I’m trying to work out a solution to a problem with a medical device. I can
limit the power to < 15w for components that are mounted on the topside of a
PCB, and underneath an elastic part that is rated 94HB, except for a few
locations that don’t have the required thickness to meet the UL flame
rating.
I was anticipating that the < 15Watt 900j area of the enclosure would then
have to be a minimum 94HB, but I ran across this deviation in UL60601-1 2nd
edition Does the IEC or national difference version have a similar clause?
(Yes I know I just said it was a deviation and that might be a big clue
but…..)
This would imply that cellulose nitrate and be acceptable.
>From UL 60601-1 2nd states
55dv.4.2 Flammability tests are not required for enclosures
housing only circuits supplied from a source, which is separated from the
supply mains, by one of the methods described in 17g), and where available
power does not exceed 15W
I don’t’ know what the country deviations etc say for the EN60601-1 2nd
edition standard says but I’m hoping it’s the same situation – and this
is really the crux of my question.
3rd edition of the standard seems to back up the no stated flame requirement
in the following paragraphs
En60601-1 Third edition states
13.1.2 * Emissions, deformation of the Enclosure or exceeding
maximum temperature
The following Hazardous situations shall not occur:
- Emission of flames, molten metal, ….
And
The single fault conditions in 4.7.8.1 b0, 8.72 and 13.22, with regard to the
emission of flames, molten metal …….
Shall NOT be applied to parts and components where:
The construction or the supply circuit limits the power dissipation in single
fault conditions to less than 15 W or the energy dissipation to less than 900 J
So bottom line seems to be that the flammability of the enclosure if power is
limited isn’t truly controlled? I must be missing something. Help please
Gary McInturff
Gary McInturff
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