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'[EE] UL question - required for under 24V?'
2008\04\07@083637 by alan smith

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It was mentioned to be by another engineer that UL testing isn't required for those devices that are 24V based systems...and essentially 30V falls within that spec as well, and the those devices running 48V (such as telcom) are under the same guidelines as 120VAC..aka..creepage and clearance.   Any truth to what he is saying?  So what it comes down to is if you have a set of devices that are using designed to use PoE (48VDC) they are under a different, more stringent testing standard than if I stuck with 24VDC?
 
 I'd like to have a NRTL reference if possible as well.
 
 Thanks in advance


     
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2008\04\07@093416 by Spehro Pefhany

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Quoting alan smith <spam_OUTmicro_eng2TakeThisOuTspamyahoo.com>:

> It was mentioned to be by another engineer that UL testing isn't  
> required for those devices that are 24V based systems...and  
> essentially 30V falls within that spec as well, and the those  
> devices running 48V (such as telcom) are under the same guidelines  
> as 120VAC..aka..creepage and clearance.   Any truth to what he is  
> saying?  So what it comes down to is if you have a set of devices  
> that are using designed to use PoE (48VDC) they are under a  
> different, more stringent testing standard than if I stuck with 24VDC?
>
>   I'd like to have a NRTL reference if possible as well.
>
>   Thanks in advance

"Required" by who, exactly? You'll see UL/CSA testing on disk drives,  
for example, which are 5V/12V, so the premise is not a reliable one.


Best regards,
Spehro Pefhany
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2008\04\07@100506 by alan smith

picon face
my point exactly.  I just wanted some background info before I confronted this engineer to tell him...he isn't quite right.

Spehro Pefhany <speffspamKILLspaminterlog.com> wrote:  Quoting alan smith :

{Quote hidden}

"Required" by who, exactly? You'll see UL/CSA testing on disk drives,
for example, which are 5V/12V, so the premise is not a reliable one.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
.....s...KILLspamspam.....interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com


2008\04\07@103555 by Alan B. Pearce

face picon face
>my point exactly.  I just wanted some background info before I
>confronted this engineer to tell him...he isn't quite right.

Are you using materials that have a UL fire rating? What happens if
something shorts, a transistor decides to spit out flame (as some power
devices can do if badly treated), and the power supply says 'how much
current would you like to draw now you have gone short circuit?'

I had exactly this situation on a midi computer, where a supply bypass
capacitor decided to become a resistor. The 5V 300A supply figured this was
just a touch more load (it was running pretty lightly loaded anyway) and
provided all the current asked for. The PCB had a hole about 1.5" diameter
before someone discovered the machine was sending out smoke signals and
kicked the emergency off button.

2008\04\07@104946 by David VanHorn
picon face
> I had exactly this situation on a midi computer, where a supply bypass
> capacitor decided to become a resistor. The 5V 300A supply figured this was


300A for midi?   What is this, a pipe organ? :)

2008\04\07@110221 by alan smith

picon face
As part of the design criteria, I would put in something like a poly fuse to protect the power delivery system, but we are only talking maybe a few amps over this supply link.  Don't take me wrong, I am not trying to circumvent the system, I am simply questioning his rational that if he uses a 24V or less supply, he doesn't have to design to UL standards.  As mentioned, 5 or 12V can do some damage if left unchecked.  I can understand different rules that need to be followed, but last time I was involved with UL certs, anything that could come into contact with a user needed to be made sure they couldnt be hurt by it, either by it dripping onto you (hot plastic) or sticking objects inside to get damaged.  Sure, 48V isn't considered lethal but its not the voltage...its the current.

"Alan B. Pearce" <EraseMEA.B.Pearcespam_OUTspamTakeThisOuTrl.ac.uk> wrote:  >my point exactly. I just wanted some background info before I
>confronted this engineer to tell him...he isn't quite right.

Are you using materials that have a UL fire rating? What happens if
something shorts, a transistor decides to spit out flame (as some power
devices can do if badly treated), and the power supply says 'how much
current would you like to draw now you have gone short circuit?'

I had exactly this situation on a midi computer, where a supply bypass
capacitor decided to become a resistor. The 5V 300A supply figured this was
just a touch more load (it was running pretty lightly loaded anyway) and
provided all the current asked for. The PCB had a hole about 1.5" diameter
before someone discovered the machine was sending out smoke signals and
kicked the emergency off button.

2008\04\07@111453 by Xiaofan Chen

face picon face
On Mon, Apr 7, 2008 at 8:36 PM, alan smith <micro_eng2spamspam_OUTyahoo.com> wrote:
> It was mentioned to be by another engineer that UL testing isn't required for
> those devices that are 24V based systems...and essentially 30V falls within
> that spec as well, and the those devices running 48V (such as telcom) are
> under the same guidelines as 120VAC..aka..creepage and clearance.
> Any truth to what he is saying?  So what it comes down to is if you have a set
> of devices that are using designed to use PoE (48VDC) they are under a different,
> more stringent testing standard than if I stuck with 24VDC?

