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
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
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. There
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
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 solve
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 heart.
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
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
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
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 of
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
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.
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
in
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
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, a
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 your
Hi Peter:
Thanks for sending the UL letter and UL Listing Mark page.
I stand corrected.
For Information Technology Equipment, UL's letter of March 31,
1995, authorizes the optional use of the file number as the
control number.
Apparently, this option is not available for non-ITE products.
Hi Robert:
I got two NAV (Norton Antivirus) msgs back from the ieee.org that said my
attachment had a virus in it.
If so, please let me know, because there is nothing but text files (that I
know of) and a simple batch program in that attachment.
The IEEE listserver checks
Hi Gregg:
The File number 'may' be used on things like cable (it is common to see UL
and CSA file numbers) and other components - Control numbers (I forget the
correct terminology) is required on some UR components but not all Listed
products.
UL Listed wire:
According to
Hi Ron:
1. UL in a circle (the famous UL Listing mark symbol),
2. The word LISTED in capital letters,
3. The assigned control number*, and
4. Product identity (e.g., NWGQ, I.T.E., etc.)
* The assigned control number is a designation that UL assigns to a
manufacturer, or
Hi Chris:
Does the file number need to be on the label? Can the manufacturer
leave the file number off of the label and simply put a generic UL (or
CSA) mark on the product along with their nameplate identifying the
manufacturer, model and serial number?
In my response to
Hi John:
Not to Continental countries, AIUI, because rewirable plugs are not
available (maybe in Denmark still).
Oh? In April, 2001, I bought a re-wirable plug in Grenoble,
France, at a major chain store. They had a nice selection!
Best regards,
Rich
Hi Brian:
I have, w/in previous 6 mos, attended seminars offered by (2) agencies. I
learned much from both, and appreciated being able to talk to the gurus.
But upon review of seminar notes and manuals from previous Product Safety
Engineers, it would seem that issued
Hi Peter:
I agree with you with your statement rather than address products, safety
standards need to address hazards. However, the hazard standards must be
made taking into consideration the environment in which the product is used
light industry, heavy industry, medical,
Hi Gregg:
Consider the number of PRODUCT standards written - these reflect the
accepted degree of protection (Operator or User) for each product under
specified operating conditions and accepted uses.
I invite consideration of INJURY, and the means by
which an injury can occur from
Hi John:
But the standards for these products have to be written by experts in
the design of these products - non-experts would not know the problems
that can arise. To produce generic safety standards, experts in the
design of ALL products would be required. These exist only on
It is the primary end use of the product that dictates the standard(s)
required.
Unfortunately, this archaic and provincial view on
the part of standards organizations that standards
should be per product has created problems that
most of us would like to avoid.
Consider product
Hi John C. and John W.:
Would anyone have any guidelines on how to design computer graphics
in such a way to avoid inducing Photo Sensitive Epilepsy in anyone
who suffers from that complaint ?
..
..
..
A web search for 'epilepsy AND photosensitivity' will probably give you
Hi John:
Are you sure that you can get appreciable X-radiation at 8 kV? In the
days of monochrome TV with 9 and 12 inch tubes running at 8 kV, we never
bothered about X rays, but projection sets running at 25 kV were known
as a radiation hazard. Maybe tolerance levels have been
[quote]Hi,
I am basically an EMC guy and do not know much about UL requirements. I
would like to know if there are any UL requirements for a driver with
output voltage swing of +/- 30V peak-to-peak. The RMS voltage will be much
smaller, and the power will be less than 0.5 watt. The driver is
Hi Rick:
I am working on a project that delivers 8 KV to 1 CRTs mounted on a
helmet mounted display. The output of the high voltage supply is limited
to 100uA and assuming that the supply complies with paragraph 2.4 (2.4.4
in particular) Paragraph 2.4.1 states that:
Note that
Sorry to post here but am running into a brick wall at trying to find out
something as simple as the resistivity and dielectric constant for skin!
Does anybody have a source? Need quick, please.
- Robert -
Hi Robert:
The skin resistivity and dielectric
Hi Amund:
UL and/or CSA certification are mandatory within the electrical safety
area, to
have access to the US and Canadian marked. Right ?
