Does Wood Conduct Electricity? Why?

Wood is generally known as an excellent insulating material, but there are instances where it seems to conduct electricity. This begs the question, does wood conduct electricity?

Is Wood a Conductor of Electricity?

No, wood doesn’t conduct electricity. Water does, though. So, if the wood is wet enough, and the current applied is strong enough, this combination could conduct electricity.

The low electrical conductivity of wood makes it an excellent choice of material in many applications where electrical insulation is important. For instance, wood is used for the construction of houses, flooring, electrical switch boxes, wooden poles are often used to support the electricity cables, etc.

See the conductivity of different types of wood.

Why Does Wood Not Conduct Electricity?

Electricity requires free electrons to travel. Wood doesn’t have this in its structure, so it can’t conduct electricity. Water has loads of free electrons and can efficiently conduct electricity, which is why wet wood can sometimes conduct electrical currents.

Wood acts as an electrical insulator. Inherent in its structure, the molecules are bound exceptionally tightly, which means that the electrons associated with them aren’t free to move around.

Wood also contains a high percentage of voids in its structure. This changes with the wood species since some hardwood species typically have a very dense structure, while softwood species contain more voids. These voids act as insulators since electricity can’t travel through a void unless the current is extremely high.

If the electrical current is large enough, the current will overpower the wood’s insulating capabilities and travel through the structure. Examples include a direct lightning strike or contact with a high-voltage line.

Wood’s potential electrical conductivity (measured in siemens) can be calculated when the material’s length, inherent resistance, and cross-sectional area are known:

ơ = conductivity
L = length
R = resistance
A = cross-sectional area

Resistivity of Wood

Alternatively, you can calculate wood’s resistivity, which is the opposite of conductivity:

Typically, wood’s electrical resistivity ranges from 1014 to 1016 ჲm (ohm meter) when dry and between 103 and 104 ჲm when wet. This is a dramatic decrease.

Conductivity of Wet Wood

Wet wood can sometimes conduct electricity under particular circumstances. Water is an excellent electrical conductor since it has loads of free electrons that can move around (electrical currents move through the flow of electrons). So, it’s not the wood that conducts the electricity, but the water in the wood.

So, suppose the wood is wet enough throughout its structure. In that case, if the charge is high enough, there might be enough free electrons available to conduct the electrical charge. This current will probably be weak since the wood’s non-conductive nature will largely insulate the current.

Wood that’s still growing, like a living tree, also contains large amounts of free electrons in its tree sap. This is an excellent conductor, hence live trees’ ability to conduct electricity. This factor also explains why trees are such frequent targets for lightning strikes. Lighting, a powerful electrical current, moves far easier through the tree’s wet structure than through the air, essentially an insulator.

So, when lightning strikes, it’s attracted to the relative ease of conductivity inherent in the tree. This strike produces heat in the tree, causing the tree sap to boil. Boiling tree sap expands, causing the tree to split or even explode.

Factors that May Affect the Conductivity

While wood in its pure form will never conduct electricity, there are exceptional circumstances where it can do so, like wetness. Factors that will influence this include

• Temperature – water’s electrical conductivity increases with temperature.
• Moisture – increased moisture, and its absorption into the wood’s structure increases conductivity.
• Species – conductivity increases if the wood’s structure allows for greater moisture penetration. This structure changes with wood species.
• Current frequency – conductivity increases with increased electrical current frequency.
• Thickness – thinner wooden sections have reduced insulating properties, increasing the conductivity.
• Impurities – some impurities increase the conductivity by supplying free electrons.
• Surface finish – some products used in surface treatments conduct electricity, effectively increasing the structure’s conductivity.

The conductivity of Engineered Wood

Engineered wood has different properties from solid wood, making it ideal for different applications. These structural changes affect the wood’s conductivity. Here are some examples.

• Plywood
  Plywood consists of wood chips compacted and glued together in layers. The wood present in this structure is an excellent insulator, but the glue is not. If water is allowed to penetrate into the plywood’s structure, it will likely conduct electricity. These factors contribute to plywood being an excellent insulator when dry but quote conductive when wet.
• MDF
  MDF consists of wooden fibers compressed and bound together with wax and resin binder. It’s typically denser than plywood and an excellent insulator. MDF is less absorbent than plywood and, thus, less likely to become wet throughout the structure.
  So, dry MDF boards are excellent insulators, but wet ones aren’t. They’re not as likely as plywood to conduct electricity, though.
• Particle Board
  Particle board is a low-density plywood made from wood chips bound with synthetic resin. It’s highly susceptible to water damage, allowing water to penetrate deep into the structure. While a dry particle board is a good insulator, a wet particle board will conduct electricity if the applied current is high enough.