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Audio-video transformer differences

Differences noted below are between UL 1411, fifth edition with pages dated February 18, 1998 and UL 6500, second edition with revisions dated up to September 28, 2001

Topic

Requirement

UL 1411

UL 6500

Marking

Manufacturer's name, trademark, or other descriptive marking

29.1

14.3.1

Type or catalog number

29.1

14.3.1

Factory identification code -- required if transformer is produced or assembled at more than one manufacturing location

29.2

5.1.k

Enclosure

Material used as all or part of the enclosure (end bells) shall have a minimum flammability rating of V-0 in accordance with UL 94

4.1

-

Materials used as part of a fire enclosure shall have a minimum flammability rating of V-2 in accordance with UL 94

-

20.2.1

Potting compound shall have a minimum flammability rating of HB in accordance with UL 94

4.3

-

Encapsulation compound covering exterior surface of a transformer shall have a minimum flammability rating of HB in accordance with UL 94

4.4

-

Lead insulation

Rated for the voltage and temperature reached under any condition of actual use

5.1.1

8.9.1

Rated VW-1

5.1.1

20.1.2

Sleeving and tubing

Rated for the voltage and temperature reached under any condition of actual use

-

8.9.1

Rated VW-1

5.3.1

20.1.2

Tape

Flame retardant

5.3.1

20.1.2

Flexible cords

Comply with UL 817 and be rated VW-1

5.2.1

16.1

NISPT-2 minimum

-

Table 9A

Attachment plug

Shall be polarized type

5.2.2

-

Comply with UL 498

5.2.2

Annex S

Conductors of a parallel flexible cord of a transformer shall not be split external to the transformer enclosure (end-bells)

5.2.3

-

Connections Between leads

Joints not soldered shall be securely connected, i.e., wire nuts, welded, etc.

5.4.1

8.11

Solder joints shall be mechanically secure before soldering

5.4.1

8.11

Mechanical securement of a lead is not required when separation of the connection does not result in a risk of fire or electric shock

5.4.2

8.11

Strain relief

Shall be provided so that stress on each individual lead is not transmitted to the connection inside the transformer

5.5.2

-

Strain Relief Test

25.1

-

Openings for wires/flexible cords

Flexible cords or wires connected in the primary circuit shall be free of burrs and fins that may damage the conductor insulation

5.6.1

16.6

Unless a bushing is provided, the edges of an opening in a sheet-metal enclosure shall be rolled or formed

5.6.1

16.6

Bushings

Shall be secured in place

5.7.1

16.6

Interconnection of windings

(Conductive path resistors) a discrete component that provides a conductive connection between the primary and secondary winding of a transformer shall have a resistance that limits the leakage current in the end use to an acceptable value that does not exceed 12-megaohms. The wattage rating of the component shall be at least ½ watt.

6.1

-

A capacitor with or without a built-in shunt resistor shall comply with UL 1414

6.3

-

Protective devices

A protective device (fuse, overtemperature and overcurrent protector, eutectic material) employed as part of the transformer shall comply with the requirements for the construction, performance, and use for such a device, i.e., shall be UL Recognized Components

7

-

Thermal cutouts shall comply with UL 8730-2-9

-

14.5.1.1

Thermal links shall comply with UL 1020

-

14.5.1.2

Fuse-links shall comply with UL 248-14

-

14.5.2.1

Separate current-limiting material

Separate current-limiting impedance's, such as positive temperature coefficient (PTC), shall comply with UL 1434

8.1

-

PTC's shall comply with IEC 60738 or UL 1434

-

14.5.3

Resistors complying with UL 1412 may be provided

8.1

-

Resistors complying with surge test may be provided. Also, resistors complying with UL 1412 may be provided if the resistance does not differ by more than 20%

-

14.1

Live part insulating material

Insulating material for the support of terminals operating at 42.4 volts peak or more or having available power of more than 15 W shall have:

