For the last two months, I have looked at
working safely near Switchgear and Switchboards. This month’s topic will continue the concept
of working safely around electrical equipment with a focus on Busways (also
known as bus ducts).
A Busway is defined as “A raceway consisting
of a grounded metal enclosure containing factory-mounted, bare or insulated
conductors, which are usually copper or aluminum bars, rods, or tubes” [1]. Most busways are located towards the ceiling
of a factory, but can be installed in vertical or horizontal positions. Busways can be located indoor or outdoor
locations. They can also be intended for
low-voltage or medium-voltage applications.
Most have seen, specified, installed, or
maintained busways. Busways can be used
to connect transformers, switchgear, switchboards, or panelboards, industrial
machines, or other equipment together.
Busways are commonly used in manufacturing facilities to connect various
types of industrial machines (e.g. injection molding machines, chillers,
furnaces, specialized equipment, etc.).
Busways can also be equipment with fused and unfused disconnect switches.
Busways are required to be installed in accordance
with all national, state, and municipal codes. Installation requirements
include those detailed in the National Electric Code [1]. General requirements include:
- The equipment shall be suitable for use, NFPA 70, Article 110.3
- The short circuit current rating (SCCR) of the equipment shall equal to or greater than the fault current at the point of application, NFPA 70, Article 110.10
- Equipment shall be marked with Arc-Flash warning signage, NFPA 70, Article 110.16
Specific requirements for Busways rated at
600 V or less are defined in the National
Electric Code, Chapter 378 and include:
- The equipment are to be marked with the voltage and current they were designed
- The equipment shall include the manufacturer’s name or trademark and are required to be visible after the installation
When installing bus plug-in devices intended
as feeder or branch circuits, the plug-in devices are required to have an
externally operated disconnect switch [1].
If the operating handle of the disconnect switch is located out of
reach, ropes, chains, or sticks shall be provided for operation when employees
are standing at floor level [1].
One of the reasons Busway is used in
manufacturing locations is because of its flexibility. Additional circuits can be added to the Busway
as needed to connect new or repositioned equipment. The connections are commonly made through
attaching bus plug-ins (Bus Plugs) with fused disconnects.
Many believe that the connection of Bus
Plugs can be done while the Busway is energized (live). Connection of Bus Plugs to live Busways is a
hazard. The manufacturer’s installation,
operation, and maintenance documents state that connection of Bus Plugs to
energized (live) Busways should not be done.
The proper method of connecting Bus Plugs to Busways is to:
- De-energize the section of Busway,
- Install the Bus Plug,
- Ensure the Bus Plug is properly seated
- Energize the Busway,
- Energize the load that the Bus Plug is intended to serve
Basic steps should be taken prior to energizing the
Busway. Some of the steps can be found
in the installation instructions from the manufacturer. Other steps are from the National Electrical
Manufacturers Association (NEMA).
Pre-energization steps include:
- Ensure all blocks, spacers, and packing materials are removed
- Ensure all grounding conductors are connected
- Manually exercise all switches, circuit breakers and other operating mechanisms
- Visually check all phase conductors to ensure that they are landed on the proper phase terminals
- Remove any foreign material
- Set all switches or circuit breakers to the OFF or de-energized position
- Ensure all panels are installed and all panel mounting screws are installed
Working safely on or near energized (live) electrical
equipment is important to minimize contact with electrical energy. Shock and arc flash hazards do happen. By following the principles outlined here, in
various standards, and those learned from electrical safety training programs
will help ensure a safe workplace.
By the way, thanks to everyone who as
has signed up to use the Day-One-Safety checklist! The list of users is growing. This tool will help your employees be safe.
If you are unfamiliar with the Day-One-Safety checklist, this software application is intended to assist people with working in new or
unfamiliar facilities or locations. This is a free on-line checklist available to
anyone who wants would like to use it. To request a password or to Login, click here.
References:
- National Fire Protection Association (NFPA). National Electric Code. NFPA 70-2014, Quincy, MA USA
