Okay, that's probably more detail than you need or want, but it's important to understand that without the circuit being completed, the energy cannot flow. In order to get the incapacitating effect of the TASER, you need to have three things: A complete circuit, adequate probe spread and sufficient flowing energy. Otherwise, all you get is pain--and while that might get a reaction from your target, it won't necessarily prevent them from doing whatever harmful act you were trying to prevent.
Probe spread needs to be at least four inches. Since the probes spread out farther as they go downrange (at an eight degree angle), as long as your target is more than three or four feet away from you, you'll get adequate probe spread. If the probes are too close together when they impact the target, there won't be enough body mass completing the circuit for neuromuscular incapacitation to occur. Again, there will be a painful effect, but probably little incapacitation.
Finally, there needs to be sufficient energy moving through the circuit. This is where a lot of people get confused over the whole voltage/amperage thing. TASERs can develop up to 50,000 volts, but that has nothing to do with the energy level moving through the wires. The voltage only serves to "push" the energy, and the 50,000 volts are enough pressure to assure that the electricity can arc across a gap of approximately two inches. This is important, since you can't always count on your probes sticking in the skin of your target. They might get hung up in his clothing. But as long as they are within two inches of his skin surface, the energy can arc across the gap (pushed by the 50,000 volts) and complete the circuit.
If the probes actually do contact the skin, and there is no gap to arc across, the 50,000 volts never develops. Actually, about 1,200 volts contact the target's body.
The amperage is very low--about 2.1 milliamps from the X26. That's enough to incapacitate, but is well below any danger threshold.
The energy from a TASER is delivered in pulses, and the number of pulses has much to do with the incapacitating effect. In the older M26 TASER, if the batteries began to run down, the pulse rate would slow down. If it got slow enough, the target individual would be less likely to be incapacitated. One of the advantages of the X26 TASER is that the pulse rate is digitally controlled at a steady 19 pulses per second.
So--Why Don't TASERs Work?
TASERs do work. However, a TASER deployment can sometimes be rendered ineffective for certain reasons. The most common reason that a TASER deployment might fail is lack of a circuit. If you miss with one or both of the probes, there will be no circuit. If a wire breaks or a probe is pulled loose during a struggle, no circuit. If there is a "clothing disconnect," i.e. one or both probes getting hung up in the target's clothing, more than two inches from the skin surface, no circuit.
You can usually immediately tell when any of these events occur. Your target may be reacting to the pain of the TASER hit, but may still be fighting. Note the sound the TASER makes while it is cycling. If it emits a loud clacking sound, there is an inadequate circuit. When a TASER circuit is complete, and incapacitating energy is being delivered into a target, the cycling sound will be much quieter.
Sometimes there may be a good circuit, but as the subject moves around, his clothing falls away from his body (especially true if he is wearing an unzipped coat or jacket). When that happens, the circuit will be broken, and incapacitation will be lost.
What to do?
If an officer is faced with one of these partial or broken circuit situations, the simplest solution may be to reload with a fresh cartridge, and try again. Absent that, and if the subject is close enough, the officer can push the TASER into contact anywhere on the subject's body. This will create a "three-point" contact, wherein the single probe hit and the TASER itself make up the two contact sites for the incapacitating circuit.
Officers should be reminded that even if they are in contact with the subject during such a maneuver, as long as they are not grasping the individual between the contact sites, they are unlikely to get any effect from the TASER.