A picture of a person installing fiberglass insulation batts, with an electrical plug graphic on the right side, including a question mark symbol in the middle of it.

When installing insulation in a building of any kind, you will inevitably have to deal with placing insulation around electrical wires. But how do you do so safely? Can insulation touch electrical wires in your home?

It is perfectly safe for household insulation to touch wires provided the wires or cables are electrically insulated. There also are techniques to make insulation fit better around wires. However, under no circumstances should thermal insulation make contact with live uninsulated wires and cables.

The techniques for fitting insulation around wires and cables differ depending on the type of insulation used. This article will explain how to safely install the four different types of residential insulation around electrical wiring and why it is generally safe to do so.

How Can Insulation Safely Touch Electrical Wires?

Electricity is potentially dangerous, and when handled incorrectly, can cause injury or fires. But if it were excessively dangerous, we wouldn’t use it in our houses. Well, we might in America.

The electrical insulation that jackets modern electrical wire prevents the electrical current from jumping to other surfaces in your house. Live electrical wires can contact most surfaces and materials in a home as long as the insulation is intact.

Electrical Insulation

Residential electrical wiring is jacketed in non-conductive material called “insulation.” An electrical insulator is a material that does not allow the flow of electricity through itself.

Some materials that act as electrical insulators include but are not limited to air, distilled water, paper, glass, and most importantly, plastic. The most common types of residential electrical wire are insulated with either thermoplastic or thermosetting plastic.

Thermoplastics are polymer-based materials that melt or become workable at elevated temperatures. While these materials can melt, the temperatures at which they do so are far higher than any that generally occur in a typical American residence.

Examples of thermoplastics used in electrical insulation are:

  • Polyvinyl Chloride (PVC)
  • Polyethylene (PE)
  • Nylon
  • ECTFE
  • PVDF

Thermosetting plastics are polymers made of viscous fluid resins that are induced to harden irreversibly through one of several processes. The hardening process can be triggered by mixing in a catalyst liquid, applying heat, ultraviolet radiation, or high pressure.

A picture showing the jacket insulation around wires, both individually, and the white insulation jacket around all the individual wires as well.

Whatever catalyst is used, the hardening reaction produces a considerable amount of heat. Thermosetting plastics used to insulate residential wiring include:

  • Cross-linked Polyethylene (XLPE)
  • Chlorinated Polyethylene (CPE)
  • Ethylene Propylene Rubber (EPR)

Electricity used in American and Canadian residences runs at a current of 200 amperes (amps) at 120 or 240 volts (v). Under these conditions, a plastic cladding of under 100 thousandths of an inch effectively blocks electricity.

As long as the cladding is intact and not punctured, the electricity will not be able to jump to other surfaces around them.

It should also be noted that the most common varieties of thermal insulation used in American residences are themselves typically made of non electrically conductive materials. Some are even rated to block high voltage electrical short circuits.

What Are the Different Types of Thermal Insulation?

There are four types of thermal insulation used in American residences. They fit in moderately different niches in residential heating and construction and have different installation procedures.

The four types of residential thermal insulation are:

  • Loose Fill
  • Blanket
  • Rigid foam
  • Spray foam

Currently, rigid foam insulation is the most efficient type of commercially available insulation.

Loose-Fill Insulation

One of the two most common types of insulation is loose-fill insulation. Loose-fill insulation consists of small pieces of fibrous, foam, or other material that are not bound together. It is the kind of insulation that might be blown into an unfinished attic floor and odd-shaped cavities made by adjoining walls.

Modern loose-fill insulation is commonly made of synthetic materials like fiberglass, Icynene (a proprietary synthetic polymer), or mineral wool. Still, it can also be derived from naturally occurring materials such as perlite and cellulose.

A person blowing in loose-fill insulation into the attic floor.

Blanket Insulation

The other most common type of residential insulation is blanket insulation. Blanket insulation takes the form of sheets of thick fluffy material. It is commonly sold in widths corresponding to standard stud lengths used in the residential construction industry, between 15 inches (38.1 cm) and 23 inches (58.4 cm).

This allows it to be installed in between studs during the construction of walls and ceilings. Blanket insulation is commonly sold in units called “batts” or rolls, between 3 inches (7.62 cm) and 10 inches (25.4 cm) thick.

Blanket insulation is often made of the same materials as loose-fill insulation: fiberglass, mineral wool, cellulose, etc. Because they’re generally made of the same materials, blanket and loose-fill insulation have similar thermal retention characteristics.

Fiberglass batt type insulation has been traditionally the most common and the cheapest material you can buy for your home.

