Will I get shocked if I drive an electric car through a big puddle?

Both hybrid and electric vehicles use large, powerful battery packs to power electric motors. These battery packs generate much higher voltages than the 12-volt batteries in most cars. For example, the battery pack in the Toyota Prius runs above 200 volts, and other vehicles have battery systems capable of generating 300 or more volts [source: Toyota Prius Battery]. If someone were to touch the power cables or a short circuit somehow diverted power into a person, the voltage level would definitely be high enough to be lethal.

Auto mechanics and rescue workers do need to be aware of the risks and take proper safety precautions; however, this doesn't mean electric vehicles are any more dangerous than gas-powered vehicles. They're just dangerous in a different way. If it's been ruptured, a full tank of gasoline adds a great deal of danger to a rescue situation, just as a ruptured battery pack or exposed power line presents a risk. Most electric and hybrid cars have extensive safety systems that automatically shut off the power and isolate the battery packs when they detect a collision or a short circuit. Circuit breakers, often located in a compartment under the hood, trip and disconnect the flow of power in the event of an electrical surge or a short circuit. If a car is submerged in water, and some of that water gets into the electrical system, the circuit breakers trip. Even simply shutting down the car interrupts the flow of power from the batteries to the motor, so the high-voltage cables that connect them are left without power. For extra safety, the high-voltage cables are colored bright orange - a visual indicator to avoid contact.

There's one danger you might not expect from mixing water and electric cars together. If water comes in contact with the nickel-

metal hydride in the battery cells, the resulting chemical reaction forms hydrogen. If enough hydrogen builds up, it could cause disorientation and dizziness, and it could also lead to an explosion. This is really only an issue for rescue crews who have to deal with ruptured batteries, and they can easily handle it by properly ventilating the wreck.

So, now we know that electric cars are safe in an emergency situation if some basic precautions are taken. But could you get shocked or cause damage to the electric components by simply driving through a large puddle? To put it simply, the answer is no. Read the next page to find why.

To understand why water doesn't bother the batteries or the motor in an electric car, first consider the fact that every car you've ever driven has had an electrical system. It operated at much lower voltages, used a different kind of battery and served a different purpose from the system in a hybrid car, but the principle is the same. All cars have batteries and electric systems, yet they don't short out or shock anyone in the rain. Even if you get water on the battery terminals, it generally just causes corrosion, not an immediate catastrophic effect. In fact, in several models, notably certain Chrysler vehicles, the 12-volt battery is mounted behind the front tire, near the bottom of the car, where it is frequently exposed to water and other road debris.

Hybrid and electric car batteries are a bit different. They're larger, have more cells and contain nickel-metal hydride instead of lead-acid. Some batteries are made using lithium-ion technology; however, lithium-ion batteries are not very common in cars -- not yet, anyway. In the most typical configuration, the batteries are placed behind the rear seat, sometimes in an enclosed section near the trunk. In the Toyota Highlander SUV Hybrid, the battery pack is underneath the rear seat, bolted to a structural cross member. In early Toyota Prius models, the battery pack was mounted flush to the back of the rear seat. The point is, in a typical electric or hybrid car, the battery pack is usually nowhere near an area where it could get splashed with water from the road.

On the other hand, in some designs the battery pack is mounted near the bottom of the car. What then? Hybrid vehicles manufactured in the United States have a battery pack encased in a sealed metal shell. The shell is electrically isolated from current flowing from the batteries and usually covered in carpet or with an interior panel. Even though the shell is metal, if it does get wet, it's treated to resist corrosion.

In the event that water does actually get inside the shell, there's still not much to worry about. The nickel-metal hydride batteries used in current hybrids and electric cars are maintenance-free sealed cells, so nothing gets in or out. The chemicals inside are designed to form a gel, so they won't spill even if the batteries are ruptured in a crash. Under normal operating conditions, it's pretty much impossible for water to come into contact with the batteries themselves. The high-voltage lines that carry the current are similarly protected and insulated.

The bottom line -- don't worry about dodging puddles in your Prius.

For more information about hybrid and electric vehicles, batteries and other related topics, follow the links on the next page.