Re: [PSES] Spark Gap PCB Layout on AC Mains

[John Woodgate]

In message <1378784340.50598.yahoomail...@web160404.mail.bf1.yahoo.com>, 
dated Mon, 9 Sep 2013, Bill Owsley  writes:


Indeed... the protection scheme that passes Safety, causes the system 
to 'fail safe'  which does not meet the EMC immunity requirements


Plain EMC requirements do not consider fault conditions. Functional EMC 
requirements do.

--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
If dictionaries were correct, we would only need one, because they would all
give the same information.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: [PSES] AF ripple in DO-160

[Ken Javor]

Derek,

Check out section 16.7 control on current ripple ac/dc, power factor,
harmonic current.

Ken Javor
Phone: (256) 650-5261



From: Derek Walton 
Reply-To: Derek Walton 
Date: Mon, 9 Sep 2013 23:22:35 -0400
To: 
Subject: [PSES] AF ripple in DO-160

Hi Folks, 

the DO-160G conducted emissions limits begin at 150 kHz, I'm curious if
there are other controlling documents that restrict emissions below 150? I
believe Boeing does, and so does Airbus, but with DO-160 I don't see it.

I must have dozed through this discussion

Insight would be most welcome.

Sincerely,

Derek Walton
L F Research EMC facility.
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Re: [PSES] Spark Gap PCB Layout on AC Mains

[Joe Randolph]

Hi Brian:
Your story about the surge failure a few years ago sounds like it *might*
have been a case of having a surge protector threshold that was so low
that it "invited" surge currents into the equipment, although
the failure could also have been due to other causes.
Lightning always seeks the lowest impedance path to ground.  So, if
you connect ten different pieces of equipment in parallel on the same AC
mains line, the one with the lowest breakdown voltage to earth will try
to draw all of the surge current.  In some cases it can become the
sacrificial element that "protects" all the other
elements.  These types of scenarios are one of the reasons that I
prefer to block surges when possible rather than conduct them, as I
described in an earlier posting.
You mention that for your current project, many of the
circuits/assemblies you are trying to protect are buy/sell products where
you don't control spacings.  If that is the case, putting big
spacings on your AC distribution board may not help much.  The surge
will just find a weaker spacing farther inside your system, which is
precisely what you are trying to avoid.
I don't know enough about your system to suggest a solution.  As you
note, one option is to put your protection right at the AC mains input
and then make sure that it holds surge voltages below the breakdown level
of the weakest circuit/assembly behind it.  Properly done, you might
be able to arrange things so that most of the predictable failure modes
damage only that front end board.  
Another option that would be technically preferable but possibly too big
and expensive would be to put a high-dielectric isolation transformer
right at the AC mains input.  That can greatly simplify the
protection scheme and make it more robust too.
One thing to keep in mind is that in large interconnected systems that
have multiple connections to earth ground, a phenomenon called
"ground potential rise" (GPR) can cause surges to come up
through one ground connection and go out another.  The GPR mechanism
is probably the most difficult one for most people to visualize.  I
included some simplified drawings of this mechanism in the IEEE paper
posted on my web site.
If your system has multiple paths to earth ground, you should look very
carefully at whether GPR presents a risk for your system.  If so,
you may need to place some requirements on how the system is installed
and bonded to earth ground.

Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
j...@randolph-telecom.com
http://www.randolph-telecom.com


What are the safety
considerations using gas tubes on the AC mains? Do you have to fuse them
or are they not likely to fail shorted? Can you use them between line and
PE? Do you have to use multiple parts in series? I often see them in
series with MOVs in a “T” configuration to protect against line to
line and line to PE surges.
 
A few year back we had a product that had several surge suppression
circuits located on different PC boards within (some assemblies were very
expensive and we wanted to protect them). Well, at our customer site they
experienced some kind of huge surge, transient or overvoltage (we do not
know what exactly happened). Of all the equipment that was on-site
including many of our competitors equipment, only our instrument was
damaged. Our surge suppressors were blown up, charred, and/or
vaporized.  The warranty repair cost was $10,000US but the hit to
our reputation was probably worst. We believed that our equipment
probably protected all the other equipment on-site but it is hard to get
your customers to believe you. So now we want to better control our surge
protection and if we see a huge surge we hope it to destroy something
much less expensive to replace or at least minimize the damage. 
 
What we are currently thinking is to use over the counter Surge
Suppressor modules, but they are only good to about 3KV – 4KV. Then we
thought we would add aa spark-gap in the board that would only kick in if
our surge suppressors failed. Maybe we can add some very high voltage Gas
Tubes also or instead of the spark-gap.  I’m not sure what more we
can do. Many of the circuits/assemblies we are trying to protect are
buy/sell components where we do not control spacings. 
 
Any comments?
 
Thanks to all.
 
The Other Brian
 
From: Anthony Thomson
[mailto:ton...@europe.com]

Sent: Monday, September 09, 2013 4:18 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Spark Gap PCB Layout on AC Mains
 
Hello Brian,
 
I've employed spark gaps, like you, not because you 'have' to but because
it seemed good practice. It involved a control installation with cables
strung externally.
 
