How buy an AC adapter that passes earth ground to the output barrel connector? - Page 1
Forum section: electronics / projects

author: appsman
author_rank: Contributor
timestamp: August 16, 2024, 10:15:53 pm
content: I need an AC adapter that passes the third prong earth ground through to the DC output barrel connector sleeve. It's for a low volume product so has to be off the shelf. I've done a ton of searching on this and results are clogged with discussions about isolation, and how grounding is good, etc., but don't come close to answering. I'm not even sure what to call this feature. I checked 5 "soap on a rope" adapters from my old stash that have 3-prong wall connections and 2 have zero Ohms from the third prong to the barrel sleeve, and three have infinite Ohms, so there is apparently no standard. What's worse is there is no hint on their labels about this. A friend tested this particular Mean Well modelhttps://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/2601/SGAS15A%20Series.pdf,and did measure continuity between grounds, but nothing I can find in the data sheet tells me that's the case, and this model is apparently is end of life. Right now it seem impossible to know what I'll be getting if I order something. Has anyone dealt with this?

author: Someone
author_rank: Super Contributor
timestamp: August 16, 2024, 10:37:45 pm
content: Quote from: appsman on August 16, 2024, 10:15:53 pmWhy?That data sheet is pretty clear on the matter, but it's written in a way that only people who already have the background/knowledge/experience understand. If its not obvious to you that is a hint you don't understand the how's and why's.

author: TimNJ
author_rank: Super Contributor
timestamp: August 16, 2024, 11:09:36 pm
content: It can still be somewhat confusing because some manufacturers often use the term "Class I" to mean "anything with a 3-conductor input", regardless of where the earth is connected or whether it is needed for a safety purpose. That said, a mention of "Class I" in the datasheetusuallyimplies that the output is earthed.The basic idea behind Class I vs. Class II is that a Class I system relies on earth as a safeguard against shock, whereas a Class II system has sufficient insulation to not need earth as a "backup". But, these days, most power supplies are designed as Class II, and then may optionally connect earth to the output forfunctionalreasons. Then there are power supplies which have an earth connection, but not made to the output, and whether or not these should be called Class I or Class II may depend on the standard, and also the degree of separation between that "functional earth" conductor and the circuits it is supposedly isolated from. For instance, in the medical standard, to call your equipment "Class II with functional earth", the functional earth conductor must be separated from mains circuits by ~4-5mm or with appropriate insulation. If the power supply cannot achieve this (for whatever reason), then it is a Class I power supply...because now that wire is deemed too close to mains and needs to be able to handle a fault current if something were to happen. Sheesh!Anyway, I say all of this to further the point that "yes, it can be confusing".You can check the "Safety" section and see if they mention a dielectric strength between output-and-earth. (e.g. O/P - PE: 1500Vac would mean that they hi-pot it at 1500Vac between earth and output. Of course, if there is a deliberate connection between earth and output, there would be no such specification.)I feel that this is the most surefire way to know.

author: CaptDon
author_rank: Super Contributor
timestamp: August 17, 2024, 12:07:43 am
content: OR, you could have told the O.P. what 'Class 1' typically indicates.

author: CaptDon
author_rank: Super Contributor
timestamp: August 17, 2024, 12:10:33 am
content: TimNJ gave a good clear answer and also indicated the word 'Class 1 usually means', which is important in this day of cheap poor quality imported junk!