Chris,
Usually the hi-pot tests done during the safety evaluation are meant
to verify spacings and insulation. The hi-pot tests I have seen
usually allow intentional paths to ground to be disconnected. It is
the trace separation,etc, you are interested in, not how well the MOV
conducts. Both MOV's are considered intentional paths to ground.
Both should to be disconnected at the ground side during the test.
If only one is disconnected, you may still have a path, whether it is
direct, or through the contacts (open or closed) of the hookswitch.
Eric Petitpierre
Pulsecom
Herndon, VA
[email protected]
______________________________ Reply Separator _________________________________
Subject: Safety: Hi-Pot Suppression for TNV lines
Author: [email protected] (Maxwell; Chris) at smtp
List-Post: [email protected]
Date: 5/22/00 10:33 AM
Group,
Is there an in-line adapter that we can install on a TNV line (in our case,
a typical RJ12 phone line) to our product that will provide a second layer
of hi-pot protection? The whole explanation follows for those who think
they can help. Others can press delete right now and get on with their day.
We produce a piece of fiber optic test equipment that is rack mounted and
operates from 48VDC. Most of our typical equipment does not have TNV
connections, however this does. We have designed a "remote reset" option.
The remote reset consists of an RJ12 jack on the back of the unit. The user
can plug a phone line into this jack. Once installed, the user can perform
a 5 second power down on the unit by dialing the unit's "phone number" and
letting the line ring 5 times.
This has proved valuable to customers because the units are designed for
remote installation. If the unit hangs up, they don't have to drive, fly,
hike or swim out to where the unit is installed to perform a hard re-boot.
This remote reset line only takes in the "TIP" and "RING" signals (the RJ12
only has pins 3 and 4 populated). Both TIP and RING have MOV's going to
chassis ground. We have had the unit safety tested. During safety testing,
the MOV's were cut (creating a single fault condition). When the MOV's were
cut, the hipot test caused an arc to ground on a circuitboard within the
unit. This arc was considered a failure. My guess is that the arc is
caused by the fact that the tip and ring signals run close to a piece of the
ground plane on the top layer of the board. My first stab at fixing this
would be to clear out the ground plane so that it is furthur away from tip
and ring.
Now, even minor changes to circuitboards can cost thousands. It can also
mean scrap. This unit is a very low volume product (hundreds annually). It
may be more cost effective for us to add some sort of in-line suppressor
external to the unit as opposed to revising the circuitboard. Given that the
unit is rack mounted, I am assuming that there would be room in the rack to
mount such a device, if it existed. Hence my question.
Anybody have any ideas?
Thank you for your time.
Chris Maxwell, Design Engineer
GN Nettest Optical Division
109 N. Genesee St.
Utica, NY 13502
PH: 315-797-4449
FAX: 315-797-8024
EMAIL: [email protected]
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