltage protection,can operate in 110/230V AC (high resistance state) continuously
    5. Low rated current
    6. Small steady resistance;
    7. Narrow resistance tolerance (resistance matching)
    8. Satisfy ITU-T K20 K21 requirement.
    –Surge current(10/700μs)
    –Induction voltage(600V,1A,0.2S)
    –Power line contact(230V,15min.)
    9.Long stability
    10.RoHS-compatible

    Dimension(Unit: mm):
    PTC thermistor dimension

    Electronic feature of PTC thermistor for circuit protection of telecom apparatus:
    Rated zero power resistance:
    Ambient temperature: 25±2℃,within the allowable tolerance.
    Non-trip characteristic:
    Ambient temperature: 40±2℃,in still air for 30 minutes, power voltage 60VDC, maximum non-trip current ON for 60 minutes. (R-Rn)/Rn≤50%
    Overcurrent trip characteristic:
    Relation between trip current to trip time of PTC thermistor.
    Over voltage withstanding:
    Power voltage: 230 Vrms /250 Vrms, maximum current ON for 30 minutes. 4 hours after restoring in room temperature, retest zero power resistance, ΔR/Rn≤20%.
    Over current withstanding:
    Power voltage 220Vrms, maximum current 60S ON/600S OFF, cycles: 20, 4 hours after restoring in room temperature, retest zero power resistance, ΔR/Rn≤20%.
    Surge current withstanding:
    Short circuit wave: 10/1000μs, minimum opening circuit voltage: 1.0KV, peak current:25A, interval time: 3 minutes, cycles: 30,4 hours after restoring in room temperature, retest zero
    power resistance, ΔR/Rn≤20%.
    Induction voltage withstanding (Only for maximum voltage over 600V):
    Power voltage: 600 Vrms /650Vrms,initial current 1.1A, 2S ON/600S OFF, cycles: 10, 4 hours after restoring in room temperature, retest zero power resistance, ΔR/Rn≤20%.
    Fail model:
    Ⅰ. Power voltage: 250Vrms,initial current: 10A.
    Ⅱ. Power voltage: 600Vrms ,initial current: 15A
    Ⅲ. Power voltage: 650Vrms,initial current: 10A
    Energized time 30 minutes, high resistance state or open circuit is allowable. Low resistance or firing is not allowed.
    Restore time:
    The time necessary for PTC thermistor returning to twice Rn. Lower than 60 seconds is required.

    Marking of Part Number:
    PTC thermistor MZ21 model number break down
    1.Series: PTC thermistor for circuit protection of telecom apparatus;
    2.Type:1-disc,2-encased,3-pin form-coating;4-pin form non-coating;
    3.R25 resistance:55R-55;
    4.Resistance tolerance:M+/-20%;
    5.Non trip current(25 ℃):070-70mA;
    6.Wire shape:S-straight, A-axis formed, U-in-formed;
    7.Max. Voltage:250-250V.

    Specification&Part no.

    Item Part No. Resistance
    R 25(Ω)
    Non-trip current
    Int(mA)
    Tripcurrent
    @25℃
    It(mA)
    Tripping
    time at
    max current
    t(Sec)
    Max.
    current
    I m a x ( A )
    Max.
    voltage
    V max  (V)
    Fail mode Dimension
    (mm)
    @25℃ @40℃ D max T max Φd
    1 MZ21-18RM110 18 110 90 220 <0.15 3.0 250 250V/10A 5.5 1.5 /
    2 MZ21-18RM125 18 125 110 250 <0.18 3.0 250 250V/10A 5.5 2.0 /
    3 MZ21-18RM130 18 130 110 260 <0.18 3.0 250 250V/10A 6.2 2.0 /
    4 MZ21-20RM085 20 85 70 170 <0.18 3.0 250 250V/10A 6.2 2.0 /
    5 MZ21-18RM135 18 135 110 270 <0.2 3.0 250 250V/10A 6.6 2.0 /
    6 MZ21-10RM150 10 150 130 350 <4.0 1.0 230 230V/10A 6.6 1.5 /

    Note:

    1. R 25 resistance tolerance and resistance matching can be selected per customer’s requirement.
    2. Encapsulation mode can be selected per customer’s requirement.

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