My specialty is mechanical engr, not electrical, but I have a project with electrical arcing being an issue so I have to reach out to others.

I have an electrical circuit that failed, with arcing the suspected culprit since the wires were melted and sometimes the wires get a little bent out of shape during manufacturing. The gold wires are extremely small with a diameter of only 0.0015", a length of only 0.044", and a nominal spacing between wires of 0.0045" (gap of 0.003"). I can calculate the deflection under a static load. What I don't know is how close these wires can get to each other (or a ground bus) before arcing. I have found equations online, but the voltages involved in the examples are usually in excess of 1000 V, and I am more likely in the range of 3-to-24 VDC.

Are those equations equally valid at low voltages, or is there a voltage below which you have to make contact?

The deflections under load that I'm calculating are on the order of only 1E-6 inches, but I have seen wires bent such that they very nearly touch adjacent wires. I understand that the surrounding atmosphere matters. I am investigating if the circuit while under operation is in a vacuum, air, or some kind of dry noble gas under pressure.

Thanks!

 

Vacuum should be more insulating than air. A noble gas might make things worse, since they can still ionize (think neon light).

Arcs can form spontaneously when the electric field exceeds ~10kV per inch. That's my old rule of thumb but we had a fairly long discussion on this topic a while back and I remember learning that my rule-of-thumg wasn't terribly useful. I'll see if I can find it. But nevertheless, I believe arc formation depends on field strength and not so much on scale.

 

According to this, the field strength needed for break-down in air is about 3E6 V/m.
Thus for 24V, the air would break-down and arc at a distance of 24 / 3E6 = 8μm (basically they have to nearly touch).

 

Vacuum should be more insulating than air. A noble gas might make things worse, since they can still ionize (think neon light).

Arcs can form spontaneously when the electric field exceeds ~10kV per inch. That's my old rule of thumb but we had a fairly long discussion on this topic a while back and I remember learning that my rule-of-thumg wasn't terribly useful. I'll see if I can find it. But nevertheless, I believe arc formation depends on field strength and not so much on scale.

I can find a lot of info regarding high voltage arcing, but very little regarding low voltages. I have some prior experience with high voltage arcing since I once worked at General Electric designing discharge-based lighting. I just don't know how valid the equations are at low voltages. There just seems to be an assumption that if there is arcing then there is are high voltages involved.

 

According to this, the field strength needed for break-down in air is about 3E6 V/m.

Huh. That's 76,200V/inch. Seems high.

 

Huh. That's 76,200V/inch. Seems high.

That may be for ball terminals.
Needle point terminals will be less.

 

I did find this reference, but not the thread I was looking for.

http://www.dragonfly75.com/motorbike/gapvoltage.html

Found it!

https://forum.allaboutcircuits.com/threads/breakdown-voltage-of-air-at-given-distance.115070/

 

Many thanks for the replies! I think I have what I need!