Hi Jim:
Thanks for your remarks.
You CAN remove the VDR during hi-pot testing.
This is specified in 5.2.2:
"To avoid damage to components or insulation
that are not involved in the test,
disconnection of integrated circuits or the
like and the use of equipotential bonding are
permitted."
This is for the "type" test, not the "routine"
test. Nevertheless, your point is well taken.
Also note that 5.2.1 specifies:
"The electric strength of the SOLID INSULATION
used in the equipment shall be adequate."
So, the hi-pot test only applies to solid
insulation.
The other option is to specify the VDR at a higher
voltage than the hi-pot test voltage.
Regarding VDRs, I don't know why any equipment
would need a VDR between mains and earth. The
requirements for clearance, creepage, and solid
insulations require an electric strength at least
as great as the expected transient overvoltage,
regardless whether a VDR is between mains and
earth or not. So, the VDR does not protect
anything against any voltage up to the required
electric strength of the equipment.
The VDR *may* be useful to protect against
transient voltages exceeding the required electric
strength.n which case it will pass the hi-pot
test.
In the new IEC 62368, the requirement is that any
VDR between mains and earth shall be rated greater
than the required electric strength.
Best wishes for the Christmas season,
Rich
On 12/15/2010 11:27, JIM WIESE wrote:
> Rich,
>
> The issue we ran into with this is that UL and other NRTL's require
> factory hi-pot testing on AC interfaces as part of follow-up services.
> The product will obviously fail at that point. The original 60950-1
> safety testing is done with the VDR's removed. But for the factory
> hi-pot the VDR's often cannot be removed without disassembly of the
> product, and even if they could be removed it violates the intent of the
> test, which is to perform the factory hi-pot right before it is boxed up
> for shipping, not rip it apart, do a hipot, and then re-assemble the
> product.
>
> As you point out the conditions necessary to allow the VDR's to ground
> in the first place already require the assumption that the VDR can go
> short and not create a hazard.
>
> So 60950-1 now allows the VDR's to ground, but the follow-up services
> and listing requirements for the factory hi-pot here in the US and
> Canada more or less prevent doing it.
>
> So, there should be some kind of waiver from the factory hi-pot if the
> product has VDR's to ground as permitted in 60950-1, but unless that
> happens it is silly to allow it in the UL/CSA version, unless people
> feel tearing a product apart to disable VDR's, then doing a hi-pot, then
> reassembling the equipment makes sense.
>
> Best regards,
>
> Jim
>
> Jim Wiese
> Senior Compliance Engineer
> ADTRAN, Inc.
> 901 Explorer Blvd.
> Huntsville, AL 35806
> 256-963-8431
> 256-714-5882 (cell)
> 256-963-6218 (fax)
> [email protected]
>
>
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