UFC 3 -520-01
June 10, 2002
11-2.2.5 Point-of-use (plug -in type) surge protectors should be used to protect specific
critical equipment that plugs into wall receptacles.
11-3
INSTALLATION CRITERIA.
11-3.1
Minimizing Lead Length for Parallel Surge Protectors.
11-3.1.1 Lead length refers to the length of conductor between the circuit connection
and the surge protector, and is the critical installation attribute for parallel-type surge
protectors. For typical installations, the lead conductor has negligible resistance, but a
significant inductance when subjected to a high frequency surge transient. This
inductance can develop a substantial voltage drop under surge conditions, thereby
proportionately increasing the let-through voltage. Refer to Appendix B for an exa mple
calculation of the lead length effect.
11-3.1.2 Some lead length is unavoidable in an installation; however, make every
effort to minimize the lead length and associated inductance. Figures 11-2 and 11-3
show examples of optimal installations in whi ch the lead conductors are less than 1 foot
in length. Notice that the leads have been connected to the circuit breaker panel
without making any high-inductance coils or sharp bends in the conductors.
Figure 11-2. Optimal Installation of Surge Protector Leads First Example
11-4
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