  1. Acceptable mechanical strength
  2. Minimum flammability rating of V-2 in accordance with UL 94
  3. Temperature rating suitable for end-use application
  4. Suitability for the sole support of live parts as determined by investigation regarding factors such as hot-wire ignition, high-current-arc ignition, volume resistivity, and dielectric strength

See clause 9.1 for exceptions to the above requirements

9.1

-

Polymeric or fiber parts in contact with a component located in a potential ignition source (see clause 2.8.11 for definition) circuit shall have a minimum flammability rating of V-2

-

20.1.4, table 13

Bobbin material

Bobbin material must be UL Recognized V-2 at minimum bobbin thickness except where the bobbin thickness is < 1/16-inch. Bobbin material with a thickness < 1/16-inch must be UL Recognized V-2 at 1/16-inch.

10.1

-

May be rated HB or less if the transformer is encapsulated by material rated V-0 or better

10.1

-

Shall have a thickness of at least 0.4 mm

-

8.8, 14.3.4.1

Bobbin material must be UL Recognized V-2 at minimum bobbin thickness

-

20.1.4, table 13

UL 1411 insulation requirements

Note: the insulation requirements are based on the type of insulating materials employed within the transformer. The table below provides a summary of the requirements. For complete details a complete review of the requirements in clause 11 is required.

Topic

Requirement

UL 1411

Coil insulation

Insulation shall :

  1. Be resistant to moisture unless inherently moisture resistant. Acceptability of material based on insulation resistance test (see clause 26)
  2. Be of equivalent mechanical strength when compared to electrical grade paper
  3. Have equivalent dielectric voltage-withstand strength when compared to electrical grade paper
  4. Be acceptable for the temperature involved in the end-use product

11.3

Equivalent generic materials

Generic materials that have been found to be equivalent to electrical grade paper may be used.

13, table 13.1

Required locations for coil insulation

Electrical grade paper (having a total minimum thickness of 0.30 mm) or the equivalent of such insulation shall be used between:

  1. Uninsulated, primary wires of opposite polarity
  2. Multiple primary windings
  3. Body of a primary-connected thermal protector and the adjacent windings
  4. Body of a secondary-connected thermal protector located adjacent to a primary winding

11.6

Insulation between the primary and secondary windings and between the primary winding and the core shall be:

  1. Electrical grade paper >=0.30 mm thick
  2. Polymeric coil form >=0.64 mm thick
  3. Equivalent insulation material

11.7, 11.8

Insulation between the primary winding lead connections and the shield or the transformer enclosure (end bells) shall be:

  1. Electrical grade paper >=0.30 mm thick if used in conjunction with an air spacing of 1/2 that specified in 14.1
  2. Electrical grade paper >=0.58 mm thick if the insulation is in contact with the end bell
  3. Equivalent insulation material

11.9

Insulation between the crossover leads and the adjacent winding, transformer enclosure (end bells), or core shall be:

  1. Electrical grade paper >=0.30 mm thick
  2. Electrical grade paper having 1/2 the thickness specified in (a) if used in conjunction with an air spacing of 1/2 that specified in 14.1
  3. Equivalent insulation material

11.10

High frequency transformers

Requirements in clause 11.6 - 11.13 are not applicable to insulation in thin sheet materials, irrespective of its thickness, when used in high frequency transformers if:

  1. Employed in an end-product enclosure and not subject to handling or abrasion during operator servicing
  2. Insulation comprises three layers of material for which all combinations of two layers together comply with the dielectric voltage withstand test
  3. Insulation comprises at least two layers of material, each of which complies with the dielectric voltage withstand test

11.14

Outer-wrap and crossover-lead insulation

Shall not be less than 0.028 inch (0.71 mm) thick.

12.1

UL 6500 insulation requirements

The insulation requirements are based on the type of insulation required (basic, supplementary, reinforced or double insulation), the class of the end-product apparatus, i.e., class I or II, and the type of insulation materials employed within the transformer. In the end-product the apparatus shall provide protection from the user to accessible parts. Accessible parts require two levels of protection against electric shock. This can be achieved by one or more of the insulation types identified below.

