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How to apply external voltage to SIP/SOP

Benjamin Weber

Involved In Discussions
Since SIP/SOP with external voltages is a current topic in some discussions here I would like to raise the following question:

Consider a ME equipment which has its own mains supply connection but that is controlled by another PC (no ME equipment) via USB. The ME equipment can only be operated when the PC is connected and a connection is established. If I wanted to apply mains voltage to the USB I couldn't operate the ME equipment properly, e.g. to bring it to its maximum power input. The ME equipment would just be in some kind of standby mode.

Do you think that is OK to do so? Or should I try to bring the ME equipment to operation and simultaneously apply mains voltage to the USB? I don't have any idea how this could be done, to be honest.

Best regrads,


Involved In Discussions
my understanding is.the ME equiomwnt is.connected to a PC through a USB. Before answer this question, you may need to determine how is this USB is isolated from the PC. Is PC's USB 2MOP isolated from mains? if the PC isolation is not specified, you need to apply mains to both ME and USB SOP/SIP. If PC &USB is 1MOP, MAINS shall be applied to SIP/SOP in SFC.

Just personal view, please advise.

Benjamin Weber

Involved In Discussions
OK, I try to explain my problem a little more detailled:

Let us assume the case I have seen most: The device itself is powered via a power supply cord from the mains supply. To operate the device a PC is connected via USB, there is no other way to control the device. The USB port shall be separated by 2MOPP for a working voltage of 240Vrms (maximum mains voltage) from accessible and applied parts. Mains voltage at the USB port is considered normal condition because there is no restriction from the manufacturer what kind of PC shall be connected, IEC 60601-1, cl. 8.1 a). In order to operate the device correctly and bring it to normal operation, the USB connection to the PC must be established and the control software must run at the control PC. Maybe there is even a relay in the device, that closes the mains part only when the USB connection is OK and the software can give the correct command.

If I wanted to apply 240 Vrms to the USB lines (all connected together incl. shield, otherwise I would probably have a breakdown in the USB connectors itself), the device will not operate, maybe the relay mentioned above wouldn't even close. Is it sufficient to perform e.g. touch current measurement this way? Or should I try to close the relay by an external signal voltage? OR should the manufacturer provide any means to operate the device, if it cannot be operated normally in this setting? Or should I consider the not-operating device as normal condition/operation because it would never be functional, if mains voltage is present at the USB lines?

Are there other testers, that would share their experience with us?

Kind regards,
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