My advice is to use propriatory discharge tubes. They're cheap and 
their performance is more predictable than engineering your own air gap
across PCB tracks or using pointy pins and are much less influenced
physical and environmental conditions such as temperature and humidity,
etc. And s

Re: [PSES] Spark Gap PCB Layout on AC Mains

[Bill Owsley]

Indeed... the protection scheme that passes Safety, causes the system to 'fail 
safe'  which does not meet the EMC immunity requirements.
The previous 'remove the protection from the circuit for the hi-pot test' seem 
to have been removed. Now the IGBT's serve to cause the fuse to go open, which 
is fine for the Safety guys.




>
> From: "McInturff, Gary" 
>To: EMC-PSTC@LISTSERV.IEEE.ORG 
>Sent: Monday, September 9, 2013 11:42 AM
>Subject: Re: [PSES] Spark Gap PCB Layout on AC Mains
> 
>
>
> 
>Yet another example that transistors and IC’s were invented to protect fuses 
>and surge protectors. 
> 
>Gary
> 
>From:Kunde, Brian [mailto:brian_ku...@lecotc.com] 
>Sent: Monday, September 09, 2013 8:31 AM
>To: EMC-PSTC@LISTSERV.IEEE.ORG
>Subject: Re: [PSES] Spark Gap PCB Layout on AC Mains
> 
>What are the safety considerations using gas tubes on the AC mains? Do you 
>have to fuse them or are they not likely to fail shorted? Can you use them 
>between line and PE? Do you have to use multiple parts in series? I often see 
>them in series with MOVs in a “T” configuration to protect against line to 
>line and line to PE surges.
> 
>A few year back we had a product that had several surge suppression circuits 
>located on different PC boards within (some assemblies were very expensive and 
>we wanted to protect them). Well, at our customer site they experienced some 
>kind of huge surge, transient or overvoltage (we do not know what exactly 
>happened). Of all the equipment that was on-site including many of our 
>competitors equipment, only our instrument was damaged. Our surge suppressors 
>were blown up, charred, and/or vaporized.  The warranty repair cost was 
>$10,000US but the hit to our reputation was probably worst. We believed that 
>our equipment probably protected all the other equipment on-site but it is 
>hard to get your customers to believe you. So now we want to better control 
>our surge protection and if we see a huge surge we hope it to destroy 
>something much less expensive to replace or at least minimize the damage. 
> 
>What we are currently thinking is to use over the counter Surge Suppressor 
>modules, but they are only good to about 3KV – 4KV. Then we thought we would 
>add a spark-gap in the board that would only kick in if our surge suppressors 
>failed. Maybe we can add some very high voltage Gas Tubes also or instead of 
>the spark-gap.  I’m not sure what more we can do. Many of the 
>circuits/assemblies we are trying to protect are buy/sell components where we 
>do not control spacings. 
> 
>Any comments?
> 
>Thanks to all.
> 
>The Other Brian
> 
>From:Anthony Thomson [mailto:ton...@europe.com] 
>Sent: Monday, September 09, 2013 4:18 AM
>To: EMC-PSTC@LISTSERV.IEEE.ORG
>Subject: Re: [PSES] Spark Gap PCB Layout on AC Mains
> 
>Hello Brian,
> 
>I've employed spark gaps, like you, not because you 'have' to but because it 
>seemed good practice. It involved a control installation with cables strung 
>externally.
> 
>My advice is to use propriatory discharge tubes. They're cheap and  their 
>performance is more predictable than engineering your own air gap across PCB 
>tracks or using pointy pins and are much less influenced physical and 
>environmental conditions such as temperature and humidity, etc. And should 
>they ever be needed, the consequences can be much less messy.
> 
>I found a good selection available and looked at PCB mounting tubes with 
>breakdown voltages of between 3 and 12 kV. I finally used 4kV, 5kA/10kA (10/1 
>discharges) devices having been influenced by what professional LAN & GPS 
>installers were using which largely ranged between 3 and 6 kV.
> 
>Just my thoughts.
>T
> 
> 
> 
> 
> 
>- Original Message -
>>From: Kunde, Brian
>>Sent: 09/06/13 04:56 PM
>>To: EMC-PSTC@LISTSERV.IEEE.ORG
>>Subject: [PSES] Spark Gap PCB Layout on AC Mains
>> 
>>Our engineers are working on an AC Mains Distribution PCB. Like most 
>>electronic devices, we have seen the damage caused by lightning strikes. So 
>>we are increasing our creepage and clearance distances as wide as we can and 
>>still meet other requirements.
>> 
>>But no matter what spacing you design to, there is a lightning bolt out there 
>>that will exceed the design and it will arc somewhere. So the question came 
>>up to whether it makes sense to deliberately make a weak spot, or an area 
>>where the clearance is slightly smaller to control where a lightning/surge 
>>pulse will arc and/or discharge, like a Spark-Gap.
>> 
>>I have seen spark-gap lay outs on PC boards on I/O connectors; usually for 
>>ESD protection,  but not on AC Mains. Is this a bad bad idea or something 
>>worth doing?  Pros and Cons? Other suggestions??
>> 
>>Thanks to all for your help.
>> 
>>The Other Brian
>>
>>
>> 
>>LECO Corporation Notice:This communication may contain confidential 
>>information intended for the named recipient(s) only. If you received this by 
>>mistake, pleas

