Introduction to EMC and Electrical safety

[audiox]

My idea is to collect here information about Electrical safety and EMC. I know that it is going to take a long time but I believe it is worth it. The emphasis will be in professional audio equipment. The point of view will be European but I hope that others find it usefull too.

I have two goals:
1. To make the DIY equipment built by the forum members more safe and EMC compatible.
2. To help those thinking of starting their own small business.

To be honest, this was the trigger:
http://www.gearslutz.com/board/high-end/101221-hand-crafted-labs-products-17.html#post4441700
I really hope that I never see something like that again.

I have asked Jonte Knif to help me. He is an example of person who has taken Electrical safety and EMC things very seriously in his business. I really hope that he has time to share his expertise.

If YOU have something to share or any comments please let me know.


EMC Directive

The EMC Directive 2004/108/EC governs on the one hand the electromagnetic emissions of equipment in order to ensure that they do not disturb radio and telecommunication as well as other equipment. In the other hand the Directive governs the immunity of such equipment to interference and seeks to ensure that they are not disturbed by radio emissions normally present.

List of harmonised standards (in case your application is not professional audio):
http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:C:2009:126:0001:0021:ENDF


Standards describing the requirements (and containing instructions how to do the measurements):

EN 55103-1: Electromagnetic compatibility. Product family standard for audio, video, audio-visual and entertainment lighting control apparatus for professional use. Emission

EN 55103-2: Electromagnetic compatibility. Product family standard for audio, video, audio-visual and entertainment lighting control apparatus for professional use. Immunity


Low Voltage Directive

The Low Voltage Directive 2006/95/EC seeks to ensure that electrical equipment within certain voltage limits both provides a high level of protection for European citizens and enjoys a Single Market in the European Union. The Directive covers electrical equipment designed for use with a voltage rating of between 50 and 1000 V for alternating current and between 75 and 1500 V for direct current. It should be noted that these voltage ratings refer to the voltage of the electrical input or output, not to voltages that may appear inside the equipment.

List of harmonised standards (in case your application is not professional audio):
http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:C:2009:126:0022:0100:ENDF


Standards describing the requirements (and containing instructions how to do the measurements):

EN 60065: Audio, video and similar electronic apparatus - Safety requirements


Also good to know:
RoHS directive
WEEE directive


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The following information is based on my conversation with an EU official (can be inaccurate).

The directives don't force to use official test houses or even test the product. Writing a declaration of conformity is enough. The manufacturer is naturally responsible that the product meets the requirements and suffers the consequences if it doesn't. It is a good idea to make sure that at least electrical safety and EMC emission requirements are met.

What happens if the authority finds out that your product doesn't meet the requirements of the directives? The most common sanction is a note. That is usually the consequence if the product doesn't meet the EMC requirements. Ban of sales is likely if there are safety weaknesses or the emission limits are exeeded roughly. In some extreme cases they can decide to collect back the equipment already sold (the manufacturer pays the costs). In practice it applies only to equipment that are very dangerous for the user. Only a few percent of equipment they have something to complaint are collected back.

If you are a small manufacturer making professional products, it is very unlikely that the authority ever test your product since they usually buy their test samples from normal shops. The amount of money that can be used for testing is also very limited. That is why they concentrate in consumer products that are widely used. It is quite common to select a theme every year (e.g. they buy a sample of every extension cord in the market). In practice the only possibility that a small manufacturer gets tested is that if someone reports to the authority that your products is dangereous.


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Disclaimer: This is just a start and this collection of information will never be complete. It can be and probably is inaccurate or dated. Use at your own risk.

 

[Jonte Knif]

Hi All,

I have asked Jonte Knif to help me. He is an example of person who has taken Electrical safety and EMC things very seriously in his business. I really hope that he has time to share his expertise.

Thanks. That is a bit of an overstatement. I am taking safety seriously but I'm not an expert outside EN60065 and basic tube gear.

I have some ideas how we could divide the topic. Lets see if anyone is interested, but I hope so!

1) requirements of the standard. Some parts are a bit hard to read. It is a standard written by safety engineers for safety engineers and that doesn't really make it easy reading for us mortals.
We have to figure out a way for all to have access to the paper if everyone doesn't feel like buying it. I don't know how that could be made legally...