Yes -- sort of. Safety certification of IT equipment
is mandatory in both Canada and the USA. However,
both countries accept safety
Hi Jim:
There are a number of ways to prove traceability
of bulk-labelled components, i.e., components
that are not indivually marked.
- unmarked components - may not be able to tell mfr and cat. no, let alone
agency status and ratings
These are really bulk-labelled components.
If
Hi Amund:
We want our IT product to be UL approved. We purchase a modified power
supply
(PS) which is not UL appoved. The original PS is UL approved. The only
difference in the PS is the value of one resistor which means that we now
can
take 2.3A/28VDC out instead of
Hi Lauren:
Does anyone have a practical or authoritative definition of Sound
Engineering Practice?.
The key word is sound. Presumably we all know
what engineering practice is.
I checked Merriam-Webster's on-line Collegiate
Dictionary and found the following definition.
The 3rd
Hi Richard:
A number of good comments have been made.
I'm not sure anyone covered the fact that
two wires make a bundle, and therefore each
single in that bundle must be derated.
So, a single 10 AWG is good for 32 amps at
20 C. But, two 10 AWG wires in the same
bundle are only good for
Hi George and Ravinder:
We really like to discourage off-topic discussions,
including virus warnings.
Here are some points I'd like to make:
1. The IEEE majordomo listserver includes virus checking
(for known viruses) of all messages posted to the
listserver. IEEE virus
Hi Ghery:
Also EN 61000-3-3 needs to be considered. Useless standards, if you ask me.
Agreed!
EN 61000-3-2 is driven by Euro power distributors
who don't want to correct for non-linear loads.
(But who have no quarrel with correcting for
phase angle.)
I don't understand the drive for
Hi Dan:
with a three prong NA cord set. I have found that if I bypass the earth
ground plug I can measure a 80 VAC potential from my chassis to earth
This is normal.
Consider the circuit:
L o- 120 V rms
|
|
2200 pf
The RCIC archive for emc-pstc messages will be shut
down, permanently, some time this week.
The archive itself is preserved.
We are working on a new web site for the archive.
We expect to announce the new web site along with
a number of other web-based features some time this
Fall.
We
Okay... more nostalgia and a bit on safety
back in those days... so that we don't stray
too far from the subject matter of this
forum.
My first TV was a Motorola 7-inch round in
a Bakelite cabinet. The speaker was the
same size as the CRT.
My second was the famous RCA 10-inch round
chassis
Hi Terry:
I don't recall the Sony but do recall the Philco and that Zenith held out
with the `hand wired' chassis.
Now that you mention it... I do indeed
recall that campaign. But, I did not --
then -- realize the context.
Today, looking back, that campaign was
really quite absurd!
I saw the first PCB show up in TVs,
Would you care to put a date on that?
You can't change the facts. So yes! In the Middle to late 50's. :-)
Having been a TV serviceman until 1960 (end of
my college days), I saw no PCBs in USA TVs.
I do recall PCBs in circa 1963 TVs.
Hi John:
This came up at IEC TC74 WG8 and was the object of several
proposals. We could come to no agreement about whether Class III
included TNV, earth connections, internally generated voltages of
assorted energies, etc., so we dropped the subject. It plays no
Hi Kyle:
I have a new product that includes an off the shelf UPS that is rated for
230V ac operation and has an internal single pole circuit breaker on the
mains inlet. We want to target this product world-wide. The UPS presently
is CB and certified to EN60950 european only.
Hi Tania and Richard:
When you find out any papers on this subject, please share with us.
I stumbled across a short, authoritative discussion
about why a mechanical vibration can feel like a
small electric shock. Actually, it is the other
way around. At small voltages and currents,
Hi Peter:
For back-up power supply connections to a device which has means for
connection to a floating dc input of 44-57 Vdc / 15 A max (to serve as
back-up source for the internal power over LAN source), what is the proper
way of marking with symbols to IEC60417
Does the
Hi Doug:
done, the entire safety approval reduced to a simple
cfm rating fan for a chip both on the secondary
side of the power supply.