Re: [PSES] Spark Gap PCB Layout on AC Mains

[Joe Randolph]

Hi Gert:
Thanks, it's nice to see that gas tubes rated at several thousand volts
do exist.  
I looked at the data sheet and it is unclear whether these gas tubes
would reset to the off condition after the surge ends, given that in
Brian's application there might be 120/240 VRMS across the gas
tube.  The so-called "follow-on" current that the normal
120/240 VRMS supply can deliver might keep the gas tube in the on
condition, unless the gas tube extinguishes very rapidly in response to a
zero crossing of the 50/60 Hz waveform.
This may be one of the reasons why some applications use an MOV in series
with the gas tube.  The MOV would block the follow-on current, while
the gas tube would set the turn-on voltage.

Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
j...@randolph-telecom.com
http://www.randolph-telecom.com


The First Google hit …..
 
http://www.littelfuse.com/products/gas-discharge-tubes/high-voltage-gdt.aspx
 
(no connections with them)
 
Anyway, the primary circuit always need to be build for high surge
currents, 
and one should always insert induction to limit surge currents.
As the impedance of the spark gap is low, only a small amount of
induction
will reduce the surge current substantially.
 
Regards,
Ing.  Gert Gremmen, BSc
 
 
 
 
 
Van: Joe Randolph
[mailto:j...@randolph-telecom.com]

Verzonden: Friday, September 06, 2013 11:32 PM
Aan: EMC-PSTC@LISTSERV.IEEE.ORG
Onderwerp: Re: [PSES] Spark Gap PCB Layout on AC Mains
 
Hi Gert:
Do you know of a source for a small, inexpensive gas tube with a rated
breakdown voltage in the range of 6 KV to 10 KV?  I don't, but I'd
like to know of a suitable source.
As I noted, conventional gas tubes are typically rated at a few hundred
volts.  Putting a 400 volt gas tube across a barrier that breaks
down at 6 KV to 10 KV invites surge currents that otherwise would not
occur.

Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
j...@randolph-telecom.com
http://www.randolph-telecom.com



An air gap is a gas tube without the tube……
And the air properties vary, and so the performance with altitude ,
humidity and pollutions.
So just use a commercial available gas discharge tube ….!
 
I have seen and recommended ( in that order ;<) mains wire coiled
into
a 10 cm coil before being connected to a spark device., thus adding a bit
of inductance
to reduce the current. That fits nice with  your observations on
high breakdown voltages.
 
Gert Gremmen
 
Van: Joe Randolph
[mailto:j...@randolph-telecom.com]

Verzonden: vrijdag 6 september 2013 21:06
Aan:
EMC-PSTC@LISTSERV.IEEE.ORG
Onderwerp: Re: [PSES] Spark Gap PCB Layout on AC Mains
 
Hi Doug:
You mention that there are companies that make air gaps.  Are these devices anything like what I described?  
What I have in mind is an inexpensive component about the same physical size and cost as a gas tube, with two tungsten electrodes separated by an air gap of 5 to 10 mm to achieve a nominal air breakdown levels in the range of 6 KV to 10 KV.  I don't think corona would be an issue in an application where the normal working voltage is just 120/240 VRMS AC main voltages.
The intended use would be what I think Brian had in mind, which is to provide a known path for surges that exceed the rating of the insulation.  If the size of the air gap is coordinated properly with a good insulation barrier, the gap could be expected to trigger very rarely (if ever) in the product's lifetime.

Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
j...@randolph-telecom.com
http://www.randolph-telecom.com


Joe,
 
Yes we are in agreement, and you make several valid points regarding gas discharge tubes.  As is always the case in any design, there are trade-offs.  
 
I have found it beneficial to use a combination of the very good ideas being discussed on this thread.  For example, solid insulation barriers in combination with EMI filtering and surge suppression.  The solid insulation an be judicially placed with thickness sufficient to prevent punch-thru and sufficient creepage distance to prevent flashover.  An EMI filter adds come level of series impedance to high frequencies and surge suppression devices behind this are less likely to fail.  Gas discharge tubes have another problem in that a poorly selected voltage breakdown may cause the gas to glow under normal operating conditions and these devices are nothing like the old neon lamps, they will fail as a result.  In addition, when they do fire, they are unlike MOVs in that they clamp to near zero volts and the only way to extinguish the plasma within the tube is a zero crossing of the line voltage.  MOVs are always suspect because of the leakage current heating problem and catastrophic failure mode where they sputter metal on nearby surfaces.  There are companies who make air gaps and these are viable so long as they do not have a problem with corona when the electrodes erode (due to arcing) into r

[PSES] AF ripple in DO-160

[Derek Walton]

Hi Folks,


the DO-160G conducted emissions limits begin at 150 kHz, I'm curious if there 
are other controlling documents that restrict emissions below 150? I believe 
Boeing does, and so does Airbus, but with DO-160 I don't see it.


