# Proper implementation of creepage and clearance on high-voltage PCB

I am designing a 3-phase voltage detector based on optocouplers as shown below:

simulate this circuit – Schematic created using CircuitLab

For this I need to follow DIN 60664-1 and my biggest problem is to understand how to apply those rules for creepage and clearance. Namely, I figured out that with polution degree 2 I need to stick to the following measures: 3 mm minimal clearance and 4 mm minimal creepage. Fine, but how is that achieved in practice? From the circuit that I have shown, how do I determine the creepage and distance between L1_1 and L2_1, or between L1_2 and L2_2? Does that mean that for every point in the circuit I must calculate the voltage and then determine the creepage and clearance in the standard?

Take a look at the resistor connected to L1 and L1_1. It is 0805 size, but should leg L1_1 also have clearance and creepage of 3 mm and 4 mm with respect to the L1?

At which point may I bring lines closer to each other - legs of the capacitors connected with the optocoupler - there can never be a breakdown between them because the diode keeps that voltage low.

• "there can never be a breakdown between them because the diode keeps that voltage low" ... until the diode gets broken: a single fault making the whole thing unsafe again. Iirc, you should design against single faults as well Jan 24, 2020 at 18:17

Disclaimer: I am a complete and utter n00b at EE that probably knows less than you do. Take this with an enormous grain of salt.

how do I determine the creepage and distance between L1_1 and L2_1

You don't. Clearance and creepage don't mean anything in a schematic. They come into play when you start to physically lay out a device... and hopefully your design software will help you out, here.

Clearance is the shortest air distance between exposed conductors. Imagine taking a string and pulling it taught between the nearest two points where conductor is exposed (e.g. a component lead or solder pad). Insulators may push the string aside, increasing clearance distance.

Creepage is the shortest distance along a surface (usually, your PCB). Similar principle, but the string has to stick to the surface, and now it is air gaps that may increase creepage.