clearancecreepagepcb
Does a cut or a slot in a printed circuit board increase clearance, creepage or both?
Some say it will increase clearance, but I don't think clearance will change because, even with a cut in the PCB, distance over the air will be the same. Thus, a cut will only affect the creepage distance. Please correct me if I'm wrong.
Or does it have nothing to do with either clearance or creepage, and is only for isolation?
Here is a diagram that should help: -
Picture taken from this document.
Please also note that creepage distances might have to be bigger dependent on your pollution category and your material group. See this document for further info.
There is also this calculator - I have tried it and for 250V AC, the protection distances seem to be right i.e. basic creepage is 2.5mm with 2.5mm for supplementary making a 5mm total for reinforced. Ditto the clearance figures - they add up to 4.0mm for reinforced: -
You does not need to drive the LEDs via an isolator.
First of all, Ethernet specifies 1.5 kVrms @ 50/60 Hz @ 1 min basic isolation. What does it mean? It means that typically the voltage applied/existing between the sides of the isolating transformer must be around zero all the time the device works and only during the specified time (generally, once in the life cycle) the voltage could be 1500 Vrms sine (not distorted heavily) continuously during 60 sec max. Once you'll have that voltage happen you need to stop using the device and re-test its isolation properties. It is hard to say before what voltage difference between the transformer sides (windings) the device will still work, but the basic isolation conditions mean that any voltage outside a "technical" zero leads the device not to work. For opposite example to an Ethernet transformer for which only basic isolation parameters (Viso @ freq @ time) are specified, an ADuM isolating device is additionally determined with the parameters (Viorm < Viso) specifying the max voltage diff between the chip sides before which the device will continue its function properly.
Second, look at your design. Why do you aware about the tx/rx pairs but not about the traces from RJ45 to the BS termination? And why not between the LEDs traces and the chassis ground? Also, recall that the RJ45 jack has a metal shield connected to (chassis?) ground and the only one that separates it from the tx/rx pairs is the top mask layer. Again, wired Ethernet is designed to (properly) operate in well-grounded, earthed environments where a hi-pot between a two points shall not occur. If a hi-pot occurs it is a fault condition and the points must (try to) withstand it during a very short time a little bit (but guaranteed) longer that the time needed by an external devices (breakers) to isolate/eliminate/shutdown/etc the hi-pot and/or fault conditions. If you need to deal with hi-pot and/or other electrical faults, you need to use glass/plastic fiber optic Ethernet.
Third and last, there are many pcb routing examples provided by Ethernet chip manufacturers, i think there are may cases similar to your interest/design goals. You need to lurk more and better :-)
Best Answer
You are correct:
Here is a nice picture of the definitions of creepage and clearance:
Note that adding a barrier will increase the clearance. Adding a barrier increases the physical length of insulated material between conductors, and that is what is considered when defining clearance. Normally a barrier is inserted into a slot (or slots) in the PCB.
Creepage and clearance are of great importance for high voltage isolation.