I must have dozed through this discussion


Insight would be most welcome.


Sincerely,


Derek Walton
L F Research EMC facility.

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[PSES] SAE document

[Derek Walton]

HI All,


does anyone know where I can get AIR6219 


The SAE site says not available for purchase right now.


Sincerely,


Derek.

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Re: [PSES] Spark Gap PCB Layout on AC Mains

[mark gandler]

Brian,

The main safety considerations in using VDR/MOV or MOV and GDT in series in 
primary circuit  (at least per 60950) are outlined in  section 1.5.9 and Annex Q

 

One key factor is about to change in EN60950-1 A2 (currently released as 
IEC60950-1 ed2.2 and draft A2 for EN60950-1). Previous revisions allowed BASIC 
insulation to be bridged by MOV and GDT if met certain conditions (perm. 
Connected equipment, Pluggable Type B and perm. Connected earth) and GDT 
complying with FUNCTIONAL insulation requirements and spacing.

 

New A2 will require GDT bridging BASIC insulation to comply with BASIC 
insulation requirements and spacing. 

 

And it is not allowed to bridge Double, re-enforced or supplementary insulation 
by VDR.

 

mark

 

From: Kunde, Brian [mailto:brian_ku...@lecotc.com] 
Sent: Monday, September 09, 2013 8:31 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Spark Gap PCB Layout on AC Mains

 

What are the safety considerations using gas tubes on the AC mains? Do you have 
to fuse them or are they not likely to fail shorted? Can you use them between 
line and PE? Do you have to use multiple parts in series? I often see them in 
series with MOVs in a “T” configuration to protect against line to line and 
line to PE surges.

 

A few year back we had a product that had several surge suppression circuits 
located on different PC boards within (some assemblies were very expensive and 
we wanted to protect them). Well, at our customer site they experienced some 
kind of huge surge, transient or overvoltage (we do not know what exactly 
happened). Of all the equipment that was on-site including many of our 
competitors equipment, only our instrument was damaged. Our surge suppressors 
were blown up, charred, and/or vaporized.  The warranty repair cost was 
$10,000US but the hit to our reputation was probably worst. We believed that 
our equipment probably protected all the other equipment on-site but it is hard 
to get your customers to believe you. So now we want to better control our 
surge protection and if we see a huge surge we hope it to destroy something 
much less expensive to replace or at least minimize the damage. 

 

What we are currently thinking is to use over the counter Surge Suppressor 
modules, but they are only good to about 3KV – 4KV. Then we thought we would 
add a spark-gap in the board that would only kick in if our surge suppressors 
failed. Maybe we can add some very high voltage Gas Tubes also or instead of 
the spark-gap.  I’m not sure what more we can do. Many of the 
circuits/assemblies we are trying to protect are buy/sell components where we 
do not control spacings. 

 

Any comments?

 

Thanks to all.

 

The Other Brian

 

From: Anthony Thomson [mailto:ton...@europe.com] 
Sent: Monday, September 09, 2013 4:18 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Spark Gap PCB Layout on AC Mains

 

Hello Brian,

 

I've employed spark gaps, like you, not because you 'have' to but because it 
seemed good practice. It involved a control installation with cables strung 
externally.

 

My advice is to use propriatory discharge tubes. They're cheap and  their 
performance is more predictable than engineering your own air gap across PCB 
tracks or using pointy pins and are much less influenced physical and 
environmental conditions such as temperature and humidity, etc. And should they 
ever be needed, the consequences can be much less messy.

 

I found a good selection available and looked at PCB mounting tubes with 
breakdown voltages of between 3 and 12 kV. I finally used 4kV, 5kA/10kA (10/1 
discharges) devices having been influenced by what professional LAN & GPS 
installers were using which largely ranged between 3 and 6 kV.

 

Just my thoughts.

T

 

 

 

 

 

- Original Message -

From: Kunde, Brian

Sent: 09/06/13 04:56 PM

To: EMC-PSTC@LISTSERV.IEEE.ORG

Subject: [PSES] Spark Gap PCB Layout on AC Mains

 

Our engineers are working on an AC Mains Distribution PCB. Like most electronic 
devices, we have seen the damage caused by lightning strikes. So we are 
increasing our creepage and clearance distances as wide as we can and still 
meet other requirements.

 

But no matter what spacing you design to, there is a lightning bolt out there 
that will exceed the design and it will arc somewhere. So the question came up 
to whether it makes sense to deliberately make a weak spot, or an area where 
the clearance is slightly smaller to control where a lightning/surge pulse will 
arc and/or discharge, like a Spark-Gap.

 

I have seen spark-gap lay outs on PC boards on I/O connectors; usually for ESD 
protection,  but not on AC Mains. Is this a bad bad idea or something worth 
doing?  Pros and Cons? Other suggestions??

 

Thanks to all for your help.

