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
Hi Charles:
a) Does anyone one know the genesis
of the requirement to lift the Neutral
AND the Ground simultaneously
during a leakage current test??
(I am referring to UL6500)
While I am not familiar with UL 6500 per se,
I believe I can comment on the lift of the
neutral.
Some fire tests use a methenamine timed burning
tablet.
This tablet is specified in USA government
standards for furniture flammablity testing.
(See 16 CFR Part 1630.4 or CPSC standard FF 1-70.)
It is also specified in ASTM D2859. I have also
seen it used to test fire enclosures
in
Hi Tom:
In 60950, applicable clauses are 2.10.5.3 and 2.10.5.1 (I'm not
reading genuine IEC/EN 60950, and I'm sorry if I'm wrong) -
the former states that distance through insulation would be applied
in such situation, and the latter set minimum thickness of 0.4mm
for
Hi Chris:
To me, it's sort of funny in that it just says that the Creepage and
Clearance distances do not apply on inner layers of void free PCBs.
That's nice; but I can't find where a distance is specified. I mean, I
would think that there should be some minimum distance between
Hi Chris:
To me, it's sort of funny in that it just says that the Creepage and
Clearance distances do not apply on inner layers of void free PCBs.
That's nice; but I can't find where a distance is specified. I mean, I
would think that there should be some minimum distance between
Hi Kris:
The markings on the power supply are: (also as per UL file)
Date code
model number
electrical ratings
Class 2 transformer
The additional markings are:
CAUTION, Risk of electric shock and Dry location use only and Do not
expose to liquid, vapor, or rain
Hi Kris:
A product from manufacturer X is delivered with a (direct plug-in) power
supply from mftr Y to customers in Canada.
Regarding the power supply, it is UL approved + UL listed and has the UL
marking with C and US.
The warning marking on the power supply is only in
It has been some time since I have had to explain
or justify product safety activity to a high-level
manager-type. As others have said, it is fraught
with difficulties.
Success depends on first determining the mindset
of the person asking the question. I believe I
would first ask a
Hi Ged:
In transformers with REINFORCED INSULATION or DOUBLE INSULATION the
insulation between 1ary and 2ary windings shalll consist of -
- 1 insulation layer having thickness at least 1mm, or
- at least 2 insulation layers with total thickness not less than 0.3mm, or
- 3
Hi Ron:
Two years ago, Jim Bacher presented my paper,
Equipotentiality and Grounding -- Deriviation
of Grounding Resistance for Equipment
at the IEEE EMC Symposium Product Safety Workshop.
This paper is available for download from the IEEE
PSTC Mindcruiser web site:
Today, a message was posted that violates IEEE
emc-pstc rules against advertising. Here is
our rule:
-
5. Blatant or overt advertising of goods or services is not permitted.
The listserver is provided as a service by the IEEE, whose policies
prohibit anything that might be
Hewlett-Packard Company San Diego site is looking
for a high-level product safety engineer.
The major job function is that of advising product
designers on
1) innovative safeguards for new products, and
2) safety certification requirements for new
products.
The ideal
Hi Xing Weibing:
We can read from table 5A of IEC60950:1999:
Touch current limit for accessible parts and circuits not connected
to protective earth: 0.25 mA
question 1 : How does it (0.25mA) come from and what it is based on?
For grounded (Class I) equipment for the home, the UL
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Hi Gert:
I also tried the discharge between two fingers, and found the result to
be unpleasant at least.
Time to change standards...
Now we must ask the question:
Is the purpose of the standard to prevent
injury or to prevent an unpleasant experience?
I presume that
Hi Gert:
I also tried the discharge between two fingers, and found the result to
be unpleasant at least.
Time to change standards...
Now we must ask the question:
Is the purpose of the standard to prevent
injury or to prevent an unpleasant experience?
I presume that
Hi Tom:
So, for voltage up to 450V d.c. (i.e. up to 318V a.c.), capacitor
up to 0.1uF will become a Limited Current Circuit, hence the voltage
is not Hazardous Voltage (1.2.8.4) - no additional condition would
be required for the capacitor connected to the primary circuit.
Hi Tom:
So, for voltage up to 450V d.c. (i.e. up to 318V a.c.), capacitor
up to 0.1uF will become a Limited Current Circuit, hence the voltage
is not Hazardous Voltage (1.2.8.4) - no additional condition would
be required for the capacitor connected to the primary circuit.
