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 fa
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 re
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 inaccur
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 th
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
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
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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 adjust
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
work
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 li
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; I
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
Hi Peter:
> Regardless of any particular view on intent to do harm, intent implies human
> action. Similar levels of harm can be accomplished using the items I
On this subject, here are a couple of web sites
that address behavior as an effective means of
achieving safety, and "target" r
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
21.375DB740@roncone>
> From: Paolo Roncone
> To: "'bogdan matoga'" , Rich Nute
> Cc: "allen_tu...@pairgain.com" ,
> "emc-p...@ieee.org"
> Subject: R: Voltage Breakdown
> Date: Tue, 11 Jul 2000 10:17:26 +0200
>
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
field
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 whe
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
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 origina
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
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 mai
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 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 o
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
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 electri
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
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
d
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 la
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 lif
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.
> Fro
Hi Joe:
> Does anyone know the clause or statement that
> identifies "L" for Line voltage and "N" for
> Neutral A.C. mains marking in the LVD or any
> EU standard published?
Clearly, L and N are abbreviations.
There is confusion whether L means "live" or "line."
N, in this con
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 t
> 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
quot;
Enter job number,
Submit Search.
(Contact me for info for job number 679159.)
Rich Nute
HP San Diego
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This message is from the IEEE EMC Society Product Safety
Technical Committee emc-pstc discussion list.
To cancel your subscription, send mail to
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/q&a/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 o
Hi Muriel:
This web site should either provide the answer or
provide links to the answer:
http://www.osha-slc.gov/SLTC/elfradiation/index.html
Here are some other sites that might be of interest:
http://www.niehs.nih.gov/emfrapid/html/Q&A-Workplace.html
http://www.niehs.nih.gov
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 requirement
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 1
Here's a web site to start:
http://www.mcw.edu/gcrc/cop/cell-phone-health-FAQ/toc.html
It is rich with references, so you will be able to
find lots of data. The site includes data measured
at schools in Vancouver, BC, including measurements
from antennas on the roof of the school.
B
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 deali
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)
co
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 t
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 e
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-
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 Dan:
> Last year, sometime, reference was made about the possible creation of a
> University program to teach Product Safety. I was wondering if anybody has
> heard anything further about this program?
I probably was the one who mentioned that engineering
schools should include a 1-
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 docume
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 h
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 i
daily (weekday) 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 Nu
Hi John:
> More significantly, its resistance affects the maximum short-circuit
> current that can flow.
This is a valid consideration with regard to safety.
Given a 6-amp maximum, 0.75 sq mm size, and 2 meters
length.
In North America, 2X rated current is the 1-minute
operating time
> For an IT product there is a restriction in the use of mains cords with a
> cross
> sectional area of 0.75mm2 for units up to 6 amps when the cord is greater
> than
> 2m in length (EN60950: 2000 section 3.2.5)
I am curious as to the hazard that is prevented by
this length require
Hi Xing Weibing:
Here is my answer to the question.
>Hi group I have a question regarding clearance and working voltage of
> IEC60950. If I HAVE A AC ADAPTER(AC 100-240V 50/60Hz) ,THE WORKING
> VOLTAGE MEASURED ARE AS FOLLOWS: Nominal supply voltage: AC240V PRIMARY
> AND SECONDARY
> On the aspect of the "where to put Product Safety/Compliance in the
> organization" discussion bears mentioning on the forum. In general I
> advocate that the Product Safety/Compliance department be separate from
> Engineering, Sales, and Operations. The Safety/Compliance group sho
Hi Jerry:
> Will a production line hipot test be required?
As far as I know, the only certification house that
requires a production-line hi-pot test of TNV circuits
is UL. The test is specified in the gray pages as a
separate test from that of the mains hi-pot test.
