Potential Equalization Conductors

  • Thread starter Agust Sigurdsson
  • Start date
A

Agust Sigurdsson

Hello.
I have a few question regarding IEC 60601-1 and- Potential Equalization Conductors.

We are designing a device for medical use, intended to be attached to another medical device and collect data from it. Both are Class I devices and have their own power supplies and fulfill the required levels of protection for patient and operator safety. They have a Functional Earth connection to each other but their frames do not have other galvanic contact to each other. If they are connected to separate wall outlets there is a potential risk of electric shock for a person who touches them simultaneously.
Rather than to demand use of a Medical Multi-Socket Outlet we selected to address this risk by permanently interconnecting the frames of the devices by means of a short piece of wire.

Now my questions:
Would this wire qualify as a Potential Equalization Conductor and then be subject to all requirements for such parts in IEC 60601-1 ?

If so ? would the requirements in section 8.6.7 apply or is a ?Terminal for the connection of a Potential Equalization Conductor? something quite different ?

If section 8.6.7 applies to our case ? how should we address the apparently contradicting demands for minimizing the risk for accidental disconnection but still allow it to be detached without the use of a tool ? Would for instance an ordinary blade connector on one end of the wire qualify ?

Are there any restrictions in 60601-1 which may have escaped me, prohibiting situations like this ?

Finally: Can someone explain the reason or scenario behind this requirement for a Potential Equalization Connection to be detachable without the use of a tool ?


Thanks in advance
Agust Sigurdsson
 

Peter Selvey

Leader
Super Moderator
Potential equalization was originally intended for cardiac areas where even small potentials (e.g. 0.1V) could theoretically cause electric shock, e.g. open heart surgery, cardiac catheter procedures.

It is generally not necessary outside of these areas although it is one of the options which can be used to in a "system" to prevent cumulative leakage currents.

In the case you described there should be no risk of shock if each device is plugged into the wall separately in the same room. Since we assume that only one earth can break at a time, the leakage current will simply flow through the functional connection to the other device, not away from the enclosure. Potential differences in the earth from different wall sockets is only assumed to exist if the wall sockets are in different rooms.

If a tool was required for potential equalization, there would be other risks such as interfering with normal procedures such as moving the patient around, transferring critical equipment from operating room A to room B), and probably lack of use because it is too much trouble.
 
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