Hi Jack:
While your specific question is off the mark of this
discussion group, there is a related issue that is on
the mark for this discussion group...
1) Is there a policy governing activity directed towards
standards and research into standards issues? Does
management condone
Dear Group,
2.4.2 of UL1950 defines the upper current limit for Limited Current Circuits
when the frequency is above 1kHz as 0.7mA multiplied by the frequency in
kilohertz (up to 70mA peak). Since the limit increases (up to
70mA) as the frequency goes up, one can assume
Hi Bob:
Electric shock requires both voltage AND current. Most
safety standards specify conditions for electric shock
when the voltage is 30 volts rms or more AND the current
is either 0.25, 0.5, or 3.5 mA rms or more.
Think of it as an AND gate. Voltage exceeding 30 V rms
AND current
Hi Doug:
Probably the best single reference to non-ionizing
radiation safety is:
http://www.osha-slc.gov/SLTC/RadiofrequencyRadiation/index.html
Best regards,
Rich
-
Richard Nute Quality Department
Hi Doug:
For reliable safety data on non-ionizing radiation,
check out the following web pages:
1. http://homepage.seas.upenn.edu/~kfoster/comar.htm
This is the IEEE Committee on Man and Radiation, COMAR.
Probably has the most reliable information on body
susceptibility to
Hi George:
With respect to the VN issued by the NRTL...
The inspection process is to compare the product to
the report.
Following this comparison, the inspector simply
reports any discrepancies. By reference to page and
paragraph of the product report. Black and white.
Then, the
Hi Richard:
* What is the legal basis (document) upon which SABS claims that
compliance is mandatory? How can I obtain a copy of that document?
(trust but verify).
Here is what the SABS web page says about mandatory
standards:
In terms of the Standards Act, a number of standards
Hi Judd:
We are currently designing an ac filter assembly. The board is extremely
small and we need to put text in etch (copper) on board. About the only
place is an area that provides basic insulation from ground.
Essentially, the text in copper shorts out some of the basic
Hi Dan:
Can anyone explain the advantages/disadvantages of going through a notified
body for CE Mark as opposed to self certifying? It costs a load of money to
retain the services of a notified body and I was wondering what you really
get from it.
Its a business decision.
Hi Jim:
1. Am I correct that the North American agencies (CSA, UL, ETL, etc.)
allow line-to-ground MOV's? The standards we work with do not
disallow
them, but this is the sort of issue for which agencies often invoke
desk drawer requirements.
Can't answer this one.
But, why use surge
Hi Joe:
liability and such. Can anyone share some more info as to their reasons for
listing or not listing such a product which is well below hazardous limits.
There are two schools of thought:
1. Because of its low-voltage supply, the unit is exempt from
most safety
Hi Moshe:
The voltage of the neutral with respect to the ground wire
is a function of its resistance and its current:
E = I * R
Maximum normal current is the rating of the fuse or circuit-
breaker protecting that particular circuit. For a 120-volt
circuit in the USA and Canada, the
Hi Tania:
I, too, have had the same inspection experiences (saw a transformer
and prove solder time-temperature).
In the case of the transformer, I offered to take the inspector to
the transformer manufacturing plant to make the measurments during
the manufacturing process.
The
Posted on behalf of Gary Jong:
--
I'm the Staffing Manager for the Philips Mobile Computing Group (PMCG)
PMCG designs and develops new generations of the award winning Velo
and other mobile computing and communications platforms based on the
Windows CE operating
Hi George:
Pal is primarily used throughout Europe and NTSC is used in USA, Canada,
Mexico and Japan.
Does anyone know of any other countries that may use NTSC ?
Check out the following web sites:
http://www.bbc.co.uk/aberdeen/eng_info/world_tv_standards.shtml
Hi George:
Could someone give me an explanation of what makes a power source
Inherently Limited..
Others have provided excellent responses to your question.
Perhaps I can embellish their answers.
A doorbell transformer is the prime example of an inherently
limited power source.
The
of SELV
To: Rich Nute ri...@sdd.hp.com
Cc: [unknown] emc-p...@ieee.org
Message-ID: 199910270218_mc2-8a97-1...@compuserve.com
MIME-Version: 1.0
Content-Type: text/plain;
charset=ISO-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
X-MIME-Autoconverted
Hi Kevin:
Can anyone please provide the SELV definition from IEC 364?
