Hi James:
On further consideration, the standard’s “NOTE” following 6.7.3.1 is incorrect.
When a hi-pot test is done on the primary (mains) circuit, the voltage
(attenuated) will also appear (where it can) in secondary circuits due to the
capacitance to the primary circuits. In other words, the primary circuit
hi-pot test tests all possible insulations, whether primary or secondary.
Of course, the standard requires hi-pot tests of the secondary circuits
regardless of my assertion.
Best regards,
Rich
From: James Pawson (U3C) <ja...@unit3compliance.co.uk>
Sent: Tuesday, May 16, 2023 11:08 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG; Richard Nute <ri...@ieee.org>
Subject: Re: [PSES] EN/IEC 61010-1 insulation question
Thanks Richard!
---- Richard Nute wrote ----
Hi James:
My answers to your questions:
1. Does 6.7.3 <tel:6.7.3> apply for the clearance between the secondary
winding and earth as indicated?
Yes.
2. If NO to 1) then what parts should this insulation be between?
3. If YES to 1) then:
a. what is the safety hazard that is being addressed by applying Basic
insulation values from Table 6 here?
The standard’s assumption is that transient voltages do appear in secondary
circuits. See NOTE following 6.7.3.1 <http://6.7.3.1> . A transient voltage
can cause a clearance or creepage to fail. Solid insulation is required to
have suitable electric strength to withstand the transient voltage.
b. Why isn’t this shown on Figure D.1e) as being required?
I assume that the figures are either insulation in general, including
clearances (air insulation) or just for solid insulation.
4. If the working voltage between terminals X and Y in the sketch is less
than the Hazardous Live thresholds in 6.3.1 <tel:6.3.1> then it is be
permitted to be present on an Acccessible external terminal, correct?
Yes.
5. Earthing either end of this winding will make 6.7.3 <tel:6.7.3>
redundant, correct?
I wouldn’t describe the requirement as “redundant.” If one end of the winding
is connected to earth, then clearly the clearance and creepage requirements do
not apply to that one terminal. However, the other terminal still must meet
the clearance and creepage requirement.
The standard seems not clear as to whether clearance (air insulation) is
considered as insulation or a separate parameter.
Note that the values for creepage distance are based on rated voltage, not
transient voltage. This is because failure of a creepage is caused by a
long-term voltage. However, physically, a creepage cannot be less than a
clearance.
Good luck,
Rich
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