UFC 3 -520-01
June 10, 2002
Additional evaluation is necessary for these other features as described in subsequent
sections.
D-2.2
UL 1449 Surge Suppression Rating.
D-2.2.1 The lowest possible UL 1449 surge suppression rating is 330 volts and the
highest possible rating is 6,000 volts. Contrary to intuition, lower ratings are better. A
6,000 volt rating could mean that the surge protector will still allow a 6,000 volt surge to
be transmitted to downstream equipment, with little or no attenuation.
D-2.2.2 Table D-1 lists the maximum recommended surge sup pression ratings.
Considering how the UL 1449 listing process determines these ratings, a good quality
surge protector should have no difficulty meeting these limits.
Table D -1. Maximum Allowed UL 1449 Surge Suppression Ratings
Line-to Neutral
AC Power
Maximum
System Voltage
Suppression Rating
Single-Phase
120
600
120/240
600
Three Phase Wye
208Y/120
600
480Y/277
1,200
D-2.2.3 Table D-1 specifies the maximum recommended UL 1449 surge suppression
ratings. Lower ratings are preferred.
D-2.3
Maximum Continuous Overvoltage Rating.
D-2.3.1 The maximum continuous overvoltage rating (MCOV) is the rated continuous
voltage that can be applied to the MOV elements without having the surge protector
start to operate. If the normal system voltage exceeds the MCOV, the surge protector
will conduct continuously and eventually fail. Everything else equal, a higher MCOV is
desirable; a lower MCOV rating increases the surge protector's susceptibility to a
temporary overvoltage such as a momentary voltage swell.
D-2.3.2 Table D-2 lists the preferred minimum MCOV rating for surge protectors.
Lower MCOV ratings can be used provided that the manufacturer provides
documentation of the surge protector performance during voltage swell events.
Temporary overvoltages cause a large proportion of the total surge protector failures.
D-3
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