Chris,
As a manufacturer of surge protection devices, I can relate to what you have
experienced. In the safety testing of the design, a hi-pot is performed to
without the surge components to ensure a good design.
In product, we have three different requirements from our safety agencies
(UL and CSA).
1. No hipot is required as it was performed on the initial design.
(DO NOT LIKE THIS ONE)
2. Hi-pot the product before the surge components are installed.
3. Hi-pot the product using a power supply with a limited current
of 1 mA.
Requirements 2 and 3 work well.
With your set-up of a MOV/GDT, you may experience some problems with
Requirement 3 unless you have balanced the capacitance between the MOV/GDT.
Until the capacitance was balanced between these devices, our product
failure rate in hi-pot remained high. Once the capacitance of the MOV/GDT
has been balanced, you also have to re-examine the surge response.
If you have any questions, please let me know.
Thanks,
Bryan.
From: Chris Maxwell
To: EMC-PSTC Internet Forum
Sent: 8/28/03 11:45 AM
Subject: Hi-Pot testing
All,
We have a product that runs from AC power.
During safety testing at the lab, the unit passes HiPot testing.
However, the unit is broken by the testing.
Rigorously, the unit "passes" its type testing because it doesn't become
unsafe by the Hipot. However, it isn't functional after the test; and
it requires repair. The unit does meet surge test requirements. (EN
61000-4-5, Class II).
The unit has surge protection circuitry installed from line to earth
(MOV in line with a gas tube). This surge protection is disabled before
the hipot test.
So, here are a few of my random thoughts on this process.
1. I can't break every unit by hipot testing it before I ship it.
2. When the unit is in the field, it will have the surge protection
installed, which will essentially limit any "real life hipot" voltages
to about 500V (230V gas tube, 275VAC MOV). In real life, the unit would
experience a maximum 500V hipot. However, in the case of a single fault
(surge protection disabled), the unit could experience higher hipot
voltages, which would cause damage, but not an unsafe condition (as
shown by type testing).
3. The surge protection is not easily removed for hipot and then
reinstalled after hipot.
So...are there any alternative test or inspection methods that can be
used on this product?
Thanks in advance,
Chris Maxwell | Design Engineer - Instruments Group
email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797
8024
NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA
web www.nettest.com | tel +1 315 797 4449 |
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