I'm working from some old documents, but...
SELV is not expressly defined in IEC 364-4-41. Instead,
it specifies Protection by safety extra-low voltage.
It says:
Protection against electric shock in normal
Hi Laura:
Could someone please tell me where previous EMC and safety discussions are
posted on the internet.
emc-pstc messages are archived at:
http://www.rcic.com/
Click on Virual Conference Hall. The archives can
be searched by topic.
Also I am interested to know if a
BTW, you may find a 50mm diameter ball bearing, but will it weigh 500g
+/-25g? And then you'l have to drill and tap it for an eyelet for the
string.
The impact ball spec was written around a 2-inch diameter
ball bearing.
Drilling and tapping the ball bearing requires some sort
of
Hi Doug:
Isn't this a variation of using the traces as a fusing element
instead of using a real fuse?
Not necessarily.
In Peter's situation, the test was that of the integrity
of the insulation between the TNV circuit and the other
circuits.
So, if the fused trace did not bridge
)
id QAA09924; Thu, 7 Jan 1999 16:18:12 -0500 (EST)
From: pe...@itl.co.il (Peter Merguerian)
To: dmck...@corp.auspex.com, Rich Nute ri...@sdd.hp.com
Date: Thu, 7 Jan 1999 23:12:35 +0200
MIME-Version: 1.0
Content-type: text/plain; charset=US-ASCII
Content-transfer-encoding: 7BIT
Posted on behalf of a colleague:
The Electric Strength test conducted after abnormal testing in accordance with
IEC 60950 may be performed at room temperature, after the EUT has cooled down.
5.3.8.2 says the test is to be conducted in accordance with 5.2.2. 5.2.2 does
not say anything
Hi Peter:
After an Abnormal Test for UL1950/EN60950, should the Electric Strength be
done a) immediately after the Abnormal Test or b) after Abnormal Tesrt when
unit has cooled down to room temperature c) after Abnormal Test when unit
has cooled down to Normal Heating Temperature
Hi Chris:
There are two kinds of circuits that may be connected
to the equipment protective earth terminal:
1) Protective earthing circuits.
2) Functional earthing circuits.
Protective earthing wiring must be colored green/yellow.
Functional earthing wiring can be colored any
Hi Barry:
Thanks for the URL.
An even better paper at the FCC web site is:
http://www.fcc.gov/oet/info/documents/bulletins/#56
OET Bulletin Number 56 (Fourth Edition August 1999)
Questions and Answers about Biological Effects and
Potential Hazards of Radiofrequency
Hi Robert:
But what about permanently connected products?
For the purposes of Article 400-22(c), the NEC does
not distinguish between permanently-connected and
plug-and-socket-connected appliances. The rule is:
Specifically, 400-22(c):
For jacketed cords furnished with
Hi Ken:
What determines whether equipment gets a green wire or not? TVs, toasters,
handheld hair dryers and just about anything for home use get two wire power
cords. Computers and other ITE get three wire cords. Is the distinction
commercial vs. residential (class A vs. Class
Hi Barry:
Chaz, Why do they call UL a non-profit organization?
UL, as a corporation, is chartered as a not-for-profit
organization.
This means that it cannot distribute retained earnings
to the owners. Instead, it uses retained earnings to add
to endowment funds for financing future
Hello from San Diego:
Many thanks to Sean for posting the URL for the
Washington Post article on UL.
While I am notorious as a UL-basher, I think
the focus of this article is misplaced.
This article presumes that UL puts the safety
into products. Unfortunately, many manufacturers
also
Hi Richard:
Are there currently any
alternative wire and cable constructions that comply with UL and NEC flame
requirements without the use of halogenated flame retardants?
I believe PVCs are naturally flame-retardant materials
i.e.,
Hello Israel:
Unfortunately, safety standards only address one of the
critical parameters, temperature, when specifying
requirements for protection against a burn injury.
You are absolutely correct that a metal surface with a
temperature exceeding 50 C is capable of producing a burn
Hi Jim:
Aren't there any permanently connected ITE equipment mfr's on this
forum?! What do you provide in the way of knockouts or ...???
