Medical Device Electronics - Secondary to output isolation for 1 MOPP

[Joho Zollo]

Hi,

For a medical AC/DC adapter, what is the required isolation voltage between secondary (output) and earth ground for 1 MOPP? Some say 500VAC while others say 1,500VAC. Would anyone please classify?

For type BF application, is 500VAC isolation between secondary DC output (19V) to earth ground OK?

Thanks in advance,
Joho

 

[MedMartin]

Hello Joho,

I would say 1500 VAC for your secondary voltage is correct.

The reason for this higher test voltage is that you have to consider a single fault causing mains voltage on applied part (see 60601-1 figure J.7). The requirement for this isolation is 1 MOPP for mains voltage.

A voltage of 1500 VAC results for 250 V mains supply. This might be lower depending on your country (110V ...).

Best regards,
Martin

 

[VinceTech]

Hello Joho,

I would say 1500 VAC for your secondary voltage is correct.

The reason for this higher test voltage is that you have to consider a single fault causing mains voltage on applied part (see 60601-1 figure J.7). The requirement for this isolation is 1 MOPP for mains voltage.

A voltage of 1500 VAC results for 250 V mains supply. This might be lower depending on your country (110V ...).

Best regards,
Martin

Hi Martin

Isn't the 1500V is the testing voltage between patient connection point and 2nd voltage and between patient connection point and earth, not between secondary voltage and earth? This is considering that the SFC , applied part on mains voltage through patient body needs to be isolated from 2nd voltage and earth bound. Is this right understanding?

Thanks
Regards,

 

[MedMartin]

Hello VinceTech,

can you elaborate on your question? The testing voltage results from tables in the standard depending on the working voltage.
Applied part and secondary voltage may not be isolated.

Best Regards,
Martin

 

[VinceTech]

Hi Martin

Excuse me for not making clear.

If a Type F applied part is not isolated from 2nd voltage, the Patient Connections still need to isolated from other part with 1MOP for Mains.
My understanding is, for example, if the 2nd voltage is reference to the earth (FE), there will need a MOP for mains between 2nd voltage and Patient Connections.

My understanding maybe not right.

Regards,

 

[MedMartin]

Hi VinceTech,

your assumption seems correct. But could you provide a diagram of your problem? This would be easier to discuss.

Best Regards,
Martin

 

[VinceTech]

Hi Martin

The drawing is attached. This is an example of body temperature measurement device. The device has a power supply unit which has a metal enclosure with protective earth. A temperature sensor lead is connected to the supply unit. the lead and sensor are embedded in their insulation. The applied part is the sensor as it will connected to patient body. The patient connections is the outer insulation of the sensor. The sensor is powered by the floating 2nd voltage of 5V. The mains and 2nd side are isolated by insulation providing 2MOPP for mains voltage.

My question is if two 1MOPP from the patient connection (outer insulator of sensor) shown in the drawing are needed?

Thanks

 

[MedMartin]

Hi VinceTech,

thank you for the diagram. It is much easier to discuss the issue with the diagram.
This depends on the classification of your device. If the applied part is of type B there is no need for additional isolation. If the applied part is of type BF or CF than additional isolation of 1 MOPP(230V) is necessary.

Please be aware that I have only limited knowledge of your system and this is just my opinion. Your test house may have accept lower requirements if you can plausibly justify it.

Best regards,
Martin

 

[VinceTech]

Thank you Martin

 

[peihua yan]

Hello VinceTech,

can you elaborate on your question? The testing voltage results from tables in the standard depending on the working voltage.
Applied part and secondary voltage may not be isolated.

Best Regards,
Martin

No, it needs insulation between AP and secondary voltage (since the secondary voltage is accessible )