UL 60950 3rd Edition (formerly UL 1950, 3rd edition)
Overvoltage Flowchart
The overvoltage flowchart in Figure 4.5 shows specific guidelines for determining
overvoltage requirements applicable to specific designs.
Connects to Outside Cable
Yes
No
No Overvoltage Testing
100 A2-S
Limiting1
26 AWG
No
No
Pass 1
Yes
No
Line Cord3
Yes
Yes
No
1.3 A
Limiting2
Pass 6.1.24
Yes
No
No
Pass 5
Yes
Yes
Fire
Enclosure
No
Pass 26
No
Fire Enclosure
and Spacings5
Yes
No
Pass 3, 47
Yes
Yes
Not
Acceptable
Acceptable
Notes:
1. Current Limiting — Equipment that has a method for limiting current to an I2t rating of 100A2s
2. Current Limiting — Equipment that has a method for limiting current to 1.3 A max steady state
3. 26 AWG Line Cord — Minimum 26 American Wire Gauge (AWG) telecommunications line cord either supplied with the
equipment or described in the safety instructions
4. Clause 6.3.3 — The telephone line must be adequately isolated from earth for the operating mode being considered and
at a voltage of 120 V rms. Refer to Section 6.1.2 of UL 60950.
5. Fire Enclosure and Spacing — Fire enclosures minimize fire hazards by containing any emission of flame, molten metal,
flaming drops, or glowing particles that could be emitted by the equipment under fault conditions. Fire enclosure
construction is covered in Section 4.4.6 of UL 60950. Spacing applies to parts in the TNV circuits that might ignite under
overvoltage conditions. Spacing requirements mandate that parts be separated from internal materials of flammability
class V-2 or lower, by at least 25 mm of air or a barrier material of flammability class V-1 or better. Parts also should be
separated from openings in the top or sides of the enclosure by at least 25 mm of air or a material barrier.
6. Test Condition 2 is not required for equipment with 1.3 A limiting.
7. Test Conditions 3 and 4 are not required for connections limited to outside cable less than 1,000 m.
Figure 4.5 Overvoltage Flowchart
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