Does Garage Wiring Need to Be in Conduit? Comprehensive Guide [2024]

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Does Garage Wiring Need to Be in Conduit?

A new garage requires wiring to power the garage door opener, lights, etc. Even an old garage may need new wiring. But does garage wiring need to be in conduit?

Surface wiring on solid garage walls must be in a conduit, as electrical code does not permit exposed wiring. Romex cables can be run without a conduit, provided they are behind drywall or other sheathing. However, THHN/THWN wiring must always be in a conduit, even when placed behind drywall or sheathing

So the answer to the question of whether garage wiring needs to be in conduit depends on the type of cable or wire and whether it is exposed or not. Exposed wires and cables are required to be in a conduit.

What Is the Purpose of a Conduit?

The purpose of a conduit for garage wiring is to protect the cable or wire from physical & chemical damage as well as moisture & water. 

Article 334.15 (B) of the 2020 National Electric Code (NEC) states that

Protection from Physical Damage: Cable shall be protected from physical damage where necessary by rigid metal conduit, intermediate metal conduit, electrical metallic tubing, Schedule 80 PVC conduit, Type RTRC marked with the suffix -XW, or other approved means.

What Kind of Wire Do You Use in a Garage?

The two most common types of electrical wires used for wiring interior spaces, be it your bedroom, basement, or garage, are Romex and THHN/THWN. So what are they and what is the difference between Romex and THHN/THWN?

Romex Cable

Romex® NM-B is a nonmetallic-sheathed cable that may be used for both exposed and concealed work. NM-B cable is primarily used in residential wiring as branch circuits for outlets, switches, and other loads.

Romex® is a product from Southwire®, a reputable cable and wire provider. (Information Source: Southwire)

Romex has become synonymous with the generic category of nonmetallic sheathed cable just like Sheetrock has for drywall and Kleenex has for facial tissue.

THHN/THWN Wire

THHN/THWN Wires are individual strands, unlike Romex, which is a cable. A cable has 2 or more THHN/THWN Wires sheathed in a PVC jacket.

THHN/THWN wires are best for insulated wires inside conduits. The letters indicate specific properties of the wire insulation:

• T: Thermoplastic
• H: Heat-resistant; HH means highly heat-resistant
• W: Rated for wet locations
• N: Nylon-coated, for added protection

Romex is generally suitable only for dry interior spaces with moderate temperatures. THHN/THWN Wire is not only suitable for indoor applications but also for outdoor applications. 

When to use Romex?

• For branch wiring
• Concealed applications

When to use THHN / THWN

• In high temperature and/or high humidity environment
• Within conduit

Running garage wiring behind drywall, without a conduit, is a well-accepted best practice! Romex is generally used for branch circuits from the garage subpanel to the garage door opener, garage lights, and GFCI-compliant receptacles.

Can You Run Romex in a Garage Without Conduit?

As mentioned earlier, you can run Romex in a garage, without a conduit, provided it is not exposed. The Romex cable has to be behind drywall or some other kind of sheathing such as plywood, OSB, or Fiber Cement Board.

Not only that, local inspectors and best wiring practices demand that the Romex cable is secured to a stud, joist, base plate, or top plate. Romex cable should never sag and must be supported every 6’ using staples. The final staple should be no further than 12” from the outlet.

When running Romex horizontally, from one end of the garage wall to another, the best practice is to drill a hole in the center of each garage wall stud. Make sure that the holes are at the same height. Then run the Romex cable through those holes. The cable will be straight and well-supported.

NOTE 1: While running Romex cable through holes in garage wall studs is permitted, running it on the face of the studs is not, as there is a risk of physical damage.

NOTE 2: Adding insulation such as Rockwool around the Romex cable in the stud cavity is not only permitted but even encouraged.

Running Romex through a conduit is quite difficult and is not favored by most electricians. The code however, permits running Romex through conduit.

Can THHN/THWN Wires Be Run Without Conduit?

The answer is NO. The reason THHN/THWN wires must be in a conduit is that they are thin and have less coating on them. If not enclosed in a conduit they can get damaged very easily.

Though THHN/THWN wires must always be in a conduit they have a few advantages over Romex when it comes to garage wiring.

As long as THHN/THWN wires are in the appropriate conduit they can be used

• Outdoors
• Underground
• Hot & Humid Environment

THHN/THWN wires are most suited for pulling through a conduit as they are thin and have a smooth nylon coating. THHN/THWN wires are also relatively inexpensive.

How to Wire a Garage?

Here is a general guide to give you an idea. Specific requirements may vary based on your location and the complexity of your project. PLEASE SEE THE DISCLAIMER BELOW BEFORE COMMENCING.