The following definitions have been provided for your reference:

  • Class I -- product which has provision for grounding (i.e., accessible conductive parts are connected to the protective (earthing) conductor.
  • Class II - product which has no provision for grounding.
  • Basic insulation -- insulation applied to hazardous live parts to provide basic protection (one level) of protection against electric shock.
  • Supplementary insulation -- independent insulation used in conjunction with basic insulation in order to provide protection against electric shock in the event there is a failure of basic insulation.
  • Reinforced insulation -- provides two levels of protection against electric shock. A single insulation system equivalent to double insulation..
  • Double insulation -- provides two levels of protection against electric shock. Comprised of basic and supplementary insulation.

Note: the table below provides a summary of the requirements. For complete details a complete review of the requirements outlined in clause 8, 13, and 14.3 shall be conducted.

Topic

Requirement

UL 6500

Protection against electric shock

Insulation of hazardous live parts shall not be provided by hygroscopic materials.

  1. Compliance is checked inspection and/or
  2. Conducting humidity conditioning of insulating materials test (see clause 8.3)

8.3

Transformer employed in a class I apparatus -- insulation requirements

Insulation between hazardous live windings and accessible parts or parts intended to be connected to accessible conductive parts, i.e., iron core, shall be separated by basic insulation according to clause 8.8.

8.8, 14.3.5.2

Compliance of insulation is determined by:

  1. Humidity treatment test (see clause 10.2)
  2. Insulation resistance test (see clause 10.3)
  3. Dielectric strength test (see clause 10.3)
  4. Creepage and clearances of clause 13
  5. Requirements for protective screens (see clause 14.3.4.2)

8.8, 14.3.5.2

Transformer employed in a class II apparatus -- insulation requirements

Insulation between hazardous live windings and accessible parts or parts intended to be connected to accessible conductive parts, i.e., iron core, shall be separated by double or reinforced insulation according to clause 8.8.

8.8, 14.3.5.1

Compliance of insulation is determined by:

  1. Humidity treatment test (see clause 10.2)
  2. Insulation resistance test (see clause 10.3)
  3. Dielectric strength test (see clause 10.3)
  4. Creepage and clearances of clause 13

8.8, 14.3.5.1

Note: for coil formers (bobbins) or partition walls a thickness of 0.4 mm is required.

8.8, 14.3.5.1

UL 1411 spacing requirements

Note 1: the table below provides a summary of the spacing requirements. For complete details a complete review of the requirements outlined in clause 14 shall be conducted.

Note 2: the spacings identified below are required in addition to the insulation requirements of clause 11.

For various examples of bobbin wound transformers refer to figures 14.1, 14.2, 14.3, 14.4, and 14.5 of the standard.

Topic

Requirement

UL 1411

Spacings

Spacing shall be provided between:

  1. Uninsulated live primary parts of different potential
  2. Uninsulated live primary part and any dead metal part (core)
  3. Uninsulated live primary part and any uninsulated secondary part

14.1

Spacings shall comply with table 14.1

  1. Exception: does not apply to a transformer intended for use in an appliance where the core and secondary windings will be electrically isolated from all accessible metal parts.

Table 14.1

Table 14.1

Potential, volts (rms)

Through air (clearance), (mm)

Over surface

(Creepage)

Protected against dirt, (mm)

Not protected against dirt, (mm)

0 - 50

1.6

1.6

1.6

51-150

1.6

1.6

3.2

151 - 250

3.2

3.2

6.4

Note: the spacings apply to coils, crossover leads, splices, uninsulated lead wires, and any turn of the primary winding to any turn of the secondary winding. The spacings do not apply to turn-to-turn spacings of a coil.

UL 6500 creepage and clearance requirements

Note 1: the table below provides a summary of the spacing requirements. For complete details a complete review of the requirements outlined in clause 13 shall be conducted.

Note 2: the creepage and clearance distances identified below are required in addition to the insulation requirements of clause 8 and 14.3.

