Hi Chris:
In other words: don't test if you know already the result before the test
is made.
A good safety engineer can predict the result
(not pass-fail but the measured value) of each
and every safety test.
For example, a good safety engineer can predict
leakage current to
Hi Richard and Dave:
In answer to Richard's comment:
The neutral is never to be tied to the chassis of equipment. It is not
allowed by any safety standard nor the National Electrical Code. The neutral
is to be tied to earth at one and only one point and that is that the
service
Hi Richard:
When a PCB is rated 105C or 130C or whatever, what does that really mean?
Can I really operate a 130C rated board at a maximum surface temperature of
130C for years without being concerned about reliability or safety? Is there
a relationship between de-rating and
I think this discussion has bogged down into too much
detail.
Overcurrent protection is required to provide protection
against overheating and fire (and sometimes shock) when
a fault occurs.
For plug-and-socket connected products, a mains fuse is
used to provide protection against LOAD
Regulatory/Power Systems Engineer
Main Responsibilities
Become part of a multi-functional system's
engineering team in the process of developing
a state of the art photo-finishing system
incorporating technologies from Eastman Kodak
Co. and Hewlett Packard Co. Responsible for
product
Hi Randy:
http://kropla.com/electric.htm
http://www.clary.com/Service/IntVoltage.asp
http://www.quail.com/locator/index.html
http://www.fele.com/empd/tech/fe-power.html
http://www.panelcomponents.com/guide.htm
http://www.ets-tele.com/tics/global/volt_freq.htm
Best regards,
Rich
Hi Ken:
I found something interesting today. While measuring leakage current with a
digital multimeter, I noticed a high amount of leakage. The unit
incorporates a switching power supply, with some EMI/EMC circuitry. Anyhow,
I read somewhere that DMMs are some times inaccurate
Hi Ron:
In the USA, NRTL safety approvals, thus NRTL safety marks, for equipment
intended for the commercial
environment, in fact, are required AND mandated through legislation. This
requirement is found in
the US's Code of Federal Regulations (29CFR Part 1910 Subpart S) and is
Hi Mike:
I'm posting this for a friend who is having a problem with CSA and hipot
testing. He has several products which operate on 115/230 VAC. They are
industrial control products (don't know the CSA standard number but they
fall under UL508 is the US). In one CSA report he is
Hello from San Diego:
One of our colleagues has asked me to discuss further
the reason behind the hi-pot test.
The insulation between the mains and accessible
conductive parts (including low-voltage-energized
accessible conductive parts) is critical to the
scheme of protection from
Hi Paul:
My manufacturing contacts have asked for a lead on a supplier of test
equipment that I can use to be able to test the Hi pot lead for it not to
be open. If you run the Hi Pot test holding the lead in the air it will
pass . We need a way to test that the lead is not open
Hewlett-Packard's Home Products Division is looking for an
EMC Project Engineer on the development of the Pavilion
Personal Computer in sunny Cupertino, California. The
individual must be highly motivated to work in a fast
paced team environment, and must want to take on the
following
Hi Jeffrey:
In answer to your questions...
1. Advantages / Disadvantages of using a ramping function vs. zero crossing
?
Back in the old days, some hi-pot testers simply had
an off-on switch. No ramp. No zero crossing. And,
no problems with the equipment.
The ramp function is
Hi Andy:
I have been told that either double crimp terminals (fast-ons, ring,
spade) must be used for insulated wire, or a secondary method must be used
to secure the wire's insulation near the point of connection. I have not
seen this described in the standards I have read or
Hi Peter:
A manufacturer has an IEC 950 type equipment with a polymeric enclosure
meeting the fire enclosure requirements, in this case, enclosure is flame
rated min. 94V-1. Assuming he now painted the enclosure to give it a better
look, will this have an effect on the original
Hi Joe:
What should be the duration for the production line continuity test? How
did
you arrive at that duration? Please include what standard you are using
and any
specific references.
According to EN 50116, sub-clause 5.1:
The test shall be carried out... for
the
Hi Ed:
Great description of your test technique. BTW, I would think that the
temperature of the oil in the ladle should be specified, as this seems to be
a critical variable.
The temperature of the oil is established by the
1-minute burn period (in the ladle) BEFORE the oil
is
Hi Susan:
to my products. Is there a general guideline for separating traces to meet
isolation requirements and survive a 2000 VDC (input to chassis) hi-pot
requirement?
There are regs and there are rules of thumb and there are
physics...
...that govern the distance at which
Hi Ken:
The standards specify the oil as being:
distillate fuel oil which is a medium volitile distillate having a mass
per
unit volume between 0.845 g/ml and 0.865 g/ml, a flash point between 43.5C
and 93.5C and an average calorific value of 38MJ/l.
I've found that this is
Hi Mike:
I've been asked why a routine hipot test is required on an end assembly
computer when it uses a Listed power supply that has already been hipot
tested. So far I don't like the way I've worded my response. Basically
what I've said is that a power supply is approved as a
Hewlett-Packard Company has an opening for a
high-level, senior safety and EMC engineer in
Roseville (Sacramento) California.
