Earthing of moving parts, designing tips

[Schwarzyzi]

Hi everyone,
We are a small company developing a medical device, our device is class I, meaning the metallic parts of the device are protectively earthed.
However our device have a metallic drawer that would allow the surgeon to put instrumentation on it, what would you suggest regarding the earthing of this moving part ? Will we be able to have 0.1 Ohm from the drawer to the ground pin through all the metallic connections in between ?
Thank you for your answers

 

[Benjamin Weber]

A device with protection class I is not required to have all metal parts protectively earthed. This is a very commom misunderstanding. You can have class I device with metallics parts not earthed. But as soon as you have at least one part that is connected to protective earth for dafety reasons it becomes class I. All parts in a class I device which are not protectively earthed shall be separated from potential hazardous live voltages by two means of protection, i.e. double or reinforced insulation.

In your particular case: Moving parts can be earhted according to 60601. But in this case you have to provide objective evidence, that the performance over the whole lifetime will not drop. There are so caled drag chains, that protect the conductor from being jammed adn which limit the mimumim bending radius. This might be a solution, but it is maybe a little to much for a "simple" drawer.

If you don't see a proper and reliable solution to connect the drawer to the PE, think about isolating it accordingly to achieve the required two means of protection.

 

[Schwarzyzi]

Thank you very much Benjamin, we will apply this to our device.