USB-C connector with isolated shell? - Page 1
Forum section: electronics / projects

author: CookieMonster
author_rank: Contributor
timestamp: August 16, 2022, 09:58:52 am
content: Hi,I am developing a device with a galvanically isolated USB type C input.The problem is, that this device has a metal enclosure and all USB-C connectors I know also have a metal shell, so there would be a ground connection between the isolated USB input and the enclosure which is connected to the isolated ground.I am looking for a USB-C connector which has some kind of plastic separation on it so that it cannot make contact with the enclosure.This needs to be a regular small horizontal PCB-mount connector, not an industrial style panel mount type.The only thing similar I've been able to find are waterproof types which have a non-conductive gasket, but if you mount them according to the datasheet, there is still a chance the metal makes contact with the enclosure.Thanks for your replies!

author: Gribo
author_rank: Frequent Contributor
timestamp: August 17, 2022, 12:19:13 pm
content: You can leave the shell not connected and insulated from the enclosure in your design.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 17, 2022, 12:56:06 pm
content: 3D print a bushing for insulation.Have you accounted for the USB connector making contact with the case while the user is connecting or disconnecting it?

author: ejeffrey
author_rank: Super Contributor
timestamp: August 17, 2022, 03:35:28 pm
content: Quote from: Gribo on August 17, 2022, 12:19:13 pmLeaving the shell unconnected on the PCB won't help as the cable shield is connected to the signal ground at the remote end of the cable. The concern is about inadvertent contact between the connector shell and the chassis.What kind of isolation voltages are you talking about? What is the consequence of a touch? Is it degraded performance, possible equipment damage, or a safety hazard? Does it matter if you have contact when the cable is not connected?If this is only for something like ground loop breaking with low offset voltage then for small volume I would just oversize the chassis cutout or if that is unappealing 3D print a plastic spacer as suggested above. For high volume an injected molded part could make sense. The user may still make contact between the cable and chassis during insertion, but if that just causes excess noise then it will go away once the cable is inserted.If there is potential equipment damage, then I think you need to reconsider the metal chassis, and provide a protected insulated shell around it.If there is possible dangerous voltages present then USB-C is not an acceptable connector as it is not protected from user contact.

author: alm
author_rank: Super Contributor
timestamp: August 17, 2022, 06:18:13 pm
content: If grounding the chassis damages it, then I doubt the USB-C connector is your greatest worry. How about the user putting it on top of a grounded appliance? Or putting something grounded next to it?

author: CookieMonster
author_rank: Contributor
timestamp: August 20, 2022, 09:35:47 am
content: Thanks for your suggestions!Quote from: NiHaoMike on August 17, 2022, 12:56:06 pmI did consider that, but it would be another BOM item, so I wondered if there is an off-the-shelf solution.Quote from: ejeffrey on August 17, 2022, 03:35:28 pmThis is only for ground loop breaking.The consequence of touch is somewhere between nothing and degraded performance.This is not a mains appliance.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 21, 2022, 04:32:35 am
content: Might be able to just enlarge the hole in the case to guarantee a gap, but then you'll be relying on the PCB for mechanical support. Or you could enlarge the hole so the plastic molding around the plug snugly fits and then recess the socket.