Post by thread:[EE] UL question - required for under 24V?

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 --------------------------------- You rock. That's why Blockbuster's offering you one month of Blockbuster Total Access, No Cost.

Quoting alan smith <spam_OUTmicro_eng2TakeThisOuTyahoo.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 -- "it's the network..." "The Journey is the reward" .....s...KILLspam@spam@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com

my point exactly. I just wanted some background info before I confronted this engineer to tell him...he isn't quite right. Spehro Pefhany <speffKILLspaminterlog.com> wrote: Quoting alan smith : {Quote hidden}> 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 -- "it's the network..." "The Journey is the reward" .....s...KILLspam.....interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com

>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.

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_OUTTakeThisOuTrl.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.

On Mon, Apr 7, 2008 at 8:36 PM, alan smith <micro_eng2spam_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

On Mon, Apr 7, 2008 at 11:01 PM, alan smith <@spam@micro_eng2KILLspamyahoo.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

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 <KILLspamwdmyrickKILLspamearthlink.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}

> 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 -- FCC Rules Updated Daily at http://www.hallikainen.com - Advertising opportunities available!

Spehro Pefhany wrote: {Quote hidden}> Quoting alan smith <RemoveMEmicro_eng2TakeThisOuTyahoo.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 > 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

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

Quoting Harold Hallikainen <spamBeGoneharoldspamBeGonehallikainen.org>: {Quote hidden}> >> 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 http://engineers.ihs.com/document/abstract/HEGVIBAAAAAAAAAA Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" TakeThisOuTs...EraseMEspam_OUTinterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com

Quoting alan smith <RemoveMEmicro_eng2TakeThisOuTyahoo.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...EraseME.....interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com

{Quote hidden}> Quoting Harold Hallikainen <EraseMEharoldhallikainen.org>: > >> >>> 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 > > http://engineers.ihs.com/document/abstract/HEGVIBAAAAAAAAAA > > > > Best regards, > Spehro Pefhany 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 -- FCC Rules Updated Daily at http://www.hallikainen.com - Advertising opportunities available!

--- alan smith <RemoveMEmicro_eng2EraseMEEraseMEyahoo.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 ____________________________________________________________________________________ You rock. That's why Blockbuster's offering you one month of Blockbuster Total Access, No Cost. tc.deals.yahoo.com/tc/blockbuster/text5.com

On 08/04/2008, Stephen R Phillips <RemoveMEcyberman_phillipsspam_OUTKILLspamyahoo.com> wrote: {Quote hidden}> > --- alan smith <RemoveMEmicro_eng2TakeThisOuTspamyahoo.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 > IIRC it depends more on what the customers insurace company wants. RP

> 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 -- FCC Rules Updated Daily at http://www.hallikainen.com - Advertising opportunities available!

On Mon, Apr 7, 2008 at 11:34 PM, alan smith <EraseMEmicro_eng2spamspamBeGoneyahoo.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

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}

On 4/8/08, Kenneth Lumia <RemoveMEkenneth_lumiaKILLspamcomcast.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