CE marking - Minimum size of ventilation holes - Page 1
Forum section: electronics / projects

author: ciccio
author_rank: Frequent Contributor
timestamp: October 31, 2011, 12:47:58 pm
content: I've a problem with the CE marking of a professional power amplifier that has a forced air cooling.An engineer at the conformity assessment laboratory says that, to comply with regulations about fire propagation, the ventilation apertures must have a maximum size of 1.0 mm.In the prototypes these apertures are:- some slits on one side, for cool air input, about 3 x 100 mm each (the case is made of 1.2 mm steel, and it is not possible to punch it with a die smaller than 2.5- 3.0 mm or the sheet will be deformed).- the exhaust fan, low voltage DC, with finger guard. A screwdriver inserted there will touch only low voltage parts.I test and open everyday professional equipment that has similar construction, and I do not see any aperture smaller than 3 mm (this size assures safety against contact with dangerous internal parts), and the chrome wire fan guard is standard.Where is the catch?Is there any expert member that can give me an opinion?I'm waiting for a mail message that reports the point of the regulations that require this, but I want to be ready for an answer, and cannot find any information on the subject.

author: amspire
author_rank: Super Contributor
timestamp: October 31, 2011, 01:50:16 pm
content: I am not an expert on the CE rules, but CE is basically a mass of directives and guidlines that you may or may not have to comply with in a particular case.So you need to ask the engineer which directive or guideline requires the 1mm maximum aperture size, and why you need to comply with that directive or guideline in your particular case.I would imagine that your equipment has to meet the requirements of the LVD (Low Voltage Directive), just like PC power supplies (which have apertures bigger then 1mm) , unless you indicated uses of the amplifier that exclude the LVD like medical uses or uses in an explosive environment.

author: ciccio
author_rank: Frequent Contributor
timestamp: October 31, 2011, 06:05:19 pm
content: The applicable standard is IEC 60065 / 2001 amendment 1 / 2005: "Safety requirements for Audio Video and similar electronic apparatus"The standard defines a FIRE ENCLOSURE as "part of the electronic apparatus intended to minimize the spread of flames from within".It goes on about resistance to fire, saying that the equipment must:use good engineering practices to prevent the start of fire AND use low flammability materials in the vicinity of potential ignition sources AND use FIRE ENCLOSURES to limit the spread of fire.Later on FIRE ENCLOSURES are defined as having ventilation holes of a maximum diameter of 1 mm.I'm sure the engineer at the test laboratory got confused by this, because FIRE ENCLOSURES are, in my opinion, something that is used to enclose part of the internal circuitry or components that may start a fire in normal or faulty condition, and if no such sources exist because of their nature or because a protective circuitry is used, then there is no need for them, but the standard is, in fact, not clear at all....She (the lady engineer) insists that there must be a FIRE ENCLOSURE because of the AND written before, and if this FIRE ENCLOSURE is not inside then the whole cabinet is the FIRE ENCLOSURE...If this 1 mm rule is applicable to the cabinet ventilation holes there should be no need for the minimum 3 mm rule that applies to ventilation holes...

author: amspire
author_rank: Super Contributor
timestamp: October 31, 2011, 07:49:28 pm
content: I believe the FIRE ENCLOSURE is relevent only for parts of the circuit operating above 4kV.Seehttp://www.ul.com/global/eng/pages/offerings/industries/hightech/consumerelectronics/pag/

author: FreeThinker
author_rank: Frequent Contributor
timestamp: October 31, 2011, 07:55:17 pm
content: Could you not cover the ventilation holes with some sort of fine mesh or filter to comply?

author: ciccio
author_rank: Frequent Contributor
timestamp: November 01, 2011, 09:34:27 am
content: Thanks to everyone for the responses.Quote from: FreeThinker on October 31, 2011, 07:55:17 pmSorry, but a mesh wit 1 mm holes will get clogged with dust (there is a forced cooling) in a very short time.It must be mechanically resistant (a force of 30 N is used for testing) and it's almost impossible to find one at a reasonable price.Quote from: amspire on October 31, 2011, 07:49:28 pmI'm not sure of this, there are many OR in the standard's wording. It is clear only for projection TV sets (not my case).For certain the current is more than 0.2 A, there are windings connected to mains, power is more than 15 W.I'm looking for a copy of the standard written in Italian (the same that the lady is reading), because I fear the risk of mis-wording in the translation, and I'll visit the certification lab for a discussion.

author: amspire
author_rank: Super Contributor
timestamp: November 01, 2011, 10:09:47 am
content: I don't have the standard to read, but it seems there are two terms: FIRE HAZARD and FIRE ENCLOSURE.An audio power amplifier is definitely a FIRE HAZARD since I assume there are voltages over 35V and currents over 0.2A.But a FIRE HAZARD does not imply a need for a FIRE ENCLOSURE. I believe the two are not connected.It would be easy to assume a FIRE HAZARD requires a FIRE ENCLOSURE, but I don't think so.Richard.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: November 01, 2011, 01:54:31 pm
content: Quote from: ciccio on November 01, 2011, 09:34:27 amWon't 1mm holes clog up to exactly the same extent? A fine mesh with a pitch of 1mm and a very fine thread or wire would create very little in the way of resistance while still complying with the 1mm rule, but as you say it will clog with dust eventually but if that's the rules you have to meet I don't see an alternative.

author: ciccio
author_rank: Frequent Contributor
timestamp: November 01, 2011, 04:01:15 pm
content: Yes, both 1 mm holes and fine mesh will clog with dust..The simple fact is that I've checked a lot of other similar products, having a CE declaration of conformity that affirm to comply to the same standard, and NONE of them has a FIRE ENCLOSURE or 1 mm ventilation opening, so there is a problem in understanding what regulation should apply.

author: amspire
author_rank: Super Contributor
timestamp: November 01, 2011, 07:59:48 pm
content: The important question - is there anything in the spec that refers to FIRE ENCLOSURE specifically below 4 kV?Ignore references to FIRE HAZARD.I just don't believe an audio amp need a FIRE ENCLOSURE..Richard.

author: ciccio
author_rank: Frequent Contributor
timestamp: November 02, 2011, 08:18:14 am
content: Thanks to everybody.I've solved the issue with the testing lady engineer (I believe that she asked for clarifications to her boss):a fire enclosure is needed only if, when testing in faulty conditions, there is evidence of a risk of fire spread.That means that if, for example, a shorted output transistor result in flames spreading from the PC board, then the PC board must be enclosed in a fire enclosure, that can be an internal enclosure or the product cabinet, if it is suitable as per fire resistance.Best regards