In my project I need to control 2 relays from ESP-12E, I have isolated AC & DC side in my PCB design by 4mm

PCB Material : FR4, with general Silkscreen coating (green polymer coated)

According to this clearance calculator & studying other sources, clearance is 1.8mm & creepage is 2.5mm

Current required at output terminals : 4.5A, Voltage : 230Vac

Relay used : Hongfa 5Vdc 5A Subminiature relay - HF46F

Connected RC Snubber circuit in parallel with relay switching contact for protection

Question 1 : Do I need mentioned clearance & creepage distance between all of the AC voltage traces on my PCB ?

Just to elaborate the question : The current is flowing from LINE of terminal block then goes to Common of relay, then from NO of relay goes to Fuse terminal and parallel RC snubber circuit, then from fuse to again at output port of terminal block. So will all the traces of this path need to have calculated clearance-creepage with each other? or only needed at different voltages, components or paths?

Question 2 : Do the traces of RC snubber circuit needs same width as of relay-output traces(as same amount of current will flow through RC snubber)?

Question 3 : Is needed clearance in my design 1.8mm or 0.4 mm? From mentioned calculator image which value of clearance is appropriate, and from IPC2221A table my value comes around 'B4' Track-Track 0.4mm & 'A6' Track-Pad 0.8mm, so which is correct?

Clearance calculator Ref

IPC2221A Table


1 Answer 1


Voltage : 230Vac

That's a peak voltage of \$230 \times \sqrt2\$ = 325 volts and not 250 volts (as per your calculation).

But, if you are using a regular household 230 volts AC supply, you need to take account of indirect lightning surges and their protection devices. This generally limit the peak voltages to about 1500 volts.

So, for external conductors you should use column B2 of below: -

enter image description here

And, a peak of 1500 volts implies a minimum spacing of 0.005 mm per volt = 7.5 mm.

  • \$\begingroup\$ Oh yes I definitely need to consider that as this PCB is going to be used for household application, so 7.5mm clearance should be only between AC to DC separation or between all individuals AC voltage traces? \$\endgroup\$ Commented Jan 19, 2022 at 15:12
  • \$\begingroup\$ Given that I see you haven't followed advice given here on how to upvote and accept answers to your previous questions, if you want more help I would do what is expected from you. Stack Exchange gives free advice but not to those who don't respect the expectations of those giving that advice. \$\endgroup\$
    – Andy aka
    Commented Jan 19, 2022 at 15:17
  • \$\begingroup\$ I’ll unquestionably follow your advice, and I agree with what you’ve said, it was just because I’m not a frequent user! \$\endgroup\$ Commented Jan 19, 2022 at 15:36
  • \$\begingroup\$ DC side is not connected to user directly, user have switches which goes to controller inputs to operate respective relays from controller outputs, I’ve already placed 1-2mm slots for increasing creepage distance and total gap I’ve kept between AC-DC was 4mm, so I’ll increase that gap to 7.5mm, and what should be the clearance between all AC voltage traces? Is it same 7.5mm? \$\endgroup\$ Commented Jan 19, 2022 at 15:40
  • 1
    \$\begingroup\$ Between AC voltage stages it is less - you just need a distance that is "operational quality" (not safety related) for these. So, I'd just go with the 301-500 volt numbers. I’ll unquestionably follow your advice - there's no such thing as free beer (or wine or bread or money etc..) \$\endgroup\$
    – Andy aka
    Commented Jan 19, 2022 at 15:44

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