Dear Mr Ling
Why do we believe that IEC 60601 is better then IEC 62353?
More often than not people pick and mix from IEC 60601 (see previous forums), make there own tests up (within the limits of safety analysers), do not test on TN systems (mainly outside UK) or power the safety analyser from an isolated supply.
For this reason, IEC 62353 does not follow the new limit in IEC 60601 3rd for earth leakage. This is a safety concern with the 3rd edition when the test is not performed as per the standard conditions.
IEC 62353 refers to the enclosure / touch leakage (for Direct and Diff. method);
The 3rd edition Earth Leakage limit of 5mA (NC) and 10mA (SFC) are potentially dangerous and can only be tested safely on an isolated supply. This is not always possible when testing “on location” as carrying such transformer would require a decent trolley. The new pass/fail limits on normal non-isolated supplies are potentially fatal (macroshock) within the limits of IEC 60601.
The European Directive EN 50191 (guideline for test environment) calls for maximum leakage to earth of 3.5mA. Any potential greater leakage must be supplied through an isolated supply.
I would like to know why the limit went from 0.5 and 1mA (SFC) to 5 and 10mA (SFC)??, when enclosure leakage open earth is still at the 2nd edition limit. Surely in those cases where this is possible and acceptable, you would handle this under a specific standard (ie 601-2) rather than under the general?
The IEC 62353 specifies direct leakage (as per IEC 609601) current limits under SFC only (open earth and mains in applied parts) and are identical to IEC 60601 2nd and 3rd edition.
Equipment leakage (Direct method) is equal to enclosure leakage open earth (SFC) and Applied Part leakage is equal to Mains on Applied Parts and has equal limits to 2nd and 3rd edition.
Only differences are;
o The way in which the current is limited (3ma in IEC 62353 vs 5mA in 60601)
o Compensation of measurement; ie no compensation in 60601 for voltage drop over current limiting resistor which causes the actual voltage on the Applied PArt to drop significant.
o Mains on Applied Part Voltage is 230V vs 253V in 60601.
o CF Patient connections are shortened instead of measured individually.
I am interested in your views on this.
Those interested in EN 50191 guidelines, email me for a free booklet. (same for IEC 62353)
Thanks
John