2) basic info for DIY:rs. I am _sure_ that not every part of the standard has to be read and understood to make perfectly safe studio gear, but it gives extremely good info anyway. But not every issue is discussed in the standard. Actually I would say it is quite restricted and can not serve as a text book for safety.

3) hints for safe construction. Anything. Materials, parts, soldering. I'm sure we'll get a lot of info if people care to share it.

4) a thread for cursing, confusion, disturbance and annoyance because some of the requirements (and rip off test costs). The standards are sometimes strict to absurdity. We are dealing with rules written to make _any_ piece of equipment safe for _anyone_ in _any place_.  It also includes absurdities like the drop test. If your gear weighs less than 6kg (or was it 8kg) it is subjected to the test, and the drop is pretty severe and they think long and hard which direction causes the most damage and drop it several times. If it weighs more than 8kg the test is NOT REQUIRED. Big joke. I checked for fun that all my basic rack units weigh more than 8kg. Good for me.  If I send gear to be officially approved at least I get it back in shape.

-Jonte

 

[VacuumVoodoo]

This is a very good idea. This thread will be dealing with issues that may have legal consequences. I think a sort disclaimer is needed stressing that this is general information only, not a 100% foolproof guide guaranteed to make the equipment you design/build compliant with normative requirements.

As for professional equipment weighing over 8kg, this is a vibration test I had to do on my amps per EN60065:

I'll be happy to contribute with whatever info/knowledge on CE testing/certification I have.

 

[abbey road d enfer]

Safety is relatively easy, if you use your brains. You build a piece of gear, would you be confident to let your 5-year old kid (or grandson) play with it? If you have left unprotected bare live wires, left insufficient spacing between PSU components, if there is a hole in which he (or she) can put his (her) little fingers in, you won't... You'll also be careful at not letting the unit get too hot, with a well dimensioned mains transformer and a properly rated fuse in the unit.
EMC is another story. In terms of emissions, most of the analog stuff is simple. Things get a little more complicated when you use switching PSU's. You will need a mains filter, at least.
The worst is susceptibility. Your equipment is supposed to operate unharmed with a portable phone in its immediate vicinity. I reckon not many units pass this test, even with a CE marking. The biggest challenge is the electrical continuity of the enclosure. The typical construction of most rackmount gear (a flat front panel affixed to a tray and cover) does not lend itself to electrical continuity between the facia and the chassis; very often, a counter-facia is needed, which makes the box more expensive. Boxes using an extruded aluminium front rely on a large number of screws or a special conductive gasket.
And you will find out that some of these measures will hinder the performance of your equipment. The simplistic answer to the so-called Pin 1 problem, "stick Pin 1 to chassis ground" has created more problems than it has solved, because chassis ground is connected to safety ground, which is not the nice equipotential some would want us to believe.
It seems important to me to focus on the understanding of the mechanisms of electrical pollution. One needs to consider a ground connection as a series of wires of definite resistance AND as an inductance through which magnetic fields create voltage.

 

[dmills]

Not really sure how far I agree on the pin one thing....
Sure, current flows in the screen, so what (SCIN is seldom IME a problem in real installs)?

It only becomes a problem when that current either gets converted to a differential mode signal on the signal pair or when that current encounters something that is single ended or has a pin one problem, the rest of the time, who cares?
You do need to provide longitudinal mode suppression to suppress common mode as far as the internal electronics is concerned (CMRR drops fast with increasing frequency in most cases) and a input stage with a very high common mode impedance helps (as does low pass filtering at as close to the top of the audio band as you can without introducing weird phase shifts), but an input and output stage that will survive a GSM phone is really not that hard as long as you think about RF immunity from the start.

Alocrom 1000 treatment of the metalwork (if ally) really helps as it results in a surface layer that is actually conductive which makes a huge difference when it comes to not accidentally forming slot radiators.

I cannot remember the last time I built a box that picked up cell phones (Gram amps can be a bit of a challenge, but even then it is possible).

On the safety front, I would note that speaker outputs can in some cases push sufficient voltage to be a potential hazard (Speakons are a good answer to this), also output transformers in valve gear should consider what might happen in the event of a primary/secondary short (grounding one side of the output may be sufficient to protect against this?).

Regards, Dan.

 

[AudioJohn]

There is plenty of good information on EMC in the various articles by Tony Waldron:
http://www.fragrantsword.com/twaudio/

 

[bruno2000]

How about this?