Hi Rob:
I am in discussions with a potential supplier of IT equipment, Its our
usual policy to request testing to a listed standard
such as UL 60950 for safety in North America.
The supplier has replied that this is not mandatory.
Is he correct? what compels safety
Hi Rob:
I am in discussions with a potential supplier of IT equipment, Its our
usual policy to request testing to a listed standard
such as UL 60950 for safety in North America.
The supplier has replied that this is not mandatory.
Is he correct? what compels safety
Hi John:
I read in !emc-pstc that Crabb, John jo...@exchange.scotland.ncr.com
wrote (in B6CD5947CF30D411A1350050DA4B75FF03C2341C@sgbdun200.scotland.n
cr.com) about 'South Korean Power System', on Wed, 20 Feb 2002:
Typically I would expect IT equipment to be safe if line and
Hi Chris:
1. Can anyone else verify the breakdown voltage of 1Megavolt/meter for
air? Seems different than what I can remember; but I don't have a
reference handy. It also seems to me that this would be very dependent
upon humidity and pollution degree?
In a separate message,
Hi Scott:
The scope of EN 60825-1 says LEDs are included whenever the word laser
is used, meaning they are to be evaluated the same way lasers are. Does
this apply to status indicating LEDs (non-lasing)? If so, are
manufacturers expected to test every status-indicating LED on
Hi Ed:
With few exceptions, most power distribution
systems have one pole of the supply, the
neutral, grounded. (Indeed, the definition
of neutral for single-phase systems is the
grounded conductor.)
In the IEC scheme of the world, a power
distribution system where the neutral is
A good source is http://kropla.com/electric2.htm
http://kropla.com/electric2.htm .
According to that site:
Japan100V50/60 Hz*
*Eastern Japan 50 Hz (Tokyo, Kawasaki, Sapporo, Yokohoma, and Sendai)
*Western Japan 60 Hz (Osaka, Kyoto, Nagoya, Hiroshima)
A request from your list administrators...
Except... I (and other classic Compuserve users) won't see these messages
at all, unless and until they appear in someone else's REPLY in a form
Compuserve can send. It LOOKS great - but please don't send HTML to the
list.
Cortland is
Hi Richard:
We may soon be privately labeling our products for a particular customer,
and I have a question concerning the EU Declaration of Conformity. We will
be shipping products to our customer's distribution center, and they will be
responsible for sales to their customers.
Hi Dan:
I have received no emails today. Did my subscription cease?
No, your emc-pstc subscription is not terminated.
Today is the most unusual day in the history of
emc-pstc in that there were no postings to the
listserver between 5:30 PM PST Tuesday and 11 AM
PST Wednesday.
I,
Hi Pierre:
Unfortunately, Hexamine is temporarely unavailable from IMSPLUS, and,
furthermore, this product cannot be sold outside the US.
If somebody knows another source, he's welcome !
I did a Google search and found at least one more source:
Hi Pierre:
Reading the standard, I understand that the cloth used on the front of the
loudspeaker (external to fire enclosure) has to be tested according the
tablet test (see Table 13).
As I recall (from the UL standard), the tablet is
hexamine.
I have purchased tablets from:
Hi Joe:
We have a customer that is concerned about how our product, laboratory
equipment, will respond to electromagnetic disturbances from a high speed
train that runs close to their lab. The customer states that the
disturbance will be around 0.7-1.2 m Teslar.
I believe you
Hi George:
However, for the U.S. OSHA establishes acceptable NRTLs, and the
CFR uses the words NRTL, so I do not see how an electrical
inspector could object to what the Federal Government has sanctioned.
The inspector must abide by the certifications
approved by the local
Hi Gregg:
My understanding if that:
where OSHA is applicable then UL or equivalent is mandatory.
True. However, replace UL or equivalent with NRTL.
where OSHA is not application then Local Code is mandatory - and LOCAL
Code
requires NRTL (UL or equivalent)
Not
Hi Gregg:
Let me start by asking one simple question - WHAT IS THE PURPOSE OF
CERTIFICATION?