There is a bit of truth here. I do not have the standard here but I remember
for UL508 (for industrial control equipment) and UL840 (evaluation of creepage
distance and clearance), there is quite a bit of difference below 30V and over
30V. Similar for the Europe side (EN50178 last time). I think UL will normally
not look at secondary side below 30V (Class 2 circuit, Limit Voltage/
Current circuit, Limited Voltage circuit, etc).

But anyway, you need to check the standards which apply to your product.

Xiaofan

2008\04\07@111529 by Derward

picon face
Alan, I recently got approval, for a device, by an agency that requires UL.
I used a 12 Volt UL approved wall transformer and the device did hot need
UL because all voltages were less than the required buy UL.

Derward


{Original Message removed}

2008\04\07@111804 by Xiaofan Chen

face picon face
On Mon, Apr 7, 2008 at 11:01 PM, alan smith <@spam@micro_eng2KILLspamspamyahoo.com> wrote:
> I am simply questioning his rational that if he uses a 24V or less supply,
> he doesn't have to design to UL standards.

Whatever you do you need to follow the UL Standards at least for US. But
if you specifies that your power supply need to be a Class 2 power supply,
then the requirement is much lower.

Xiaofan

2008\04\07@113433 by alan smith

picon face
OK...so this agrees with the other engineer I'm dealing with....the voltage was less than what UL requires for certification.  Does anyone have a reference to what that voltage is?

Derward <KILLspamwdmyrickKILLspamspamearthlink.net> wrote:  Alan, I recently got approval, for a device, by an agency that requires UL.
I used a 12 Volt UL approved wall transformer and the device did hot need
UL because all voltages were less than the required buy UL.

Derward


{Original Message removed}

2008\04\07@113541 by Harold Hallikainen

face
flavicon
face

> Whatever you do you need to follow the UL Standards at least for US. But
> if you specifies that your power supply need to be a Class 2 power supply,
> then the requirement is much lower.
>

What exactly is class 2? I think it MAY include the following, but don't
know for sure:

1. Low output voltage for electrical shock protection.
2. Low leakage current for electrical shock protection.
3. Double insulation for electrical shock protection.
4. Higher than normal hipot test requirement for electrical shock protection.
5. Overtemperature protection to prevent fire in the power supply.
6. Power output limitation to reduce possibility of fire in the equipment
driven by the supply.

So... what makes a power supply a class 2 supply?

THANKS!

Harold


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2008\04\07@115508 by Bob Axtell

face picon face
Spehro Pefhany wrote:
{Quote hidden}

The last info I had was  that UL cert was required if less than 24V AND
the max possible current was
less than 8 Amps. But my client is exempt now because of the nature of
the product being designed,
so I haven't kept up.

--Bob A

2008\04\07@132326 by Apptech

face
flavicon
face
> The last info I had was  that UL cert was required if less
> than 24V AND
> the max possible current was
> less than 8 Amps. But my client is exempt now because of
> the nature of
> the product being designed,
> so I haven't kept up.

Only capable of producing about 200 Watts. These are not the
ones you want. Move along. Flames ... .


       Russell

2008\04\07@132326 by Apptech

face
flavicon
face
The original comments were quite possibly related to the
voltages being above or below the "Extra Low Voltage" / ELV
limit. The actual voltage varies with administrations but is
typically 50 VDC or about 33 VAC. Below this level the
voltage is deemed non lethal in typical situations, even
though in fact voltages at this level OF COURSE, and AS WE
ALL KNOW, (don't we?) can kill.  I am only on nodding
acquaintance with UL specs but I would be surprised if UL
were not interested in voltages at levels where very very
serious energies can be conveyed with ease.

Thought experiment:    Hold auto starter motor shaft
tightly. Energise. QED. A 12V car battery will happily
enough deliver several kiloWatts for long enough to do
immense damage.

SO

I'm sure that UL will be interested while wearing one of
their hats. BUT the ELV restrictions will probably reduce
the danger to human life aspects.



       Russell

2008\04\07@140228 by Spehro Pefhany

picon face
Quoting Harold Hallikainen <spamBeGoneharoldspamBeGonespamhallikainen.org>:

{Quote hidden}

http://engineers.ihs.com/document/abstract/HEGVIBAAAAAAAAAA



Best regards,
Spehro Pefhany
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2008\04\07@141337 by Spehro Pefhany

picon face
Quoting alan smith <RemoveMEmicro_eng2spamTakeThisOuTyahoo.com>:

> my point exactly.  I just wanted some background info before I  
> confronted this engineer to tell him...he isn't quite right.

If you want that kind of information, simply pick up the phone and
call UL and ask them if testing is not required under the stated
conditions. That will be a conservative answer.

Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
s...EraseMEspam.....interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

2008\04\07@170426 by Harold Hallikainen

face
flavicon
face

{Quote hidden}

Thanks!

The scope says "for use on alternating current branch circuits with a
maximum potential of 150 V to ground." Paragraph A allows use on 240V
branch circuits, but in the US, these are "center tap grounded," so the
RMS voltage on each line is 120V. For Europe and other 230V areas, is
there a class 2 equivalent?

So, it looks like the output must be limited to 42.4Vp for AC and 60V for DC.

They can provide up to 660W (that's a BIG wall wart!).

I see nothing here regarding hipot, but this IS just the scope, not the
standard.

I'd still like to find a way of going through UL testing with an internal
power supply by having them just look at the power supply label and saying
"OK, you pass." That power supply would include the inlet, be enclosed,
etc., and we'd just bolt it in our cabinet.

Harold




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2008\04\07@172748 by Ed Browne

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Buying a UL and CE listed power supply goes a long way towards meeting that goal.  Anymore when an input voltage is high enough to cause expensive testing, I'll slap down an approved supply and deal with the much less stringent low voltage requirements.

{Original Message removed}

2008\04\07@174356 by Stephen R Phillips

picon face

--- alan smith <RemoveMEmicro_eng2EraseMEspamEraseMEyahoo.com> wrote:

> It was mentioned to be by another engineer that UL testing isn't
> required for those devices that are 24V based systems...and
> essentially 30V falls within that spec as well, and the those devices
> running 48V (such as telcom) are under the same guidelines as
> 120VAC..aka..creepage and clearance.   Any truth to what he is
> saying?  So what it comes down to is if you have a set of devices
> that are using designed to use PoE (48VDC) they are under a
> different, more stringent testing standard than if I stuck with
> 24VDC?
>    
>   I'd like to have a NRTL reference if possible as well.
>    
>   Thanks in advance

It depends. You require UL approval on battery powered instruments.
Basically UL approval means it meets certain specifications.  If you
don't meet them then you don't have them.  UL approval is optional
really, however if you wish to SELL something that is a different
matter .  You should check with the customer what they want before
making such a decision.  24V system may or may not require it.  It
depends on what the customer wants.

Stephen


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2008\04\07@191606 by Richard Prosser

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On 08/04/2008, Stephen R Phillips <RemoveMEcyberman_phillipsspam_OUTspamKILLspamyahoo.com> wrote:
{Quote hidden}

IIRC it depends more on what the customers insurace company wants.

RP

2008\04\07@192544 by Harold Hallikainen

face
flavicon
face

> Buying a UL and CE listed power supply goes a long way towards meeting
> that goal.  Anymore when an input voltage is high enough to cause
> expensive testing, I'll slap down an approved supply and deal with the
> much less stringent low voltage requirements.


Thanks! Our customers want the supply in the box instead of an external
supply. I understand we were charged $16k to safety test a product that
had, as its line connected components, a UL listed filter/inlet, a UL
listed power supply, a UL listed switch, a few wires, and a ground lug.

That's about $4k to $5k to look at each component that was already UL
listed...

Harold


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2008\04\07@194915 by Xiaofan Chen

face picon face
On Mon, Apr 7, 2008 at 11:34 PM, alan smith <EraseMEmicro_eng2spamspamspamBeGoneyahoo.com> wrote:
> OK...so this agrees with the other engineer I'm dealing with....the voltage was less
> than what UL requires for certification.  Does anyone have a reference to what that
> voltage is?

I do not think that no UL required for certification is the correct
way. It all depends
on your product. Last time for sensors (UL508 applies), we still need to get
UL certification even when we specify to use Class 2 power supply. It is just
the evaluation becomes easier. UL is more than power supply.

If you are dealing with UL so often, maybe it is good idea to buy the
UL standards
relevant for you. We always have UL508 and some other UL standards and I have
read UL508 over and over.

Xiaofan

2008\04\07@205831 by Kenneth Lumia

picon face
Probably different for various applications, but IIRC,
UL60950 (actually several variants on xx60950 for
various coutries) tells quite a bit about temperatures,
fire enclosures requirements, etc.  Total wattage of
the supply comes into play here (both internal and
external supplies).  The purpose of UL approval is for
the safety of the SYSTEM, not just the supply.

Ken


{Original Message removed}

2008\04\07@230333 by Xiaofan Chen

face picon face
On 4/8/08, Kenneth Lumia <RemoveMEkenneth_lumiaKILLspamspamcomcast.net> wrote:
> Probably different for various applications, but IIRC,
> UL60950 (actually several variants on xx60950 for
> various coutries) tells quite a bit about temperatures,
> fire enclosures requirements, etc.  Total wattage of
> the supply comes into play here (both internal and
> external supplies).  The purpose of UL approval is for
> the safety of the SYSTEM, not just the supply.
>

Exactly.

UL60950 comes from (adapts or adopts) IEC60950,
which covers IT equipment.

Xiaofan

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