RISK CONTROL
REDUCE RISK. PREVENT LOSS. SAVE LIVES.
Voltage surge: protecting sensitive electronic equipment
Introduction
Personal computers, servers, microprocessor-based controllers, telephone switchboards, robotics, cash registers
systems… the list goes on. All of these are electronic equipment types named in loss reports where the cause of the
damage was a voltage surge.
Most voltage surges are weather-related caused by lightning strikes on the electric utility’s distribution system. Other
causes are possible, such as a high-tension line falling on a lower voltage distribution line, or surges from switching or
current zero forcing caused by over-current device operation. The cause of the voltage surge is not the issue as much as
is the absence or presence of surge protection. If your sensitive electronic equipment is not properly protected, it will be
damaged. A well-designed surge protection scheme can help to prevent damage to expensive equipment and even
costlier business interruption.
Installing surge protection devices
Your facility electric distribution system should be provided with lightning arresters at the service entrance on the primary
bushings of the utility transformer. The secondary bushings of the transformer should also be equipped with lightning
arresters if the secondary bushings or feeder conductors are exposed to lightning strikes. If you own the transformer the
lightning arresters are your responsibility. A properly designed, properly installed, and well maintained lightning arrester
system will protect most of your connected electrical equipment.
The service entrance lightning protection is your first line of defense, but lightning arresters alone are not enough to
protect sensitive electronic equipment. To get the additional protection needed, Transient Voltage Surge Suppressor
(TVSS) devices are recommended for installation at certain locations on the electric circuit between the service entrance
and the appliance to be protected. TVSS devices are available in a variety of designs for specific locations on the electric
power distribution system. TVSS devices designed for use on data circuit lines are also available. Before installing these
devices, always specify underwriters’ Laboratory (UL) listed TVSS devices. Then:
•
Install TVSS devices at the power connection of the electronic appliance. For cord set powered equipment this is at
the power outlet. Use TVSS device designed for use at this location – Category A type.
•
Install TVSS devices on each sub-distribution panel board if there is more than 50 feet of electric circuit separation
between the panel board and the electronic equipment. If the distance is 50 feet or more the voltage surge wave can
be reflected back. The voltage magnitude of the wave will double at the point of reflection, which is the end point
where the appliance is located. The TVSS at the panel board is necessary to prevent the TVSS at the appliance from
being overwhelmed. Use panel board TVSS devices designed for this location – Category B type.
Install a TVSS device on the main switchboard if there is more than 50 feet of electric circuit separation from the main
switchboard and the appliances to be protected. Use main switchboard TVSS device designed for this location – Category
B type.
•
Install TVSS devices on the copper signal lines coming into the building from remote transmitters. Use signal line
TVSS devices designed for this purpose.
Maintaining electrical grounding system
TVSS devices connect between the power conductors or signal conductors and the system ground to divert surge energy
ground. A well maintained grounding system is necessary for TVSS devices to function properly. Your grounding system
should consist of grounding conductors that connect the appliance and distribution equipment back to a driven ground rod
located at the service entrance. Larger facilities will have a buried grounding mat in the main substation. Check these
items:
•
Test your system ground resistance at the grounding rod. There are several methods. The most common is to use a
“fall of potential” setup. The National Electric Code specifies a maximum ground resistance of 25 ohms but this is too
high to adequately protect electronic equipment against surge damage. For TVSS devices to work correctly the
ground resistance should be 5 ohms or less.
PAGE 1
RISK CONTROL
Voltage surge: protecting sensitive electronic equipment
•
Driving additional ground rods and bonding them together, burying a ground plate, or treating the soil with salts can
reduce ground resistance.
•
Do not use isolated grounds. All equipment grounding should connect to the facility grounding system using copper
conductors. Otherwise, damaging potential differences can arise during surge occurrences.
•
Inspect the grounding system conductors to make sure these are all sized to National Electric Code Article 250-93.
•
Check grounding system continuity from the point of use back to the ground rod and repair any broken or high
resistance connections that exceed a few micro-ohms.
Proper surge protection can make a difference to the status of your equipment when a power surge occurs. Sensitive
electronic equipment can be damaged if not properly protected, irrespective of the cause of the surge. A well-designed
surge protection plan can help protect expensive equipment from damage and business interruption. Consider seeking
the advice of a professional to evaluate your premises and electrical system to ensure the electronic equipment has the
proper voltage surge protection.
To learn more, visit BoilerRe.com.
boilerre.com
The Travelers Indemnity Company and its property casualty affiliates. One Tower Square, Hartford, CT 06183
The information provided in this document is intended for use as a guideline and is not intended as, nor does it constitute, legal or professional advice. Travelers does not
warrant that adherence to, or compliance with, any recommendations, best practices, checklists, or guidelines will result in a particular outcome. In no event will Travelers or
any of its subsidiaries or affiliates be liable in tort or in contract to anyone who has access to or uses this information. Travelers does not warrant that the information in this
document constitutes a complete and finite list of each and every item or procedure related to the topics or issues referenced herein. Furthermore, federal, state or local
laws, regulations, standards or codes may change from time to time and the reader should always refer to the most current requirements. This material does not amend, or
otherwise affect, the provisions or coverages of any insurance policy or bond issued by Travelers, nor is it a representation that coverage does or does not exist for any
particular claim or loss under any such policy or bond. Coverage depends on the facts and circumstances involved in the claim or loss, all applicable policy or bond
provisions, and any applicable law.
© 2014 The Travelers Indemnity Company. All rights reserved. Travelers and the Travelers Umbrella logo are registered trademarks of The Travelers Indemnity Company
in the U.S. and other countries. 927-bre
PAGE 2