IEC60601-1-11 Home Healthcare + IEC60601-1-2 EMC (Functional Earth allowed?)

[lauxt]

Hi all,

The IEC60601-1-11 home healthcare standard states that a solid earth connection cannot be assumed in a home setting. Therefore, earth may not be used as a protective means.

Does this imply that EMC requirements must be met if the earth connection is absent? (We typically use earth for EMI mitigation.)

How about patient leakage current? If the earth connection is absent, is this considered a Normal Condition or Single Fault Condition? Typically, open earth is SFC for a device with a functional earth, but I'm not sure if this still applies for home healthcare, since they are saying we can't assume a solid earth connection.

Thanks,
Tim

 

[Benjamin Weber]

60601-1-11 does not allow class I equipment, so you shall not use the PE a means of protection. So the earth conductor can only be functional (FE) in a class II equipment. Interruption of the FE during leakage currwnt testing is NORMAL CONDITION in this case.

During EMC testing it depends, e.g. if your equipment has Essential Performance. If yes, you should consider FE interruption as normal condition, and test if your equipment still complies during immunity testing. SFC testing scenarios should be a result from risk management.

 

[lauxt]

60601-1-11 does not allow class I equipment, so you shall not use the PE a means of protection. So the earth conductor can only be functional (FE) in a class II equipment. Interruption of the FE during leakage currwnt testing is NORMAL CONDITION in this case.

During EMC testing it depends, e.g. if your equipment has Essential Performance. If yes, you should consider FE interruption as normal condition, and test if your equipment still complies during immunity testing. SFC testing scenarios should be a result from risk management.

Thank you Benjamin! This is certainly an interesting discussion.

I think my confusion is related to the idea of MOPP and how that relates to leakage current. Being relatively new to the field, I think of MOPP as the actual insulation system used to prevent transformer/isolation boundary breakdown. The leakage current concept seems separate from that.

Our "functional" earth connections actually help to reduce patient leakage current...so it almost seems like we should call it a "protective" earth connection, in that case. Is that true?

Just to make sure I'm not going insane, in a hospital/non-home healthcare setting, open earth is SINGLE FAULT CONDITION, right?

Our product is an external switch-mode power supply brick. As I mentioned, I'm new to this, without much guidance. My first estimation is that our product does not have Essential Performance, but I'm not sure

Thanks,
Tim

 

[Benjamin Weber]

If you define the earth conductor as PE, you end up with class I equipment. No way out. Definiton of class I: Protection against electrical shock depends on the protective earth and maybe insulation. Class II: Protection against electrical shock depends on reinforced or double insulation only.

The insulation concept assures that:
- short term / transient overvoltage do not result in an electrical shock
AND
- long term exposition / standard use does not result in an electrical shock.

To achieve both, you have to implement the required clearances, creepages and dielectric strengths (MOOP, MOPP) and you have to pass the relevant leakage current test. But you cannot say, that creepage, clearance and dielectric strength is only important for transient overvoltages. This will certainly help you, to be below the leakage current limits. I have seen a lot of devices, having the required creepages, clearances and dielectric strengths, but still failing the leakage currents tests (for example due to Y-caps not selected properly).

Your device is not an actual ME equipment. But if you want to market it to be combined with ME equipment, you should pass the relevant requirements of 60601-1 / -1-11. Patient leakage current is not really aplicable here, but I have seen other manufacturers of power supplys, who make the patient leakage current test between secondary out and mains in. And if you are going to sell it to ME equipment manufacturers who want to comply with -1-11, you should try to pass patient leakage current tests without the earth. FE interruption is considered normal condition during leakage current testing.

And yes you are right, in "normal" hospital / professional setting PE interruption is single fault condition.

Regarding essential performance: I don't think that a power supply like yours has EP. It does not have a clinical function, were the degradation or loss of that functions leads to an unacceptable risk. Take care to not confuse essential performance with basic safety!

EP: Your device does not do something, that it actually should do (ventilate the patient, give an accurate reading, give an alarm)!
BS: Your c´device does something, that it actually should not do (shick you, start to burn, crush a finger).

Regarding EMC testing: As I have written in my first post, you should apply your risk management process here. 60601-1-2:2014 explicitely requires you to do this! You have to evaluate, if there are EMC related problems, that could lead to an unacceptable risk. But to be honest, I am not sure, if SFC condition have to be tested during EMC and if FE interruption is an "official" normal condition to be tested?!? Maybe an EMC expert could help here!?!