 

The Other Brian


  _  


LECO Corporation Notice: This communication may contain confidential 
information intended for the named recipient(s) only. If you received this by 
mista

Re: [PSES] Spark Gap PCB Layout on AC Mains

[John Woodgate]

In message 
<64D32EE8B9CBDD44963ACB076A5F6ABB0266533F@Mailbox-Tech.lecotech.local>, 
dated Mon, 9 Sep 2013, "Kunde, Brian"  writes:


What are the safety considerations using gas tubes on the AC mains? Do 
you have to fuse them or are they not likely to fail shorted?


Not likely, but in theory anything with metal electrodes can arc over, 
and the arc has negative resistance. Fuses may not help, because they 
can arc over as well.


Can you use them between line and PE? Do you have to use multiple parts 
in series? I often see them in series with MOVs in a “T” 
configuration to protect against line to line and line to PE surges.


Opinions tend to differ on this. The text in IEC 60950-1 was quite 
controversial.

 

A few year back we had a product that had several surge suppression 
circuits located on different PC boards within (some assemblies were 
very expensive and we wanted to protect them). Well, at our customer 
site they experienced some kind of huge surge, transient or overvoltage 
(we do not know what exactly happened).


That's a pity. It might have paid to hire an expert to try to find a 
cause.


Of all the equipment that was on-site including many of our competitors 
equipment, only our instrument was damaged. Our surge suppressors were 
blown up, charred, and/or vaporized.  


Surges can be extremely selective like that.

The warranty repair cost was $10,000US but the hit to our reputation 
was probably worst. We believed that our equipment probably protected 
all the other equipment on-site but it is hard to get your customers to 
believe you. So now we want to better control our surge protection and 
if we see a huge surge we hope it to destroy something much less 
expensive to replace or at least minimize the damage.


Do you know about the collection of science and lore on protection in 
the ITU-T series K publications? You can get these from: 
http://www.itu.int/rec/T-REC-K/e
and I think they are free, but there may be a limit on how many one 
person can download.


What we are currently thinking is to use over the counter Surge 
Suppressor modules, but they are only good to about 3KV – 4KV. Then 
we thought we would add a spark-gap in the board that would only kick 
in if our surge suppressors failed. Maybe we can add some very high 
voltage Gas Tubes also or instead of the spark-gap.  I’m not sure 
what more we can do. Many of the circuits/assemblies we are trying to 
protect are buy/sell components where we do not control spacings.


I suggest you look at the K series publications before making any 
decision.

--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
If dictionaries were correct, we would only need one, because they would all
give the same information.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

-

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Re: [PSES] Spark Gap PCB Layout on AC Mains

[Boštjan Glavič]

Hi Brian,

Standard IEC 60950-1 only allows  use of MOV or combination MOV + GDT in 
primary circuit. No other surge protectors are allowed.

As you mentioned, manufacturers are mostly using T protection (2 MOVs and one 
GDT).
Best regards,
Bostjan


On 9. sep. 2013, at 18:00, "Cortland Richmond" 
mailto:k...@earthlink.net>> wrote:

Some years ago I was working at in a wireline telecomms equipment maker.  
Robust protection was the order of the day; the outside physical plant was just 
*waiting* for lightning.

We protected each circuit to a level it could withstand, and worked back to the 
line inputs, where (IIRC) we had to withstand 2 KV Oc or 500 Amp short circuit 
lightning transients.   It helped that everything in the Central Office had a 
common-point ground, even if it was 150 feet below, in the basement, as this 
made backdoor entry less likely.

In a later incarnation, I found aviation customers who wanted to test transient 
protection without opening the equipment, which is another story -- and on 
these, we had to inject transients on the CASE.

I suggested some commercially available modules for AC power protection here 
because one does NOT want to try to protect the AC power network, only what he 
builds, and just throwing in spark gaps, gas tubes, Tranzorbs(tm) or MOV's 
might be asking for trouble. Know the threat, and protect against THAT.

Cortland Richmond


On 9/9/2013 1130, Kunde, Brian wrote:
What are the safety considerations using gas tubes on the AC mains? Do you have 
to fuse them or are they not likely to fail shorted? Can you use them between 
line and PE? Do you have to use multiple parts in series? I often see them in 
series with MOVs in a “T” configuration to protect against line to line and 
line to PE surges.

A few year back we had a product that had several surge suppression circuits 
located on different PC boards within (some assemblies were very expensive and 
we wanted to protect them). Well, at our customer site they experienced some 
kind of huge surge, transient or overvoltage (we do not know what exactly 
happened). Of all the equipment that was on-site including many of our 
competitors equipment, only our instrument was damaged. Our surge suppressors 
were blown up, charred, and/or vaporized.  The warranty repair cost was 
$10,000US but the hit to our reputation was probably worst. We believed that 
our equipment probably protected all the other equipment on-site but it is hard 
to get your customers to believe you. So now we want to better control our 
surge protection and if we see a huge surge we hope it to destroy something 
much less expensive to replace or at least minimize the damage.

What we are currently thinking is to use over the counter Surge Suppressor 
modules, but they are only good to about 3KV – 4KV. Then we thought we would 
add a spark-gap in the board that would only kick in if our surge suppressors 
failed. Maybe we can add some very high voltage Gas Tubes also or instead of 
the spark-gap.  I’m not sure what more we can do. Many of the 
circuits/assemblies we are trying to protect are buy/sell components where we 
do not control spacings.