I don't have any first-hand experience... but...
On good authority, a major mainframe manufacturer
uses cord-and-plug connection for EVERYTHING!
Hewlett Packard's Network Server Division in Cupertino, CA is looking
for a Senior EMC Engineer to work on EMC requirements for electrical
and mechanical development. This position is an Architect position
looking at future product designs. The person will establish
Hi John:
the largest size listed in the table is 1.00mm minimum metal thickness,
2.00mm maxhole dia., and 3.00mm minimum center-center hole spacing. If my
metal thickness was greater (1.27mm), and my center-center hole spacing was
4.75mm, could I not go to a larger hole (3.175 -
Hi Peter:
Well, can you share how your compliant products (ie double insulated to earth
Class I products) comply at the transistor/earthed heat sink interface? Do you
have at least two layers of insulation where each layer meets the reinforced
insulation dielectric strength test requirements?
Hello from San Diego:
One thing that might be a problem is if the heat sink of the primary
switching
transistor is grounded.
Then it might be difficult to reinforced isolate the primary switching
transistor as changing the isolation material will also influence the heat
Hi Rick:
Do any of you know where I can find a 1 1/4 fuse, that meets IEC 127 (EN
60127)?
As I recall, IEC 127 does not include the 1-1/4 inch
dimensions, and therefore there are no IEC 127 fuses
in the 1-1/4 inch dimensions.
Indeed, this would be dangerous as the methods of rating
Hi Peter:
This is the exact deviation which I was referring to. One of my
clients states that a distributor wishes the product to be safe for
those establishments where earthing cannot be relied upon. Does
this mean to provide double or reinforced insulation from hazardous
Hi John:
Rich, you said below Assuming you are using IEC 60950, a fire
enclosure is required for any circuit exceeding the limits of ELV,
independent of available current or power.
Why did you mention exceeding the limits of ELV ?Surely specific
components
Hi Dan:
According to both IEC 384 and UL 1414, Y capacitors are rated
up to 250 V rms, not higher.
However, RIFA offers ac capacitors in their Y capacitor
catalog pages rated up to 440 V and 500 V rms (without
certifications). If you were to use one of these in a
certified product, then
Hewlett-Packard's High Performance Systems Lab has
an opening for a regulatory engineer with experience
in product safety.
HPSL is located in Richardson, Texas (20 minutes
north of Dallas). Our product line is high-end
servers (V-Class, SuperDome).
For more information
Hi Kyle:
I presently use a system of lot marking codes with a simple one-page
document that is shipped with each batch of parts from the vendor. The
document has the name of the vendor's QA person in signature and the
relevant lot numbers for each shipment from the factory and
Hi John:
My question: we have a UL mark on a box we build. One of the requirements
that the auditors check is flammability of materials. 2 parts give us
trouble - a molded bezel and a plex screen. Both are materials purchased
elsewhere by our fabricators. UL says either assemble a 'paper
Hi Jeff:
I am trying to find a basic document from UL and or CSA regarding the legal
requirement of
UL or CSA listing. I am thinking along the same lines as the European LVD.
Can anyone
offer insight as to whether this documentation exists?
UL and CSA are private
Hi Alan:
We have recently had an EN60950 safety report from a local consultant on a
piece of IT equip we designed which commented that a fuse may be required
on both the live and neutral of the mains input for certain countries in
Europe.
EN 60950, Sub-clause 2.7.1 states:
Hello from San Diego:
If you have the ability to print your own labels all of the IEC 417 symbols
are available on the web at
http://w3.hike.te.chiba-u.ac.jp/iec417/ver2.0/html/index.html. These are in
bitmap format. I have included the symbol for 5041 in this email in case you
Hi Pierre:
Here is an ASCII block diagram of the construction the way
I interpret your message:
+---+
| |
| dc-dc |
12 V dc ---| converter |---+
| | |
| | |
Hi Nick:
According to IEC 384-14 (1993):
Class X and Y capacitors are ac capacitors. An ac capacitor is
a capacitor designed essentially for application with a power-
frequency alternating voltage.
Class X
===
A Class X capacitor is a capacitor where failure of the capacitor
will
IEEE Meeting Notice and News from The San Diego Chapter
Wednesday, September 15, 1999.
