Ventilation; Accessibility; Transformer Sound Levels; Cable Connections - HPS NH Serie Guía De Instalación, Operación Y Mantenimiento

locations capable of supporting their weight with the
proper accessories attached. Refer to Appendix B
(page 8) for wall mounting kits.
Conventional open ventilated dry-type
transformers have a bottom screen for air convection.
When transformers are mounted above the ground
surface a catcher plate should be installed under each
transformer as a safety precaution against any hot
particles that may fall through the screen in the event
of a faulted condition. Refer to Appendix B (page 8).
It is important that ventilated transformers be
installed in a dry area where the ambient air is clean and free of dust, dirt, corrosive fumes, moisture, heat
or other adverse conditions. Transformers should not
be installed in such a place having the possibility of
water logging inside the enclosure.
In the event that a transformer has been
subjected to moisture or dampness before installation,
ensure that it is completely cleaned and dried before
energization. The blowing of warmed air through the
transformer is recommended to dry internal
components. Refer to the section on dry-out of
transformers.
b) Indoor/Outdoor Transformers with Non-
Ventilated Type 4, 4X or 12 Enclosures.
Transformers equipped with non-ventilated type
4, 4X or 12 enclosures maybe located either indoors or
outdoors in any similar location noted above. Non-
ventilated enclosed transformers, although slightly
larger, offer much greater protection against a variety
of elements such as dust, dirt, snow, moisture, rain
etc.
For any outdoor location, the appropriate
applicable codes must be followed including cable
installation and hardware suitable for outdoor service.

VENTILATION

Transformers are required to be installed in an
area where they can be cooled by means of the free
circulation of air where the average ambient
temperature is 30°C (86°F) and should not exceed
40°C (104°F) at any time.
Adequate ventilation is essential for transformers
to meet their nameplate kVA capability. All general
purpose transformers should be located away from
walls or any other obstructions (at least 6 inches when
floor mounted and 4 inches when wall mounted) to
allow free, clean circulation of air through the
ventilation openings or around a non-ventilated unit.

ACCESSIBILITY

NEC standards require that transformers be
accessible for inspection and located accordingly.
However, transformers should not be located in
areas where stored items are likely to interfere with
either natural air convection or the capability to have
them inspected. Passage ways or other areas where
people could be exposed to live parts during
inspection should also be avoided.
Adequate protection should be provided under
any circumstances.

TRANSFORMER SOUND LEVELS

Transformers are an electrically energized
apparatus and by their nature emit sound due to their
component materials.
Transformers are required to meet NEMA
standards for the maximum sound levels permissible.
These sound level standards vary from 40 to 60 DB
and hence, can be an annoyance if located in close
proximity to where people work or reside.
Care should therefore be exercised in selecting
sites for transformers particularly to avoid sensitive
areas like hospitals, classrooms, medical or office
facilities.
The following guidelines may be helpful:
 Units should be mounted away from corners or
reflecting walls or ceilings.
 Cable or other flexible conduit should be
considered to make connections.
 All dry-type transformers are provided with
isolation rubber mounts between the core and
coil assembly and the enclosure. However,
sound absorbing vibration isolators may also be
installed between the transformer and its
mounting surface.
 Acoustically absorbing materials could be
considered for walls and ceilings around the
unit.
 The location of the unit should be located as
far as practical from areas where sound levels
could be considered undesirable.

CABLE CONNECTIONS

The connecting cable size is determined from the
line current rating of the transformers primary and
secondary windings and may be selected from the
information in Appendix A (page 7). Cables rated for at
least 90°C (194°F) is recommended as are ALC9CU
lugs.
Convenient pre-punched knockouts are provided
on all ventilated transformer enclosures up to 150 kVA
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