Any comments?

Thanks to all.

The Other Brian


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formats), large files, etc.

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discussion list. To post a message to the list, send your e-mail to 


All emc-pstc postings are archived and searchable on the web at:
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Attachments are not permitted but the IEEE PSES Online Communities site at 
http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used 
formats), large files, etc.

Website:  http://www.ieee-pses.org/
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Re: [PSES] Spark Gap PCB Layout on AC Mains

[McInturff, Gary]

Yet another example that transistors and IC’s were invented to protect fuses 
and surge protectors.

Gary

From: Kunde, Brian [mailto:brian_ku...@lecotc.com]
Sent: Monday, September 09, 2013 8:31 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Spark Gap PCB Layout on AC Mains

What are the safety considerations using gas tubes on the AC mains? Do you have 
to fuse them or are they not likely to fail shorted? Can you use them between 
line and PE? Do you have to use multiple parts in series? I often see them in 
series with MOVs in a “T” configuration to protect against line to line and 
line to PE surges.

A few year back we had a product that had several surge suppression circuits 
located on different PC boards within (some assemblies were very expensive and 
we wanted to protect them). Well, at our customer site they experienced some 
kind of huge surge, transient or overvoltage (we do not know what exactly 
happened). Of all the equipment that was on-site including many of our 
competitors equipment, only our instrument was damaged. Our surge suppressors 
were blown up, charred, and/or vaporized.  The warranty repair cost was 
$10,000US but the hit to our reputation was probably worst. We believed that 
our equipment probably protected all the other equipment on-site but it is hard 
to get your customers to believe you. So now we want to better control our 
surge protection and if we see a huge surge we hope it to destroy something 
much less expensive to replace or at least minimize the damage.

What we are currently thinking is to use over the counter Surge Suppressor 
modules, but they are only good to about 3KV – 4KV. Then we thought we would 
add a spark-gap in the board that would only kick in if our surge suppressors 
failed. Maybe we can add some very high voltage Gas Tubes also or instead of 
the spark-gap.  I’m not sure what more we can do. Many of the 
circuits/assemblies we are trying to protect are buy/sell components where we 
do not control spacings.

Any comments?

Thanks to all.

The Other Brian

From: Anthony Thomson [mailto:ton...@europe.com]
Sent: Monday, September 09, 2013 4:18 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Spark Gap PCB Layout on AC Mains

Hello Brian,

I've employed spark gaps, like you, not because you 'have' to but because it 
seemed good practice. It involved a control installation with cables strung 
externally.

My advice is to use propriatory discharge tubes. They're cheap and  their 
performance is more predictable than engineering your own air gap across PCB 
tracks or using pointy pins and are much less influenced physical and 
environmental conditions such as temperature and humidity, etc. And should they 
ever be needed, the consequences can be much less messy.

I found a good selection available and looked at PCB mounting tubes with 
breakdown voltages of between 3 and 12 kV. I finally used 4kV, 5kA/10kA (10/1 
discharges) devices having been influenced by what professional LAN & GPS 
installers were using which largely ranged between 3 and 6 kV.

Just my thoughts.
T







- Original Message -

From: Kunde, Brian

Sent: 09/06/13 04:56 PM

To: EMC-PSTC@LISTSERV.IEEE.ORG

Subject: [PSES] Spark Gap PCB Layout on AC Mains

Our engineers are working on an AC Mains Distribution PCB. Like most electronic 
devices, we have seen the damage caused by lightning strikes. So we are 
increasing our creepage and clearance distances as wide as we can and still 
meet other requirements.

But no matter what spacing you design to, there is a lightning bolt out there 
that will exceed the design and it will arc somewhere. So the question came up 
to whether it makes sense to deliberately make a weak spot, or an area where 
the clearance is slightly smaller to control where a lightning/surge pulse will 
arc and/or discharge, like a Spark-Gap.

I have seen spark-gap lay outs on PC boards on I/O connectors; usually for ESD 
protection,  but not on AC Mains. Is this a bad bad idea or something worth 
doing?  Pros and Cons? Other suggestions??

Thanks to all for your help.

The Other Brian

LECO Corporation Notice: This communication may contain confidential 
information intended for the named recipient(s) only. If you received this by 
mistake, please destroy it and notify us of the error. Thank you.

-


This message is from the IEEE Product Safety Engineering Society emc-pstc 
discussion list. To post a message to the list, send your e-mail to 
>

All emc-pstc postings are archived and searchable on the web at: 
http://www.ieee-pses.org/emc-pstc.html

Attachments are not permitted but the IEEE PSES Online Communities site at 
http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used 
formats), large files, etc.

Website: http://www.ieee-pses.org/
Instructions:

Re: [PSES] Spark Gap PCB Layout on AC Mains

[Kunde, Brian]

What are the safety considerations using gas tubes on the AC mains? Do you have 
to fuse them or are they not likely to fail shorted? Can you use them between 
line and PE? Do you have to use multiple parts in series? I often see them in 
series with MOVs in a “T” configuration to protect against line to line and 
line to PE surges.