DESIGNING FOR SAFETY for the Year 2000 and Beyond.
Charles M. Bayhi, P.E.
About the Topic: The principles of product safety will
be discussed as they relate specifically to EMC as outlined
below:
Hi Kevin:
Interesting P.S. comment. Surely this can only be so if one is not dealing
with a CE country. I don't see how a test agency can waive the requirements
for meeting the LVD in Europe. If it is indeed as you say, then where does
it put those of us who have in house safety
Hi Rick:
The obvious question I would have is... why couldn't you test at a higher
current for longer time meeting both requirements? For example 30A for two
minutes. I know the document indicates a maximum current, but does this make
sense?
The original question appeared to me
Hi Carmen:
You ask how to resolve the difference between two,
different production-line (routine) test standards.
If your product is certified by CSA, then you test
to the 30-ampere value.
If your product is certified by a CB Certificate
and Test Report, and the issuing body invokes
EN
Hi Doug:
Some years ago I did some tests on my concrete garage
floor using aluminum foil laid down on the floor.
I applied 120 volts through an ammeter to the foil,
and then measured the current from the 120 volts to
the foil. I wanted to learn how much current would
be conducted by the
Hello from San Diego:
Please respond privately to Steve on this topic.
We all need to protect both ourselves and the IEEE
from possible libel or slander.
If you want to discuss this request, please contact
me privately.
Thanks, and best regards,
Richard Nute
co-administrator, IEEE
Hi George:
I've read these sections of the CFR many times, and always interpreted them
to apply to end user equipment, as you imply. However, I am beginning to
see
that this may be somewhat like quoting the Bible out of context. The
context
in this section of the CFR (before
Hi George:
So here is the challenge. Can anyone prove that 29 CFR 1900
or the NEC specifically requires ITE to meet more than some
grounding/marking requirements, or be required to be approved by
an NRTL. Proof is citing clearly stated sections obviously
applicable to typical
Hi George:
Just a clarification and amplification or your message...
There are TWO laws that govern product safety:
1) OSHA.
Your remarks thoroughly covered this law.
2) The National Electrical Code.
This is a model building code intended for adoption by
local building
Hi Kathy:
Someone who seemed to believe such a edict was sent
out resently asked me to check to I asked this group.
Maybe this is just a very bad joke from someone who
really doesn't know what he is asking.
I wouldn't cross off the question this way.
Be aware that there are a
Hi Bob:
A company I represent has a problem with their switching power supply.
A single point failure in the regulator can cause the output voltage to
rise higher than the voltage ratings of the electrolytic capacitors. As
a result, the capacitors are overstressed and fail in a
Posted on behalf of Bobbie Cronquist, John Wright, and
Julie Gaevert.
Some sad news about Joe Wujak, whom many of you may know and remember.
Bobbie Cronquist
- Forwarded message --
I have the very unfortunate task of telling everyone that Joe Wujek
and
Hi Peter:
There are two schools of thought:
1) Clearance is an independent, stand-alone criterion.
2) Clearance determines electric strength of air and is
an alternate means for determining the electric
strength of air.
If you are in the first school, then there is no reason
Hello from San Diego:
What countries and what standards require the indoor use:
symbol?
This symbol is comprised of a stick-figure house with an
arrow pointing from outside to inside.
My experience with this symbol is through TUV Product Service.
They require
Hi Doug:
This subject is NOT in the you got to be kidding me
category.
Many years ago, such a fuel-cell generator was installed
at IBM Kingston and ran for a year as an experiment.
Since this is a SOURCE of electric energy, it falls into
the same category as home wind generators and home
Hi John:
The subject here is regarding the words 'shall' vs. 'must' in various of
product safety standards (including UL 1950 3rd Ed. and EN60950).
Does anyone have any insight into the definitions of these as applicable to
product safety? I have heard there are differences,
Hi Rick:
If a product has a 4A rated input current (120V AC), how does one
determine the rating of the in-line Fuse for safety/Fault testing?
There is no relationship between input rating and the fuse
rating.
The input rating is the maximum input under normal operating
conditions.
