PCB isolation requirements, what a mess?

Thread Starter


Joined May 14, 2021
Actually I wonder about clearence and creepage requirement for two conductor in different pcb layers. However during my research, I could not find any clear information. Also there are inconsistencies for normal insulation requirements. For instance, different standards suggests quite different distances for same isolation voltage. I don't know that should I comply with which standard. I examined IPC standard but I could not find creepage requirement for IPC 2221. For example; if I use air gap, what will be according to IPC2221? Are there differences between smps isolation and measurement systems isolation? There are many questions in my head. Can someone recommend to me a book or something detailed source for understand the isolated pcb design requirements.

Thanks in advance.


Joined Jul 1, 2009
@obione Why are you trying to isolate? Are you
  • Trying to prevent other signal from interferring, or
  • Trying to prevent your device from generating signals into other things (radiating), or
  • Trying to eliminate noise between traces?

If it's #3, try noise-immunity instead. You use current to overcome interference. If you want to isolate traces, seperate them with a grounding plane in between.


Joined Aug 21, 2008
Use the standard most relevant to the circuit's use. If it is going to be used in a home environment that is one standard. If it is to be connected to a medical patient that's another. Variations also take into account the environment, such as how much humidity something is subjected to and the temperature range.

If you are able to find out what standards a commercial product similar to what you are designing, then those standards will probably be most applicable.

Thread Starter


Joined May 14, 2021
@MisterBill2 I want to make a new PCB for my academic project. This is not a commercial product but I want to learn the isolation needs for proper working. I just wonder why there is not complete guide for solving isolation standards problem.


Joined Jan 23, 2018
There are volumes written about PCB design optimization, reduction of crosstalk, and reducing voltage drops and ground bounce. And the expensive layout programs have built in design rules checkers that deliver warnings. I have created a few board designs and they all worked but they were for lower frequencies and DC logic running at lower speeds. This is not the best venue to learn about PCB design rules and cautions. Possibly one of the other forums will be a better choice.