1- to meet the legal requirement
2- help market the product
3- do the 'right thing'
4- not to kill anyone
5- make sure that the product is nor recalled
Most
Hi John:
But whichever method is adopted, the customer pays the bill eventually
and I
have more confidence in the highly competitive world of electronic
products
to come up with a cost-effective solution in a timely manner.
One of the USA's major objections to
Hi Keith and Ghery:
There are a number of effects of harmonic current
emission from non-linear loads.
1) When a large number of loads rich in triplen
harmonics are supplied from a 3-phase source,
the neutral current can be as high as root 3
of the phase current. (This effect
Hi Amund:
I suggest you and your client and the regulatory
authority meet to address the situation.
Here are the issues as I understand them from your
message:
1. In idle mode, the emissions are comfortably
below the maximum allowed emissions.
2. In transmit mode, the emissions
Regarding postings, here is a re-statement of our
guidelines that were sent to you when you
subscribed:
1. No attachments (because many of our subscribers
use dial-up modems for which message size
determines the download time).
If an attachment is appropriate or necessary to
docopocoss
This word was unknown to me. I checked an
American dictionary and could not find it.
Then, I called up the Google search engine
and entered the word, hoping to find an
English dictionary.
Google immediately came back with the
definition.
Rich
Hi Chris:
OSHA rules apply to employers.
OSHA electrical rules require employers (1) to
use only electrical products that have been
certified by an NRTL, or (2) in the case of
custom products, to test the product in place.
If you sell a non-NRTL-certified custom product
to an employer
Hi Stephen:
I think I missed the beginning of this thread, so
please forgive me if I rehash old ground.
The 'vertical line' and 'circle' you refer to, are
actually a 1 (One) and 0 (Zero); as in digital
logic on/off respectively.
My original posting on this subject
Hi Serge:
O = Out of Circuit
I = In Circuit
Note: while many people believe the symbols are O 1, they are in fact
O I
IEC 60417 Symbols 5007 and 5008 are neither:
the numbers 1 and 0, nor
the letters I and O.
They are the symbols depicted in the 60417
Hi Neil:
The origin may be true, but IEC60417 is quite clear. ON is a vertical line
(symbol 5007) and OFF is a circle (symbol 5008).
Agreed.
And thank you for the clarification.
Best regards,
Rich
---
This message is from the IEEE EMC
A week or so ago, I asked about the origin of the
0 and 1 symbols for off and on.
I mentioned that it was my recollection that the
the symbols came from early safety standards where
the off and on functions were by means of a
rotary switch where the 0/zero position was off.
I found some
I am looking for the origin of the power symbols
0 (off) and 1 (on).
The earliest standards that I have are CEE 10
and similar where the standard specifies something
like:
Where a rotary switch is used for power,
the 0 position shall be off and the 1 and
higher position shall be
Hi Richard:
What is a good source that explains the rational for the values for creepage
distances?
There was a good deal of research done in the late
'70s and early '80s on creepage distances and the
deterioration due to deposition of foreign materials
and the effects of humidity.
Hi Tom:
With a bit further search, I found:
http://w3.hike.te.chiba-u.ac.jp/iec417/html/doc/5180.html
This site specifies the use and the referring
standard:
Application: On any kind of equipment. To
identify equipment meeting the safety
requirements specified for class
Hi Tom:
I guess what you think is IEC 60417 No. 5180, which shows III
in diamond shaped frame (45 degree rotated square).
(http://member.nifty.ne.jp/tsato/terms/iec417-5180.gif)
Yes, this is the mark that was mentioned
to me.
However, I don't know which standard require the
A colleague recently showed me a Class III
identification mark. However, he had no
further information about the mark.
(The Class III mark would be used to identify
a Class III product similar to the way the
Class II mark square-within-a-square is used
to identify a double-insulated
Hi Tom:
Is it permitted to use PTC as an overcurrent protective device
for power sources not inherently limited?
I don't have EN60950-1 here, but I remember it must be a fuse
or other non-autoreset device.
I said:
The trick is to determine if your test houses can
Hello from San Diego:
One of our subscriber colleagues has pointed out that
my assertion that Europe uses yellow as the color of
the earthing wire is incorrect.
I recall when the green-yellow was agreed to for
power cords and internal equipment wiring. My
recall was that both yellow and
Hi Greg:
Why does True SELV require basic insulation
between SELV and earth?
What is the hazardous voltage source, and what
is the current path through the body if that
basic insulation should fail?