Hi Allen:
I'll take a shot at this one! (At one time I dealt with high-
fidelity high-frequency signals where the effects of connectors
could be observed in the waveforms.)
The ideal transmission line is terminated at both ends with its
characteristic impedance.
In some circumstances, you
Hi George:
Can anyone point me to a resource (Book, Chart etc) that lists ignition
points for various (flammable) materials ?
Flash-ignition temperatures and self-ignition temperatures for
various generic plastic materials are published in:
International Plastics Flammability
Hi Peter:
The Dielectric Voltage Withstand Table in UL1950/EN 60 950 lists
equipment with Mains DC. What does this mean?
You make it difficult to answer this question because you
used a term that does not appear in UL 1950:
Mains DC
I did an electronic search of the standard for
Hi Lauren:
At the risk of being shown otherwise...
Determining the actual heat dissipation of your product could be very time
consuming. It would involve, in part, knowing the electrical efficiency of
I would argue that, using the law of conservation of
energy, this is not at all time
Hi Scott:
Under the law of the conservation of energy, all of the energy
going into a product must be accounted for.
Energy is measured in joules.
One joule is one watt-second.
One watt is one joule/second.
All of the watts entering the product must be accounted for.
All of the watts are
Hi Jeff:
If a component abnormal test generates excessive and sustained smoke
(several minutes), but does'nt breach reinforced or double insulation, nor
emit flame from the enclosure, is it considered a failure? Intuitively, it
seems like it would be, because of toxicity, but I
Hi Jeff:
I need to clarify my earlier question on conductive paint. We bond our
enclosure panels together with screws. We use external-tooth starwashers
between the screws and sheet metal to achieve a reliable, protective-earth
bond. On our painted panels, we mask the paint so
Hi Jeff:
My company is proposing to use conductive paint on our enclosures, and I
would like your input as to the acceptability of this vis-a-vis protective
earth bonding of enclosure panels. I am interested in the perspective of
both European and North American requirements.
The
Hi George:
Along this line, I was asked, if placing power and ground traces on
separate (PCB) layers would be an acceptable way of reducing clearance
requirements between (gndpwr) traces. Is there anyway to anticipate
clearance between PCB layers of a multi layered board? Is
Hi Ali:
Today I received a call from one of distributors stating that as of August
of this year, Argentina will have their own power cord requirements. I
believe Argentina has the same configuration as Australia. Does anyone know
where I can find out more about this requirement?
Hi John:
In the CB Scheme National Differences document, Danish and Norwegian
requirements (in 6.3.3.1 and 6.2.1.2, respectively) make reference to
equipotential bonding. Can anyone tell me exactly what equipotential bonding
is? I assume that it is some form of grounding...would having a
Hi Doug:
My question is this, is it because the inverter has a low voltage input and
they do not have to comply to a standard like EN61010 or UL1950, or is this
something the manufacturers haven't addressed because no one has ever asked?
I don't think anyone but the manufacturers can
Hi Ray:
I know that at one time, UL had accepted a HAR type cordset. Now, I have
...
...
Does anyone know why UL stepped back away from accepting EU cords?
My guess is:
UL accepts HAR cordage (not cordsets) for products going
to countries where the HAR certification is accepted.
UL
Hi John:
He sees the video distorted and was wondering
about any health risks.
The first thing you should do is ascertain that the
distortion is caused by an external source or an
internal (to the monitor) source. It is possible
that the degauss circuit has failed, in which case
Hi Peter:
I understand the construction to be that of a mains
extension from a wall outlet outside the safe via a
plug to two socket-outlets inside the safe.
Your question is Does the safe now fall under the LVD?
Plugs, mains cordage, and socket-outlets are NOT
included in the LVD as they
Hi Jim:
You ask a number of questions about fire enclosures for
IT equipment.
Section 4.4.5 of UL1950 appears to require a fire enclosure for essentially
anything that contains a printed circuit board assembly
Sub-clause 4.4.5.1 essentially says that all conductors
and components
Hi Frank:
Interesting. During an audit of the facilities of a former employer, the
auditor specifically requested that we didn't use the Simpson 228 for
EN60950 because of the roll-off of the analog movement above 100Hz. The
suggested fix was to build the network as described
Hi Pete:
It seems to me that there are several kinds of conductive
parts that we need to be concerned about from a safety
perspective:
1. Energized parts at hazardous voltage.
2. Energized parts at non-hazardous voltage.
3. Energized parts at non-hazardous current.
4. Grounded/earthed
A meter for IEC 60950 may not be adequate for IEC 61010,
especially if the unit under test has a reasonably high
frequency switch mode power supply.