Its a challenging opportunity for someone who
can work independently with engineers, OEMs,
and worldwide HP regs staff.
For details, see:
I think we must be careful not to confuse two
subjects:
1) Nominal power line voltages and variations.
2) Power line voltages for safety testing.
For the purposes of safety testing, some test
results may be a function of the power line
input voltage. Therefore, it is appropriate
to
Hi Fabian:
We have a potential supplier of an OEM equipment that is not
NRTL listed. They suggested we have it listed (i. e. pay for the testing
ourselves) as part of our system. I am not aware of any case histories of
this nature. Has anyone had this experience?
What safety lesson we may learn from Concord crash?
There are lot of Safety standards in Electronic and Electrical
industries. If we strictly follow them we can avoid fatal accidents.
True.
Because, the standards specify safeguards
for KNOWN failures that lead to injury.
Is
The subject answers your question about the constraints
on such testing:
Equipment insulation testing.
For the purposes of this discussion, there are two
applications (or kinds) of insulation:
1) Insulation between the poles of a circuit or the
insulation within a circuit (also
(Posted for Joe O'Banion)
I am one of the volunteer co-coordinators for the
2000 IEEE International Symposium on Electromagnetic
Compatibility to be held in Washington DC from August
21 to the 25. I need volunteers to help with
registration and support for the various sessions and
As you know, this list is adminstered by volunteers.
Jim Bacher has been administering the emc-pstc
listserver for several years. Its time to give
him a rest, and ask for a volunteer to take his
place.
We are seeking a volunteer to help administer the
emc-pstc subscription e-mail address
Hi Barry:
Unfortunately, Tom Bao, curator of the RCIC
archives, has been unable to keep up all of
the archive functions.
Tom is currently looking for someone to take
over the archives. He will be happy to send
details of the job to any interested party.
I did a non-comprehensive search;
Safety standards specify topics which must be
addressed in manuals. Only those portions of
the manual addressing those specific safety
topics are controlled by the certifier. The
remainder of the manual is controlled by the
product manufacturer; this remainder may be
provided in any
Peter Tarver and Gary McInturff bring up the topic
of inherently unsafe products.
Peter identifies these products as inherently unsafe:
three-ring binders (mechanical hazard)
any pointed writing implement (mechanical hazard)
plain old mechanical staplers (mechanical hazard)
Hi Phil:
Does anyone have the least inkling of any safety requirements specific to a
firearm with an electronic trigger. I am not particularly interested in
firearms laws/regulations etc but any requirements that the electronics may
fall under. This device will be powered by a
Hi Allen:
The voltage breakdown of air is presented in
IEC 664.
There is no fixed number (i.e., mm/kV) that
describes or predicts voltage breakdown of air.
The principle factor that affects voltage
breakdown is the shape of the electrodes
(degree of homogeneousness of the electric
Here are some more strange warnings on items:
On a packet of juggling balls:
This product contains small granules under 3
millimeters. Not suitable for children under
the age of 14 years in Europe or 8 years in
the USA.
Seen on a camera:
This camera only works when
Hi Duncan:
Robert Johnson has provided an excellent answer.
I'd like to amplify on his comments.
The fuse rating is selected not for maximum normal
current, but for minimum fault current.
So, you need to examine your circuit to see what
components are likely to fault, and you need to
Hi George:
I am confused. Which is the correct spelling:
Dentori or Dentory
The word is a Japanese word. The translation of
a Japanese word is a phonetic translation. The
spelling of the word is inconsequential as long as
the phonetic is maintained.
Spelling is an english
Here is some info from the Symantec web site about the
virus apparently distributed by EMC-PSTC listsever:
VBS.Stages.A
This worm appears as an attachment titled LIFE_STAGES.TXT.SHS.
Execution of this attachment will open a text file in Notepad
displaying the male and female stages of
WARNING!
The message distributed under this subject line
appears to include an attached uncleanable virus.
The virus is: SHS_STAGES.A
In file: LIFE_STAGES.TXT.SHS
Message headers are attached for your info.
Best regards,
Richard Nute
co-administrator, EMC-PSTC Listserver.
Hi Rick:
Somewhat related to this discussion is the opportunity I had last week to
perform surge testing on an off-the-shelf, rack mounted PC. The power supply
in question was from a reputable manufacturer and had safety, EMC and CE
markings. The system (power supply) passed the
Why do you need the MOVs? Why not just take the L N to ground via a gas
tube each?
Indeed!
Why, even, use any suppressors?
Supposedly, there is only insulation from L and N
to ground (earth). As such, it is easy to achieve
5 kV worth of insulation. Without much effort, this
can
.
(Contact me for info for job number 679159.)
