I know most of you don't use EN61131-2 (Safety for Programmable Controllers
but I'm hoping the questions I have can be answered in general terms. And
if anyone does have/use EN61131-2, I provide paragraph and table reference
numbers.
This is a very convoluted and confusing standard but I think we have looked
at the creepage and clearance section long enough that we finally have it
figured out. But before I commit to something, I'd like confirmation from
this group. The standard provides definitions for basic, supplementary,
double, and reinforced insulation (paragraph 1.4.26). It also provides a
general rule of thumb, worst case creepage and clearance table for basic and
supplementary insulation (paragraph 4.3 subparagraph 3) and its table). I
interpret this to mean, if I use these very conservative creepages and
clearances, I more than meet anything presented later in the standard. I
also interpret this to mean the numbers within this table provide double
insulation since the definition of double insulation is basic and
supplementary insulation combined.
The standard then provides several tables of creepage and clearances under
very specific conditions that includes material types and pollution degrees.
The one I'm most concerned with is the table for basic and supplementary
creepage distances for printed wiring boards (Table 23). As with the
previous paragraph, I interpret this to mean double insulation.
The standard provides definitions for pollution degrees (paragraph 1.4.42).
It says:
Pollution degree 1: No pollution or only dry, non-conductive pollution
occurs. The pollution has no influence.
Pollution degree 2: Normally, only non-conductive pollution occurs.
Occasionally, however, a temporary conductivity caused by condensation shall
be expected.
Pollution degree 3: Conductive pollution occurs, or dry, non-conductive
pollution occurs which becomes conductive due to condensation which is
expected.
Our products, are intended for industrial or commercial environments and are
specified to be mounted in a metal enclosure where pollutants are sealed
out. Further our specifications clearly state our products work 5% to 95%
non-condensing relative humidity. Thus I interpret the standard to mean our
products should be evaluated under pollution degree 1.
Lastly, paragraph 4.3.4 states creepage distances for reinforced insulation
"shall be double the value for basic insulation". I interpret this
paragraph to be non-applicable to the work we are doing since all the tables
list basic and supplementary (double) creepage and clearance distances. It
does not list basic creepage and clearances individually and thus I have
nothing to double. But by using the values provided in the tables, I meet
double insulation requirements.
I apologize for this lengthy message. And I apologize if I haven't provided
enough information to understand the situation. As I said, this is very
confusing for we, the uninitiated. My questions center around my
interpretations and can be distilled down to one question; have I
interpreted each point above correctly? Any advice, general or specific,
will be greatly appreciated.
Happy Holidays all.
Dan Kinney
Horner APG
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