Hi Pot Test -when is it a must

[udir]

Hello All,
I have a question to address this forum.
I am the service manager in a medical device company which manufactures and sells medical equipment.
As part of the obligations, each and every device manufactured has to undergo a few tests including safety test such as dialectic strength,i.e hi-pot.
My question is:
Should a device is malfunctioned on the field, and i replaced a component on the board, or replace the complete board, am I obliged to preform again hi-pot test after each repair?
To me it sounds un reasonable as not all Tech labs who service machine has this tool , moreover if i understand correctly, applying this test various times on the same board may damage it.
Can someone direct me to the law/guidance dealing with such cases?
Thanks a lot
Udi

 

[D.A.(Tony)Stewart]

laws are local with guidance by IEC regulations.
When we did any refurbishment , equivalent to new, always HIPOT, repair related to power supply, always test HIPOT.
Other repairs at discretion of engineer.

Worst case test is when floating ground is connected to AC earth ground, which triggered failures in production in one case with catastrophic high failure rate until quality issues fixed.

 

[udir]

Yes,for power supplies I agree,but I am reffering to simpler cases of replacing a cmponent on a board or after de soldering a wire and connecting it back,ect.it doesn't seem resonable to me that each of this cases requires a repeated safety tests.

 

[schmitt trigger]

I understand where are you coming from. If the component or circuit which was replaced is on the low voltage side, why hi-pot the unit?

Although I sympathize with your plight, you must follow the applicable regulations.
This may mean not only hi-potting the unit, but providing evidence that you actually did it including the dates when the service was performed.
This is after all, a medical equipment.

 

[udir]

Hi again
The wand in this case is connected to a device.the whole assembly is hi poted in the manufacturing line. The wand receives from the machine low voltage signals as well as an RF signal of 100v RMS that is then delivered to the patient. If I were to repair this wand at the component level without DDD king anything to the original PCB or wiring except for desoldering them,I still have to perform the same safety tests as for a new wand that has jist finished its aassembly and has never undergo any safety test?

 

[D.A.(Tony)Stewart]

Without seeing the AC isolation design for safety, a Safety Engineer would have to sign off on the process, as applicable or not.

As far as EMC, an EMC engineer would have to sign off on the test process.


As I noted before we had power supplies with isolation transformer (SMPS) that caused HIPOT failure by merely connecting the secondary isolated ground to primary ground, resulting in more capacitive load to the primary side and more stress on other components on the primary side with breakdown across transformer isolation as a secondary chain reaction and follow trip current damaged the PSU. I fixed the damage issue by current limiting the HIPOT tester with a few ~1 MOhms in series which could still trip current but not induce failure.

If no such recognized experts, then Dept. or Customer Service Eng Mgr. must approve any deviations.