Avoiding an Ultrasound System HIPOT Test during Manufacture

[Phloogy]

I am developing an ultrasound system and am looking to see if getting the power supply or the entire system UL certified will allow the device to skip HIPOT testing during manufacture. Is this a true statement? Is this a good idea? Any feedback is appreciated!

 

[isoalchemist]

Just because the system is approved doesn't mean you manufactured it correctly and no danger exists. Every computer we made had HIPOT testing and the tester was one of the first things checked every time UL (our electrical assessor) was in.

 

[PaulJSmith]

Correct. The UL certification only approves the design based on the performance of the submitted sample unit. HIPOT testing will confirm that there are no failures during the manufacturing process on each individual unit.

I'm not sure why you would want to avoid it. That's a very important test, and takes only a few seconds to perform (takes longer to connect it than to test it).

 

[Phloogy]

Thanks for the feedback! I agree, there may be issues/mistakes during manufacturing where HIPOT would be beneficial. We are looking to be as lean as a possible and cut out the non-value added steps.

This is something we are only considering if our PFMEA supports it. Ex. the occurrence of relevant failure modes are low... So if we need HIPOT as mitigation, then we will have it.

 

[somashekar]

Thanks for the feedback! I agree, there may be issues/mistakes during manufacturing where HIPOT would be beneficial. We are looking to be as lean as a possible and cut out the non-value added steps.

This is something we are only considering if our PFMEA supports it. Ex. the occurrence of relevant failure modes are low... So if we need HIPOT as mitigation, then we will have it.

Think of the risks along with the lean and non - value as you say of testing for safety.
If your product is going to be with a safety mark on it (Ex. UL mark) then the UL product file will contain what you are required to test on 100% of manufactured devices. Certainly it would contain the HIPOT, along with conditions of testing. The followup services inspection will be keen to see these records of devices made and dispatched.

 

[Pads38]

Remember that hipot (dielectric strength tests) only apply to solid insulations. Where insulation is provided by creepage and clearance distances it is evaluated by measurements.

Also, where the dielectric test of 60601-1 says that the high voltage should be maintained for 1 minute (with no breakdown) this is not suitable for a production test. Instead the high voltage should only be held for 5 seconds.

(The parts that I test for dielectric strength during a "Type Test" I consider to have invisibly damaged insulation and quarantine them from further use).

It is also worth realising that, particularly with modern power supplies and isolation systems, the value of a "front-to-back" dielectric test is very limited. When the patient isolation is comprised of several parts (so MOPPs are in more than one place) any high voltage applied from the power supply input to the applied parts will be (unevenly) divided across those insulations.

I now only do dielectric tests on component parts, although we do retain the test as a brief production test.

 

[hcrook]

Additionally, IEC 62354 3.0 ed Annex K provides some guidance on production line hipot testing, such as having a 1 second hipot test duration at a higher voltage. 60601-1 also mentions in Subclause 5.1 that tests from this standard shouldn't necessarily be repeated, especially in regards to hipot. "Production tests need not be identical with TYPE TESTS, but can be adapted to manufacturing conditions and possibly invoking less RISK for the quality of the insulation or other characteristics important for BASIC SAFETY and ESSENTIAL PERFORMANCE."

 

[Candi1024]

Also keep in mind that 100% testing your product, MAY keep certain manufacturing steps from being "special". Special meaning that the output is not 100% verified. If they are special processes, you need to do process qualification. This may or may not apply to you.