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Isolation requirements for high voltage spikes

Discussion in 'IEC 60601 - Medical Electrical Equipment Safety' started by Monica, Sep 29, 2015.

  1. Monica

    Monica New Member

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    Hi all. I'm searching for more information on the safety parameters to be applied according to IEC60601-1 to a device including a transformer which generates (internally to the device) spikes up to 11kV with minimum energy. The negative of the transformer is referred to the internal circuitry gnd. How must this be handled from the regulatory point of view? are the insulation requirements for transitory spikes the same than those required for equivalent constant voltages? Do we have to consider all the internal circuitry as having a working voltage of 11kV? Thanks to anyone that can help...
     
  2. nikolaos

    nikolaos Member

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    Hello Monica,
    I suppose that the 11kV spike does not damage any internal component. When this spike occurs? During power on/off or during normal operation? Is this spike a functional requirement of the device? if not you can use a transient suppressor.
     
  3. Monica

    Monica New Member

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    HI Nikolaos, thank you for answering.
    Unfortunately, the spikes are functional requirements . The device is designed so that the spike does not damage any component (functional insulation) but we are trying to understand if the safety insulation requirement from IEC60601-1 are the same for both short repetitive spikes and a more continuous (e.g DC or sinusoidal) waveform with the same peak level.
    Thank you for any suggestion
     
  4. Pads38

    Pads38 Member

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    60601 makes no consideration for high voltage pulse waveforms. The defined terms used, Working Voltage and Peak Working Voltage, refer to "the highest voltage to which the insulation is subject to, in normal condition..."

    With reference to Table 12, (cr and cl for MOPP) you may see that the second column refers to Vr.m.s. and think "my high voltage but very low duty cycle waveform is, effectively, only a few volts r.m.s. so I can use a much lower requirement" but, I believe, that this would be a mis-interpretation. If you look at Table 13 (the corresponding table for MOOP) you see that the equivalent column now identifies that r.m.s. voltages refer to sinusoidal waveforms.

    I seem to remember a similar discussion previously on the Elsmar forum. One of the resident experts did admit that this is a problem area for 60601. IIRC he did say that an experienced test lab may disregard the strict requirements for something like a fluorescent backlight supply, operating at thousand of volts, but with no real energy to cause harm.

    Or, I might suggest, that as the required creepage and clearance distances would become excessive, you may be better to use solid insulation and possibly encapsulation to get around this. It may be an area where discussion with your test house would be beneficial.
     
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  5. Monica

    Monica New Member

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    nice to meet you here, Pads38... I really miss Elsmar and all its experts! I too remember that there was a similar discussion, but, since it is no more available, I had to ask about the issue again... :(

    thank you for the interpretation
     
  6. nikolaos

    nikolaos Member

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    I don't think this spike has to do with the Working Voltage and Peak Working Voltage. The Risk Management File can help in this case. Can this high voltage low energy spike cause a harm to the patient or the operator in normal or fault condition? If yes mitigation is necessary to reduce this risk as possible. But as Pads38 suggests discuss with your test house.
     

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