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I have PCB design where there are two pads the may be shorted (manually in assembly) or left as is, depending on the product model. The through hole circular pad is actually for a terminal block. I wanted to maintain ~3mm clearance between CN3 and CN8 since there is at least on case wherein: CN3 is connected (via leadwire) to a 2nd relay's common (COM) pin and CN8 is connected to 1st relay's normally closed pin (NC). I want to isolate the contact lines of two different relays.

However, I also want to make it easier for the worker who will short CN3 and CN8. There is a case wherein CN3 and CN8 are shorted because: In one product model, there is only one relay. In one-relay model, there are "submodels" wherein the NC of relay is accessible to user or not (User access is via CN3 since it is connected to terminal block). So for NC-accessible type, CN3 and CN8 should be shorted by a vertical solder bridge.

We find it hard to do this with a leadfree solder. Our two options:

  1. User a wire or a resistor leg to make shorting CN3 and CN8 easier.
  2. Add a dead metal between CN3 and CN8 to make shorting easier.

I am curious about 2. Will adding dead metal affect the designed 3mm clearance/creepage between CN3 and CN8?

I am more inclined that the answer is no, because of how clearance (pt-pt distance between the two copper in question) and creepage (distance between the two copper along an insulator) is defined. But I also know that some high voltage can cause "arcing" when two conductors are close to each other.

Addition note: Relay loads are: 250VAC or 30VDC, both 5A max

enter image description here

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  • \$\begingroup\$ I must be slow tonight... could you explain if there is a case when you need both leadwire to CN3 and a bridge simultaneously? \$\endgroup\$
    – Maple
    Dec 3, 2021 at 8:38
  • \$\begingroup\$ Nope. It's one or the other. CN3 is connected to only of the following at a single time: 1. 2nd relay N.O contact (For 2-relay models) 2. 1st relay N.C contact 3. Floating (This happens if the product is a single relay model, but the N.C pin is accessible to user) \$\endgroup\$
    – user139731
    Dec 3, 2021 at 8:48
  • \$\begingroup\$ In that case I'd suggest going with @SpehroPefhany answer, using through-hole jumper resistor or simply piece of wire as fastest and cheapest for manual assembly. However If you have automated assembly step where jumper wire can be inserted, you may consider adding couple more pads. Then all your worker has to do is cut that wire, instead of soldering it \$\endgroup\$
    – Maple
    Dec 3, 2021 at 9:03

2 Answers 2

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The metal would (at best) subtract from the clearance by its width. It may be worse than that as deemed by safety agencies.

I suggest a through-hole zero-ohm resistor as an option.

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Dead metal is conductive and at potential so it reduces clearance. In the standards usually there's also a rule for 'jumping' from live to dead metal to something else.

Personally I would use a cut-off jumper or a tht zero ohm (which is almost the same)

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    \$\begingroup\$ cut-off jumpers are OK for some hobby projects, but I've seen (and made myself) so many botched PCBs due to cutting tool slipping and slicing traces nearby. At some point I switched exclusively to either smd 0Ohm or standard pin header, depending on how often I expected it to be changed. \$\endgroup\$
    – Maple
    Dec 3, 2021 at 8:45

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