The high frequencies generated in a switching mode power supply
are negligible in the presence of the mains-frequency leakage
Hi Doug:
Thanks for sharing your findings on insulating tape
and anti-static tape.
All insulators have the property of insulation
resistance. Modern insulations have insulation
resistances in the gigaohm and teraohm ranges.
I would guess that anti-static insulators have a
relatively low
Hi John:
Now we have sub-classes Y1 to Y4. Y capacitors can be used in locations
where neither side is grounded, but in the OP's context, grounding is
involved.
What are the definitions of the various Y
capacitors in the most edition of IEC 384?
OP?
A Y-cap can be used
Hi John:
Ground connections is usually nice to have when dealing with EMC. But what
about EMC and a class 2 (double insulation) power supply (shall comply with
MIL-STD-461E) . I'm thinking on, what to do with the regularly Y-caps,
does it really have any meaning with these
Hi Chris, Bill, and all other subscribers:
A message with the subject:
A very nice game
was sent to the IEEE (emc-pstc) for posting by
our listserver.
The original message contained a virus known
as KLEZ.G.
The IEEE computer detected the virus.
This virus was stripped from the
Hi Amund:
Being a safety guy and not an emc guy... (disclaimer)
Ground connections is usually nice to have when dealing with EMC. But what
about EMC and a class 2 (double insulation) power supply (shall comply with
MIL-STD-461E) . I'm thinking on, what to do with the regularly
Hi Pierre:
You did not state whether or not your secondary circuit
is intended to be SELV or not. This is critical to your
choice of capacitor. However, you did ask whether the
circuit is equivalent to reinforced insulation, so I
assume that your secondary circuit is SELV.
By
Taking John Woodgate's usual response to such
an inquiry, I did a Google search on inrush.
Surprisingly (to me), there is a wealth of
reasonably good info on the web under the subject
of inrush, including switches rated for inrush
current.
Best regards,
Rich
Hi Chris, Andrew, Carmen:
With regard to safety, both effects of altitude
must be considered:
1) effect of air pressure on the electric
strength of air (clearance), and
2) effect of lower density air on the
temperature of solid insulation.
(Creepage is a
No, it's simply that it isn't considered reasonable to have a radio and
a CFL in close proximity. If you want a lamp and a radio close together,
use an incandescent lamp.
That's the bottom line, isn't it?
Somebody has decided for me (in terms of
what is reasonable) that if I use a
Hi John:
I've replaced the incandescent lamp on my bedside
table with a new energy-saving compact flourescent
lamp. With the lamp on, I cannot listen to even
the strongest AM radio station on my clock radio
(on the same bedside table) due to the lamp
interference.
Hi Ken:
Trial lawyers and their clients have an obvious interest in portraying
consumers as helpless and child-like, and rich corporations as robber-barons
preying on the poor and weak. But why does the rest of society jump on that
bandwagon? Because profit and wealth, once
Hi Ken:
The Forrestal incident occurred during the Vietnam conflict, July 1967. It
was pretty much as you describe except I would not say EMI was not
controlled. All DOD services had EMI requirements at his time. In fact,
1967 was the year that MIL-STD-461 was adopted as a
Hi George:
The key word in EMC is compatibility. This implies that electrical and
electronic
equipment are (ideally) designed so that each can operate normally in the
presence
of another. This requires limiting both the emissions and sensitivity of
such
devices.
EMC?
Hi John:
Is there a value (or range of values) for the
resistance of water?
The data exists; it depends, of course, on solute nature and
concentration. Try a web search.
I did a web search before my post. There is lots of
data on the use of water resistance and
Hi Jason:
Water comprises a 3-dimensional resistor.
The value of the resistor depends on:
* the purity of the water itself (the
resistance is inversely proportional to the
purity);
* the dimensions of the electrodes (i.e., the
conductors in contact with the
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