EBME Forums Forums Maintenance Technical Assistance Class one electrical safety test

Is there an exception for not testing the protective earth conductor on a class 1 test? I have a piece of equipment that has no accessible metal part to connect to complete my test. therefore I'm of the opinion that I cannot verify it's electrical safety, I don't feel comfortable omitting the test from the schedule to make the equipment appear to pass the test. Should the manufacture supply equipment that is not testable by field service engineers and EBME depts.

Are you sure it's Class I?

(which piece of kit are we talking about?)

In reply to your last question ... my own preferred answer would be:- No.

It is not uncommon these days to have equipment that is shown as class 1 but has no accessible earth on the case or that the case screws that are so far set back within the case that you cannot really get at them.
The main thing to keep in mind here is, would anyone be able to contact any metal part of the case such that, if there were a fault, the might get a shock. If the answer to that is no, then all we can really do is test the earth in the mains lead. If it is not a detachable lead then really nothing more can be done so, move on..

Hope this helps, Dave

Yes; move on ... to the Earth Leakage Test (which will rapidly indicate whether or not you've got a half-decent "earth").

Not being able to find "a decent earth on the equipment" ("accessible metal part" on the enclosure etc.) has been a feature of electrical safety testing of medical equipment since the Dawns of Biomed ... that's (one of the reasons) why biomeds (should) know what they're doing - and why EST of medical equipment should never be left to our old friends Mutt 'n' Jeff of Bodgit and Scarper (your local "PAT" testers).

Bottom line:- just test what you (sensibly) can, and document* it.

BTW, which Standard are you following, Colin?

* In Ye Olde Days we used to make notes like:- "found an earth on the 4 BA screw underneath" and so forth (remember them days, Big Tony?).

OK ... here's some more "historical" (pedantic) trivia ...

"Officially", you were supposed to always carry out the Protective Earth Continuity test first, and were not to carry on to the more (potentially) "hazardous" tests (insulation resistance, and - if you insisted - the dreaded "Mains on Applied Parts", etc.) if the first test failed.

Bearing in mind that I'm thinking of Class I equipment here, and at a time (back in an era) when most electromedical equipment had a fixed mains cable ... and a lot of it wasn't even fused at the input (apart from at the mains plug - in the UK, that is) like the kit is today.

In other words, you only moved on to insulation tests if the EUT was at least basically safe (protected by a known good protective conductor - or, if you must, "earth"). This advice was, of course, for your own protection.

This was the reason I always reckoned that the "Rigel tests" (that is, the Good Old Rigel 233) started off in the wrong order - in my opinion 1,2, then 5, then 3,4 ... 6 etc. may have been a better sequence ... especially for those biomeds who liked to just crank the knobs (and throw the switches) without seeming to bother too much about what they were actually trying to do. Yes; we had them back then, too (in fact a fair number, if I pause to recall).