You're right, the requirement to have 18" of copper just for bonding in a primarily PEX system sounds ludicrous. Let's break down the code requirements and what's likely happening

What the Code Actually Says (or Doesn't Say):
Purpose of Bonding/Grounding

The primary reason for bonding metal water piping is to provide a low-impedance path for fault current back to the electrical panel. This helps to trip the circuit breaker in the event of an electrical fault within the water heater, reducing the risk of electric shock.

National Electrical Code (NEC)

The NEC is the foundation for electrical codes in most states, including NJ. Here's what it says about bonding metal water piping:

NEC 250.104(A): Metal Water Piping. “The metal water piping system shall be bonded as required in (A)(1), (A)(2), or (A)(3) of this section.”

NEC 250.104(A)(1)

“Metal water piping system(s) installed in or attached to a building or structure shall be bonded to any of the following:" (lists options like the service equipment enclosure, grounding electrode conductor, etc.).

Key Considerations for PEX



Interrupted Metallic Path

PEX is non-conductive. If your plumbing system is primarily PEX, the metallic water piping system is not continuous throughout the building.

Exception

NEC 250.104(A) generally requires metal water piping to be bonded. HOWEVER, there are exceptions:

NEC 250.104(A)(4)

“Metal water piping systems that are used for grounding of electrical equipment or conductors shall be bonded as required in 250.104(A)(1). Where isolated from the metal water piping system, the equipment grounding conductor for the branch circuit supplying the water heater shall be installed to the water heater.”

NJ Amendments and Local Codes



NJ Adopts NEC

New Jersey generally adopts the NEC with some amendments. You'd need to check the current NJ adopted version of the NEC and any state-specific amendments to 250.104. Contacting your local electrical inspector is the best way to determine local interpretation and enforcement.

Local Variations

While the NEC provides a baseline, individual municipalities can adopt stricter codes. This is less common for something like this, but always worth checking.

Why the Plumber Might Be Saying That (and Why It's Still Problematic)



Misunderstanding/Outdated Information

The plumber might be working based on outdated code knowledge or a misunderstanding of the code's intent. Older codes may have been stricter about bonding to the water heater specifically.

"Playing It Safe"

Some plumbers default to the most conservative (and often unnecessary) approach to avoid potential issues with inspectors.

Home Inspector Expectations

This is the most likely reason. Home inspectors often check for things they think are code requirements, even if they aren't. It's easier to point out a missing bond than to research the entire plumbing system's configuration. However, a home inspector's opinion does not change the requirements of the electrical code.

Lazy/Cheap Solution

Adding a short copper stub is easy compared to figuring out a proper grounding method for an isolated water heater.

What You Should Do


Consult the Current NJ-Adopted NEC

Find the current version and read NEC 250.104 specifically. Look for any NJ-specific amendments to that section.
2.

Contact Your Local Electrical Inspector

This is the most important step. Explain your situation (primarily PEX system, water heater electrically isolated from the main plumbing) and ask them what is required to pass inspection. They can tell you definitively what they expect.3.

Document Everything

Keep records of your conversations with the inspector and any code research you do.4.

Alternative Solutions (if needed)



Equipment Grounding Conductor

If the electrical inspector agrees that your water heater is considered isolated and not part of a continuous metal water piping system, then NEC 250.104(A)(4) allows you to run the equipment grounding conductor for the branch circuit that supplies the water heater back to the electrical panel. This means the grounding wire in the cable feeding the water heater must be properly connected to the water heater's grounding lug.

Supplemental Electrode

In rare cases, the inspector might require a supplemental grounding electrode near the water heater (e.g., a ground rod).

In Summary:The plumber's blanket statement about needing 18" of copper for bonding in a PEX system is highly questionable and likely based on misinformation or outdated practices. The actual code requirements are more nuanced and depend on whether the metal water piping system is continuous. Do your research, consult with the local electrical inspector, and ensure that your water heater is grounded properly according to the current code, regardless of what a home inspector might expect. Flag for review