Electric spark

most likely, without being able to see what you have going on, the  metal wheels and axles of your rolling stock are trying to complete the circuit of your un-wired track. finish wiring your system, and the sparks (for the most part) should go away.

Thank you for the response.

If the only wiring missing is to the switch machine (not the switch itself) you might check for dirty track or dirty wheels on your trains. I believe that has also been reported to cause sparking. Reason being is poor contact.

Right. Will check track, switch and wheels for rust/crud. I have not put power to the switches anywhere. I suppose they grab power from neighboring straight powered track. 

The two machines associated with the switches, were not powered, but are wired now. 

Stay tuned. 

I am not familiar with Ross track or switches and I really don't know if the switch tracks need power anywhere or not? I am guessing they shouldn't, other than for non-derail wiring, but don't know for sure. I do know Ross has a few different ways you can order their switches, but I have never looked into the differences.  Anyway, good luck and I am staying tuned, Good Luck!

The wheels might be brushing against the center rails, causing a momentary short long long enough to pop a breaker.  Try crawling over the switch and see what happens.  I have found some cars have the wheels slightly closer, and the flanges cause issues.

Your wheels might be contacting the guiderails on the turnout or if your track isn't level the un-coupler button is touching the turnout.  Also, clean the rails and wheels.  Specific to one or two cars or all of them?  There are a few things to rule out

A spark means loss of contact most of the time, but not always. It's hard to say without seeing it. Fields are funny things present in everything around us in varying degrees. It could be a sort of static build up in the area too. (Misted Static Gaurd is pretty safe on about anything and works well. I've "bathed" static prone electronics in it)

Running through a switch, your moving and changing contact points. They will spark. If you hook up a motor jump wire and kill the lights, you'd be hard pressed to jump to power without some type of tiny spark being seen, over and over again, even with a second jumper connected as you touch and remove it. 

Dirty track, rollers and wheels are a usual culprit but sometimes cleaning won't do it. It can be metallurgy too. Some folks replace the rollers, etc. with various results.     I let them spark and it always goes away  

 So it boils down to your judgement on how clean things are vs knowing some sparking isn't really that unusual, especially in the switches.

"A spark means loss of contact most of the time"

Don't know that I agree.  When I see sparks as locos and cars go through switches, it's usually a quick short, and the cure is either don't run that car, or put liquid insulation of the side of the offending rail

Rolling stock should not spark. A spark indicates a point from high to low voltage (like ground or neutral) where there is resistance like dirt or grit or a small air gap where current is flowing. For rolling stock, wheels on each side ride on neutral rails with the exception of insulated track or the non derailing part of a switch. these are times when the wheels carry current. Could you post a picture of where this is happening?

RJR posted:

"A spark means loss of contact most of the time"

Don't know that I agree.  When I see sparks as locos and cars go through switches, it's usually a quick short, and the cure is either don't run that car, or put liquid insulation of the side of the offending rail

"Loss of contact"for sure as well as shorts...A couple of my 3 rail RK six axle diesels(only 2 wheels really provide outside rail electrical path) struggle to make contact through some ancient Atlas turnouts..some minor arcing plainly visible at the wheels especially with the lights out.