What's the minimum surface clearance you consider adequate for 230VAC, on FR4 without slots or added creepage? Forget about IPC-2221 unless you base your layout strictly on it.
Personally, I try to maintain 3mm edge-to-edge between tracks and pads, more if space permits. What do you think?
The distance along a surface is called creepage in the standards.
The required distance depends on whether the insulation is supposed to be single insulation (functional, basic or supplementary) or double insulation (reinforced insulation).
Basically, if the insulation failing ought not to kill someone because the part that would become live is either protectively earthed or separated by supplementary insulation from the user, then a smaller creepage is allowable.
If the insulation failing could immediately give someone a shock because there is no protective earthing or supplementary insulation, then a larger creepage distance is required.
The exact distances required in different standards tend to be different, though I think a lot of different products that used to be subject to different standards have recently been grouped into one set of standards, IEC62368-1.
There are some tables here:
I’d also want to consider if the pcb tracks are naked or covered with solder mask or conformal coating .
This photo shows the underside of a two phase HVAC PCB:
This particular PCB's pulled from the Heating and Air Conditioning unit from one motel room in a chain franchise. It's found, one PCB per room, in motels and hotels throughout America. In other words, it's acceptable to appropriate authorities.
If you look at the dark defect near the left edge you can see part of the conformal coating melted away.
Relays are located at near the bottom of the PCB. The larger gaps measure about 3mm and separate phase voltages from each other. The smaller gap measures about 2mm and separates one phase voltage from neutral.
Long story short, your 3mm separation seems adequate, IMHO.
Danke,
What about voltage clearances for inner-layer traces on a multilayer board? Same layer and between layers?
Its all in the standard. I could look it up tomorrow if you like. John
See e.g. the IPC 2221 standard, clearance chapter 6.3 and table 6.1, at
Arie
For <230V working voltage supplied ac equipment 3mm Basic insulation and
5mm reinforced is typical. Notice that often clearance is larger distance than creepage. Creepage is also easier to handle, since you can add slots. You can't do that for clearance
Typical inner layers in x-y direction is 1.2mm for reinforced. If you do impulse voltage testing, you may get that down to 0.5mm
In the z direction, it's 0.4mm IIRC
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