Rigid Foam Insulation

Also called foam board and rigid panel insulation, rigid foam insulation is a newer type of insulation that was first used in residential construction in the 1970s.

It is a derivation of panel insulation that has been around since the 19th century when it was commonly made of condensed plant material such as reeds and cork. Rigid foam insulation is currently the most efficient type of commercially available insulation.

Rigid foam insulation consists of a layer of expanded foam sandwiched between two plastic or metal panels. The foam is typically made of synthetic polymers such as polyurethane or polyisocyanurate, although mineral wool and fiberglass are used in some brands.

A picture of a person in a white construction outfit installing rigid foam board insulation on a wood wall.
Worker placing styrofoam sheet insulation to the wall.

Chemical propellants such as pentane or CFC/HCFCs are used to create bubbles in the foam, although the latter group of propellants has been phased out in most countries due to the environmental effects.

Rigid foam panels are typically between 0.5 in (1.27 cm) and 3 in (7.62 cm) thick, although they can be available up to 6 inches (15.24 cm) thick in extreme climates. It is usually sold in standardized 4-foot (1.2 m) by 8-foot (2.4 m) panels, which can easily be cut down to smaller sizes.

This type of insulation can be installed in many places inside typical American residences, including but not limited to unfinished walls, basements, ceilings, and underneath building siding.

Foamed in Place Insulation

Foamed-in-place insulation, also called “spray foam insulation,” is likely the most versatile type of insulation. It consists of a mixture of two chemicals which, when mixed, will expand between 30 and 50 times their original volume before hardening.

Before it hardens, foam-in-place insulation is essentially a liquid and will flow and expand to fill practically any shaped volume. It can be installed in unfinished walls and floors, ceilings, and otherwise inaccessible spaces in your house.

A man in full protective gear is sitting on the attic floor while he sprays spray foam insulation on the underside of the attic ceiling.

While it can be made of more natural materials like cellulose, foamed-in-place insulation is usually made of synthetic polymers like polyethylene or polyurethane. It used to be expanded with HCFC-based propellants, but due to these chemical’s negative environmental impacts, they have been largely phased out.

How Do You Install Insulation Around Wires and Cables?

Depending on the type, there are different ways to install insulation around the wiring in your house. To reiterate, it is perfectly safe for thermal insulation to touch insulated wires and cables.

Before working around wiring, you should turn off the electrical power to that part of your home for your safety.

Of the four types of insulation, loose-fill is the simplest to install around electrical wiring. Because the pieces of insulation are not bound together and are very light, loose-fill insulation can be blown in or poured around wiring without special preparation or effort.

Wiring and loose-fill insulation are most likely to encounter each other in unfinished attic floors and ceilings, where the wiring is connected to light fixtures illuminating lower floors.

Rigid foam panels are thin and can be cut down to any size and shape, so they can generally be installed behind electrical wiring and outlets. The most common brands available on the market are made of materials that can serve as electrical insulators and are often rated to resist electrical short circuits.

Blanket insulation is thicker than rigid foam insulation, so generally cannot fit behind residential wiring. There are two ways to fit blanket insulation around electrical wiring, as demonstrated in this video by YouTuber Corey Binford.

The first way is to split the insulation blanket in half up to the height of the wires or cable. The insulation itself is easier to break apart by hand, though you should wear protective gloves while working with it.

Then you orient the blanket with the split part down and slide one side behind the wiring with the other in front. When you are done, the wiring should be roughly in the middle of the insulation blanket.

The other way to install blanket insulation around the wiring is to cut a slit for it. Before placing the blanket, stand it on one end in front of the wall, and fold it in half at the height of the wire.

Then with a sharp knife, cut the blanket parallel to yourself about halfway through its thickness. This creates a slit that fits around the wiring. Similarly, you can cut a gap in an insulation blanket to accommodate an electrical outlet.

As mentioned above, foamed-in-place insulation can fit into practically any space, and if you wish, you can entomb electrical wiring in it without issue. According to EcoStar Insulation, the expert thing to do is leave a gap of about 3 inches (7.62 cm) between the newly applied insulation and any wiring and allow the insulation to expand toward the wiring.

If the insulation expands to cover the wiring, wait until the insulation hardens and cut a channel around the wire or cable. Please make sure the power to this part of your house is turned off before doing so. Spray foam insulation is commonly used to insulate around electrical outlets when other types of insulation do not easily fit.

Conclusion

In summation, it is perfectly safe for thermal insulation to touch electrical wires as long as the wires are electrically insulated. The method for fitting insulation around wiring depends on the type of insulation being used.

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