60601-1 : Integrated Dry ECG Electrodes = 2 Patient connections inside 1 applied part?

[Ash Watson]

Context: 2xAAA battery powered body worn device; 2X integrated dry ECG electrodes integrated into plastic enclosure.

1. Are these contacts considered 2 PATIENT CONNECTIONS within the same APPLIED PART?
2. Does 60601-1 Clause 8.5.2.1 apply for MOPP across the two contacts?
3. Does 60601-1 Clause 8.5.2.2 apply for MOPP to the accessable battery connectors or terminals of the batteries themselves?

 

[Ash Watson]

Hmm, that message looks a bit curt now that I look at it . Been trying to keep them super concise recently. I'm actually quite a nice guy!

Carrot: I'll buy a six pack for whoever posts the best answer!

Really it comes down to this: do 60601-1 Clause 8.5.2.1, and Clause 8.5.2.2 apply if my part is a single type BF applied part?
Note: it has 2 ECG dry electrode contacts, so there is a path across the body when they are used as intended.

The standard says to implement one MOPP that can meet requirements and pass tests for a 250V + 10% working voltage (this is what it says for internally powered systems).

For Clause 8.5.2.1 and the ECG Electrode to ECG electrode MOPP:
I think the device is categorised as a single Type BF applied part, so maybe 8.5.2.1 doesn't apply?
... but if it does...
Air gap, Creepage distance: can't be done at the component level (super teeny BGA)
Dielectric isolation: maybe? If some kind of potting were to be used and the ECG component were to fry safe.
The actual working voltage will not exceed 6V dc.
The device is never externally powered.
I think the device is categorised as a single Type BF applied part, so maybe 8.5.2.1 doesn't apply?

For Clause 8.5.2.2 - Battery terminals/contacts to ECG contacts:
Maybe this doesn't apply if the battery contacts are internal to the single applied part?

If anyone has any insights here, I'd love to hear them. It makes a huge difference!
Thanks!

 

[Loekje]

equally curt:
1. Yes (if you define them as such)
2. No (if 1 is valid. You need MOPPs between parts and you have just defined them the same part in 1)
3. That one requires more information. Is the battery compartment accessible without a tool and are the contacts accessible parts while the patient is connected? Then yes.

Succes!

 

[Ash Watson]

equally curt:
1. Yes (if you define them as such)
2. No (if 1 is valid. You need MOPPs between parts and you have just defined them the same part in 1)
3. That one requires more information. Is the battery compartment accessible without a tool and are the contacts accessible parts while the patient is connected? Then yes.

Succes!

Thanks Loekje! PM me how best to send you your internet beer!

3. The battery compartment is accessible without the use of a tool, and potentially while the patient is connected.
I am unsure of the meaning of
"...unless
- the metal ACCESSIBLE PART is physically contiguous with the APPLIED PART and can be
regarded as a part of the APPLIED PART; and
- the RISK that the metal ACCESSIBLE PART will make contact with a source of voltage or LEAKAGE CURRENT above permitted limits is acceptably low."

What does "physically contiguous" mean in this context? ... the same lump of metal?
Where are the permitted acceptable limits for source voltage set out?

 

[Loekje]

Hello Ash,

Physically contiguous was interpreted by one our test houses as being a connected string of conductors. I do not know if the test house implied metal conductors only. In our case it went from silver/silver-chloride to nickel to brass to copper and some solder in between, I guess using carbon or doted silicon in this path may inflict a lot of discussion. The four different test houses I have worked with all claimed that they do not interpret the standards but take them literally. But in practice that means literally four different interpretations of the standard.

You wrote that your device has a BF part, not just B. Then you must also comply with the F requirements which states that you need at least one MOPP between all parts, not just only between applied parts. So it makes a difference if your wearable is worn on skin which makes your housing part of the same applied part. If your wearable has insulated leads to a separate housing off skin then you need a MOPP for maximum mains voltage from the housing (and other parts) to the applied part. Wearing it on skin may be easier on this requirement but opens up a lot of implications regarding biocompatibility, I'm not sure which one is worse.

Regarding having touchable (60601-1-11 home environment with the children test finger) battery contacts when opening the battery compartment, or generally speaking lacking MOPP's in there, I suggest to take it up with your test house.
I once encountered a test engineer who did not allow a contact to be touchable while the only situation it could occur is when the touching person is so close to the patient that it would be hard not to have physical contact at all. So touching skin to skin was allowed but touching battery contact to skin was not allowed. Others were very lenient.

We once had a device of which a pin on the battery lid would close switch contacts, thus separating the battery contacts from the device when the lid was removed. First it was approved, but with a later variant of the device on it was rejected because the creepage between the open contacts was not the 3,4mm needed for 2MOPPs for 5V. I still think the idea behind this solution is great, if well executed.

Please share the beer with someone you love or merely enjoy.

Kind regards,
Loek

 

[Ash Watson]

Thanks again Loekje

We once had a device of which a pin on the battery lid would close switch contacts, thus separating the battery contacts from the device when the lid was removed. First it was approved, but with a later variant of the device on it was rejected because the creepage between the open contacts was not the 3,4mm needed for 2MOPPs for 5V. I still think the idea behind this solution is great, if well executed.

I like this idea! I think it could be done easily enough.
These creepage distances will be the death of me