The issue for me is: What is the safety requirement
that requires cfm (I presume a minimum cfm)?
Reading between the lines...
The fan
Hi Ken:
In conclusion, dithering will help you meet a test requirement, but it might
not actually reduce potential interferences.
I have come to the same qualitative conclusion,
and the EMC experts with whom I have discussed
this concept agree.
But, is there any evidence, anecdotal,
EMC Forum,
I apologize for the Shameless Advertisement on the Technocal Forum. It was
not my intention to break any rules of the IEEE society. I have been a
member for quite some time and thought that I have seen similar FREE OPEN
HOUSE events in the past. I have learned much from this
Hi Chris:
Consider a product with two, independent protective
grounding/earthing connections. This may be by
means of two power cords (as is done for uptime
reliablity by employing parallel power supplies) or
by means of one power cord and a separate ground
connection (as, for example, by
Hi Dave:
Can anybody tell me where it is defined at what point in production it is
permissible to apply the UL mark? Can it only be done after the hi-pot has
passed? Or is it OK to have the label applied before the test as long as the
units are clearly marked as having failed
Hewlett-Packard has 3 product safety jobs available.
Requisition Position Location
number
--- -
711022Safety EngineerVancouver, Washington
713386Regs/Safety Engineer Vancouver, Washington
713501
Hi John:
Because continuity at low current does not ensure that the protective
circuit will carry a large fault current - it might be 'hanging on by
one strand'.
Yes, for one strand. No, for five strands.
Some years ago, I did some experiments on what
problems the 25-amp test
Hi Tania:
I hate to call you an old-timer;-- I would rather state that you might be
thinking of UL 114 and UL478 standards that are no longer in force. B
ut I don't believe that even they allowed a willy-nilly change from groun
ded equipment to one that is ungrounded, unless
Do EU manufacturers have to fit a suitable mains plug
to appliances when exporting to USA?... or can it
be supplied without a plug, putting the requirement on the user
to follow the instructions - in my case, stating that
a grounding plug must be used ?
There are two answers:
Here's a web site that reports that CDs will come
apart if attempted to be read at 64x.
http://www.qedata.se/en-cdrom.htm
There is no data as to what happens in a real CD
drive.
Enjoy!
Rich
---
This message is from the IEEE EMC Society
I am in the UK, a customer in USA wants us to fit
2 pin mains plugs to the Class 1 appliances he
is going to be buying from us.
He is very firm that there are no regulations in US
that requires this to be so. Is that true?
The simple answer is that there is no regulation
Hi Ravinder:
I am interested in knowing if a 120V, 60Hz microwave oven can be safely
used on a 240V, 50Hz mains supply with a step-down transformer.
In essence, you are asking if a microwave oven
rated for 60 Hz will operate safely at 50 Hz.
I would guess that the microwave oven uses
A summary of the emc-pstc survey results is now available
on the Product Safety Newsletter web site:
http://www.ewh.ieee.org/soc/emcs/pstc/
The results are in a 16k pdf file. If you are unable to
access our web site, send e-mail to either Jim or Rich
and we will be happy to send you
Hell Duncan:
- Would they use S1 when leakage testing our type of equipment?
Your equipment is cord-connected equipment, not
direct-plug-in equipment. Therefore, S1 is not
used when testing leakage current from your
equipment.
- What is the definition of 'direct plug in' (it is
If you haven't filled out the IEEE emc-pstc survey,
please do so no later than 05 May.
Please go to this URL for the survey:
http://www.ewh.ieee.org/soc/emcs/pstc/Survey/
At my last check, only about 20% of our subscribers
have completed the survey. I'd really like to get
80% or
Hi Rick:
There are three issues which we must address:
1. The safety function of the switch.
2. The safety function of all-pole disconnect
versus one-pole disconnect.
3. The marking of the function of the switch.
*
The safety function of a disconnect device (for
which a
Dan Kinney asks about pole-to-pole hi-pot testing.
