The Jacob’s Ladder is a classic physics toy that produces high-voltage climbing arcs. It is not hard to build but if you are planning to use one to demonstrate the concept to kids in school, you should take proper safety measures. This Jacob’s Ladder from Science First has you covered. It has a clear polycarbonate tube that shields the electrodes.
This unit has a power supply that generates 15kv voltage between two brass electrodes to ionize the air and turn it into plasma. Each electrode is capped with ceramic to extinguish the arc. The built-in fuse prevents overloads.