A cycling and flow of knowledge and ideas.

Monday, 3 November 2014

Markings and Symbols on transformers and electronic transformers

Symbols and marks on electronic transformer I have been looking at the symbols which are found printed on transformers. This actually proved much more difficult than I imagined. Essentially the symbols represent standards and indicate the capabilities of the transformer.

Here are a number of covers of both lighting transformers and electronic transformers. Looking at the pictures it was apparent they had a lot of product information printed onto them. Most of the time I suspect it is only cursorily checked and it's assumed that the relevant tests and accreditation's have been sort and gained, for the particular country it was bought in.

Symbols and marks on electronic transformer
Symbols and marks on electronic transformer
Unsurprisingly, quite a lot of these symbols relate to standards the transformers comply with. So in the spirit of my previous posts, I thought it would be nice to list these dispersed snippets of information in one location. What I didn't expect was the difficulty in finding and documenting this information.

Symbols and marks on Magnetic transformer
Symbols and marks on Magnetic transformer
Annoyingly, I couldn't find a convenient Internet based English language document with the various symbols neatly stacked in one location, so I have had to scour information from Chinese, German and Italian documentation. If you are interested in what I used to identify these various symbol elements then please see my link to the references which I have at the end of this article and this will take you to my reference page. If you're interested then you can find the link to it here.

Sadly on a negative note, I'm of the opinion; If you cannot easily identify and confirm the standards these symbols represent, then they are little better than exotic decoration on the case!

Symbols and marks on electronic transformer
Symbols and marks on electronic transformer
I assume that many people have had transformers fitted without a second thought or understanding what, or why, compliance symbols are displayed on the case. Some of the information is quite useful to understand fitting requirements and suitability. If you do become curious then, hopefully, the table will give you some insight and comfort to know what these symbols actually indicate. Anyway below, I have compiled a table with symbols and their meanings that I've managed to find. I hope that my efforts to collate this information will be helpful to you.

Table of some common symbols found on Extra Low Voltage transformers


Explanation of symbol.
Inverted triangle with "F" in it
  • For discharge lamps for direct mounting on or at normal or slightly flammable building materials such as wood.
  • IEC Annex C.
  • If the value exceeds 130°C, "F" marked luminaires shall in addition be tested in accordance with IEC 60598-1 with respect to luminaires without temperature sensing controls.
Inverted triangle with "F" in it and a hat
  • For mounting in suitable order on normally flammable surfaces lamp, if thermal insulation material wraps up the lamp.
Inverted triangle with "F" in it but crossed through
  • Not intended for direct mounting on normally flammable surfaces suitable light.
  • Only suitable for mounting on non-flammable surfaces.
Inverted triangle with "P" in it
  • "Class P" thermally protected lamp control gear
  • lamp control gear incorporating a thermal protector which is intended to prevent overheating under any conditions of use and which will protect the luminaire mounting surface against overheating due to end-of-life effects.
Inverted triangle with "100" in it
  • Temperature declared thermally protected lamp control gear.
  • Lamp control gear incorporating means of protection against overheating to prevent the lamp control gear case temperature, under any conditions of use, from exceeding the indicated value lamp control gear marked with temperature values up to 130°C.
  • Provide protection against overheating due to end-of-life effects in accordance with luminaire marking requirements. See IEC 60598-1
  • Symbol for temperature declared, thermally protected control gear (see annex 6). The number in the triangle shall be the rated maximum case temperature in degrees Celsius assigned by the manufacturer, values increasing in 10°C increments.
  • In this example legend it indicates that it will operate to the temperature below or equal to 100°C.
House outline with inward arrow
  • Equipment designed for indoor use only.
  • The IEC 60417-5957 (ISO symbol does not have the arrow)

ta = 45°C

  • Ambient temperature.

tc = 75°C

  • Case temperature.
  • This acronym represents the term Saftey Extra Low Voltage but it can also mean Separated Extra Low Voltage. This is a standard which is different in different countries but generally means that it is less than 60V and is insulated from both the mains and ground circuits.
TUV rheinland safety mark
  • Meets the TUV Rheindland relevant safety standards.
  • Until 2012 now superseded.
VDE standard mark
  • The VDE(Verband Deutscher Elektrotechniker) means association of German electrical engineers.
  • The VDE mark denotes conformity with the VDE regulations or European or internationally harmonised standards and confirms the compliance with the safety requirements of the directive. The VDE mark stands for the safety of the product in terms of electrical, mechanical, thermal, toxic, radiological and other hazards.

Double inverted triangles with "M" in them
  • Complies with the German standards body, DIN VDE 0710-14
  • Electronic transformer can be placed on wood surfaces in accordance with: DIN VDE 0710-14

One box inside another

  • Class II equipment according to IEC 60536
  • Class II insulation: no earth connection is required.
  • Double insulated category of device.

Circle with a hat in it

  • Independent electronic transformer: it can be installed separately outside a lighting fixture without an additional housing.
  • To identify independent lighting auxiliaries for discharge lamps such as fluorescent lamps or high-pressure mercury vapour, low-pressure sodium vapour, high-pressure sodium vapour and metal halide lamps.
  • This symbol is taken from IEC 60920, IEC 60922, IEC 60926, IEC 60928 and IEC 601046.
  •  IEC60417-5138 (DB 2002-10)
Shield with intersecting circles in it
  • This is a compound symbol made from the following elements which can be mixed and matched, re Annex C
  • Intersecting circles
    • Means transformer.
    Intersecting circles with line in middle
    • Means isolating control gear.
    • IEC60417-5221 (DB 2002-10)
    Intersecting circles with line in middle open circuit
    • Means non short circuit proof isolating control gear.
    • IEC60417-5944 (DB:2013-06) 
    Intersecting circles with line in middle short circuit
    • Means short circuit proof isolating control gear.
    • IEC60417-5945 (DB:2013-06)
    Shield with intersecting circles in it
    • Means safety isolating control gear with short circuit protection.
    • IEC60417-5947 (DB:2002-10)

For further reading and references: please see my resource page


  1. Very useful..! People say we can find anything in internet, but nobody recognizes that someone had to invest time to make it happen. So thank you!


  2. Very useful..! People say we can find anything in internet, but nobody recognizes that someone had to invest time to make it happen. So thank you!

  3. Very useful, just what I was looking for. One more question - what would EMC and SGS product in the same "box" mean on an electrical transformer? Thank you!

    1. Hi Tammy,
      The acronym SGS represents the testing centre. SGS originally stood for "Société Générale de Surveillance" which is a Swiss based international testing/inspection centre. The EMC represents the term, "ElectroMagnetic Compatibility," and is a standard that SGS would test to. The EMC standard would be different in different countries but for Europe that would mean conforming to: "EMC Directive 2004/108/EC."

      Thanks to the font of all knowledge that is Wikipedia, I hope that answers your query sufficiently.

    2. Oh...! ElectroMagnetic Compatibility (EMC) relates to electrical interference such as, but not limited to, communication devices like: radios, TVs, mobiles etc.

  4. would anyone know what the marking of a transformer terminal as SCN would mean ?

    1. I Would have to see the transformer to get some context as the most likely suggestion but the abbreviation for "screen" comes to mind. If the transformer has a metal outer jacket that would be earthed to act as the screen to help reduce electrical noise and/or interference. Most people would just ground a screen but that is not necessarily the optimal choice where you might have unintended resonance or end up generating a ground loop by accident. Manufacturer's specs, if you can find them, would be a good start. Here is an interesting starting point for your investigation: Transformer screening

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