oil-immersed equipment will be provided with an
explosion-proof or dust-ignition-proof housing, as
appropriate. Transformer tap adjusters will be
provided in cases where an automatic system is not
provided.
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Rectifier unit shall consist of a transformer, rectifying elements,
[transformer tap adjuster,] terminal block, [one dc output voltmeter, one
dc output ammeter,] [one combination volt-ammeter,] one toggle switch for
each meter, fuse holders with fuses for each dc circuit, variable
resistors, an ac power-supply circuit breaker, lightning arresters for both
input and output; all wired and assembled in a weatherproof cabinet. The
overall efficiency of the rectifier shall be not less than 65 percent when
operated at nameplate rating and shall be capable of supplying continuous
full rated output at an ambient temperature of 44 degrees C 112 degrees F
in full sunlight with expected life in excess of 10 years.
2.2.1.1
Transformer
Transformer shall conform to UL 506.
2.2.1.2
Rectifying Elements
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NOTE: Below about 500 volt-amperes of dc rated
output, single phase selenium rectifiers cost less
to acquire and operate than silicon rectifiers.
Above 1000 volt-amperes silicon rectifiers are more
economical for both single phase and three phase.
Silicon rectifiers are more economical to repair.
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Rectifying elements shall be [silicon diodes] [selenium cells] connected to
provide full-wave rectification. [Silicon diodes shall be protected by
selenium surge cells or varistors against over-voltage surges and by
current limiting devices against over-current surges.]
2.2.1.3
Meters
Meters shall be accurate to within plus or minus 2 percent of full scale at
27 degrees C 80 degrees F, and shall possess temperature stability above
and below 27 degrees C 80 degrees F of at least 1 percent per 5 degrees C
10 degrees F. Separate meters shall be 63.5 mm 2-1/2 inch nominal size or
larger.
2.2.1.4
Circuit Breaker
A [single] [double] [three]-pole, flush-mounted, fully magnetic, properly
rated nonterminal type circuit breaker shall be installed in the primary
circuit of the rectifier supply transformer.
2.2.1.5
Fuses
Cartridge-type fuses conforming to NEMA FU 1 with suitable fuse holders
shall be provided in each leg of the dc circuit.
SECTION 13111A
Page 13
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