Topic

Requirement

UL 6500

Clearances and creepage distances

Creepage and clearance distances shall be provided between:

1.    Primary and secondary windings

  1. Primary windings and core
  2. Parts of different polarity directly connected to the mains

13

Creepage and Clearance distances shall comply with Figure 9, of the standard

Table 14.1

Creepage and clearance distances based on figure 9 of UL 6500

 

Potential volts (rms)

insulation type

Through air (clearance) &
over surface (creepage), (mm)

120

Basic or supplementary

1.5

240

Basic or supplementary

3.0

120

Reinforced

3.0

240

Reinforced

6.0

Exception: the creepage and clearance distances in the above table may be reduced by 1 mm for basic and supplementary insulation and 2 mm for reinforced insulation if all the following conditions are met:

  • They are not between accessible conductive parts of an enclosure and hazardous live parts, if they can be reduced by external forces, as specified in 9.1.7
  • They are maintained by rigid construction
  • Their insulation properties are not likely to be significantly affected by any deposition of conductive dust produced inside the apparatus

Creepage and clearances shall not be reduced below 2/3 of the values given in Figure 9

UL 1411 performance requirements

Note: the table below provides a summary of the performance requirements. For complete test specifications a complete review of the requirements outlined in the clause 17, 23, 24, 25, 26, & 27 identified in the table shall be conducted.

Topic

Requirement

UL 1411

Performance testing

When the following tests are not conducted as part of the transformer, they are to be considered in the end-product.

  1. Power input test (clause 18)
  2. Temperature test (clause 19)
  3. Abnormal operation tests, 7 hour or 15 day (clause 27)

17.3

Dielectric voltage-withstand test

Test specification:

  1. 2875 volt, 40 - 70 Hz sinusoidal potential shall be applied for a period of 1 minute

23.1.1

Test Location:

  1. Primary and core
  2. Primary and secondary

 

23.1.1

Thermoplastic bobbin temperature stability test

Test specification:

  1. Three samples shall be conditioning in an air-circulating oven for 7 hours
  2. Following conditioning samples subjected to a 900 Vac dielectric voltage-withstand test for 1 minute

24.1

Test location:

  1. Primary and core
  2. Primary and secondary

 

24.1

Strain relief test on insulated leads

Test specification:

  1. Force equal to the weight of the transformer (not less than 3 pounds and no more than 10 pounds)
  2. Force shall be applied for 1 minute

25.1

Insulation resistance test

Test specification:

  1. Sample is exposed for 24 hours to moist air having a relative humidity of 85 ± 5 percent at a temperature of 32.0 ± 2.0 ºC.
  2. Insulation resistance shall not be less than 10 megaohms

26.1

Test location:

  1. Primary and core
  2. Primary and secondary

26.1

UL 6500 performance requirements

Note: the table below provides a summary of the performance requirements. For complete test specifications a complete review of the requirements outlined in clause 10 shall be conducted.

Topic

Requirement

UL 1411

Humidity treatment

Test specifications:

  1. A sample shall be placed in a humidity chamber operating at one of the following conditions:
    1. 28 to 30 ºC with a relative humidity between 90-95% for a period of two days (48 hours)
    2. 38 to 42 ºC with a relative humidity between 90-95% for a period of five days (120 hours) for an apparatus to be used under tropical conditions

10.2

Insulation resistance and dielectric strength

Immediately following the humidity treatment test the sample shall be subjected to the following tests (see clause 10.3):

  1. Insulation resistance
  2. Dielectric strength

10.3

Test specification:

  1. Test voltages for dielectric strength and values for insulation resistance are provided
  2. Test voltages are based on the type of insulation provided, i.e., basic, supplementary, reinforced, or double insulation
  3. Tests shall be carried out for a period of 1 minute

10.3

Surge test

Insulation between accessible parts or parts connected to them and hazardous live parts shall be subjected to the voltage surge test.

10.1

Test specifications:

  1. 50 discharges, at a maximum rate of 12 per minute, from a 1 nF dump capacitor charged to 10 kV

10.1

Test locations:

  1. Primary and secondary
  2. Primary and core

10.1

Test is followed by:

  1. Dielectric strength test
  2. Insulation resistance test

10.1