The AC input of the rectifiers shall be 115, 230 or 460 VAC – single or three-phase – 60 Cycle.

ENCLOSURE

The rectifier case shall be NEMA 4X, completely weatherproof for outdoor use. The case shall be constructed of not less than eleven gauge steel. All fabrication welds shall be clean and smooth. The entire case shall be hot dip galvanized per ASTM-123. The cabinet shall be equipped with an instrument compartment welded to one end of the case prior to galvanizing. This compartment shall house the circuit breaker, output meters and the output terminals, and shall have a hinged door and lockable stainless steel latch. The lid on the oil chamber shall be hinged on one side and have a minimum of four stainless steel latches to provide a moisture proof seal. The gasket on the lid shall be an oil-resistant neoprene sponge. On rectifiers 500 watts and above, the transformer and stack shall be mounted on separate removable racks in the oil chamber. The internal horizontal panel on which the voltage adjustment taps, AC input terminals and DC terminals are mounted shall be at least four inches below the recommended oil level as marked within the oil chamber. All connecting wires from oil chamber to the instrument compartment shall be sealed with an oil resistant compound. These wires shall have a 1/2" gap in the insulation above oil level to prevent siphoning. Grounding lug to accommodate a #6 wire shall be provide on the outside of the cabinet.

TRANSFORMER

The transformer shall be specifically designed for use in a cathodic protection rectifier, having separate primary and secondary copper windings. Wire size on both windings is to be based on a minimum of 1,000 circular mils per ampere. The material used in the core of the transformers shall be of such quality that core losses do not exceed 0.62 watts per pound. The amount of core material shall be no less than the amount given by the following formula:

AC = The square root of the watts in the primary divided by 5.58
AC = The minimum core area in square inches, figured as the cross sectional area of that portion of the core which passes through the coil.

The transformer shall be immersed in class F transformer varnish until all taps, insulating materials, outer wrapping and coil windings have been completely saturated. The transformer will then be oven baked until completely dry.

When a three phase rectifier is specified, it shall be provided with a three phase transformer with three separate wound legs or three separate transformers.

The secondary shall have a sufficient number of coarse and fine taps to provide a minimum of 18 equal step of adjustment. These taps shall be brought out to link bar arrangement for adjusting the output of the rectifier.

The link bars shall be terminated on at least a 5/16" stud lug that has one end drilled out so that the transformer tap wire can be soldered to the back of the stud. Quick change plastic knobs with brass inserts shall be used to connect the link bars to the studs.

RECTIFYING ELEMENTS

The rectifier stack shall consist of high current density selenium cell arranged to give full wave rectification. Ratings shall be within the manufacturer’s recommended current rating for continuous operation with a 50°C ambient temperature. The RMS voltage rating of the rectifier stack shall be sufficient to withstand, without damage, the full output of the transformer secondary when the load is disconnected from the DC terminals, i.e., under open circuit conditions.

When silicon is used as the rectifying element, current rating for continuous operation shall be for 50°C. ambient and the PRV rating of the diodes shall be at least 1200 PIV. The diodes shall be protected against high voltage surges with selenium surge suppressors.

Current and voltage shall be de-rated for higher ambient temperature, where required, and in accordance with the manufacturers recommendations.

PROTECTIVE DEVICES

The entire unit is to be protected against overload and short circuit with a fully magnetic circuit breaker of proper rating connected between the AC supply and transformer primary.

Circuit breakers shall have two poles for single phase units and three poles for three phase units. In the case of silicon rectifiers only, fuses shall be inserted in one leg of the AC secondary of single phase units and in at least two of the secondary legs of a three phase unit. All fuses greater than 35 amps shall be bolt in style and shall not rely on pressure type fuse holders.

DC METERS

One DC voltmeter and one DC ammeter shall be provided. Each will have an accuracy of 2% full scale. Hoyt # 17/3 meters or approved equal shall have minimum scale lengths of 1-5/8". The ammeter shall be connected to an external shunt with and accuracy of at least 1%. The shunt shall be plainly marked to show ampere rating and millivolt drop. This shunt shall be mounted on the front panel of the rectifier so as to be readily accessible for meter accuracy checks.

DC TERMINALS

Solderless lugs rated for full rectifier output current shall be provided for the positive and negative output terminals of the rectifier and shall be mounted on an insulated panel. Output terminals shall be clearly identified on the panel as "Positive" and "Negative".

WIRING & CONDUCTORS

All wiring within the rectifier, except the meter circuits, shall be of the high temperature motor lead wire with a minimum of 105°C rating. Wire size shall be based on not less than 500 circular mils per ampere. All current carrying bolts, terminals and connections made through the panel shall be either soldered to the bolt head or made by use of double nut method, so as not to depend on the compression strength of the panel to maintain a tight connection. Tap changing studs and output lugs shall be a minimum of 5/16" diameter.

RECTIFIER DATA

Each rectifier shall be provided with an engraved metal nameplate with the following information.

1.  Name of manufacturer
2.  AC input voltage 
3.  AC input amperes 
4.  AC frequency
5.  Phase
6.  DC output volts
7.  DC output amperes
8.  Ambient temperature in °C.

In addition, a waterproof envelope, placed in a suitable holder in the rectifier door, shall contain a complete wiring diagram, operating and maintenance manual and a copy of the test data obtained on the final bench check out of the rectifier.

INSTRUMENT PANEL

Phenolic grade XXX, non conductive, moisture resistant, specifically designed for panel board use.

APPLICABLE STANDARDS

The rectifiers shall meet the appropriate sections of the following standards:
NEMA Publication No. MR 20-1958, reaffirmed by NEMA 1971 - Semiconductor Rectifiers, Cathodic Protection Units.
NEMA Standard Publication No. 250-1979, including Rev. No. 1 – December 1980, Enclosures for Electrical Equipment (1000 Volts maximum)