While I don’t know if I’m truly a green engineer anymore, I’m definitely a little wet behind the ears when it comes to standards. I thought it might be a good exercise to determine the creepage and clearance requirement for isolation on my ethernet circuit. The result was/is a large can of worms.

What are the requirements?

 I’ve seen the requirement waved around on several occasions… ethernet transformers are designed to survive 1500Vac, and sure enough looking at 802.3 (IEEE standards that outline ethernet) you can find this spec listed in various locations throughout the PDF. Interestingly its only ONE of 3 possible isolation tests. from 802.3; “this electrical isolation shall withstand at least one of the following strength tests”. The other options include being exposed to 2250Vdc or a short impulse.

Bare minimum – Withstand 1500Vac @60

Approach Number 0

The zeroth approach might be just to look at the IPC-2221B(?) design standard for C&C (creepage and clearance) recommendations. I didn’t go down this route. Though this standard can be invaluable, I don’t believe any safety standard would point us in its direction.

Approach Number 1 - Start from the directives

My first thought was to start from the directive and work down to the product standard, if one exists. I’m a little more familiar with the EU framework, so I’ll start there by looking at Harmonized Standards listed by the European Commission.

Scrolling down the list there are several directives that would be of interest. General Product Safety (GPSD), Low Voltage (LVD), and Electromagnetic compatibility (EMCD). I’m adding the “D” here in the acronym since I’m referring to the directive (though I think GPSD is now a regulation?).

NOTE. If you click on the directive and scroll down to the bottom of the webpage you can look at a “summary list as pdf document”, this is how I found the list of harmonized standards for each directive.

Not having too much experience with standards my C&C spec could be hiding under any one of GPSD, LVD, or EMCD. I quickly learned my product doesn’t fall under the LVD since that directive covers “electrical equipment operating with an input or output voltage between 50-100Vac or 75-1500Vdc”. From the GPSD, it seems like I need to consider EN IEC 62368-1:2020, this standard concerns “Audio/video, information and communication technology equipment – Part 1 : Safety requirements”. My project is essentially a big communication adapter, so I believe it would comfortably fit here. From EMCD I’ll be looking into EN 61000-6-1:2007, EN 61000-6-3:2007, EN 55032:2015, and EN 55035:2017. These standards relate to immunity/emission “for residential, commercial and light-industrial environments” and “Electromagnetic compatibility of multimedia equipment”.

Already I’m not a happy camper, this is a lot of overhead to get one value…

After looking at each standard, it seems like 62368-1 has the info I need. Table 14 provides the “minimum clearances using required withstand voltage”. If I assume the definition of withstand voltage is the same between IEEE 802.3 and IEC, then I should be able to read the clearance right off the table. The lingering question is, does my application require reinforced insulation? Very likely it doesn’t, but I want to know how to find out.

I read the entirety of the standard the next day and I wasn’t able to gain much clarity over my initial understanding. So much of the C&C is depended on a mains connection, which I do not have for my product. I’ll do some more reading but the expected C&C value is 1.5mm.

Expected Clearance Requirement 1.5mm

Approach Number 2 - When in doubt, phone a friend

Every product with a CE mark needs to have a declaration of conformity (DoC) that outlines which standards the product complies to. If we can find a similar product’s DoC, we can get some good nuggets about the standards we should be looking at.

A quick google search for “ethernet switch with USB port” and I was able to find a nifty device that provides USB over ethernet. As far as I’m concerned, this product would fall under the same product category as my widget. The DIGI AW02-G300 has a certification tab and if you dig around the EU relevant documents, we can find the DoC for that product.

Our “phone a friend” approach quickly gave us some good standards to look at. Checking with my results in approach 1, it looks like friend’s homework is very similar to my own. Beware, I’d strongly discourage copying his homework. Best to come to your own conclusion, and use your friend as a quick gut check.

Note that 2x of my standards seem to be missing from their DoC (EN 61000-6-1(3)). If I want some more reassurance, I can always phone another friend… my next friend includes these two missing standards but also adds some extra ones (seemingly to support some directives I hadn’t identified).

Using approach 2, I was able to get some reassurance that I’m in the right place. EN 62368-1 is where I should be looking for C&C requirements.

Approach Number 3 – Start from the ethernet standards

For my last approach I will be starting from the IEEE 802.3 and then I’ll work backwards to see what standards it prescribes (if any). This approach was recommended to me by a colleague (and seems like a great idea, maybe where I should have started).

*TO BE UPDATED*