Intrinsically safe PCB connectors?

On  9-Jan-2007, "ElderUberGeek" <aribloch@gmail.com> wrote:

> > I used to design intrinsically safe systems. If the device is not
> > certified
> > by a independent testing agency, then basically, you can't hook a wire
> > to it, which means it can only be used as a door stop (and that's
> > only if there is no stored energy in it).
> >
> > Get a copy of the requirements for testing/certification from a testing
> > agency, like Factory Mutual.
>
> Thanks, points well taken. I am reading up everything I can get, and
> hope to get the standards soon.
>
> Could you elaborate from your experience on some real life issues
> regarding Ex certification, good design rules, common pitfalls (both
> technical and procedural) and how to avoid them? That would be great
> and much appreciated.

Remember that the only reason this thing has to be intrinsically safe
is because it's going into a hazardous environment. That may sound
like kind of a dumb statement, but a spark caused by this device
doesn't just fail to meet code, but may very well kill people.

Early in my career, I spent a few weeks wondering if a product I had
designed had caused two people to be burned to death. Turned out a
bad hose fitting on somebody else's equipment killed them. I have to
say though, it wasn't an experience that I soon forgot.

In addition to being safe, the thing has to work properly. If it's powered
through a safety barrier, then of course, you have to take the
characteristics
of the safety barrier into account. In addition to the current limiting of
the
barrier, you will see resistance and capacitance that must be accounted for.

At the system level things become a little more complicated. We forgot to
disconnect all safety barriers on a large control pannel one time after we
had done some testing. The pipefitters showed up the next day and started
welding on the connected equipment, which blew out all the barriers. (About
$20K worth).