Touch Current Measurement and Limits of 42.4V peak or 60Vdc

W

william_N

#1
Hi All,
clause 8.4.2 c) states that following parts are excluded from the touch current mearsurement
– accessible contacts of connectors;
– contacts of fuseholders that are accessible during replacement of the fuse;
– contacts of lampholders that are accessible after removal of the lamp;
– parts inside an ACCESS COVER that can be opened without the use of a TOOL, or where a TOOL is needed but the instructions for use instruct any OPERATOR other than SERVICE PERSONNEL to open the relevant ACCESS COVER.

provided that if the probability of a connection to a PATIENT, either directly or through the body of the OPERATOR, through which a current exceeding the allowable TOUCH CURRENT could flow, is negligible in NORMAL USE, and the instructions for use instruct the OPERATOR not to touch the relevant
part and the PATIENT simultaneously.

continuously, the standards regulated the voltage limits( 42.4v peak or 60v dc) and energy limits ( 240va, 60s/2J, at potential up to 2J) for such parts.
and has a note : If voltages higher than the limits specified in 8.4.2 c) are present, the LEAKAGE CURRENT limits referred to in 8.4.2 b) apply.

questions is, such as an illuminating lamp derives its power from the manis directly (ac 240v), conductive parts of the lampholder can be operator accessible and the voltage exceeds 42.4v peak, does the conductive parts of the lampholder subject the test of touch current?
obviously it's failed...
 
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Peter Selvey

Staff member
Super Moderator
#3
Interesting point: a quiet difference from the 2nd to 3rd edition.

Under the 2nd ed, Clause 16 e) 2) gave a specific exclusion for lamps, even mains powered lamps.

But this exclusion is missing from the 3rd edition (8.4.2).

I guess the design of a standard lamp holder (e.g. Edison screw E27) is historical and as such it has been allowed to exist even though it does not meet current safety expectations. It's a long term backwards compatibility issue: houses use them and houses stick around for a long time.

But perhaps the writers of the 3rd edition thought (quite reasonably) that as there are so many other design options around now, there is no reason to have a dangerous type of lamp holder in an accessible place in a medical device.
 
W

william_N

#4
peter, thanks for your replay.
for above situation, is it mean that if the mfg designed the mains powered lamps, it will not comply with 3 rd 601?
How about the cap-type mains fuse-holder, if the operator change the fuse when the equipment is still powered, there is a possiblity that the operator gets shock.
is there another option that: put a warning mark and statements ( cut-off the power before replacement )?
 

Peter Selvey

Staff member
Super Moderator
#5
Fuse holders have for a long time been designed in a way makes it very difficult to contact live parts during replacement. I'm not sure if they are fully compliant with 8.4.2 (they could be), but in any case, they are a different ball game compared to an E27 type lamp holder.

For IEC 60601-1:2005 there is no option that I could find. Of course, modern regulation does not require compliance (e.g. risk management justification), but you would not be able to claim compliance with IEC 60601-1:2005. You would need to declare this deviation in all regulatory applications (and justify it), and you may not be able get third party product certification.
 
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