I am designing a simple switch-controlled relay board. On the board I have two 5 VDC, 10 A Sugar Cube relays which will receive 230 VAC from a terminal block connector and will be controlled with 5 VDC input via an SPST Switch.

Operating current: 10 A
Terminal block pitch: 2.54 mm
According to trace width calculation, trace width required for 10 A is 4.2 mm.
PCB copper thickness: 60 micron
PCB schematic and layout:

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Will a 230 VAC LINE trace from the terminal block (pin 1) to both relays (via relay K1) need to be 4.2 mm or 8.4 mm (i.e. double), or something else, as a single trace is coming from the terminal block and going to both relays?

  • 3
    \$\begingroup\$ Your layout has inadequate clearances between the mains and the extra low voltage circuits. The relays you’ve chosen make it more difficult as you need slots in the pcb to ensure creepage distance. Look at G2R series relays - the coil pins are far away from the contact pins. \$\endgroup\$
    – Kartman
    Mar 12, 2021 at 2:51

2 Answers 2


You are designing a product that has voltages over 60 VDC or 42 Cop inside.

That means that you should look for the right UL norm and read it.

An UL safety engineer would help you a lot.

The distances in air 4.2 mm or 8.4 mm that you mention are from the primary circuitry to the secondary circuitry (SELV circuit).

Those distances actually depends on the maximum voltage that your product develops. There is a table that gives you the minimum distance as a function of the maximum voltage that the UL engineer measures on your product.

In a dusty environment (class 3) also distances are further increased.

The relays must be UL recognized components.

From the Line trace and the Neutral trace the distance is solely regulated by the electric arc that may arise. At 230 VAC the minimum distance is 2.4 mm.

UL doesn't care if you draw those traces at a distance of 0.1 mm. The UL engineer says "The fuse will blow but the end user is safe".


Yes, your Line trace between the terminal block and the first relay needs to be more than twice as wide to maintain the same temperature rise. Do that calc for 20A on that trace with the same temperature rise. It should be somewhere around 11 mm.


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