I have built of several Tesla coils over the years and I can say that this is a REALLY good coil once it is properly adjusted.
First insure that the 3rd coil is extended to the full length of the blue connecting wire and that the blue connecting wire is elevated above whatever surface the device is sitting on
Then make sure the spark gap is closed to the smallest possible gap space, if the gap is too large then the primary coil will arc to the secondary coil and the 3rd coil will arc all along its surface and eventually short out the coil itself.
Also ensure the the blue connecting wire is positioned up and over the primary and secondary coil, not lying over the side of the primary and secondary coil or this will cause arcing as well.
Hope this helps

This is one of the best medium sized Tesla coils I've purchased, and it has a unique design with a rotary spark and a secondary coil which can be placed separately from the main transformer. Excellent value

so this is my 8th tesla coil I've bought complete online, I have built 3 kits and built 1 from scratch, buying items to make my 2nd and biggest now. So I am not a expert here but I do know a good bit oj coils and shop them all the time ( it's even been a issue with my wife when she sees tesla coils on my phone screen ) I say this so you know I am not new to these devices or how they work... this is by far the coolest and most unique tesla coil at the spark gap spins letting off a constant and multiple sparks as it spins...the primary also spins, for 99 bucks this is a great coil. It also let's off decent arcs I'd say at least 6 inches maybe more.... it looks really cool, Now I was stupid as I did ask for help or I guess confirmation on setting it up as there are just some wires and things that need to be hooked up but nothing that requires a lot of knowledge....the kit itself is complete.. just hook the parts together and to the power supply. which is included, it is also adjustable so you can adjust rotation speed and arc output or power output..... lastly and maybe most importantly, was their customer service.... based is china I was worried they might not understand my question as I am horribly bad at punctuation and Grammer. But this was not the case, they replied in great detail and were very quick and just great at making sure I was all set... I even asked some dumb questions and they responded fast and again in great detail sometimes writing me back in paragraphs and also they sent pictures of the coil completed for me to go off of, they put this together just for me so they could send me a visual aid.... they went above and beyond what I was expecting and to be honest after comparing prices and coils on ali Express and ebay ( the 2 sites I always used for my coil purchases ) I will be doing all future purchases with Enginediy, just based off their customer service.... If you ever bought coils from ebay they are 99.8% only from over seas and if you are missing parts or having any issues they usually are not at all helpful, or even act like your trying to get over on them... or the famous " we dont know we just sell them " .... I will end this review now as I have written a book... but if you are in the market for a tesla coil I would definitely buy from these guys, maybe buy this one as your 2nd as I recommend just buying a normal basic coil at first... nothing cheap you want a good arc, I'd say spend at least over 100$ on a coil and do not run them for long periods of time even if they cost 500$ they can get hot and blow capacitors..... if they do not come with a fan get a small fan and set it up to blow on the PCB board to just help out. .. but anyway this would make a great tesla coil for any collector ....... or if you are just going to buy 1 coil and be done then I would buy this in that case as well as it has more cool features to show off to people.... great products and great service !!!!!!