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Clearance and Creepage according to Subclause 8.9.1 for MOPP IEC 60601-1

#1
In the subclause 8.9.1 of IEC60601-1 what is the meaning of the "highest peak value of the withstand voltage" in the case of applied part MOPP. How to determine the clearance from this value? Does this mean we do not need the table 12 for clearance?
Can we also determine the creepage from table 12 with long term RMS according to this subclause?
 

Peter Selvey

Staff member
Moderator
#2
For MOPP, Table 12 only uses Vdc or Vrms, the peak value does not have any impact (there is a long story and history behind this).

The phrase "long-term" only appears in the informative appendix. Strictly speaking, "rms" needs to have supplementary definition of the time or period in which the averaging is done (since rms = root-mean-squared, it has to be defined over what period is the mean calculation). I could not find anything in IEC 60601-1, but generally for stable repetitive waveforms this is taken to be over one full period of the waveform, during the time in which the circuit is energised. Also for reference, most rms responding instruments use around 1-2s period for the averaging, which should give the same result provided the waveform is stable.

The general standard does not take into account circuits whether or not the circuits are energised continuously. However, some particulars have much lower values in part due to recognition that many functional circuits are not subject to long term stress (e.g. IEC 60601-2-4 for defibrillators).
 
#3
For MOPP, Table 12 only uses Vdc or Vrms, the peak value does not have any impact (there is a long story and history behind this).

The phrase "long-term" only appears in the informative appendix. Strictly speaking, "rms" needs to have supplementary definition of the time or period in which the averaging is done (since rms = root-mean-squared, it has to be defined over what period is the mean calculation). I could not find anything in IEC 60601-1, but generally for stable repetitive waveforms this is taken to be over one full period of the waveform, during the time in which the circuit is energised. Also for reference, most rms responding instruments use around 1-2s period for the averaging, which should give the same result provided the waveform is stable.

The general standard does not take into account circuits whether or not the circuits are energised continuously. However, some particulars have much lower values in part due to recognition that many functional circuits are not subject to long term stress (e.g. IEC 60601-2-4 for defibrillators).
Hello there
I have a (partly) related question.
In case of the defibrillation shock, IEC 60601-1 clearly states the clearance / creepage distances between the (patient connections of the) the protected applied parts and the rest of a device (>= 4 mm).

However, I could not find any clear statement about the distances between the body itself and other conductive parts of a device?
In our case, the device has no patient connection in the sense of IEC 60601-1. However it has externally accessible charging pads used for charging an internal battery (the charger is not connected in normal operations) .
Could you enlighten me on the clearance / creepage distance that we should consider between the patient's body and these pads, to avoid having to consider the pads as protected applied parts falling under 8.5.5.1 and 8.5.5.2 ?

Is it reasonable to say that according to table 2 of 60664-1, and considering modern biphasic defibrillators between 1.5 and 2 KV, we could consider a clearance of 1 mm ? And if so, what is the probability to find older defibrillators delivering higher peaks in real life?

Or should we be conservative and consider a distance of 4 mm corresponding to a peak of 5 Kv, following the same rationale as developed in IEC 60601-1 Annexe A page 267 for the protected applied parts?

(Of course, the pads as protected against ESD, but although in that case the voltage of the peak is much higher than the defibrillation shock, the duration is also much shorter)

Thanks so much, Francois
 
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#5
Hello

8.4.2c is applicable to the leakage currents (generated by the device itself), which I think is a different case. My question relates to the (external) defibrillation voltage, and the minimal clearance distance required to avoid having to consider the charging pads as protected applied parts falling under 8.5.5.1 and 8.5.5.2, considering the risk that the defibrillation current might traverse the air gap between the patient's body and those pads and consecutively put the device (not the operator) at risk.
 
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