Hi Dave:
Based on what you have said, I would treat (for
safety purposes) the non-PELV as 208 volts.
Clearances don't exist within an optocoupler as
there is no air within the optocoupler. Likewise,
there is no creepage distances within an
optocoupler. (Creepage is the interface between
solid and air insulation, and since there is no
air within the optocoupler there can be no
creepage within the coupler.)
I don't know what "UL single protection" means.
However, since the rated withstand is 5000 volts,
one can surmise that the internal insulation is
homogeneous solid insulation (i.e., with no air
gaps - which would otherwise break down since air
is about 3000 volts/mm). If IEC 60664-1 is
applied, such solid insulation would qualify for
reinforced insulation.
If you assume that the non-PELV is 208 volts and
the opto is reinforced insulation, then the
construction is okay (complies with the
requirements of 60664-1).
Best regards,
Rich
From: Nyffenegger, Dave
[mailto:[email protected]]
Sent: Sunday, June 28, 2015 4:33 PM
To: [email protected]; [email protected]
Subject: RE: [PSES] Optos for PELV isolation
Hi Rich,
Thanks for the feedback. In the application I
have in mind the non-PELV is nominal 24VDC.
Obviously this voltage is within PELV limits
however the cabling for this application is such
the 24VDC circuit runs along with 208VAC, sharing
the same connectors and wire troughs and physical
separation is not practical. There is only basic
insulation on both 208VAC and 24VDC wiring and the
connectors do not have any special insulation
ratings between contacts. I'm not sure if the
basic insulation on the 208V together with the
basic insulation on the 24V wiring would meet the
requirement of maintaining a PELV voltage in the
event of a single fault on one of the basic
insulations or not. I'm even less sure of the
ability of a single fault in the connector housing
to maintain PELV voltage. The source of the 24VDC
is a transformer and I've not confirmed if it
meets the requirements for safety isolating
transformer. This is an existing application
being reviewed and I'm going on the assumption
that the 24VDC circuit is not PELV.
The 24VDC circuit does not need to be PELV by
itself however it interfaces to a PELV circuit via
an existing optocoupler. Physical clearances on
the PCB layout and optocoupler pins are greater
than 3.0mm so no concerns there. The only
component in question is the internals of the
optocoupler itself. The opto data sheet does not
publish internal clearance specs on the opto,
only that it is UL 1577 approved for single
protection and the input/output isolation voltage
is min 5000V @60sec. So it would seem the opto
meets the voltage requirements of IEC 60664-1.
I'm just not clear if the UL single protection
rating is sufficient for this application. If it
takes a single fault to get 208V on the opto and a
second fault at the opto to get hazardous voltage
to the PELV side then perhaps the opto is OK as is
in this application. The opto is also available
with an IEC60747-5-5 rating with VDE mark as an
option. The OEM says the only difference with
these optos is an additional non-destructive
production line voltage test on each opto.
-Dave
-
----------------------------------------------------------------
This message is from the IEEE Product Safety Engineering Society emc-pstc
discussion list. To post a message to the list, send your e-mail to
<[email protected]>
All emc-pstc postings are archived and searchable on the web at:
http://www.ieee-pses.org/emc-pstc.html
Attachments are not permitted but the IEEE PSES Online Communities site at
http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used
formats), large files, etc.
Website: http://www.ieee-pses.org/
Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe)
List rules: http://www.ieee-pses.org/listrules.html
For help, send mail to the list administrators:
Scott Douglas <[email protected]>
Mike Cantwell <[email protected]>
For policy questions, send mail to:
Jim Bacher: <[email protected]>
David Heald: <[email protected]>
