UFC 3 -520-01
June 10, 2002
Clamping Voltage. Disregard references to clamping voltage unless it can
be confirmed that the meaning is equivalent to let-through voltage as defined in this
manual. Depending on its use, the clamping voltage can be the voltage at which the
surge protector starts to operate. In this case, the clamping voltage does not provide
adequate information regarding the actual let-through voltage. Manufacturers that
provide only a clamping voltage might be disguising poor let-through voltages. UL 1449
listing establishes a standardized suppression voltage rating that can be used for
evaluation purposes. Compare the UL 1449 suppression voltage rating to the stated
clamping voltage to identify any significant differences. If necessar y, request the
manufacturer to provide a copy of the UL listing test file to assure that clamping voltage
is not inappropriately stated.
Response Time. Manufacturers advertise response time but the meaning is
not always clear. Response time is not important; let-through voltage is important. If
the surge protector response time is slow, the let-through voltage will be high.
Joules Rating. The joules rating (sometimes referred to as surge energy
capability) is not an important performance a ttribute and is frequently misunderstood. If
the surge protector is listed to UL 1449 and has demonstrated acceptable operational
cycling, the surge protector will have an acceptable energy dissipation capability.
Sine Wave Tracking. The suppression of the surge voltage throughout the
sine wave has been referred to as sine wave tracking and it can provide an added level
of protection for sensitive loads. The term sine wave tracking is not used in industry
standards, it is not confirmed as an attri bute by UL 1449, and its meaning does not
appear to have an industry-accepted definition. Sine wave tracking is not considered a
design requirement for surge protectors. Manufacturers that market sine wave tracking
as a design feature are claiming that t he surge protector will provide a certain level of
suppression throughout the sine wave. This suppression is usually achieved by
installing capacitors. If sine wave tracking is a feature desired by the user, ensure that
the manufacturer provides certified test data that demonstrates this capability. The test
data should include surge applications at different points on the sine wave.