Since you mentione
Hi Dan:
> Dell Computers, as well as a few other major players, take a proactive
> approach to compliance and actually have a VP position for compliance. With
> a little investigation into the benefits of having a first rate compliance
> department with the ability to design for compl
Hi Alan:
> Two questions, does the group see a time when we have a VP Compliance on
> level terms with VP Finance, VP Marketing etc, or is this already
> happening in the US.
No. And not likely to happen in companies with ordinary
products.
As a general rule, "compliance" is seen a
Hi Chris:
> What is clear from IEC60065 is that if a product is capable of being
> switched on or off or both by a timer or a data link, a front panel
> mechanically operated switch is not required. What is not clear is the
> definition of off.
Hmm. For me, the question is: What i
Over the years, this listserver has never had a problem
with decorum. We have had no rules addressing decorum.
I and the other administrators do have expectations for
decorum in posted messages. Here are our expectations.
Decorum:
-Propriety and good taste in conduct or appearance.
Hi John:
> It seems to me that the actual word 'tetanus' is not used for this in
> Britain, maybe because of the risk of confusion with the infection.
Reilly uses the word "tetanus."
Guyton uses the word "tetanization."
Tetanization would seem a better choice of
word to describe the el
Hi John:
> Also consider that the rectifier will very probably fail due to
> excessive reverse voltage under the fault condition, thus allowing fault
> current to flow through the transformer winding.
Will the rectifier fail open or short?
This SELV grounding scheme certainly doesn't
Hi John:
> >I presume that the fault current path for the ungrounded
> >SELV pole must be routed through the SELV source to ground
> >as that path is the lowest impedance path to ground. It
> >seems to me that the fault current would have to pass
> >through the transformer wind
Hi John:
> >> SELV can protect under single fault conditions. BUT, as I tried to
> >> explain, under some conditions, it can allow a single fault *to persist
> >> undetected*, until eventually a second, unrelated fault occurs which
> >> then results in a serious hazard.
> >
Hi Vito:
> Could either of you clarify why a double insulated SELV circuit can not be
> grounded? Is it a 60950 based or based on some other performance(?) based
> requirements?
This requires a bit of history. I don't have all of
the history, but I can fill in some of the blanks.
IEC
Hi John:
> My point is that, if attention-demanding words of differing intensity
> are considered necessary, how can they be chosen, other than the way
> they are at present?
>
> Of course, you may deny that differing intensity is necessary, so that
> only one word is required, b
Hi Ted:
> The electrician's rule of thumb when working on domestic wiring was to
> always check the wire is dead, even though you isolated it, in case of
> bridging or faulty connection. The technique used was to brush the
> exposed conductor lightly with the back of the fingers. An
Hi John:
> SELV can protect under single fault conditions. BUT, as I tried to
> explain, under some conditions, it can allow a single fault *to persist
> undetected*, until eventually a second, unrelated fault occurs which
> then results in a serious hazard.
This is a problem of the
Hi John:
> Tetanus is a disease caused by a bacillus. Muscles spasm is tetany.
Not according to my (American) dictionary.
Tetanus has two definitions.
The first is the disease or the bacterium that causes
the disease.
The second is a "prolonged contraction of a muscle
resulting from r
Hi Dan:
> Does anyone know what voltage is used in electric chairs? Just Curious.
I'm sorry you asked. The electric chair is one of
the more barbarous methods of execution.
The voltage is a function of time, and varies with
the execution authority. The voltage is in the range
of 1000-2
Hi John:
> >I feel the authors of these definitions neither consulted
> >a dictionary nor the users of warnings.
>
> I'm sure that you are right, but what is the alternative to using
> existing words but with special definitions that make their meanings
> more precise? If you so
Hi Gregg:
> There was also a very good (but short) article by Tektronix in the 70's
> called The Lethal Current.
>
> It concluded that currents between 100 mA and 3 Amps were more lethal that
> currents of more than 3 Amps because those high currents tended to 'restart'
> the hea
Hi John:
> I have never been very keen on the concept of SELV, and I am glad to see
> that others are now recognizing the problems.