 

[lauxt]

If you define the earth conductor as PE, you end up with class I equipment. No way out. Definiton of class I: Protection against electrical shock depends on the protective earth and maybe insulation. Class II: Protection against electrical shock depends on reinforced or double insulation only.

The insulation concept assures that:
- short term / transient overvoltage do not result in an electrical shock
AND
- long term exposition / standard use does not result in an electrical shock.

To achieve both, you have to implement the required clearances, creepages and dielectric strengths (MOOP, MOPP) and you have to pass the relevant leakage current test. But you cannot say, that creepage, clearance and dielectric strength is only important for transient overvoltages. This will certainly help you, to be below the leakage current limits. I have seen a lot of devices, having the required creepages, clearances and dielectric strengths, but still failing the leakage currents tests (for example due to Y-caps not selected properly).

Your device is not an actual ME equipment. But if you want to market it to be combined with ME equipment, you should pass the relevant requirements of 60601-1 / -1-11. Patient leakage current is not really aplicable here, but I have seen other manufacturers of power supplys, who make the patient leakage current test between secondary out and mains in. And if you are going to sell it to ME equipment manufacturers who want to comply with -1-11, you should try to pass patient leakage current tests without the earth. FE interruption is considered normal condition during leakage current testing.

And yes you are right, in "normal" hospital / professional setting PE interruption is single fault condition.

Regarding essential performance: I don't think that a power supply like yours has EP. It does not have a clinical function, were the degradation or loss of that functions leads to an unacceptable risk. Take care to not confuse essential performance with basic safety!

EP: Your device does not do something, that it actually should do (ventilate the patient, give an accurate reading, give an alarm)!
BS: Your c´device does something, that it actually should not do (shick you, start to burn, crush a finger).

Regarding EMC testing: As I have written in my first post, you should apply your risk management process here. 60601-1-2:2014 explicitely requires you to do this! You have to evaluate, if there are EMC related problems, that could lead to an unacceptable risk. But to be honest, I am not sure, if SFC condition have to be tested during EMC and if FE interruption is an "official" normal condition to be tested?!? Maybe an EMC expert could help here!?!

Thanks again, Benjamin. It's interesting because the company I work for defines any power supply with an earth connection that is not tied directly to the output as Class II with FE. Maybe that's true for a hospital-use only power supply.

However, in the case of 60601-1-11, since this earth connection actually reduces the patient leakage current, it sounds like it's actually a protective earth. Typically, when I think of Class I PE, it's with the classic example:

-High voltage wire comes loose within chassis
-Wire comes in contact with earth referenced chassis
-Chassis shunts current to earth, blows fuse and protects

As you describe above, 2x MOPP is to ensure long term exposure (steady state leakage current, for example) does not cause physiological harm/electric shock. There's more to the story than a wire simply coming loose and causing a one-time dangerous situation!

Thank you for the explanation of essential performance.

Regarding EMC, I think we'll start by seeing how close/far we are to passing EMC with FE interrupted. We are planning to build these for a large medical device company, so maybe they can help us here, specifically with their acceptable risk. Any other insights greatly appreciated!

Thanks for help. It makes everything a little less scary!

 

[Jaydub]

For EMC tests, SFCs are not usually considered, unless Risk Analysis indicates they should be. It would be pretty unusual to perform EMC tests with an open PE or FE.

 

[lauxt]

Jaydub, thank you for that information.

Here is a functional earth configuration we ship on many of our power supplies. These are the two capacitors across the isolation boundary between the primary and secondary.

 

[Benjamin Weber]

Jaydub, thank you for that information.

Here is a functional earth configuration we ship on many of our power supplies. These are the two capacitors across the isolation boundary between the primary and secondary.

View attachment 26166

In case you are not already aware: Regarding Y-caps bridging isolation barriers there are explicit requirements concerning component safety standard compliance of these Y-caps (IEC 60384-14 compliance is required, see IEC 60601-1, cl. 8.5.1.2 and 8.5.1.3)! And there is an very important note to the necessary number and type of Y-caps being in series to achieve the required dielectric strength (IEC 60601-1, Annex A, Note to subclause 8.5.1).