Series MC Guideform Specification


This specification covers the detail requirements for RF (Radio Frequency) interference power line filters, hereinafter referred to as “filters”, to be used on RF shielded enclosures and parent rooms where referenced in each specification section for those constructions.

  • Related Sections
  • Specification Section 136073 – RF Testing for Shielded Enclosures
  • Division 13 – Parent Room Specifications
  • Division 13 – Enclosure Specifications
  • MIL-F-15733: General specifications for filters and capacitors, military
  • MIL-STD-202: Test methods for component parts, military
  • MIL-STD-220: Test method of insertion loss as applicable
  • OR CISPR17
  • NFPA 70: National Electrical Code, standards
  • NEMA ICS6: Enclosures
  • UL1283: Underwriters Lab filter requirements
  • UL486A-486B: Wire Connectors
  • Parent Room (PR): Outer room which contains a shielded enclosure.
  • Shielded Enclosure (SE): A special construction with specific attenuation properties for the applicable enclosure type that is tested in relation to those properties.
Government approval is required for submittals with a “G” designation; submittals nor having a “G” designation are for Contractor Quality Control approval. When used, a designation following the “G” designation identifies the office that will review the submittal for the Government.  The following shall be submitted in accordance with section 01 33 00.

  • SD-02 Shop Drawings
  • Filter assemblies
  • Installation details shall show location, number, and method of penetrating shielding material.
  • SD-03 Product Data
  • Filter units
  • Filter enclosure
  • Power factor correction coils
  • For filter units, submit data for each ampere rating, frequency, and voltage.
  • SD-09 Manufacturer’s Field Reports
  • Insertion loss test
  • Voltage drop test
  • Harmonic distortion test
  • Terminal strength test
  • Temperature rating test
  • Current rating test
  • RF radiation test of load terminal compartment
  • Dielectric withstand voltage test
  • RF current attenuation test
  • Submit reports indicating results of the test specified in paragraph entitled “Source Quality Control”
  • SD-10 Operation and Maintenance Data
  • Filter assemblies, Data Package 5
  • Submit in accordance with section 01 78 23 OPERATION AND MAINTENANCE DATA
Radio frequency interference (RFI) power line filters for shielding enclosures specified in this section and shall be manufactured by the shielded enclosure manufacturer.

Provide filtered units for operation on electric power lines of 50 to 60Hz rated as indicated.  Design filters to reduce conducted RF energy in electric power lines according to MIL-PRF-15733 an UL 1283 for facility type power line filters.  Insertion loss between load side of filter and power supply side shall be not less than 100dB at 14kHz to 10 GHz.

Each filter unit shall be capable of being mounted individually and shall include one filter for each phase conductor of the power line and the neutral conductor.  Neutral conductor shall be in accordance with “Isolation / Non Isolation Installation Guidelines.” 2.3.1 Filter Enclosure:
Provide filter units in RF modified NEMA type 1 in accordance with enclosures made of steel not less than 14 gauge with welded seams.  Enclosures shall be hot tin dipped or primed with a coat primer after fabrication and welding.

2.3.2 Internal Configuration:
Separate load terminal compartment from power input compartment by a solid steel barrier plate of same gage as filter unit enclosure extending across entire width of enclosure.  Power input compartment shall house individual power line filters and power the input terminals of filters.

2.3.3 Individual Filter Mounting:
Attach load terminal end of individual filter cases to RF barrier plate between the two compartments to provide an RF tight seal between RF barrier plate and filter case.  Load terminals of filters shall project through openings in the RF barrier plate into the load terminal compartment.  Attach case of each filter to enclosure to prevent stress from being applied to RF seal between filter case and RF barrier plate.

2.3.4 Neutral Connection:
When neutral conductor is not filtered, route it through the enclosure and connect it to a stud welded to each side of the RF barrier plate, so that the neutral is electrically connected to the filter unit enclosure.

2.3.5 Conduit Connections to Enclosures:
Load terminal and power input compartments shall have no knockouts, and each compartment shall have one threaded conduit hub.  Seam weld hubs in place and size and locate hubs as required for conduits indicated.