A few year back we had a product that had several surge suppression circuits 
located on different PC boards within (some assemblies were very expensive and 
we wanted to protect them). Well, at our customer site they experienced some 
kind of huge surge, transient or overvoltage (we do not know what exactly 
happened). Of all the equipment that was on-site including many of our 
competitors equipment, only our instrument was damaged. Our surge suppressors 
were blown up, charred, and/or vaporized.  The warranty repair cost was 
$10,000US but the hit to our reputation was probably worst. We believed that 
our equipment probably protected all the other equipment on-site but it is hard 
to get your customers to believe you. So now we want to better control our 
surge protection and if we see a huge surge we hope it to destroy something 
much less expensive to replace or at least minimize the damage.

What we are currently thinking is to use over the counter Surge Suppressor 
modules, but they are only good to about 3KV – 4KV. Then we thought we would 
add a spark-gap in the board that would only kick in if our surge suppressors 
failed. Maybe we can add some very high voltage Gas Tubes also or instead of 
the spark-gap.  I’m not sure what more we can do. Many of the 
circuits/assemblies we are trying to protect are buy/sell components where we 
do not control spacings.

Any comments?

Thanks to all.

The Other Brian

From: Anthony Thomson [mailto:ton...@europe.com]
Sent: Monday, September 09, 2013 4:18 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Spark Gap PCB Layout on AC Mains

Hello Brian,

I've employed spark gaps, like you, not because you 'have' to but because it 
seemed good practice. It involved a control installation with cables strung 
externally.

My advice is to use propriatory discharge tubes. They're cheap and  their 
performance is more predictable than engineering your own air gap across PCB 
tracks or using pointy pins and are much less influenced physical and 
environmental conditions such as temperature and humidity, etc. And should they 
ever be needed, the consequences can be much less messy.

I found a good selection available and looked at PCB mounting tubes with 
breakdown voltages of between 3 and 12 kV. I finally used 4kV, 5kA/10kA (10/1 
discharges) devices having been influenced by what professional LAN & GPS 
installers were using which largely ranged between 3 and 6 kV.

Just my thoughts.
T







- Original Message -

From: Kunde, Brian

Sent: 09/06/13 04:56 PM

To: EMC-PSTC@LISTSERV.IEEE.ORG

Subject: [PSES] Spark Gap PCB Layout on AC Mains

Our engineers are working on an AC Mains Distribution PCB. Like most electronic 
devices, we have seen the damage caused by lightning strikes. So we are 
increasing our creepage and clearance distances as wide as we can and still 
meet other requirements.

But no matter what spacing you design to, there is a lightning bolt out there 
that will exceed the design and it will arc somewhere. So the question came up 
to whether it makes sense to deliberately make a weak spot, or an area where 
the clearance is slightly smaller to control where a lightning/surge pulse will 
arc and/or discharge, like a Spark-Gap.

I have seen spark-gap lay outs on PC boards on I/O connectors; usually for ESD 
protection,  but not on AC Mains. Is this a bad bad idea or something worth 
doing?  Pros and Cons? Other suggestions??

Thanks to all for your help.

The Other Brian

LECO Corporation Notice: This communication may contain confidential 
information intended for the named recipient(s) only. If you received this by 
mistake, please destroy it and notify us of the error. Thank you.

-


This message is from the IEEE Product Safety Engineering Society emc-pstc 
discussion list. To post a message to the list, send your e-mail to 
>

All emc-pstc postings are archived and searchable on the web at: 
http://www.ieee-pses.org/emc-pstc.html

Attachments are not permitted but the IEEE PSES Online Communities site at 
http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used 
formats), large files, etc.

Website: http://www.ieee-pses.org/
Instructions: http://listserv.ieee.org/request/user-guide.html
List rules: http://www.ieee-pses.org/listrules.html

For help, send mail to the list administrators:
Scott Douglas >
Mike Cantwell >

Re: [PSES] Spark Gap PCB Layout on AC Mains

[Cortland Richmond]

Some years ago I was working at in a wireline telecomms equipment 
maker.  Robust protection was the order of the day; the outside physical 
plant was just *waiting* for lightning.


We protected each circuit to a level it could withstand, and worked back 
to the line inputs, where (IIRC) we had to withstand 2 KV Oc or 500 Amp 
short circuit lightning transients.   It helped that everything in the 
Central Office had a common-point ground, even if it was 150 feet below, 
in the basement, as this made backdoor entry less likely.


In a later incarnation, I found aviation customers who wanted to test 
transient protection without opening the equipment, which is another 
story -- and on these, we had to inject transients on the CASE.


I suggested some commercially available modules for AC power protection 
here because one does NOT want to try to protect the AC power network, 
only what he builds, and just throwing in spark gaps, gas tubes, 
Tranzorbs(tm) or MOV's might be asking for trouble. Know the threat, and 
protect against THAT.


Cortland Richmond


On 9/9/2013 1130, Kunde, Brian wrote:


What are the safety considerations using gas tubes on the AC mains? Do 
you have to fuse them or are they not likely to fail shorted? Can you 
use them between line and PE? Do you have to use multiple parts in 
series? I often see them in series with MOVs in a “T” configuration to 
protect against line to line and line to PE surges.


