JMeller:
UL60950
6.4mm or greater of separation between lines is safe.
Several years ago one of my customers wanted to pass UL/CSA on his product. The 1600 volt testing caused arcing between pads on a series of resistors and caused several different board redesigns.
One of my current customers is doing the same test with the 1600 volt test and as of Friday had destroyed 5 units.
So, you should also be aware of the standard tests, even though you are not certifying anything for sale. I don't think any of the little Chinese relays will pass the test. Certainly not the circuit boards they are mounted on.
Be careful!
Paul