Interesting statement. In contrast, I don't see how we
can get along without SELV.
My concept for SELV is that of ELV so protected from a
higher voltage
Hi Chris:
I'll attempt to answer the question as to the effect of
ac and dc current on the body (the "hazard").
The discussion is in regard to three waveforms:
1) ac sinusoidal -- 50-60 Hz.
2) dc
3) dc interrupted (equal on and off times) up to 200 Hz.
Each has a different e
> According to ANSI Z35.4 the following definitions are provided:
>
>
>
> DANGER - Indicates an imminently hazardous situation which, if not
> avoided will result in death or serious injury. This signal word is to
> be limited to the most extreme situations.
>
> WARNING -
Hi Chris:
I wonder why you need to hi-pot test a SELV-powered
product? (I presume your external 48-volt dc source
is SELV.)
We make products intended for connection to an external
dc source (SELV). We have never been required to
perform a hi-pot test on such products.
The production-line
Hi John:
> No; France and Norway have 'IT' systems, in which grounding is only to
> prevent static charge build-up; the neutral is grounded through an
> impedance at the sub-station. AIUI, this is used in mountainous
> districts where ground paths are long and of low conductivity. The
Hi Peter:
As I have already written, I feel that "safety-critical
component" as well as "safety-related component" are terms
that require more consideration than is necessary.
Basically, as I understand what you have said, a safety-
critical component is one where its failure creates a
hazar
Hi Lauren:
There are different definitions for "safety-critical
component" based on the different needs for identification
of such components. I'd like to list a few, and then
offer yet a different definition of a safety-critical
component.
1. A safety-critical component is a component w
Hi Jack:
> I'm having a problem with Rich's explanation in this particular case (I know
> it's often true, though). How did resisitive heating occur *without*
> current flow? It was clearly stated that the heater was switched OFF.
I believe that the process I described takes a
lot o
Hi Jim:
> Thanks Rich: I suspect you're right. Isn't that mechanism exactly what the
> tracking index tests are meant to address? I thought that any UL-approved
> wiring device like this would have a material that is designed to resist
> tracking, hence my speculation that contamina
Hi Jack:
> You are implying, but not stating, that NEC has the force of law
> regarding the domestic environment.
I meant to state that the NEC does indeed have the force
of law not only for the domestic environment but for all
electrical installations within the scope of the NEC.
> T
Hi Jim:
> I'm curious: given that North American plug blades are >1/2" apart, there
> must have been substantial contamination to aid in 120Vac jumping that far
> (arcing). Did you identify any sort of contamination or moisture?
I don't believe contamination is a significant factor
i
Hi Gregg:
> Just to ensure that I have my understanding right - if the equipment is used
> where OSHA applies then it must be approved by a third party like UL
Yes. More specifically:
If... the product is used by an employee in the workplace...
Then... the product must be certi
Hi Gary:
Somewhere in my past, I've heard the rationale for
this conundrum. I'm just guessing here.
Power cords and similar mains devices are sized
based on rated load, and are not sized based on
fault-condition load.
The requirement should be that, under fault
conditions, the device is
Hi Mike:
> Can someone point me to a section in the NEC that says a piece of
> RESIDENTIAL computer equipment must be "listed" (NEC definition). Article
> 645 which requires a "listed" piece of equipment appears to apply to a
> computer room and not a residence.
In terms of the NEC
Hi Peter:
As a general rule, the insulation on the outside of
an electrolytic capacitor is considered functional
insulation. (Indeed, the insulation between the
elements of the capacitor and the aluminum can is
clearly functional insulation.)
As far as I know, only X- and Y-capacitor insu
Hi Peter:
> Any limitations/requirements for amount of light emitted from professional
> photography flashes? Any UL, IEC or European standards which specify
> limitations?
>
> I know how many you like being photographed - but imagine what harm one of
> these flashes can cause to
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