Rich Nute
HP San Diego
---
This message is from the IEEE EMC Society Product Safety
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To cancel your subscription, send mail to:
majord...@ieee.org
Hello Alfred:
For a good summary of limits for 50-60 Hz electric
and magnetic field strength and the standards, see:
http://infoventures.com/private/federal/qa/qa-gact2.html
This source provides state standards, IRPA/INIRC
standards, and ACGIH standards. IRPA/INIRC specifies
1 gauss
Hi Doug:
IEC 60950 differs from IEC 60664 in that the clearances
are for sea level, not 2000 meters. See Table 18, Note
2.
Since 664 is the reference standard, I suppose one can
ask whether the 950 authors correctly transposed the
2000-meter clearances from 664 to sea level clearances
for
Hi John:
clause 5.3 allows for altitude correction, but the standards dont mention
any
correction factors with regard to clause 6.4.
Sub-clause 5.3 invokes electric strength testing.
Physics correctly predicts breakdown voltage for
a given clearance decreases with altitude. The
Recently we discussed levels for injury from
low-frequency electromagnetic fields (EMF).
The May 15 issue of Forbes Magazine has a good
article on the science behind the worldwide
scare from power lines.
Voodoo Science and the Power-Line Panic
by Robert L. Park.
The effect of
Hi Doug:
Does this section mean to say that the voltage on internal SELV may in
fact go higher than the 71V Peak and 120 V DC for a short time? Naturally,
The standard says:
In a single circuit... other parts of the same circuit
do not comply with all of the requirements
Hi Jon:
UL has several different certification marks. The two
that most of us are concerned with are:
UL LISTING mark.
Comprised of four data:
* UL in a circle;
* the word Listed;
* the type of equipment or UL file number;
* the UL control number.
This mark is
Hi Doug:
Without knowing the issue, we connected two different machines
with a coax. Each machine eventually connected to different
substations by way of differently sourced outlets. And we
watched with amazement as the rubber jacket of the coax melted.
All with a 15V
Hi Kelly:
First, I presume you are considering the TN power
distribution system. The answers to your question
are dependent upon the type of power distribution
system, whether TN, TT, or IT. My response does
not apply to the TT and IT systems.
The first question that must be asked in
Hi Robert:
I am running into a problem with UL not accepting the Brown/Blue color code
due to UL 2044 and The NEC stating that the Neutral must be white or Natural
grey.
The NEC specifies colors for the neutral (grounded)
conductor and for the protective earthing (grounding)
Hi Martin:
There are three issues in your message:
1) compliance to the standard;
2) reasonableness or appropriateness of the standard;
3) value added to the product through compliance.
You point out that messages posted to this list address
compliance to the standard, but not the other
Hi Tania:
For example, I always thought that it was a perfectly ridiculous idea to
require that all equipment falling under the scope of IEC 950 should be
double insulated, as pushed by certain Nordic countries many ages ago.
Until--- until it was pointed out to me that certain
Hi Peter:
For the novice designer, does anyone have a Table which references North
American and European sizes/cross-sectional area of cords/cables/wires? Of
course, these Tables depend on the type of insulations and temperature
rating of the cord/cable?
At one time, the IEC
(c) Copyright 2000, Richard Nute
Hi Richard:
You posted an interesting approach to fire. For me,
it triggered a number of comments that I hope you
will find useful.
Objective:
I suggest that the objective of the design in
respect of fire is:
No fire shall spread from the
Hi Gary:
Just curious here, Obviously, the question was asked, and my people have
responded. Is anyone actually counting or even seriously contemplating the
breakup. Just because a question was asked doesn't mean any action is going
on?
As list administrator, I own the emc-pstc
Regarding a possible EMC and product safety split...
I want to thank each of your for your contributions to this
topic. As with our technical discussions, your comments are
of high quality and are highly worthwhile and thought-provoking.
Each of your technical contributions make this forum
Hi Peter:
There are two issues in your question:
1. The equipment use environment.
Test and Measurement Equipment is likely to be used in
outdoor or sheltered environments, including arctic regions.
Hence, a lower temperature limit of 5 C.
Information Technology Equipment is likely to
Hi Peter:
I concur with George: Check the CB Scheme
website:
http://www.cbscheme.org/
In particular, download the white paper.
This paper provides a reasonable description
of the CB Scheme and its advantages.
If this doesn't meet your needs, then I
suggest you buy the IECEE
Hello from San Diego:
Classifying products according to EN 61000-3-2 is
not straight-forward.
A product with the special waveshape (i.e., the
waveshape created by a rectifier-capacitor circuit
of a switching-mode or linear power supply) is
Class D.
A product with input current waveform
Hi Bill:
I have a request for interpretation of requirement. Which symbol is correct
for use on a chassis for protective earthing - the upside down tree or the
circle upside down tree or the pitchfork?? (Note:- the ground on the back
of the box is generally marked GND and is
) attention.
We have two such admins that share the work. One
does all of the work when the other cannot.
If you would like to help keep this listserver
going, or would like to learn more about the job,
please send e-mail to one or all of us:
ri...@sdd.hp.com(Rich Nute)
jim_bac
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 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 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.,
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
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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
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
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