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Tesla Coil, Van de Graff Generator, & Jacobs Ladder

The basic construction and principle of a Jacobs ladder is that a metal vee is formed from two bits of wire and a high voltage is applied across them. The electricity arcs across at the bottom of the vee where the electrodes are closest together. The air that the spark is passing through is ionised making it a preffered route for the arc, so when it heats up and begins to rise it drags the arc up the metal vee pulling it wider as it goes. In a correctly set up ladder the arc will travel all the way to the top where the wires have a sharp outward bend in them to pull the arc apart to the point that it extinguishes and the whole process starts again at the bottom of the vee.

If the base is too close then the arc won't rise all the way to the top of the ladder because it's easier just to jump the gap at the bottom again. If the base is too far apart then there is the serious risk of the arc not striking at all meaning that the unit will look as if it's switched off when in fact the full voltage is across it.

If you decide to use a unit like this on set, then you must fit a dead mans switch in series with the power supply. This basically consists of a push button assembly that must be held in continuously to operate the unit. This should be done by an FX technician who has full view of the effect. In the event that something unexpected happens, or an actor gets too close, the power can be cut immediately by releasing the buttons. It is also imperative that everyone in the vicinity of the effect is warned of the dangers associated with contact. While death is very unlikely, a contact would provide an invigorating and memorable experience for the recipient. The unit COULD be encased in a glass or plastic case, but that actually detracts from the whole visual effect of a high voltage device.