Thermal-Magnetic Circuit Breaker

Discussion in 'General Electronics Chat' started by superway, Jun 19, 2012.

  1. superway

    Thread Starter Active Member

    Oct 19, 2009

    Is anyone know the inside operation on a thermal circuit breaker 250Adc? Are the Line End and Load End of this circuit breaker measuring DC current the same or differrent? I applied 48vdc to a power supply, and loaded 120Adc to power supply. I measured the dc current by current probe about 120Adc, but when I moved current probe to measure on Line End of circuit breaker, it read about 35 to 40Adc. it is different reading when measured to Load End of CB. Why?

  2. crutschow


    Mar 14, 2008
    A circuit breaker can neither generator or absorb current, so the current at the Line End should equal the current and the Load End. Don't have any explanation for why you measured different values.
  3. cork_ie

    Active Member

    Oct 8, 2011
    The heading on your post is Thermo-magnetic circuit breaker, though you mention in the question a thermal circuit breaker.
    By definition current in has to be equal to current out, for the same circuit.

    If you are measuring DC current then you will be using a Hall effect type current probe and you will be measuring the magnetic field generated by the current flowing in a wire. If there is any stray magnetic field it will affect your readings.
    It is possible, if you are using a thermal- Magnetic breaker, that you are picking up the magnetism generated by the coil in the breaker. This can happen if you are taking your measurement too close to the breaker connection. The ideal is that you take your measurement along the cable away from any possible source of magnetic interference.