Ground Bond Test for Class I Medical Electrical Equipment - calibration problems

[kchan]

Hi all,

We manufacture Class I Medical Electrical Equipment. We have recently gotten an audit finding where the auditor noticed that we do ground bond testing to 25 A, but our calibration certificate only showed it being calibrated to 6.5 amps. When asked, our calibration lab said they can't calibrate up to 25 A.

We initiated a correction by changing to a new calibration lab and having the equipment recalibrated. However, it seems that there is no tolerance for the ground bond testing. Therefore, what shows up on our certificate says "Ground check current was checked. This is not part of the calibration procedure and has no tolerances. The current level at the time of calibration was found to be 22.0 Amps".

When I search for tolerances on the ground bond equipment, I don't find anything. Has anyone had this problem before? Has anyone struggled to calibrate their tester to 25 A and can anyone suggest a calibration lab certified to ISO/IEC 17025 and can handle calibrations up to 25 A? And if not, is ANSI/NCSL Z540.1-1994 sufficient for this calibration?

Thank you in advance!

 

[Peter Selvey]

According to IECEE CB scheme, document IECEE OD-5014, the accuracy or tolerance for current above 5A should be ±2.5%. So it sounds like the equipment needs to be adjusted so that it reads within that range. 22A seems a bit too low, more than 10% error?

The calibration lab should be OK for that, 25A at mains frequency is nothing special.

 

[Benjamin Weber]

As Peter already said, IECEE OE-5014 recommends an uncertainty of 2,5%. We also work with this value. Our calibration lab states a measurement uncertainty of 0,25% for nominal value of 25 A. And I think this is not a very special challenge for a calibration lab.