Isolated SIP/SOP: 1 or 2 MOOP (Class II MEE)?

[eldercosta]

My MEE design has two electrically isolated SIP/SOP. Per 8.4.2 NOTE 4

If the SIP/SOP circuit is completely isolated from the floating (non-earth referenced) SECONDARY CIRCUIT by an own insulation barrier of at least 1 MOOP based on MAINS VOLTAGE, i.e. a SEPARATION DEVICE according to 16.5, the measurement of the SIP/SOP connector to earth TOUCH CURRENT does not need to be conducted. In such cases it is sufficient to evaluate the effectiveness of the SEPARATION DEVICE by measurement according to 8.7.4.7 c).

and 16.5,

The SEPARATION DEVICE shall have the dielectric strength, CREEPAGE DISTANCES and AIR CLEARANCES required for one MEANS OF OPERATOR PROTECTION appropriate for the highest voltage occurring across the SEPARATION DEVICE during a fault condition.
The WORKING VOLTAGE shall be the highest voltage across the SEPARATION DEVICE during a fault condition, but not less than the MAXIMUM MAINS VOLTAGE.

the insulation requirement is 1xMOOP, no insulation class specified. However a party raised the issue that, for Class II, it should be 2xMOOP based on 8.1 a) requirements (assume MAXIMUM MAINS VOLTAGE unless documentation imposes restrictions on SIP/SOP). I remember seeing a discussion on this forum, on a related subject, where someone (IIRC, Peter Selvey) commented the MAXIMUM MAINS VOLTAGE motivation considers the scenario where there is no direct connection but instead, there is some leakage between the MAINS and the device connected to SIP/SOP. Therefore, unlike e.g. 2xMOOP betwe between MAINS and accessible parts, 1xMOOP between isolated SIP/SOP and accessible parts would be enough.

I see a parallel with the case of Figure J.4 where requirement is also 1xMOP (1xMOOP in the case) for MAXIMUM MAINS VOLTAGE.

Am I missing something?

FWIW the electronics use components that stand 4000Vac test with reinforced insulation to separate the isolated part of the port from the SECONDARY CIRCUITS. Clearance and creepage are a little less than the required 6mm for 2xMOOP for 5000m altitude though.

 

[Peter Selvey]

There's two elements to the "ME system": the first is whether a device connected to the medical device complies with it's relevant safety standard. In practice this would be ensured by regulations (regional or national) that apply to any mains powered electric device no matter how small, so it's not something a typical user would care (or even know how to check). Like my laptop is connected to my monitor, audio system, router via a LAN network and so on, I should be able to assume that if these peripheral devices are sold in Japan, they will have the PSE mark and should be OK.

The writers of IEC 60601-1 don't allow for this assumption. They assume that at a base level, any device connected to the medical device SIP/SOP could be raw mains. Yeah. Not really sensible but that's the underlying philosophy of 8.1a. This would then require 2MOOP. However, as a workaround, as long as the MEE IFU has a warning that peripheral devices must comply with their relevant safety standards, suddenly the whole issue disappears. This is despite the fact that it's not really practical for the MEE user to effectively check all this. This often happens in safety where a false concern is raised and then washed away with a label or warning.

The second element of an ME system is the risk of cumulative or excessive leakage currents, which is more realistic. An isolated SIP/SOP is a neat way to deal with this. For this the isolation only need 1 x MOOP. It's job is to block the mains sourced leakage currents, not raw mains.