Martin,
I use UL 1950 and in clause 2.1.10, which covers the same requirement, it
specifically states that the test be conducted with the power switch in both
positions on and off. I feel the NRTL is correct and your equipment does present
a hazard. You either need to move the capacitors after the power switch or add
bleeder resistors across the caps to let the voltage decay to a safe level.
Capacitance can always be measured by measuring the resistance and then removing
the voltage and checking the time to 37% of the initial voltage. This is one
time constant.
marti...@appliedbiosystems.com on 05/11/2001 11:30:42 AM
Please respond to marti...@appliedbiosystems.com
To: emc-p...@majordomo.ieee.org
cc: (bcc: Ed Rauch/MAIN/MC1)
Subject: Capacitor Discharge Test
We evaluate our laboratory equipment to UL 3101-1, CSA 1010.1 and EN
61010-1.
Section 6.10.3 of UL 3101-1 states "If plug pins of cord-connected
equipment receive a charge from an internal capacitor, the pins shall not
be HAZARDOUS LIVE 5s after disconnection of the supply". We have always
performed this test with the power switch in the ON position and would have
the unit running then unplug the power cord and take our reading on the
oscilloscope. We have never measured any voltages above the HAZARDOUS LIVE
limits of 30Vrms, 42.4V peak or 60Vdc.
Our new NRTL Engineer has now also requested us to perform this test with
the power switch in the OFF position. With the switch in the off position
our voltages after 5 seconds are close to line voltage. The NRTL is
considering this a failure.
However, UL 3101-1 also states in Section 6.10.3 "For plugs receiving a
charge from an internal capacitor, the measurements of 6.3 are made to
establish that the levels of 6.3.1.3 are not exceeded." 6.3.1.3 requires
measuring the overall capacitance from the unit. Our NRTL states that
there is no method available to measure the overall capacitance of the
unit.
Has anyone else in the group had any experience with this issue? Does
your NRTL require testing with the switch in the OFF position? Do your
units fail with the switch in the OFF position? Is it a failure just
because the voltage limits are exceeded, or is it only a failure if the
current and capacitance limits are exceeded. (Similar to the Permissible
Limits Requirements). Have you had any experience with NRTL's not being
able to measure the overall capacitance?
All responses are greatly appreciated.
Regards
Joe Martin
Applied Biosystems
marti...@appliedbiosystems.com
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