The hi-pot test determines that the product's
insulation (both air and solid) is sufficient to
withstand the normally-occuring transient over-
voltages on a power line. Transient over-voltages
are both differential-mode (pole-to-pole) and
Hi Ken:
Here are some quotes:
http://www.eskimo.com/~billb/weird/microexp.html#demo:
Q: Aren't these ovens tuned to a special frequency so they only heat
water?
A: No. The usual operating frequency of a microwave oven is nowhere
near the resonant frequency of water, and the
Hi Dave:
the UL report for the PSU, it states that the output is ELV, not SELV,
because of the connector interfacing the modules to the rack.
I don't see how a connector makes the difference
between ELV and SELV.
The terms ELV and SELV imply the energy is
derived from a hazardous
expressed as 'dmax', the maximum relative voltage change, measured as an
r.m.s. value over the worst half-cycle, starting from the zero-crossing.
While I suppose there are sophisticated oscilloscopes
that will make this measurement at the touch of a button,
I wonder how many colleagues
Hi George and all:
Yes, we are having some listserver multiple send
problems. Please bear with us while we fix the
problem.
Please direct all such questions to me or to one
of our admins at the bottom of the message. Even
your message could get sent multiple times, so we
want to keep the
Hello from San Diego:
One of my colleagues has added material of interest to
one of Chris Allen's humorous stories.
Best regards,
Rich
This is actually a true story (with some adjustment). It happened at a Ford
plant back in the 1930's (which makes the $50K fee all the more
Hi John:
Of course, no one has shown that unacceptable
overheating will actually occur.
Do you have any more such gems to contribute? What do you think happens
to the total current through a capacitor when the applied voltage
contains harmonics? What happens to the I^2R
Hi John:
I must admit to several motives for posting my
message regarding the WSJ-E opinion article.
1. I wanted our subscribers to know that the
issue rated comment in the WSJ-E, a high-
level, respected newspaper.
2. I wanted our subscribers to know that the
technical
With thanks to Ed Jones...
On Thusday, February 22, The Wall Street Journal Europe
published an interesting opinion on the harmonic current
emissions standard.
The opinion is by Rob Hunter, a lawyer and Chairman of
the Centre for the New Europe, a Brussels-based think
tank.
Mr. Hunter is
Hi Kaz:
Answering the question, what's the safety concern,
is a reverse-engineering process with respect to the
various requirements contained in the standard.
Applying the requirements of the standard to the
specific construction may involve or even require
interpretetation of the
Hi Kazimier and Terry:
Kazimier suggests asking the question:
what's the safety concern
Unfortunately, safety certification houses
do not have the option of accepting products
based on the answer to this question.
A safety certification house certifies a
product to a standard.
It appears that one of our subscribers has been subjected
to a virus. The IEEE listserver stripped the virus from
the posted messages, so the virus was not passed on to
you and our other subscribers.
It appears that the worst that has happened is that
duplicate messages were posted to the
Hi Bob, Pete, Gert:
A common equipotential environment is the goal. It's unfortunate we ever
started with the terms earthing or grounding.
Absolutely!
Furthermore, the equipotential environment can
be, and in some cases is, largely independent
of whether the protective conductor is
that come up.
If you find this listserver to be of value to you, and
you can spare some time each day to help, and you have
a high-speed connection to the internet, please
consider volunteering for 2 years to help keep this
service running.
Please contact me or Jim Bacher.
Best regards,
Rich Nute
ri
Hi Andy:
Is it possible that a piece of equipment with an NRTL listing can be
disconnected by a local electrical inspector/electrician enforcing the NEC
because that paticular NRTL is not approved in their jurisdiction?
Yes.
Please recognize:
NRTL is an OSHA program governing
Hi Chris:
For instance, one of the messages says that the NEC gives an electrician the
right to unplug an un-NRTL-marked piece of equipment. Another message
states that the NRTL's mark is the proof of product safety.
NRTL is a designation issued by OSHA.
Approved is a
Hi Courtland:
I have a question concerning labeling a product. If we go to a NRTL and get
Safety testing performed, we typically put the Safety logo (UL for example)
on the product label. Our marketing people have a problem with having
different logo's. They would like to
Hi Kate:
a) Do they allow presence in lab (technical area) itself ? If not, then
where are clients who are at the lab normally placed?
