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Required. An explanation of the Causes of MCB Intermittent Tripping due to Loose Connections

The Woodster
Hello Everybody


I wish to gain a greater knowledge as to the causes of MCB intermittent tripping due to loose connections, so any help would be greatly appreciated and the more in-depth the better as that is what I want to understand, the physics behind it.

Thermal Tripping  I can understand that a loose connection can generate heat due to resistance, IR2, and I can appreciate that it could cause an MCB to thermal trip if the loose connection is at the actual MCB Terminal (OR even an MCB either side IF THIS IS POSSIBLE) but how can a loose connection further downstream, say 8 -9 metres away cause a thermal trip.  I find it hard to believe that enough heat could dissipate far enough to reach MCB and be hot enough to trip MCB.

Magnetic Tripping  How can a loose connection cause a magnetic trip.  Intuitively I guess it must be due to arcing and arc voltages but that suggests that air is a better conductor than copper (that would also suggest that air dielectric capacitors wouldn't work I think) to allow enough Amps to flow to trip MCB or there is a sudden increase in voltage over a very short period in time dv/dt and therefore perhaps capacitance plays a part.  Basically how does an MCB magnetic trip due to a loose connection downstream?


All contributions greatly appreciated


Regards The Woodster
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  • 0
    Many thanks to everybody who contributed.


    So just to clarify

    Thermal Intermittent Trip


    Can be caused by loose connections directly at MCB cable/busbar connections due to high resistance creating joule heating for Bi-metallic strip and might be possible if MCBs either side have loose connections (I did say might be possible) for the same reason.


    Also thermal trip POSSIBLY can activate if loose connections downstream if repeated disconnect and reconnect of loose cable terminal/connection if enough load (and even better if reactive load due to high dv/dt ideal for CAPS and Inductors) and therefore repeated high inrush current generating joule heating which would be present all along cable carrying the high current parts and therefore also at the MCB.

    Magnetic Intermittent Trip


    Could be caused by reactive loads causing repeated inrush currents which if timing of loose cable connection reconnecting at max or min point of AC cycle could be ideal for reactive loads to demand MAX current and cause MCB to trip.


    I guess sudden vibration for whatever reason causing rapid connect and disconnect of a loose connection would be the perfect storm for any of the above.


    HOWEVER has anyone known an MCB to intermittently trip due to a spur to a socket, the socket connected with incorrect polarity, off a ring final having correct polarity except for that one spurred socket. AND I MEAN intermittently trip with the same load plugged into that spurred socket, in this case a Router.


    The Woodster


Reply
  • 0
    Many thanks to everybody who contributed.


    So just to clarify

    Thermal Intermittent Trip


    Can be caused by loose connections directly at MCB cable/busbar connections due to high resistance creating joule heating for Bi-metallic strip and might be possible if MCBs either side have loose connections (I did say might be possible) for the same reason.


    Also thermal trip POSSIBLY can activate if loose connections downstream if repeated disconnect and reconnect of loose cable terminal/connection if enough load (and even better if reactive load due to high dv/dt ideal for CAPS and Inductors) and therefore repeated high inrush current generating joule heating which would be present all along cable carrying the high current parts and therefore also at the MCB.

    Magnetic Intermittent Trip


    Could be caused by reactive loads causing repeated inrush currents which if timing of loose cable connection reconnecting at max or min point of AC cycle could be ideal for reactive loads to demand MAX current and cause MCB to trip.


    I guess sudden vibration for whatever reason causing rapid connect and disconnect of a loose connection would be the perfect storm for any of the above.


    HOWEVER has anyone known an MCB to intermittently trip due to a spur to a socket, the socket connected with incorrect polarity, off a ring final having correct polarity except for that one spurred socket. AND I MEAN intermittently trip with the same load plugged into that spurred socket, in this case a Router.


    The Woodster


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