Low Voltage
Electrical Equipment
and Devices
EECE 475 Building
Management Systems
Low Voltage Definition
• The International Electrotechnical Commission (IEC)
Standard IEC 61140:2016 defines Low voltage as 0 to
1000 V AC RMS or 0 to 1500 V DC
• Other standards such as IEC 60038 defines supply
system low voltage as voltage in the range 50 to
1000 V AC or 120 to 1500 V DC in IEC Standard
Voltages which defines power distribution system
voltages around the world.
• In electrical power systems low voltage most
commonly refers to the mains voltages as used by
domestic and light industrial and commercial
consumers.
• "Low voltage" in this context still presents a risk
of electric shock, but only a minor risk of electric
arcs through the air.
Voltage
range
AC RMS
voltage (V)
DC voltage
(V)
Defining
risk
High voltage
(HV)
> 1000
> 1500
Electrical
arcing
Low voltage
(LV)
≤ 1000
≤ 1500
Electrical
shock
Extra Low
voltage (ELV)
≤ 50
≤ 120
Low risk
Low Voltage Switchgear
• Low voltage switchgear is a term for electrical
switchgear rated up to 1,000V AC that is used to
distribute, control, and protect electric power in
industrial and commercial applications.
• Low voltage switchgear can be metal-enclosed or
metal-clad, and it contains components such as circuit
breakers, switches, isolators, fuses, and buses that
isolate equipment from normal or abnormal currents.
• Low voltage switchgear is designed to limit the effects
of short circuit currents and provide safety to people
and appliances.
Switchboards and
Panelboards
• An electrical distribution panel, also
called a breakers panel or a distribution
board, is an enclosed steel box that
houses various circuit breakers and
other electrical components.
• It is the main source of a large set of
electrical circuits that supply electricity
to the subsidiary circuits of a home or
business.
• It can be mounted on the outside or
inside of the building, sometimes
combined with the electric meter.
Protection Devices
• A circuit breaker is an electrical safety device designed to
protect an electrical circuit from damage caused by overcurrent.
• Its basic function is to interrupt current flow to protect
equipment and to prevent the risk of fire.
• Unlike a fuse, which operates once and then must be replaced, a
circuit breaker can be reset (either manually or automatically) to
resume normal operation.
• Circuit breakers are made in varying sizes, from small devices
that protect low-current circuits or individual household
appliances, to large switchgears designed to protect high
voltage circuits feeding an entire city.
• The generic function of a circuit breaker, or fuse, as an automatic
means of removing power from a faulty system, is often
abbreviated as OCPD (Over Current Protection Device).
Safety Switches
• A safety switch is a device that monitors
electric current and detects faults in the
electrical system
• It works by shutting off power to the system in
trouble within milliseconds of detecting an
electrical leak, short-circuit, overload, or
equipment failure.
• Safety switches are commonly used as a
disconnecting means for a service entrance and
fault protection for motors.
Switching and Control
LV Devices
• Contactors and relays
• Motor starters
• Transfer switches (manual and automatic)
• Soft starters and variable frequency drives (VFDs)
Timers
• Timers automatically switch lights, machinery, and industrial
processes on and off at specific times or time intervals.
• Timers help reduce energy use by running equipment only
when needed.
• Timers are commonly used with lighting systems, HVAC
systems, pumps, fans, and appliances.
• Cycle timers is a specific type of a timer switch which perform
switch functions on 24-hour cycles. They are used in processes
and applications that require on-off switching in patterns.
Fuses and Fuse Holders
• A fuse is an electrical safety device that operates to
provide overcurrent protection for an electrical circuit.
• The essential component of a fuse is a metal wire or strip that melts
when too much current flows through it, thereby stopping or
interrupting the current.
• A fuse is a sacrificial device; once a fuse has operated it is an open
circuit, and must be replaced or rewired, depending on its type.
• A fuse offers an automatic means of removing power from a faulty
system; often abbreviated to ADS (Automatic Disconnection of
Supply).
• There are thousands of different fuse designs which have specific
current and voltage ratings, breaking capacity, and response times.
• The time and current operating characteristics of fuses are chosen to
provide adequate protection without needless interruption.
• Short circuits, overloading, mismatched loads, or device failure are the
prime reasons for fuse operation.
Wire and Cable
Management
• Cable management is how cables are installed, maintained, and organized in
various working environments.
• Cable management can provide reduce risk of injury and save space and improve
the longevity and performance of systems and equipment.
• Cable management refers to management of electrical or optical cable in
a cabinet or an installation. The term is used for products, workmanship or
planning.
• Cables can easily become tangled, making them difficult to work with, sometimes
resulting in devices accidentally becoming unplugged as one attempts to move a
cable.
• Tangled cables are known as "cable spaghetti", and any kind of problem diagnosis
and future updates to such enclosures could be very difficult.
• Cable management both supports and contains cables during installation and
makes subsequent maintenance or changes to the cable system easier.
• Products such as cable trays, cable ladders, and cable baskets are used to support a
cable through cabling routes.
Electrical Outlets and Termination Units
• Industrial plugs and receptacles
• Junction boxes
• Terminal blocks
• Cable glands and connectors
Cable Trays
• A cable tray is a unit or assembly of units or sections and
associated fittings forming a rigid structural system used to
securely fasten or support cables and raceways.
• In the electrical wiring of buildings, a cable tray system is used to
support insulated electrical cables used for power distribution,
control, and communication.
• Cable trays are used as an alternative to open wiring or electrical
conduit systems and are commonly used for cable management in
commercial and industrial construction.
• Cable Trays are especially useful in situations where changes to a
wiring system are anticipated, since new cables can be installed
by laying them in the tray, instead of pulling them through a pipe.
Electric Wire Conduits
• An electrical conduit is a metal or plastic pipe through
which electrical wires are run.
• Conduits are available in either rigid or flexible forms
• A conduit protects the wires and is used in exposed locations as
well as in unfinished areas (like basements, crawlspaces, and
attics), and in surface-mounted installations outdoors.
• Electrical conduits can also be embedded in concrete and
completely concealed like the case in most indoor wiring.
• Rigid metal (EMT), rigid plastic (PVC), or flexible metal (FMC), is
limited as regards the maximum number of electrical wires that can
be run inside the conduit.