The difference between a line conditioner and a surge protector mostly lies in their intended function. A line conditioner takes in power and modifies it based on the requirements of the machinery to which it is connected. A surge protector doesn't alter the power flowing through it at all, unless that power is over a certain amount. When the power exceeds the set amount, it blocks it from passing through. It is not uncommon for the two devices to be in the same unit.
Both line conditioners and surge suppressors are important parts of modern electronics. They protect the inner workings of devices, often without users even realizing it. Many people go the extra step of placing additional protective devices between the wall outlets and the electronic products.
A line conditioner modifies voltage as it passes through. Some systems require very tight or nonstandard power tolerances, and they use line conditioners to alter the power to meet their requirements. They are also a common method of prolonging the lifespan of electric devices, as the properly formed electricity creates less wear on the internal parts of the device.
Most electric systems have line conditioners built into them, usually as very small devices that are integrated right into an internal circuit board. They monitor the voltage moving across the board and keep it within a specific tolerance. There are larger line conditioners available, ranging from small ones in high-end surge protectors all the way to car-sized industrial units connected to factory machines.
Surge protectors prevent power overloads. When power exceeds a certain amount, they stop it from passing through. Different surge protectors do this in different ways, but the most common method is creating a shunt to a ground wire.
This connection to the ground only happens when the power is prevented from passing through the unit; otherwise, the unit would constantly waste electricity. If a surge protector is improperly plugged in, such as through a two- or three-pronged adapter, it cannot send power to the ground. In this case, the surge protector may overload and catch on fire or even send the surge through to the connected device.
It isn't unusual for a line conditioner and a surge protector to be placed in the same unit. Since these systems both work on passing voltage, it makes sense to put them together. Some systems have a very advanced line conditioner that works as a surge protector when needed; this is common in battery backup systems.