Depends on whether the lab is testing a competitor's
products. If not, then I can usually observe the
testing.
If I can't go into the lab to
Hi Paul:
However, to release the interlock, a PAUSE or STOP button is pressed which
allows the instrument to stop in an orderly way and then release the cover.
Best as I can tell, a red pushbutton, with PAUSE or STOP legend and the ! in
a triangle (to refer the operator back
I'd like to clear up a few things about the
situation regarding F-Squared Labs.
1. F-Squared Labs did NOT post its message to
the IEEE listserver. It appeared in our
distribution because one of our subscribers
inadvertantly included it as an attachment
to his posting.
Hi John:
Can you tell me the typical power consumption of a desktop
VDU. For example a Sun workstation VDU rating plate indicates
220-230 V 1.5A. Rather than assume or guess a power factor
value, what would the power reading (Watts) be approximately
at 220V for nornal
Hi Doug:
There are four observation periods listed in para 6.2.4 of A14 (table Z1), I
assume that I only have to pick the one that suitably qualifies my
equipment's operation, or must I apply each one to determine the best period
of observation?
From my reading of prA14 (I
Hi Craig:
Be careful:
EN61000-3-2 - Applies only to products with input power higher than
75W. Per paragraph 7.4 of the standard, no limits apply for equipment
with an active input power up to and including 75W.
No. The standard does NOT say that it applies only
to products with input
Hi Ed:
First of all the floating secondary ground (if not connected
directly to earth) should be treated as part of the secondary circuit
which in many cases will require reinforced insulation to the primary
circuit according to the working voltage measured.
There are two
Hi Ken:
See my paper on floating circuits in the Product Safety
Newsletter:
http://www.ewh.ieee.org/soc/emcs/pstc/tech-spk.htm
This should answer all your questions. If not, please
get back to me, and I'll answer any additional questions
you may have.
Best regards,
Rich
ps:
Hi Stig:
I believe you are interested in severity of injury,
not potential for injury, or risk of injury.
Here is a numerical assignment for severity of injury
that I found in my files. I have no idea of its
source.
10 Death
9 Long-term or permanent coma
8 Full body
Hi George:
Thanks for the quick response! Does this mean that the symbology is only
a Japan requirement? and does it apply to ITE as well as
audio-visual
equipment?
The referenced standard, EIAJ CP1104, is similar
to IEC 417. Indeed, EIAJ CP1104 contains many
Hi George:
The dc polarity symbol is specified in:
Symbol 01060 (taken from JEIDA 11)
EIAJ CP-1104 (1998)
Terms and Grpahical Symbols for Audio and Audio-Visual Equipment
Technical Standardization Committee on Audio-Visual Equipment and Systems
Electronic Industries
Hi Ken:
I wanted to pose the group a question in regards to spacing requirements for
the U.S. Many UL standards allow for the exception of components (such as
semi conductors, switches, etc) to not meet spacing requirements (as they
usually have different standards they meet
Hi Doug:
Your message was not clear whether you submitted
your product to the same NRTL that certified the
power supply.
Basically, your cert engineer has put YOU in the
middle of a beef between cert engineers or between
cert houses.
Your cert engineer found a fault in the power
supply
... check out:
http://www.ul.com/about/newsrel/nr101300.html
Rich
---
This message is from the IEEE EMC Society Product Safety
Technical Committee emc-pstc discussion list.
To cancel your subscription, send mail to:
majord...@ieee.org
Hi George and Chris:
Better still, TC76 should provide a spreadsheet such
that, upon entering all the data, the spreadsheet does
the calculations and gives you the emission level and
the emission Class.
Regards,
Rich
---
This message is from the
Hi Richard:
When testing plastics, the flame is applied for a specified period of time,
removed for specified period of time and the process is repeated for a
specified number of cycles. Is the procedure attempting to correlate with
observed fire patterns in equipment, or is it
201 - 300 of 569 matches
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