60601-1 cl:8.11.6 Internal wiring of the MAINS PART

pturcotte

Registered
Hello everyone,

We are currently designing a Class I medical device where the internal Protective Earth Wiring cross sectional area dimensions would need to be as small as 18AWG, 20AWG would be even better. This is a concept for now, but we need to validate and provide what is applicable for the Protective Earth.

In this product we will have moving parts, we know that reliability of PE will need to be demonstrated via a LIFECYCLE, etc. This part is ok and covered.

The uncertainty comes from the PE sizing, the Internal PE wire that we are using to link different metallic moving parts of the product.

IEC 60601-1 cl 8.11.6 refers us to 8.11.3.3 Title of Table 17 refers to POWER SUPPLY CORD for the cross sectional

IEC 60601-1 cl: 8.11.6 Internal wiring of the MAINS PART
Internal wiring in a MAINS PART between the MAINS TERMINAL DEVICE or the APPLIANCE INLET and the protective devices shall have a cross-sectional area not less than the minimum required for the POWER SUPPLY CORD as specified in 8.11.3.3

We are using a medical power supply 2x MOPP for the 24V. Power Supply uses a C13/C14 connector with a detachable country specific power cable.
Protective Earth wire is connected to chassis inside the product.

We are interested in the dimensioning of INTERNAL Wiring related to Protective Earth.

Where we hesitate, is with IEC 60601-1 cl: 16.9.2.2 Rationale
"Total protective earth path", does it cover all the

For each part of an ME SYSTEM that shares a SUPPLY MAINS connection, the impedance and current carrying capability of the total protective earth path of an ME SYSTEM when tested as a unit shall comply with 8.6.4.
For now, our understanding as per IEC 60601-1 cl:8.6.4 is that we shall not have more than 200mohm. Impedance would be below 200mohm and voltage would be less than 6V with 30A (using 20A x 1.5 IEC 60601-1 cl:8.6.4) ground bond testing. Ground bond test passes at 30A, but still, something feels off here.

1- Does it apply to internal wiring as well?
2- Is PE considered part of the MAINS connection?

Thanks a lot in advance for your help!
 

FelipeSchneider

Involved In Discussions
What is the maximum current for the area that you want to protect with the 20 AWG wire?
There is a nice related topic in this forum, you may find it here.
 

pturcotte

Registered
Protective Earth, so in theory as per IEC 60601-1 cl: 8.6.4 it needs to comply with 30A (20A circuit x 1.5) and be lower than 200mohm and a maximum voltage of 6V during test. Ground bond test successfully pass, but... Wire has a significant temperature rise, too high quite frankly.

This morning I also found IEC 60601-1 cl: 8.10.7 c) (Insulation of internal wiring)

c) Insulated conductors of ME EQUIPMENT that in NORMAL USE are subject to temperatures exceeding 70 °C shall have insulation of heat-resistant material if compliance with this standard is likely to be impaired by deterioration of the insulation.

This is in NORMAL USE, but still, temperature would be too high. Having to use an extra insulation of heat-resistant material will make this wire larger... So at the end, it is better to use a larger wire. 20AWG seems way too small / impedance too high.

Thanks for the link! :)
 

CharlieUK

Quite Involved in Discussions
What is this 20 AWG wire providing earthing to?
Is it earthing the mains-24V dc power supply ?
 

CharlieUK

Quite Involved in Discussions
the main earth wire would therefore also be 14AWG or 16 AWG.

Whether or not 20 AWG was suitable for part of the product depends on what circuits are present which could cause it to go live - difficult to comment without a sketch or drawing
 
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