Safety issues and CE Certification

[Bakmeel]

At school, I recently followed a few courses on electrical safety, EMC and CE certification.

I wonder how many people realise how often they put their own life at risk when using their home-built amplifiers, DAC's etc. 220V (or 110V) AC lines should not be taken lightly. Do your thoughts reach any further than an appropriate strain-relief on your power cord? Moreover, when I notice people start building amps for other people, I wonder they realise the legal trouble they can get in when something happens to the new owner? Have they ever even heard about CE certification?

There are three major considerations I believe someone should make when building a device, wether or not it is powered by AC lines, wether or not it's intended to be sold. I will try to illustrate with one or two examples. Try to think further on your own

1. Electrical safety
Metal cases should always be grounded DIRECTLY. Some people tend to use thermistors or tranzorbs for their ground connection. Apart from the fact that your case can be live for several seconds before the thermistor heats up, the residual resistance is more than enough to elevate the tension on the case to dangerous levels. Some people claim that high frequency noise on a ground line derates the "sound". I claim that one should never trade safety for sound quality.
When Power cords are directly connected to a device, first of all you should have a sturdy strain relief to prevent the power cord coming free of your device when someone exerts force on it. In dutch, see Elektuur website, I'm looking for an english page with similar info.

2. CE certification
This is something that legally only applies for builders that sometimes sell their devices on the European market. ALL devices that are intended to be sold (on a professional basis or not, and not only electrical devices), should have a CE mark. If not, your product can be removed from the market without question. Second, when a buyer gets an accident because of your device, not having a CE mark, the builder is legally responsible. Besides, It's not that difficult to obtain a CE mark. Stickers are available, so all you have to do is make sure your device is in confirmity with CE regulations (see CE marking website )

3. EMC
Not very often known, but a part of CE marking is ElectroMagenetic Compatibility. This has also to do with protecting signal lines, preventing ground loops, and blocking High-Frequency radiation. It's easy to test... fire an electric lighter near your device and see if it continues to work properly. Electric lichters cause strong EM fields when fired. Second, hold a battery powered AM radio near your device, and tune up and down. If reception of weak radio stations is disrupted, you have an EMC problem. EMC has also got to do with mains filters, and power line distortion.

I hope this gives a little push in the right direction. I know DIY builders are not professionals, but nevertheless, who would like to trade his life for an amplifier?

Bouke

[joensd]

I also think that you should always ground your metal chassis if it is a power amplifier or a power supply you´re building.
But what about all the commercial amplifiers like Sony, Pioneer?
They only come with AC-outlet cables that are 2-wire, so the earth is missing...
Do you think that´s safe?

Cheers
Jens

[Bakmeel]

Yes. Those devices are safe.

In that case, te device is so called "Class II". It is (should be) fitted with double isolated mains, and a transformer with seperate primary and secondary windings. There should be a seperation of at least 6 mm between mains and other conductive parts.

When a device is fitted with a ground wire, it becomes "Class I" In that case, single isolation between mains and other conductive parts is allowed (though double is always better). A transformer with seperate primary and secondary windings should be used, and all conductive parts on the device should have a proper ground connection.

Bouke

[Nelson Pass]

Nice point. I like to design as "Class II" and then ground
the chassis, also known as the "belt and suspenders" approach.

Thermistors are still usable from circuit ground to chassis, which
solves the ground loop problem nicely while still offering some
protection.

But let's be aware that lethal voltages are still lurking , even
when you are completely isolated from the AC line.


As regards the comments on CE and EMC, it's not all easy as that,
and getting these products properly certified is a money sink.

We recently invested a small fortune in the proper equipment and
facility to do EMC testing, and are considering opening a test
lab for other manufacturers to recoup our investment.

It is also absolutely no protection from getting sued if somebody
gets hurt, imagines they got hurt, or maybe is looking to get
hurt. Unfortunate, but true.

[purplepeople]

There is a trend towards designing electronic devices to use an AC wall adaptor for power. No doubt you've noticed some very large adaptors for some power-hungry devices.

This avoids having to certify with UL, CSA or CE for a device that is connected directly to the mains. This is because the AC adaptor must be certified in order to be available as a stand-alone unit.

It is makes it easier to design the RFI or EMI shielding to comply with the FCC or CRTC regulations (I don't know who the body is in Europe).

:)ensen.

[Nelson Pass]

I can just see an XA200 powered by a "wall wart"

[purplepeople]

Just use an external power cord, like the Sakura Humpty. Then it won't be a wall wart and more like a land lump. (heh!)

:)ensen.

[peranders]

Originally posted by Nelson Pass
We recently invested a small fortune in the proper equipment and
facility to do EMC testing, and are considering opening a test
lab for other manufacturers to recoup our investment.

Good for you Nelson that your company is one or two levels above the avarage! Maybe you want to sell your stuff in Europe? (See Freds comments about europeans.)

http://www.diyaudio.com/forums/showt...683#post244683

Originally posted by Fred Dieckmann


They will just have to sell them over here I guess. I thought the whole point of the CE approval was to keep European products from having to compete with American products. The 0.1 uf ceramics parked right next to the op amp seems like pretty good high frequency decoupling. It's an analog circuit that shouldn't radiate RFI and most of the RFI pick up is often from the cartridge and tone arm wiring. That might be an op amp with good RF characterists also, since they seem to be getting faster everytime I read a new data sheet.

[phase_accurate]

Maybe you want to sell your stuff in Europe?

There is at least a sales representative for PassLabs in Switzerland ! So I assume they passed (quite literally indeed !)those certifications.

Regards

Charles

[peranders]

Indeed, so we have to compete with Pass Labs. Hard game. Who wins?