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AMC3330-Q1: AC insulation monitoring system

Part Number: AMC3330-Q1
Other Parts Discussed in Thread: AMC3330

Hi all,

I have referred the insulation monitoring for DC load system with respect to chasis

Our requirement is to measure the AC insulation system with chassis.  Can I utilize the same system for AC as well, or do I need to take any design considerations into account?

please suggest some inputs on this.

  • Hi Manikandan,

    As the AMC3330 has a bipolar +/-1V input voltage range, so I do not see an issue with using the device for AC insulation monitoring. 

  • Hi Alex,

    Thank you for the response,

    Just clearing up a few understandings. Think about how I simply want to measure only insulation between the DC+ line and the chassis. Reference design can be found at
    The value whatever am taking for calculation is both side Positive and Negative switch which is Vn and Vp. Then only i can able find the R isoP value in this formulae

     RisoP = ((RinAMC + Rst) * (VDC + VN - VP)) / VP.

    What is the purpose of taking the RisoN into account while measuring the positive side and RisoP into account while measuring the Negative side? According to what I understand, if I need to measure AC insulation on Line (L1), I must also measure L1 W.r.t. chassis and Neutral W.r.t. chassis.The insulating resistance between the L1 and chassis will only be known then.

    Thanks in advance,

    Best regards,

    Manikandan S.

  • Hi Manikandan,

    Thank you for your question. I think it may be more clear why RisoN must be accounted for if we consider this picture:

    In order to follow the path from DC+/- to PE, RisoN must be considered as well.

    My team did not develop this design, I only support the AMC3330 specifically, so I will transfer this thread to the team that is responsible for the design for clarification. 

  • Hi Manikandan,

    In case of Isolation monitoring on AC lines it is important to consider capacitance between Line and PE. Since this capacitance will cause an impedance in parallel to the measured insulation resistance and therefore influence the measurement. Additionally the capacitance will cause a phase shift between the measured insulation voltage and the measured AC voltage, which will also influence the measurement. 
    You need to make sure that the impact of the capacitance will not have an significant influence on the measurement results.

    Best regards,