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PCB Track Clearance to earth at 400VAC

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Oct 31, 2021
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I am trying to find the best calculation for PCB track clearance to earth at a working voltage of 400VAC. The tracks in question are external layers and are uncoated.

I have been using 0.6mm + (0.005 x 565) = 3.425 mm

The 565 is the peak voltage at 400 AC. However the voltage between the Primary and Secondary (L1 to L2) is 400 Vac and is the incoming supply but between either L1 & L2 and earth is around 230 Vac

I have some external tracks that run close to a mounting screw on the PCB which is directly bolted to the metal chassis which is earthed. Between the PCB and the metal box is also a sheet of high voltage insulation material.

This equipment is for use in the UK and a Europe .

Also, what calculation should be used and what standard should be applied for the clearance between AC tracks (L1 and L2) which is also 400VAC between the two.
Seems to be so much misleading info around with so many different results.

Seems to be so much misleading info around with so many different results.
The distance depends on
* application type (commercial, industrial, medical...)
* altitude
* country
* dirt
* humidity
.... and so on. Maybe therefore there are many calculations with different results.

So saying "400V AC against Earth" is simply not enough information.


Thanks for your replies, I know that this is a subject in itself and I understand that their are so many variables, but it seems hard to get info on how to calculate clearance and or creepage required, even knowing the exact operating conditions. Trying to calculate or perhaps understand a range of figures between expected and maybe worse case conditions would help.

This is for a commercial lighting product. The actual unit is sealed to IP68 or above and operates in a dry environment around 30 Degree C ambient. The PCB inside the sealed metal enclosure is clean with no containments (Sealed at production/assembly). The internal PCB cavity sits at around 50 Deg. C.

Used in the UK and various countries in Europe at less than 10M above ground level, so the actual Altitude (ASL) is not really known. However, these will not be used in extreme conditions of altitude, like up a mountain. Just installed in 'normal' cities (Whatever that is!) As I won't know the altitude until we have customer orders, so its difficult to quantify.

So, back to my question, and yes I know its not a straight forward one answer fits all, but where does anyone who needs to know the track clearance distances go to for information that is easily understood and interpreted. Even if used as an initial guide to make a prototype.

The actual clearance required is PCB external track clearances between the two supply tracks, which is 400 Vac and also between one supply track and a physical earth connection or screw holding the PCB in place, which measures around 230 Vac.

I have read pages and pages of documents and downloaded all sorts of papers and discussions, and the result is still not specific enough to come up with an actual measurement. It would also seem seem that many guidelines are exactly that and not truly a requirement.

So, if you can offer any more help or point me in the right direction that be be great. If you need any more specific questions answered then I have all the technical info if required.I am just looking for actual clearance figure, even if I add a percent margin on top. Just need something to go on for an initial PCB layout.


External layers and uncoated is rather tempting fate a bit.
Even simple dust may be problematic long term.
Safest way is to mill a slot between high voltage tracks and anything likely to cause trouble.

for worst case conditions, 10mm for rectified 3 ph mains to earth, shiny green pcb tracks electricity very well over time, dirt / dust and then high humidity makes this even easier ....

Get the PCB toolkit to help you.

Saturn PCB toolkit reflects IPC, not safety standards. IPC gives suggestions based on know properties of PCB, safety standards, e.g. IEC 61010 have mandatory requirements.

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