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I picked up a 9V switching DC adapter from SparkFun a while back, but I've been hesitant to use it because it doesn't have any of the usual "safety" approvals that you normally see on power adapters (UL listed, CSA approved, etc.)

Is this just unfounded paranoia? Are there safety issues to think about when using a DC power adapter for a project that will run 24/7?

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In my particular case, we're talking about low-current devices/microcontrollers. I am well within the limits of the DC adapter. – Owen Thomas Jul 25 at 22:53

5 Answers

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Safety approvals cost (a LOT) of money. You won't find anything from sites such as SparkFun dispaying these logos. It's not because they're unsafe, it's because it's prohibitively expensive to get the testing done to prove they're safe.

If you are buying things from sites such as SparkFun, etc. it is also assumed that you are experienced enough to work safely. Personally, I have zero problem using unlisted equipment, but then again I am in the business of designing this kind of equipment and have a pretty good "feel" for circuit safety and design capabilities based on observing the parts and quality of manufacture. I've seen some pretty sketchy stuff in my time, but I haven't gotten the screaming heebie-jeebies from anything from sites like that.

That being said... Use it at your own risk. If something doesn't feel right to you, don't use it.

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Safety approvals may cost a lot, but they usually get done by companies that are selling a lot. The savings of manufacturing in bulk usually is pretty close to matching the cost of getting safety approval. With this said, you should be able to buy a certified adapter for about the same cost of a non-certified. – Kellenjb Jul 26 at 12:43
SparkFun is a reseller. Unless they actually make the adapter themselves, they won't be the one applying for UL. Like Kallenjb says, it's cheap enough for manufacturers selling in bulk. Personally, I would never use unlisted adapters even if the application well within it's spec. In the off chance, you get a bad part, you can't predict how it will fail. – Vineeth Jul 26 at 17:07
That's what I suspected-- I essentially have an unknown black box. Even if it is well engineered, I'll spend the $7 for a new one with the safety approval. At least I know now to check for approvals along with all the other specs on the supply. – Owen Thomas Jul 26 at 22:37
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UL listed means that even if the device shorts, you will not get electrocuted when you touch it. Given that it's not expensive to get an UL certified DC adapter (less then $10), why take the chance?

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Any tips on where to find a reasonably priced, quality adapter? ie. a switched mode power supply with reliable voltage and current ratings? If I could find one on Amazon.com, I wouldn't have ordered from SparkFun. – Owen Thomas Jul 26 at 2:56
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 I get all of my wall warts from CUI through Digikey. Their products work well, their customer support is excellent, and their prices are decent. They're also UL certified. I've found that their switching regulated power supplies (link bit.ly/aKc9kZex) do really give a +/-2% regulation even at no load and continue to do so all the way to their maximum current, after which they taper off without damaging themselves. – reemrevnivek Jul 26 at 14:44
I would be surprised if you couldn't get one in any local electronics store. On Amazon - amazon.com/15-Watt-9V-1-7A-Power-Adapter/dp/… . – Vineeth Jul 26 at 17:25
Thanks for the recommendation. I guess it just never entered my head that any adapter from a prominent retailer would lack a UL certification. My Amazon comment was just to say that the more consumer electronics stores (online and off) make it hard to determine if you're really getting a switched mode supply, current limitations, and other specs. – Owen Thomas Jul 26 at 22:33
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There are a variety of design, manufacturing and qualification requirements to meet UL, CSA and TUV. I would not use a line powered supply that does not meet these specifications.

I also tend to buy these supplies from name brand manufacturers and manufacturers that have ISO9000 approval even though it is difficult to know how/where a device was manufactured.

I would try to return the supply.

(* jcl *)

http://www.wiblocks.com

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Getting a UL stamp means you meet a number of safety tests for your equipment. In the US a UL stamp is only 'required' on some electrical equipment in some markets, generally items running on main power but there are some exceptions and only when its being sold or placed in some public areas, for instance a school. Even then a UL stamp is completely optional, however a local inspector may not allow a non-UL device in a building. Needing to be UL listed is completely a political issue not a technical one.

The documents that cover a UL listing are long and cover many issues from shock prevention, reducing the chance of a fire, RF emissions, etc.

As one example you could use a UL listed power supply to power a low voltage device, something like a laptop brick, but if you place that brick within an enclosure it is no longer UL compliant.

UL listing is really a hoop you need to jump through for safety compliance for a product your selling as defined by the market your selling that product to. I wouldn't try to put a non UL listed part in something like a school but for some applications its not needed.

Getting a UL stamp is expensive. The European version of the UL stamp is the CE stamp and it actually goes farther in various directions than a UL stamp does.

I wouldn't bother worrying or caring about a UL listing unless you know that your market or installation cares about that, the best way to determine this is to call you local electrical inspector and ask him about the issue at hand.

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Using something like that might invalidate a household insurance policy. It would be a good idea to check the small print.

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