# How should the clearance calculation be on a coated PCB?

How many mm should the clearance be between the A and B pads in the picture below?

And clearance between E pad and F track?

And clearance between F track and G track?

Voltage: let's assume 300 volts AC.

PCB: Let's assume coated,(standart settings in jlcpcb or pcbway)

Note: I randomly created the circuit so that I could ask my questions.

I need help with the importance of clearance here and how much it should be.

• The distance between A and B is already small due to H1 ... follow the tracks via the fuses
– user16222
Commented Oct 18, 2021 at 20:18
• Hey Johnny, if my answer here helped you, it would be great if you could up-vote it. If it answered [that] question, also click the checkmark. That's how this Q&A site works - useful answers are up-voted and the best are chosen as the answer. Thank you. Commented Oct 18, 2021 at 21:05
• why do you have two fuses in parallel? I've never seen that, and it sounds like a bad idea! Commented Oct 18, 2021 at 23:07

Electrical Clearance information can be found in IPC-2221.

For 300VAC rms (424V peak):
Condition B1 (internal conductors): 0.25mm minimum
Condition B4 (external conductors w/ permanent polymer coating): 0.8mm minimum
Condition A6 (external component leads, uncoated): 1.5mm minimum

Personally, I would double the IPC recommendations.

Clearance tables can be found on various Web sites.

If this is mains power, you'll need to check the various codes (UL, VDE, CSA, ...) where the equipment is used.

• let's think about STP25N80K5 Mosfet.It has TO-220 package.This mosfet is an 800 volt mosfet.But the lead-spacing are about 1.7mm for pins of mosfet.Even more interesting is that the footprint spacing is 0.5 mm.So,Where is the IPC-2221 clearance rules? Commented Oct 21, 2021 at 14:38
• @johnyadv It would be ill advised to use a TO-220 package at 800V. The D2PAK or TO-247 would be suitable. Then why have a 800V part in a TO-220 package? You could be using this in a lower voltage circuit but the transistor should withstand the occasional voltage spike.
– qrk
Commented Oct 21, 2021 at 20:07
• What about,How many volts can be used for a transistor in a to-220 package? Commented Oct 22, 2021 at 17:17
• And what categories do you think the l1,l2,l3 and l4 values in the picture belong to in the ipc 2221 table? i.sstatic.net/A2Fkv.png Commented Oct 22, 2021 at 19:58
• @johnyadv Traces on the PCB fall under "Bare Board" category. The TO-220 package falls under "Assembly" category, more specifically A6. If you want better PCB clearance for your TO-220 pads, use a triangle pattern. In IPC-2221, Table 6-1, there is a guide telling you what each category means below the table.
– qrk
Commented Oct 22, 2021 at 20:09