Step 1: Safety and Legal Considerations

It is best to entrust any electrical work to licensed professionals. Evaluate your electrical skills and knowledge, before you do the wiring yourself. Do not take unwarranted risks.

Research your state or local electrical codes and regulations. Compliance with these codes is essential for safety and legal reasons. Obtain the required permits for your electrical project.

Step 2: Gather Materials

Compile a list of the electrical supplies and materials you’ll need for the project. This includes Romex cables, conduits, gang boxes, outlets, switches, circuit breakers, wire nuts, staples, and any other tools & components required for the wiring work.

Step 3: Modify Existing Circuits

You may need to make modifications, if there are existing electrical circuits in your garage, to accommodate your needs. Reconfigure existing outlets to meet your requirements.

Install new outlets where needed while adhering to local electrical codes and safety standards.

Properly connect the wiring, ensuring that you follow the correct color coding (e.g., black for hot, white for neutral, green for ground).

Secure gang boxes to structural elements such as studs, ensuring they are level and securely fastened.

Step 4: Wiring the New Circuit

Install electrical boxes and plan your wiring scheme before running the cables between them. Use staples to secure the cables to the framing every 4 feet.

Identify the main circuit (home run) that will supply power to the new outlets. Run 12-2 Romex cable from this source to the outlets, following code requirements.

Secure the Romex cable along the walls and ceiling, making sure it is properly fastened and routed through drilled holes in the studs. Maintain a distance of at least 1-1/4 inches from the front and back surfaces of studs and joists when securing wires.

PRO TIP: When wiring an unfinished garage, the exposed electrical cable must follow the framing members (studs, plates, and ceiling joists) for protection and support.

When wiring on hard-surfaced walls (e.g., drywall, concrete), protect the cables by encasing them in conduit (PVC or metal). Use appropriate connectors, boxes, straps, and conduit sizes based on your needs.

Step 5: Install New Lighting

Remove any old lighting fixtures that are no longer needed in the garage. Install new lighting fixtures, spacing them appropriately to ensure even illumination. Use separate switches for different sets of lights, in compliance with local electrical codes.

Step 6: Final Checks and Testing

Before conducting tests, turn off the circuit breaker for the garage to prevent accidents. Inspect all wiring connections, ensuring they are secure and that there are no exposed wires.

Turn the circuit breaker back on and test all outlets and switches to ensure they are functioning correctly. Test any motion-sensing lights or special lighting features that have been installed. Review and confirm that all safety measures are in place, such as ground fault protection and tamper-resistant outlets.

If required by local regulations, schedule an inspection to verify that your electrical work complies with safety codes.

Some Common Mistakes to Avoid in Garage Wiring

Improper Grounding

Grounding is crucial for safety, preventing electrical shocks and fires. Ensure all outlets and fixtures are properly grounded to avoid hazardous situations.

Overloading Circuits

Overloading circuits can cause breakers to trip or wires to overheat, leading to potential fires. Calculate the total load and distribute it across multiple circuits to maintain safety and efficiency.

Using Incorrect Wire Types

Using the wrong wire type can lead to overheating and electrical failures. For example, Romex cable is suitable for indoor use, while THHN/THWN wire is better for conduit installations.

Always choose the appropriate wire type for your specific application.

DISCLAIMER: What Is the Safest Way to Handle Electrical Wires?

This post is for information only. I strongly recommend that all electrical work should be entrusted to licensed professional electricians. In case you do decide to do some of the work yourself, make sure that:

“Treat all electrical wiring, even “de-energized” ones as if it is live, unless it has been locked out and tagged”

You must follow the basic safety guidelines, as under:

• Use protective eyewear, especially when drilling or grinding metal
• Wear insulated rubber gloves when working on any circuit or branch circuit
• Always use insulated tools while working with electricity
• De-energize the electrical wires on which you will be working. Tag the circuit breaker to prevent someone from switching it on accidently
• Electrical wiring in wet or damp locations or underground must be within a PVC conduit
• Underground wiring conduits should be at least 18 inches below grade as per code
• All receptacles for equipment that could be in wet or damp locations should be equipped with Ground Fault Circuit Interrupter (GFCI)
• Never use old frayed cables, damaged insulation or broken plugs
• High voltage equipment should be properly grounded to insure electricity flows directly to the ground and not through the person in contact with the live wire 

Conclusion

Use Romex for garage wiring that is concealed behind drywall or other sheathing, without a conduit.

Use THHN/THWN wires in a conduit for feeder wiring from the main panel to the sub panel or outdoor & exposed applications.

Thank you very much for reading the post. I do hope you found it informative and useful.