[SOLVED] IEC 62368-1 "external circuit" - Page 1
Forum section: electronics / projects

author: C_Norris
author_rank: Newbie
timestamp: January 18, 2024, 10:04:36 am
content: I'm a bit stuck with IEC 62368-1. If someone else has experience with it I would really appreciate your insight into this.In the standard, they define "external circuit" as "electrical circuit that is external to the equipment and is not mains".This is a really broad definition, and seems to me that it would include any connection to any other device such as via Ethernet, USB, DVI, RS232, special proprietary interfaces with a D-type connectors, etc.And that's a problem when I get to 5.4.11.2, which says:"There shall be separation between circuitry intended to be connected toexternal circuitsmentioned above and any parts or circuitry that will be earthed in some applications, either within the EUT or via other equipment. [the previous section describes equipment types that are affected and it basically boils down to this affects every device that isn't bolted down and with an earth cable attached to it]The product I'm working on has a metal enclosure and D-type connectors, which connect to other equipment (which I don't control) which will be earthed and the earth is attached to the cable shield. So I can't achieve this.It's fairly clear from the context and other bits of the standard that they really have things like cable TV networks and telecom networks in mind with this definition of "external circuits" but the definition doesn't limit it to that.I found various test reports from TUV online for other products and they always say N/A for this test. No justification given unfortunately.There's a clue in Table 13 where it says "In general, for external circuits installed wholly within the same building structure, transients are not taken into account." In my application the cable won't even leave the same rack! But 5.4.11.2 isn't specifically about transients from what I can tell so I don't know if I can use this statement as an excuse to ignore 5.4.11.2.So does this come down to the specific definition of what a "circuit" is? Would say a shielded RS485 connection not be classed as an external circuit for these purposes?Cheers

author: C_Norris
author_rank: Newbie
timestamp: January 18, 2024, 10:35:59 am
content: I'm going to mark this solved.I just realized the requirementsonlyapply to "paired conductor", per the first line of 5.4.11.1. I don't believe ground is considered a paired conductor and I won't connect either side of a differential pair to ground in my device. So on that basis I am already compliant.

author: TimNJ
author_rank: Super Contributor
timestamp: January 18, 2024, 11:27:40 pm
content: My interpretation of this requirement is something like this:1. You can't necessarily trust that an external connection will truly be what it says it is.2. You can't necessarily trust that the earth connection on your device will be reliableGiven these two ideas, it's conceivable that you could have a faulty external connection (mains on a telecom cable, somehow?) with a non-existent protective earth connection. Under this circumstance, without sufficient separation between the (what should be) earthed enclosure (or other accessible parts) and the external connection, you could get a "live enclosure" scenario.I don't know why this requirement only applies to external connections made by "paired conductors", and why they don't care about coax, etc. But, I guess the general risk assessment is that you're unlikely to get an accidental hazardous voltage on some RG6 from the cable company.