How to define working voltage class net to calculate the creepage?
First you will need to get a copy of the standard that you want to design your product to. (Like IEC61010-1) This will depend on what kind of product it is and what market you are going to sell it in, I don't know which part of the IEC standards pertain to industrial products.
Then you will look at the table and determine the pollution degree:
Pollution Degrees and Overvoltages Pollution degree is divided into
four categories. The following definitions are based on those in IEC
• Pollution degree 1. No pollution or only dry, nonconductive
pollution occurs. The pollution has no influence (example: sealed or
• Pollution degree 2. Normally only nonconductive pollution occurs.
Occasionally a temporary conductivity caused by condensation must be
expected (example: product used in typical office environment).
• Pollution degree 3. Conductive pollution occurs, or dry, nonconductive
pollution occurs that becomes conductive due to expected condensation
(example: products used in heavy industrial environments that are
typically exposed to pollution such as dust).
• Pollution degree 4. Pollution generates persistent conductivity
caused, for instance, by conductive dust or by rain or snow.
Your standard will have a table like this:
Source for table and quote
You then have to keep every trace on a PCB X ammount of distance away from every other trace. So if its 480Vrms, and pollution deg 2 you need 2mm of clearance.
This is just an example, you need to find the spec that pertains to you. Get a regulatory consultant if necessary and\or buy the relevant standards (they aren't cheap)