Juniper MX240 Hardware Manual page 205

Appendix D: Power Guidelines, Requirements, and Specifications
advice. Strong sources of electromagnetic interference (EMI) can destroy the signal
drivers and receivers in the router and conduct power surges over the lines into the
equipment, resulting in an electrical hazard. It is particularly important to provide a
properly grounded and shielded environment and to use electrical surge-suppression
devices.
CAUTION: To comply with intrabuilding lightning/surge requirements, intrabuilding
wiring must be shielded, and the shield for the wiring must be grounded at both
ends.
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Site Electrical Wiring Guidelines