UL 60950 3rd Edition (formerly UL 1950, 3rd edition)
The application must meet the creepage and clearance distances and electric strength of
Section 5.3.2 of UL 60950 for functional insulation. The electric strength test (Table 5B of
UL 60950) lists 1 kV to 1.5 kV as the test voltages for functional and supplementary grade
of insulation and 2 kV to 3 kV for reinforced grade of insulation.
Separation requirements are tested (Section 6.2.2.1 of UL 60950) by applying an impulse
test and an electric strength test:
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Impulse test allows for the SIDACtor device to turn on (either a 10x700 2.5 kV 62.5 A or
1 kV 37.5 A 10 times with 60-second rest period).
Electric strength test allows the SIDACtor device to be removed (60 Hz at rated voltage
for 60 seconds).
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These are applied between Ground and all Tip and Rings connected together, and/or
between Ground and all conductors intended to be connected to other equipment
connected together.
Basic insulation is not required if all the following conditions are met:
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SELV, TNV1 circuit is connected to the protective earth.
Installation procedures specify that protective earth terminal shall have a permanent
connection to earth.
•
Any TNV2 or TNV3 circuit with an external port connection intended to receive signals in
excess of SELV (60 V dc or 50 V peak) will have the maximum normal expected
operating voltage applied to it for up to 30 minutes without deterioration. (If no maximum
normal specification exists then 120 V 100 mA 60 Hz is applied.)
(In other words, if a permanent Ground connection is made, then creepage distances may
not be required.)
Any surge suppressor that bridges the insulation (connects to Ground) shall have a
minimum DC turn on voltage of 1.6 times the rated voltage UNLESS one of the following
occurs (Section 6.1.2.2 of UL 60950):
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Equipment is permanently connected or uses an industrial plug and socket-outlet.
Equipment is installed by service personnel.
Equipment has provision for a permanently connected protective earth.
ANNEX C of UL 60950 covers transformers.
The secondary side is loaded for maximum heating effect. The maximum working voltage is
applied to the primary. The DC peak value of any superimposed ripple shall be included.
The permitted temperature limits for the windings depend on the classification:
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•
•
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Class A limit is 150 °C.
Class B limit is 175 °C.
Class E limit is 165 °C.
Class F limit is 190 °C.
Class H limit is 210 °C.
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SIDACtor Data Book and Design Guide
TECCOR [ TECCOR ELECTRONICS ]