2.3.6 Access Openings and Cover Plates:
Provide access from front of enclosure.  Access opening for load terminal compartment shall provide clear access to filter load terminals and standoff insulator terminals or insulated terminal block specified herein.  Provide power input compartment opening with clear access to filter power input terminals and standoff insulator terminals or insulated terminal blocks specified herein.  Provide easy removal of individual filters from enclosure.  Provide two access cover plates.  One plate shall cover the access opening to the load terminal compartment only and when secured in place shall provide an RF tight seal with the compartment it covers.  Second access cover plate may abut or overlap cover plate for load terminal compartment and shall cover power input compartment.  Provide an RF gasket for load terminal compartment cover plate.  Secure cover plate with bolts having maximum spacing of 75mm.  Fabricate access cover plates of steel not less than 14 gage, and having the same finish as specified for the enclosure.  Attach plates so that they may be easily removed and replaced.

2.3.7 RF Attenuation Requirements for Load Terminal Compartment:
Load terminal compartment shall provide an attenuation of not less than 100 dB to radiated RF energy from 14 kHz to 10 GHz with individual power line filters mounted and access cover plate attached.

Equip individual filters within a unit insulated terminals and incorporate suitably sized flexible leads from insulated filter terminals to standoff insulator terminals or insulated terminal blocks.  Mount standoff insulator terminals or insulated terminal blocks in terminal compartments.  Provide solderless lugs for connecting phase and neutral wires to filter units.  Lugs shall be hex head bolt or screw type and shall conform to UL 486A-486B.  Space live parts in accordance to UL 1283.  Filter leads shall be copper.


2.5.1 Filter Construction:
After filter is filled with impregnating or encapsulating compound, weld seams.  When solid potting compound is used to fill filter, filters may be mechanically secured and sealed with solder.  Use hermetically sealed impregnated capacitors, or vacuum impregnate complete filter assembly.  Fabricate individual filter cases from not less than a 16-gage steel and finish cases with corrosion-resistant plating.

2.5.2 Impregnating or Potting Compound:
Fill filter with an impregnating or potting compound meeting requirements of MIL-GPF-15733 and having a flashpoint for operating temperature range B as defined in table VIII of MIL-GPF-15733.

2.5.3 Overload Requirements:
Provide as specified in MIL-GPF-15733.

2.5.4 Current Rating:
Provide filters in ratings indicated.

2.5.5 Pass Band:
Provide pass band suitable for use with 50 to 60-Hz power source.  Total harmonics generated by the insertion of a power line filter shall not increase line voltage distortion more than 2.5 percent with a unity power factor load.

2.5.6 Voltage Rating:
As required for circuits indicated.  Direct current (resistive) Voltage drop through filter shall not exceed 0.5 volt when filter is operating at rated current.  The 50 to 60Hz ac voltage, within resistive load variations from 10 percent to 100 percent rated load, shall vary not more than plus or minus one percent of rated line voltage at unity power factor.

2.5.7 Drainage of Stored Charge
Provide filters with bleeder resistors to drain stored charge from capacitors when power is shut off.  Provide drainage of stored charge in accordance with NFPA 70, Article 460-6.

2.5.8 Temperature Rise:
Temperature rise shall not exceed 25 degrees C when operating at full rated load in a free space environment equivalent to that specified in MIL-GPF-15733 with an ambient temperature of 65 degrees C.  When filters are mounted in an enclosure as specified herein, temp rise of hottest filter shall not exceed 40 degrees C at full load when operating in an ambient temp of 65 degrees C.  Materials and components of filter shall not exceed maximum acceptable temps specified in UL 1283.

2.5.9 Dielectric Withstand Voltage:
Provide filters which, as a minimum, conform to values of dielectric withstand voltage specified in MIL-GPF-15733.

Provide manufacturer’s nameplate on each filter unit stating rated current, rated voltage, operating frequency, number of phases for which filter unit is designed, manufacturer’s name, total filter weight, and model number.  Mount nameplate on filter unit to be visible after installation without removing cover plates or disturbing interior parts or wiring.  Mark each individual filter case with rated current, rated voltage, manufacturer’s name, type of impregnating or potting compound, operating frequency, and model number.  In addition, mark individual filter cases and the filter enclosures with the following nameplate: “WARNING: Before working on filters, terminals must be grounded to ensure discharge of capacitors.”  Attach nameplates with epoxy, rivets, or sheet metal screws.

Perform factory tests for each filter unit and filter assembly.  The Contracting Officer will witness the specified factory tests.  Notify Contracting Officer at least 30 days before factory tests are scheduled to be performed.  Test data shall include a detailed description of the test instrumentation and equipment, including calibrating dates, a detailed description of the test procedure, and recorded test data.  Apply electrical ratings, tests, and requirements specified herein to unity power factor loads on the filter.  Perform dielectric withstand voltage production line test in accordance with UL 1283.

