RISK CONTROL
REDUCE RISK. PREVENT LOSS. SAVE LIVES.
Protecting electric risers in chases
Introduction
Electric power is critical to every business. It keeps the lights on, it is the motive force that runs machinery, and it helps
heat and cool your work spaces and runs the all-important point-of-sale device or cash register. However, when
evaluating systems and processes at risk, how electric power is distributed throughout a building is often overlooked. Due
to the unsightly nature of electric ducts and cables, they are usually tucked away in closets, out of sight in overhead
plenums and hidden in vertical risers; but it is very important that they are protected and maintained to ensure their
dependability and safe operation.
The electric feeders used in riser service include bus duct, unprotected cable supported by metal clamps, cable in conduit
and cable encased in concrete. Voltages used can range from 120-volt single-phase power to 13.8 kV three-phase power,
depending on the size and occupancy of the facility.
Electrical faults and arcing in these chases may result in electrical outages that can shutdown multiple floors for prolonged
periods of time while repairs are being made. In some cases the repairs can take weeks. The causes recorded for these
occurrences have been:
1. Electrical faults caused by water running down into the chase. The water was released from broken drains, fresh
water or sprinkler piping in the same chase, from the roof, or from water releases on higher floors.
2. Electrical faults started due to looseness or corrosion in bolted or plug in connections in busway.
3. Electrical faults started in cable systems due to faulty splices or terminations.
Improving electric riser reliability
Where possible, the electrical conductors should be protected from water running into the chase, from leaks outside or
from water coming from any water pipes installed in the same chase as the electrical conductors. The conductors should
be installed with protection against mechanical damage. Cables jacketed with rubber or thermoplastic materials should be
installed in conduit or armor jacketed cable should be used. Bus duct is well protected against mechanical damage, but
only rainproof-rated bus duct should be installed in vertical chases.
All installations must conform to the appropriate articles of the National Electrical Code (NEC). Overcurrent protection,
either fuses or circuit breakers, or some combination of the two, must be used to protect the conductors against faults and
overloads. Many faults start as arcing ground faults, especially those caused by moisture. These arcing ground faults can
exist for a long time before the phase protective devices trip. This is because the arcing ground faults can involve fault
and load current levels below that of the rated full load phase currents. To quickly disconnect ground faults some type of
ground fault protective relaying is required.
Article 230 of the NEC requires ground fault protection on solidly grounded wye connected circuits with voltages to ground
of between 150V and 600V which have a disconnecting means rated 1,000 amps or more.
This section, therefore, primarily applies to 480/277V systems. This section of the code was effective in 1971, so all
buildings with this configuration built since then should meet this requirement. If not, they are in violation of the code and
immediate action should be taken.
Note, however, that delta connected systems are not affected and that designers may have split systems to get under the
1,000 amp threshold. For example, a system that could have been served by one 1,500 amp breaker may have been split
into two 800 amp circuits. Ground fault protection on circuits under 1,000 amps may be desirable, but does not require it.
However, Travelers strongly recommends it.
A system with fusible protection only has no ground fault protection. To retrofit such a system to include ground fault
protection will require the installation of one or more circuit breakers. This can result in significant costs for upgrading. An
existing system with circuit breakers, depending on its design, may be easily upgraded with the addition of ground fault
protection, but some circuit breaker equipped systems may require extensive modification or replacement to add this
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RISK CONTROL
Protecting electric risers in chases
protection. The original equipment manufacturer should be consulted about adding ground fault protection to existing
circuit breakers.
Maintenance of the conductor system is essential. The support systems holding the cable, conduit, or busway in place
should be periodically inspected to make sure there is no sagging or distortion. An annual infrared thermographic survey
with corrective action taken on all indications found is essential to the maintenance plan. Busway failures usually start at
loose and overheating bolted bus bar joints or at plug-in connectors. If all the joints are not periodically inspected and/or
retorqued, an infrared survey is necessary to identify those starting to overheat. The thermographic survey will also find
indications in junction boxes and cable terminations and splices, but covers must be removed from enclosures to properly
perform the thermographic survey. Insulation resistance testing using megohmmeters is used to identify insulation
weaknesses in busway and cable systems.
Protection and maintenance of the chase
Many chases contain both mechanical and electrical services. Thus, the chase can contain various types of water pipes,
as well as electrical cables and bus duct. The pipe joints and hangers should be periodically inspected for leaks and
damage and repaired as needed.
Losses on record include many cases of water pipe breaks outside of a chase where the water flowed in and down the
chase causing arcing to start in bus duct or cable junction boxes. Where non-rainproof busway or unprotected cables are
run in risers with water lines; provide additional partitions to separate or protect the conductors from leaks as
recommended in the American National Standards Institute/Institute of Electrical and Electronics Engineers (IEEE),
Recommended Practice for Electric Power Systems in Commercial Buildings. Install dikes and use alternate drains to
prevent water from leaking plumbing, sprinklers, and other sources from draining into electric risers as recommended in
the IEEE standard.
If water has entered the chase, the conductor system should be deenergized, efforts made to dry the chase, and the
conductors’ insulation resistance (megohmmeter) tested prior to reenergizing.
Although it is a prime concern of users as well as service providers to select/design and install an electrical distribution
system of the latest and appropriate technology; you must also consider that the maintenance and protection of this
system plays a very important and vital role in keeping your building operational. Don’t find yourself left in the dark by
cutting corners with electrical system maintenance, protection and testing.
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.
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