Basic question regarding 2 x MOPP

[Daniel76]

Dear Community,

I've been working with IEC 60601-1 for some time now. But since all the time one tricky question has been on my mind. I'm sure there are some experts among who can help me or at least offer me some insights.

Presumption:

I have a Class 1 device for an endoscopic application. This means a to mains connected supply unit and a floating applied part (BF/CF). As all of us know the IEC 60601-1 requires 2 x MOP. Ignoring the operator, this means for the patient 2 x MOPP. These consist of 1 x MOPP (L1/N - PE, primary to PE) for a working voltage of 250 Vrms and 1 x MOPP (AP – PE, mains on the F-type applied parts). Both insulation areas are tested with a test voltage of 1.5 kV for one minute. BUT, and this is what I don't understand and can't explain, when I measure the isolation area from primary to applied part (2 x MOPP), I have to use a test voltage of 4 kV.

Why is 1.5 kV + 1.5 kV equal to 4 kV?

I would be very grateful for any answers.

Best regards,
D76

 

[mr9000]

Draw an insulation diagram. Where is the barrier between applied part and mains? Or is it a patient connection connecting to your secondary circuit? Since they are floating, no connecting to PE, so you need two MOPPs.
See J.5 in the annex.

 

[*KLxGray]

Since the 4kV requirement is derived from 2nd edition of IEC 60601-1, and SI requires 2U+2000V (2500V) in 2nd also. But in the 3rd edition, they replace the BI/SI with MOOP/MOPP, so there is a gap between 2MOPP with RI/DI. And you need to test each 1MOPP with 1500V and entire 2MOPP with 4000V or only test 1MOPP with more than 1500V and 1MOPP with rest voltage.