A few year back we had a product that had several surge suppression 
circuits located on different PC boards within (some assemblies were 
very expensive and we wanted to protect them). Well, at our customer 
site they experienced some kind of huge surge, transient or 
overvoltage (we do not know what exactly happened). Of all the 
equipment that was on-site including many of our competitors 
equipment, only our instrument was damaged. Our surge suppressors were 
blown up, charred, and/or vaporized.  The warranty repair cost was 
$10,000US but the hit to our reputation was probably worst. We 
believed that our equipment probably protected all the other equipment 
on-site but it is hard to get your customers to believe you. So now we 
want to better control our surge protection and if we see a huge surge 
we hope it to destroy something much less expensive to replace or at 
least minimize the damage.


What we are currently thinking is to use over the counter Surge 
Suppressor modules, but they are only good to about 3KV – 4KV. Then we 
thought we would add a spark-gap in the board that would only kick in 
if our surge suppressors failed. Maybe we can add some very high 
voltage Gas Tubes also or instead of the spark-gap.  I’m not sure what 
more we can do. Many of the circuits/assemblies we are trying to 
protect are buy/sell components where we do not control spacings.


Any comments?

Thanks to all.

The Other Brian





-

This message is from the IEEE Product Safety Engineering Society emc-pstc discussion 
list. To post a message to the list, send your e-mail to 

All emc-pstc postings are archived and searchable on the web at:
http://www.ieee-pses.org/emc-pstc.html

Attachments are not permitted but the IEEE PSES Online Communities site at 
http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used 
formats), large files, etc.

Website:  http://www.ieee-pses.org/
Instructions:  http://www.ieee-pses.org/list.html (including how to unsubscribe)
List rules: http://www.ieee-pses.org/listrules.html

For help, send mail to the list administrators:
Scott Douglas 
Mike Cantwell 

For policy questions, send mail to:
Jim Bacher:  
David Heald: 

Re: [PSES] Spark Gap PCB Layout on AC Mains

[Anthony Thomson]

Hello Brian,

I've employed spark gaps, like you, not because you 'have' to but because it 
seemed good practice. It involved a control installation with cables strung 
externally.

My advice is to use propriatory discharge tubes. They're cheap and their 
performance is more predictable than engineering your own air gap across PCB 
tracks or using pointy pins and are much less influenced physical and 
environmental conditions such as temperature and humidity, etc. And should they 
ever be needed, the consequences can be much less messy.

I found a good selection available and looked at PCB mounting tubes with 
breakdown voltages of between 3 and 12 kV. I finally used 4kV, 5kA/10kA (10/1 
discharges) devices having been influenced by what professional LAN & GPS 
installers were using which largely ranged between 3 and 6 kV.

Just my thoughts.
T

- Original Message -
From: Kunde, Brian
Sent: 09/06/13 04:56 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] Spark Gap PCB Layout on AC Mains

Our engineers are working on an AC Mains Distribution PCB. Like most electronic 
devices, we have seen the damage caused by lightning strikes. So we are 
increasing our creepage and clearance distances as wide as we can and still 
meet other requirements.
But no matter what spacing you design to, there is a lightning bolt out there 
that will exceed the design and it will arc somewhere. So the question came up 
to whether it makes sense to deliberately make a weak spot, or an area where 
the clearance is slightly smaller to control where a lightning/surge pulse will 
arc and/or discharge, like a Spark-Gap.
I have seen spark-gap lay outs on PC boards on I/O connectors; usually for ESD 
protection, but not on AC Mains. Is this a bad bad idea or something worth 
doing? Pros and Cons? Other suggestions??
Thanks to all for your help.
The Other Brian
-
 *LECO Corporation Notice:* This communication may contain confidential 
information intended for the named recipient(s) only. If you received this by 
mistake, please destroy it and notify us of the error. Thank you. 
-

This message is from the IEEE Product Safety Engineering Society emc-pstc 
discussion list. To post a message to the list, send your e-mail to < 
emc-p...@ieee.org >
All emc-pstc postings are archived and searchable on the web at: 
http://www.ieee-pses.org/emc-pstc.html 
Attachments are not permitted but the IEEE PSES Online Communities site at 
http://product-compliance.oc.ieee.org/  can be used for graphics (in well-used 
formats), large files, etc.
Website: http://www.ieee-pses.org/ 
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List rules: http://www.ieee-pses.org/listrules.html 
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This message is from the IEEE Product Safety Engineering Society emc-pstc 
discussion list. To post a message to the list, send your e-mail to 


All emc-pstc postings are archived and searchable on the web at:
http://www.ieee-pses.org/emc-pstc.html

Attachments are not permitted but the IEEE PSES Online Communities site at 
http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used 
formats), large files, etc.

Website:  http://www.ieee-pses.org/
Instructions:  http://www.ieee-pses.org/list.html (including how to unsubscribe)
List rules: http://www.ieee-pses.org/listrules.html

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Mike Cantwell 

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