Texas Electrician ExamTexas journeyman & master

The neutral-to-ground bond happens at exactly one place

Bonded at the service. Separated everywhere downstream. The reason is not tradition, and understanding it makes a whole family of exam questions automatic.

On this page
  1. The rule, in two sentences
  2. Why it matters, physically
  3. The word unspliced is doing work
  4. The grounded conductor comes to the service even when nothing needs it
  5. Separately derived systems are a separate question
  6. How to spot these questions
  7. What this page cites

The rule, in two sentences

The neutral and the ground are joined at exactly one point and separated everywhere after it At the service, the grounded neutral conductor and the equipment grounding conductor are bonded together by the main bonding jumper. Downstream of that point, in every subpanel, the two are kept apart: the neutral floats on an insulated bar and the grounding conductors land on a bar bonded to the enclosure. If they are joined again in a subpanel, normal load current returns on the equipment grounding conductor and on any metal in its path, which is the fault this rule exists to prevent. SERVICE A B from the utility neutral bar grounding bar main bonding jumper the one legal connection feeder: ungrounded and grounded plus the grounding conductor SUBPANEL neutral bar, ISOLATED grounding bar, bonded to the can no jumper here joining them twice puts load current on metal that people touch to the electrode system one bond, one place. everything downstream stays apart.
Bond once, at the service. After that, separate. Joining them twice puts load current on metal people touch. Drawn against NEC 250.24(B), 250.28 and 250.142(B). In editions before 2026 the load-side rule was 250.24(A)(5).

At the service disconnect, an unspliced main bonding jumper connects the equipment grounding conductors and the enclosure to the grounded conductor (NEC 250.24(C)).

On the load side of the service disconnecting means, the grounded conductor is not connected to equipment grounding conductors, to metal parts, or reconnected to ground, except where this article says otherwise (NEC 250.24(B)).

Bonded once, at the service. Separated everywhere after it. That is why a subpanel has an isolated neutral bar and a separate ground bar, and why the bonding screw comes out.

Why it matters, physically

If the neutral and ground are bonded at a subpanel as well as at the service, the two conductors are in parallel between those points.

Normal neutral current now has two paths back. Some of it returns on the neutral and some returns on the equipment grounding conductor, and on the metal conduit, and on anything else bonded along the way.

That means current flowing on parts that are supposed to be at zero volts under normal conditions. Metal enclosures, appliance frames, water piping. Nothing has failed and nothing will trip. The system just quietly carries current on its safety path.

Then when a real fault happens, the path that was supposed to be clean is already loaded, and if the neutral ever opens the equipment grounding conductor becomes the only return for the entire load.

The word unspliced is doing work

The main bonding jumper is specified as unspliced, and that word is on the exam.

A splice is a point of failure in a conductor whose entire job is to be there when something goes wrong. If the main bonding jumper opens, the service enclosure is no longer referenced to the grounded conductor and the fault path is gone.

The section carries two exceptions, one for multiple disconnects in an assembly listed as service equipment, and one for impedance grounded systems. Read them in your book rather than from this summary.

The grounded conductor comes to the service even when nothing needs it

On a grounded system of 1000 volts or less, the grounded conductor is routed with the ungrounded conductors to each service disconnecting means and connected to its terminal or bus (NEC 250.24(D)).

This catches people because it applies even where the load has no need for a neutral. A three-phase service feeding only three-wire loads still brings the grounded conductor to the service equipment.

The reason is that at the service, the grounded conductor is not a load conductor. It is the fault-current path back to the transformer. Without it there, a fault on the line side of the main has nothing to return through and the overcurrent device never sees enough current to open.

Separately derived systems are a separate question

A transformer inside the building creates a new system, and that new system gets its own bond and its own electrode connection. It is not covered by the service rules above.

This is why a question about a step-down transformer feeding a panel is not answered with the subpanel rule. Downstream of a separately derived system, the bond exists again at the transformer or the first disconnect, and then the separation rule applies from there.

If a question mentions a transformer between the service and the panel in question, stop and check whether you are looking at a separately derived system before applying the subpanel answer.

How to spot these questions

The single question to ask is: where is the source for this panel. If the source is the utility service, you are at the bond. If the source is another panel, you are downstream of it.

What this page cites

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Every rule here is cited to the section it comes from, and corrections are logged in public with the date. This is study material rather than electrical advice, and it does not replace your own code book or your inspector.