Are Threads the Same on Electrical Conduit and Plumber’s Pipe?

If you’ve ever tried to connect an electrical conduit to a plumbing fitting—or vice versa—you might have asked, “Are threads the same on electrical conduit and plumber’s pipe?” It’s a smart question, because using the wrong threading standard can lead to leaks, electrical hazards, or failed inspections. While both systems rely on threaded connections, their designs serve different purposes and follow distinct standards. In this guide, we’ll clarify the key differences, explain why they matter, and help you avoid costly mistakes—whether you’re a DIYer, electrician, or plumber.

What Are Pipe Threads, and Why Do Standards Matter?

Pipe threads are helical ridges cut into the ends of pipes or fittings to allow secure, leak-resistant (or mechanically strong) connections. But not all threads are created equal. The two most common standards in the U.S. are:

• NPT (National Pipe Tapered) – Used in plumbing and gas lines
• NPS (National Pipe Straight) – Often used in electrical conduit

The critical difference? Taper. NPT threads are slightly tapered (wider at one end), which creates a tight seal when tightened—essential for containing liquids or gases. NPS threads, however, are straight and rely on locknuts or couplings for mechanical stability, not for sealing fluids.

💡 Expert Insight: According to the National Electrical Manufacturers Association (NEMA), using NPT-threaded fittings on electrical conduit can compromise grounding continuity and violate NEC (National Electrical Code) requirements.

Are Threads the Same on Electrical Conduit and Plumber’s Pipe? The Short Answer

No—they are not the same. While both may appear similar to the untrained eye and might even partially screw together, they follow different dimensional and functional standards:

Even if a plumbing fitting seems to screw onto a conduit, it won’t provide a proper electrical bond, and the mismatch can lead to:

• Arcing or grounding failure
• Corrosion from improper sealing
• Inspection rejection
• Safety hazards in wet or explosive environments

🔍 Real-World Case: In a 2022 Florida commercial project, an inspector rejected an entire electrical run because NPT-threaded plumbing adapters were used on rigid metal conduit (RMC). The fix cost over $8,000 in labor and materials.

Why Confusion Happens: The Visual Similarity Trap

Many DIYers and even some contractors assume that since both conduits and pipes are metal tubes with threads, they’re interchangeable. This misconception is dangerous.

Both use inch-based thread sizes (e.g., ½”, ¾”), which adds to the confusion. But here’s the catch:

• A ½” NPT plumbing pipe has an outside diameter (OD) of ~0.84 inches
• A ½” electrical conduit (RMC) has an OD of ~0.706 inches

That 0.134-inch difference means threads won’t fully engage, leading to cross-threading or weak connections.

📚 Authority Source: The differences in thread standards are defined by ANSI/ASME B1.20.1 (for NPT) and ANSI/ASME B1.2 (for NPS). For a full technical breakdown, see the [Wikipedia entry on pipe threads](https.

Can You Ever Mix Electrical and Plumbing Threads?

Almost never—and never in permanent installations. However, in rare cases (e.g., temporary grounding in non-hazardous areas), professionals may use listed transition fittings specifically designed to bridge the gap between systems. These are UL-listed or ETL-certified and clearly labeled for dual use.

But never force a plumbing fitting onto conduit just because it “fits.” The National Electrical Code (NEC) Section 300.15 explicitly requires fittings to be identified for the specific wiring method used.

✅ Safe Practice Checklist:

1. Verify thread type with a thread gauge before connecting
2. Use only UL-listed electrical fittings on conduit
3. Never use pipe dope or Teflon tape on electrical threads—it insulates and breaks grounding
4. Consult local codes—some jurisdictions prohibit any crossover

Step-by-Step: How to Properly Thread Electrical Conduit

If you’re working with rigid metal conduit (RMC) or intermediate metal conduit (IMC), here’s how to thread it correctly:

1. Choose the Right Conduit: Only RMC and IMC are threaded; EMT (thin-wall) is not meant to be threaded—it uses set-screw or compression fittings.
2. Use a Conduit Threading Die: Select a die rated for electrical conduit (e.g., ½” NPS die).
3. Apply Cutting Oil: Use light machine oil—not plumbing dope.
4. Cut Threads Smoothly: Rotate the die steadily; aim for 10–12 full threads.
5. Deburr the End: Remove metal shavings with a deburring tool.
6. Install with a Conduit Nut: Tighten with a wrench until snug—do not overtighten, which can strip threads.

⚠️ Warning: Threaded EMT is a red flag for inspectors. If you see it, assume it’s a code violation.

FAQ Section

Q1: Can I use a plumbing pipe as electrical conduit?
A: No. Plumbing pipes aren’t listed for electrical use. They lack proper grounding continuity, may have internal coatings that inhibit bonding, and violate NEC 342.6 unless specifically listed for electrical applications (which standard plumbing pipe is not).

Q2: What happens if I use Teflon tape on electrical conduit threads?
A: Teflon tape acts as an insulator, breaking the electrical bond between conduit sections. This can prevent proper grounding, increasing shock or fire risk. Never use sealants on electrical threads.

Q3: Are NPT and NPS threads interchangeable?
A: Technically, they might screw together a few turns, but they are not interchangeable. NPT’s taper prevents full engagement with straight NPS threads, leading to weak, unsafe connections.

Q4: How can I tell if a fitting is for electrical or plumbing use?
A: Look for markings: Electrical fittings are stamped with UL, ETL, or “RMC”/“IMC.” Plumbing fittings often say “NPT” or reference ASTM standards like A53 or A795.

Q5: Do all electrical conduits have threads?
A: No. Only RMC (Rigid Metal Conduit) and IMC (Intermediate Metal Conduit) come threaded or are field-threaded. EMT (Electrical Metallic Tubing) uses clamp-style connectors and should never be threaded.

Q6: Is there a universal adapter I can use?
A: Only if it’s a listed transition fitting (e.g., a UL-listed conduit-to-NPT adapter for enclosures). Generic hardware store adapters are not safe or code-compliant.

Conclusion

So, are threads the same on electrical conduit and plumber’s pipe? The answer is a clear no—and confusing them can risk safety, violate codes, and cost you time and money. Electrical threads prioritize grounding and mechanical strength; plumbing threads focus on sealing under pressure. They serve different worlds, even if they look alike.

Understanding this distinction isn’t just technical know-how—it’s a safety essential. Whether you’re wiring a garage or renovating a kitchen, always use the right fitting for the right job.

👉 Found this guide helpful? Share it with a fellow DIYer, electrician, or plumber on Facebook, LinkedIn, or Reddit! One click could prevent a dangerous mistake.

Stay safe, stay grounded—and never assume threads are universal.