2 MOOP between SIP/SOP and mains part insulation in 60601-1

[bmezhou]

We are designing a class I ME equipment. We used a standard IEC 60601-1 AC/DC with the secondary circuit totally earthed. Our SIP/SOP is a USB 3.0 port on the secondary side. We did not apply extra isolation method on this SIP/SOP.

According to Fig. J.4 in IEC 60601-1 3.1, the isulation between the mains part and SIP/SOP should be 2 MOOP.

As a result, if we apply a 3000 V a.c. test voltage between the mains and the SIP/SOP, the test will fail. The reason is obvious. The insulation of a standard medical grade AC/DC between the mains part and the earth is larger than 1500 V but smaller than 3000 V. If a 3000 V a.c. test voltage is applied between the mains and the SIP/SOP, there will be (AC coupled) leakage along mains, earth, and SIP/SOP (USB 3.0) circuits.

Do we really perform this 3000 V a.c. test? We think a 1500-V insulation between mains and earth plus secondary circuit earthing are enough to provide a 2 MOOP, and the test voltage should be reduced to 1500 V a.c. (Table 6).

Am I correct about this understanding of 2 MOOP?

 

[Bryan Ye]

the isolation between the mains part and SIP/SOP should be 2 MOOP

This is correct. PE part on SIP/SOP is protected by basic insulation + PE
The other part of SIP/SOP is protected by double insulation / reinforced insulation.

The test you performed the dielectric strength test 3000V is wrong.
See clause 8.8.3, this test shall be performed on the solid electrical insulation of ME EQUIPMENT, not directly on ME equipment. Because 3000V is applied to reinforced insulation and at the same time 3000V is also on basic insulation.

In your case, this solid insulation is in a transformer, like a bobbin, tape, etc.

8.8.3 * Dielectric strength
The dielectric strength of solid electrical insulation of ME EQUIPMENT shall be capable of withstanding the test voltages as specified in Table 6.

 

[bmezhou]

the isolation between the mains part and SIP/SOP should be 2 MOOP

This is correct. PE part on SIP/SOP is protected by basic insulation + PE
The other part of SIP/SOP is protected by double insulation / reinforced insulation.

The test you performed the dielectric strength test 3000V is wrong.
See clause 8.8.3, this test shall be performed on the solid electrical insulation of ME EQUIPMENT, not directly on ME equipment. Because 3000V is applied to reinforced insulation and at the same time 3000V is also on basic insulation.

In your case, this solid insulation is in a transformer, like a bobbin, tape, etc.

8.8.3 * Dielectric strength
The dielectric strength of solid electrical insulation of ME EQUIPMENT shall be capable of withstanding the test voltages as specified in Table 6.

Hi Ye,

Thank you for the helpful reply.

Acoording to 8.8.3* Dielectric strength, we should apply test voltage between input and output port of the AC/DC.

Correct?

 

[Bryan Ye]

Hello bmezhou,

Not correct. The secondary side(DC) is connected to PE, if you apply 3000V to input and output, then you may also fail as this 3000V will apply to the basic insulation.

The correct way is to perform the test on a bobbin, tape, or triple-insulated wire of the transformer. It depends on the construction transformer.

If you would like to simply verify the compliance, you could apply 3000V between the input and put of the separate transformer only.

 

[bmezhou]

Hello bmezhou,

Not correct. The secondary side(DC) is connected to PE, if you apply 3000V to input and output, then you may also fail as this 3000V will apply to the basic insulation.

The correct way is to perform the test on a bobbin, tape, or triple-insulated wire of the transformer. It depends on the construction transformer.

If you would like to simply verify the compliance, you could apply 3000V between the input and put of the separate transformer only.

Hi Bryan,

Thank you. Very helpful.