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Primary Current
250% Primary
Current
Not more than
250%
Specification Guide for Transformers
General
Single and three phase distribution transformers (600 Volt and below)
Provide and install, as referenced on the electrical plans, enclosed dry type transformers as
manufactured by Sola/Hevi-Duty or approved equal.
Standards
Transformers must be listed by Underwriters Laboratory, certified with Canadian Standards
Association and designed, constructed and rated in accordance with NEMA ST 20 and
applicable IEEE & OSHA specifications.
Construction
Cores
All transformer cores shall be constructed of low loss, high quality, electrical grade laminate
steel. By design, the flux density is to be kept well below the saturation level to reduce audible
sound level and minimize core losses. The core volume shall allow operation at 10% above rated
primary voltage at no load without exceeding the temperature rise of the unit.
Coils
Coil conductors shall be either aluminum or copper and continuous. The entire core and coil
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assembly shall be impregnated with a thermal setting varnish and cured to reduce hot spots
in the coils and seal out moisture. Coils with exposed magnet wire will not be acceptable.
Transformers shall have common core construction.
All transformers shall incorporate a faraday (electrostatic) shield between primary and
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secondary windings for the attenuation of voltage spikes, line noise and voltage transients.
Transformers shall be provided with six 2.5% full capacity taps – two above and four below
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primary rated voltage.
General purpose transformers are classified as isolation transformers.
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Enclosures
Vertex Edge System
Secondary Cur-
rent
Less than 9
amps
9 amps or
more
Overcurrent Protection Rating
167 % of maximum
125% of rated primary current (or next highest
standard rating)
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User Manual
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