Quantcast Transformer Protection -10380118

Custom Search

MIL-HDBK-1038 Motor Protection.  A crane motor is considered in NEC Section
610-43 to be protected from overload by a properly selected branch circuit
overcurrent device.  The predecessor document to NEMA Publication No. ICS 8, Part
1, required the use of overload relay(s); now the use of any device which affords
protection from overload would be permitted.  However, NCC continues to require
the use of overload relays.
Unlike for other protective devices, motor nameplate amperes are used to
select the heater element in overload relays.  This is done for the protection of
a specific motor and may necessitate the replacement of the heater elements if
that motor is replaced with another motor. Control Circuit Protection.  Control circuit conductors are required in
NEC Section 610-53 to have overcurrent protection; however, they are considered
protected by an overcurrent device having a rating not in excess of 300 percent of
the conductors' ampacity. Transformer Protection.  Overcurrent protection of transformers is
required in NEC Section 450-3(b).  The primary of a transformer must be protected
by an overcurrent device rated or set at no more than 125 percent of the rated
primary current.  If the secondary of a transformer is protected by an overcurrent
device rated or set at not more than 125 percent of the rated secondary current,
the primary overcurrent protection device can be rated or set at no more than 250
percent of the rated primary current.  There are exceptions regarding the rating
or setting of overcurrent protective devices and, in NEC Section 430-72(c), for
motor control circuit transformers.  Also, there are specific requirements for
certain single-phase transformers in NEC Section 240-3(i).  These arrangements
only provide protection for the transformer; primary and secondary conductor
protection may have to be provided by other devices. Ancillary Circuit Protection.  Overcurrent protection of circuits
supplying ancillary equipment is selected based upon the applicable requirements
of the Code for the specific equipment.
Illumination.  Lighting equipment is installed on cranes for specific
illumination purposes.  In mercury exclusion areas fluorescent and high intensity
discharge lamps (which contain elemental mercury) must be installed within sealed
lenses or refractors which serve as a second means of containment for the mercury. Crane Passageways and Spaces.  On bridge cranes, footwalks are
illuminated.  Lighting is also provided in the operator's cab.  Switching is
On newer portal, floating, and container cranes, walkways, ladders, and
stairs are illuminated.  For stairways and ladders, switches are provided at both
the top and bottom; walkway lighting is switched locally.  The machinery house is
illuminated to 40 footcandles with a switch being at each entrance.  The
operator's cab is provided with two lighting systems, one provides white light and
the other red light.  Red lighting is needed for the operator to retain "night
Additionally on portal, floating, and container cranes, access lighting
is provided for use when the crane's electrical system is not energized.  This
system is supplied from the diesel engine starting batteries or other available


Privacy Statement - Copyright Information. - Contact Us

Integrated Publishing, Inc.