2.7.1 Insertion Loss Test:
Perform insertion loss measurements using procedures defined in MIL-STD-220 with the buffer networks modified to permit valid measurements down to 14 kHz.  The impedance of the modified buffer network shall be at least 10 times that of the filter under test when making the insertion loss test at 14 kHz.  Perform insertion loss measurements at 25 percent rated load, 50 percent rated load, and 100 percent rated load over the frequency range of 14 kHz to 1 GHz.  Results of insertion loss test shall be not less than 100dB.

2.7.2 Voltage Drop Test:
Measure ac voltage drop at output and input terminals of filter using the method of MIL-GPF-15733.  Make ac voltage measurements at rated voltage and frequency at 25 percent, 50 percent, and 100 percent rated load.

2.7.3 Harmonic Distortion Test:
Measure total harmonic distortion at the input and output terminals of the filter when operating at 25 percent, 50 percent, and 100 percent rated load with a unity power factor load.  Make measurements using a spectrum analyzer having a dynamic range of 100 dB or greater as a minimum frequency range of 1 kHz to 10 GHz.

2.7.4 Terminal Strength Test:
Test standoff terminals and filter terminals with external threads in accordance with method 211 of MIL-STD-220, Test Condition E. Determine applied torque values from table XIV of MIL-PRF-15733.

2.7.5 Temperature Rating Test:
Perform temp rating test in an environment having the test conditions and reference conditions specified in MIL-STD-220.

2.7.6 Current Rating and Overload Test
Test current rating and overload in accordance with MIL-GPF-15733.

2.7.7 RF Radiation Test:
Perform RF radiation test on the load terminal compartment of the filter unit in accordance with the manufacturer’s standard method of test.

2.7.8 Dielectric Withstand Voltage Test:
Perform the dielectric withstand voltage test in accordance with MIL-GPF-15733.

2.8 RF Current Attenuation Test:
Perform the following test if MIL-STD-220 tests are not performed on the specific filters provided under this contract.  Alternatively, the filter manufacturer may perform the following test in lieu of MIL-STD-220 tests.  Perform RF current attenuation test on the individual filters rated 1000 amperes and below by injecting RF current through the filters at 14 kHz, 100 kHz, 1 MHz, and 20 MHz; measuring the input and output RF current; and recording the results.  Test setup shall be as shown in figure 1.  Testing and measuring equipment required to perform the test shall be rejected, regardless of the results of other tests specified in this section.  Test procedure shall be as follows:

  • Set up signal generator and current source and data acquisition equipment in the configuration indicated and perform calibrations.
  • Weld a wire lug to the filter’s case in the output terminal compartment and attach a wire sized to carry filter rated current between the lug and filter output terminal as shown. Wire shall be no longer than necessary to make connections at each end.
  • Inject a current into the circuit under test at the lowest available output from the signal generator and current source.
  • Observe readout from spectrum analyzer to ensure proper equipment connections, operator safety, and expected equipment response before injecting rated current into test setup.
  • Apply filter rated current for 5 mins before measuring output RF current at 14kHz. Repeat this procedure at each of the other frequencies specified and record the results after each test at each frequency.
  • Filters specified as meeting MIL-STD-220 limits shall fall within the dB limits shown in table 2.
  • De-energize the test setup, remove filter, insert the next filter to be tested, and repeat the specified test procedure. Individual Filters:
Test temp rise in accordance with MIL-GPF-15733. Enclosed Filters:
Test filters provided in enclosures as a unit with the enclosures.


NFPA 70:
Install filter assemblies on the outer surface of the shielding enclosure and support them independently from the shielding.  Coordinate mounting of the power filter units with other filters and shielding enclosure penetrations.

Provide brass ground stud on line side of filter terminal compartment.

Paint the exterior surface of individually mounted filters as specified in section 09 90 00 PAINTS AND COATINGS section 26 00 00 . 00 20 BASIC ELECTRICAL MATERIALS AND METHODS.  Paint color shall be manufacturer’s standard.  Clean grounding surfaces so that they are free of paint and insulating material.

  • Current Sensing Probe
  • Equipment List for Filter Attenuation Test Using Current Injection Probe.
  • Signal Generator
  • Current Injection Probe
  • Current Sensing Probe
  • EMI Meter/Spectrum Analyzer
  • Power Amplifier
  • Current Source
Equivalent Attenuation Values for Bench Test Measurements.

125V, 100 dB at 14kHz:
Current Rating (Amps):
MIL-STD-220A + / \ Attenuation at 14kHz (dB):
277V, 100 dB at 14kHz:
Current Rating (Amps):
Attenuation at 14kHz (dB):