I believe (and I could be wrong) that it's a
Hi Alex:
We use a linear (basically a transformer with a PTC thermistor) class II
SELV O/P stand alone power supply rated 10Vac, 5A. One of the labs tested
the O/P Isc with a direct application of the sc. The other lab tested the
O/P Isc by applying a load of 8A. The results were
Hi Peter:
What is the percentage of color over a surface area for the insulated
green/yellow earthing conductor. Is it better to have more yellow than green
or more green than yellow. I know North Americans prefer more green than
yellow and Europeans like more yellow than green.
Hi John:
True SELV . requires double or reinforced insulation from hazardous
live parts/parts at hazardous voltages [different expressions used for
the same things] and basic insulation from earth. '950 SELV' allows SELV
circuits to be earthed (see 2.2.3.3 of IEC60950:1999 or
Hi John:
You may come across some distributors in Norway asking for DI or RI
between PRI-EARTH, even for Class 1 power supplies.
That's because Norway uses the 'IT' power distribution system, where
neither mains conductor is earthed directly, but one is earthed through
a
Hi John:
That depends on which variety of SELV you mean. True SELV, as opposed to
'950 SELV', requires double or reinforced insulation from earth
Why?
Best regards,
Rich
---
This message is from the IEEE EMC Society Product Safety
Hi John:
Y-caps have enough margin to easily withstand
the 4300 V dc without damage.
Without immediate failure, no doubt. But such a huge overstress may
cause latent damage that later results in failure, and, since IEC 60384
doesn't call for such an over-voltage test,
Hi Brian:
What I've always wondered about, at least for class 1 construction, is just
what is really being tested by the pri/sec hi-pot, when the customer chooses
to ground the power supply's return.
(These comments presume the secondary is SELV.)
When you use a ground for safety
Hi Brian:
I am attempting to comply with both the letter and spirit of 60950:2000, cl
5.2. Note that 5.2.2 allows for separate testing, according the type of
insulation required. When testing a (class 1) power supply, the withstand
level for primary to chassis is Basic; and for
use any plastic.
Best regards,
Rich
Rich Nute wrote:
The choice is yours. If your product is supplied by a
Limited Power Source, then you may use any plastic for the
enclosure. If your product is not supplied by a Limited
Power Source, then you must use V1 or better
Hi Doug:
I've only heard shortening the yellow light cycle
as an unconfirmed rumor. But I've been watching.
grin
According to our local newspaper, the San Diego Union-
Tribune, not only did the contract photo cops shorten
the yellow light, they also moved the sensors.
The
Hi David:
You probably already know this, but don't forget that the product will need
to pass temp tests during abnormals i.e., blocked vents.
I'm not sure if pass temp tests means compliance with
the heating requirements or the abnormal requirements,
so I offer this clarification.
Hi Paul:
Can anyone give me any information on whether a box with less than .33 cubic
feet needs to meet UL Flammability ratings?
I have been told this is true, but I can not find the location of that
information.
I believe the requirement you are referring to is
Sub-clause
Hi George:
I have a safety question for the group. I have a small (about 8 x 10 x 2
inch) piece of ITE equipment, SELV, enclosed in a plastic case, powered by
an external 12 volt brick from AC mains.
The problem is, the device tends to run a little hotter than desired.
Hi John:
I read in !emc-pstc that Rich Nute ri...@sdd.hp.com wrote (in
200202202227.oaa19...@epgc264.sdd.hp.com) about 'double-pole switching
and fusing', on Wed, 20 Feb 2002:
Tables 2E and 2F are invoked only by the Note 2
to Sub-clause 2.7.4.
A Note is informative
Hi John:
I believe the authors of 60950-22 expected that user-accessible parts would
comprise SELV circuits rather than grounded parts. See 2.1.1 and 2.2 in
60950-1.
Grounded parts would be subject to 5.1 in 60950-1.
Best regards,
Rich
- Original Message -
From: John Cochran
Subject: Re: [PSES] UL 60950-1 clause 2.2.3
In message f6d1e59f218e.540c8...@bendbroadband.com, dated Sun, 7
Sep 2014, Rich Nute ri...@bendbroadband.com writes:
I believe the authors of 60950-22 expected that user-accessible
parts
would comprise SELV circuits rather than grounded parts
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