[chbot] Why galvanic isolation is important

[Peter Harris]

 <chchrobotics at lists.linuxnut.co.nz>Hi Volker
I would like to thank you for bringing the issue of counterfeit SSRs to the
club's attention, had you not alerted me I would merrily have installed the
device putting myself at risk of electrocution and my house at risk of
uninsured fire. Please be assured that I do take this subject seriously, I
have had more than enough shocks and dealt with enough magic smoke in my
career not to take unnecessary risks.

My research into counterfeit Fotek SSRs indicated that although the units
"work" the switching devices within the units are underrated and tend to
burn out.
Testing using a 2.2kW load with no heat sink on the SSR suggest that the
device is capable of handling the required 3.5kW. Hopefully the isolation
testing to be carried out at the next meeting will also give a good
outcome.

The final design will have no external low voltage connections so if mains
should appear on the isolated side of the SSR it will be enclosed within
the case. Grounding of the DC supply should cause an earth leakage trip
under these conditions.

I look forward to further advice and discussion.
Best regards
  Peter

Regarding Peter's SSRs it was good to see that people started to see the
> isolation between the SSRs control inputs and load terminals as safety
> critical, and thanks Mark for offering to bring in your isolation
> tester. However I see this only as a good start, measuring isolation
> once I don't think is really good enough to determine whether it will be
> safe to touch the control terminals in the future. That approach may be
> good enough for sparkies and copper cables, but integrated circuits
> don't quite behave like that. Unfortunately there was a lack of interest
> in discussing that further. The issue isn't restricted to SSRs, it shows
> up much more often in stuff we fiddle around with.
>
> Volker
>
>
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