Checked against primary sources 2026-08-24

Article 250 in the 2026 edition, and where to look first

The article kept its number and most of its shape. Two things moved anyway, and one of them means a medium-voltage answer is no longer in Article 250 at all.

What left the article this cycle

Grounding and bonding for systems over 1000 volts ac and 1500 volts dc is no longer inside Article 250. It has an article of its own, Article 270, Grounding and Bonding of Systems over 1000 Volts ac, 1500 Volts dc, Nominal.

The twin sections keep their numbers and change their article. Grounding Separately Derived Alternating-Current Systems is 250.30 in the general article, and the same title sits at 270.30 in the new one.

So a search that stops at the end of Article 250 comes up empty on a medium-voltage question. The answer is not missing. It is two articles further on, at a number you can predict.

The sentence that answers most grounding questions

If you re-read one thing in Article 250, make it the performance requirements at the front.

250.4(A)(5), Effective Ground-Fault Current Paths, used to be a single paragraph. In the 2026 edition it is three lettered items: (a) opening the overcurrent protective device, (b) carrying ground-fault current, and (c) use of the earth.

The line everyone quotes is item (c). At NEC 250.4(A)(5)(c) the code states that the earth shall not be considered an effective ground-fault current path.

Ground rods do not clear faults. Bonded metal does. That distinction settles a large share of the confusion in the field.

There is a near twin at 250.4(B)(4), for ungrounded systems, and it is one word apart: effective fault-current path, with no ground in front of it. Two subsections, two kinds of system. If the question names an ungrounded system, it is pointing at the second one.

The sizing rule people apply half of

The grounding electrode conductor is sized from a table, and then three subsections cap it depending on what electrode is at the far end (NEC 250.66).

• To a rod, pipe or plate electrode, not required to be larger than 6 AWG copper or 4 AWG aluminum (NEC 250.66(A)).
• To a concrete-encased electrode, not required to be larger than 4 AWG copper (NEC 250.66(B)).
• To a ground ring, not required to be larger than the ring conductor itself (NEC 250.66(C)).

All three carry the same condition: the ceiling applies only where that conductor does not continue on to another type of electrode requiring a larger conductor. If it continues on, the ceiling is gone.

Sizing straight off the table and stopping produces an oversized conductor on any rod-only or concrete-encased system. It is the most common sizing error in the article and it costs money on real jobs.

Two rules that pull against each other

If the grounding electrode conductor is aluminum or copper-clad aluminum, two distance rules apply and they measure from different surfaces (NEC 250.64(A)).

One permits a termination within 18 inches of the bottom of an outdoor enclosure listed and identified for the environment. The other forbids terminating within 18 inches of the earth.

Same number, opposite direction. Read which surface is being measured from.

Aluminum also cannot sit in direct contact with concrete, or in corrosive conditions, unless it carries an extruded polymeric covering.

The bonding rule that surprises people on 480 volt systems

For circuits over 250 volts to ground, the continuity of metal raceways and cables carrying anything other than service conductors has to be ensured by the methods normally reserved for services (NEC 250.97).

On a 480Y/277 system that is 277 volts to ground, so the rule applies. On 208Y/120 it is 120 volts to ground, so it does not.

The section carries an exception, and it is the exception that decides real jobs. It turns on whether oversized, concentric or eccentric knockouts are in the way, and on whether the enclosure itself is listed to provide a reliable bonding connection. Where it applies it names the ordinary methods that are then acceptable, and the detail matters: two locknuts is a method on rigid or intermediate metal conduit, one inside and one outside, not a general permission. Read the exception rather than a summary of it, this one included.

The practical consequence is bonding bushings on feeder raceways in a lot of commercial work, and it catches people who think that requirement lives only at the service.

In a classified location the voltage threshold disappears entirely and the bonding methods apply regardless (NEC 250.100).

What we are not telling you

We have read the system grounding, grounding electrode and bonding parts of Article 250 in the 2026 edition, in the book. We have not read the equipment grounding conductor material, which starts around 250.109 and carries the sizing table people use most often at 250.122.

Rather than summarize a stretch of the article we have not read, we are saying so. If your question is about equipment grounding conductor sizing, 250.122 is where it lives and we are not the source for it yet.

What this page cites

• NEC 250.4 Performance requirements. 250.4(A)(5) Effective Ground-Fault Current Paths is three lettered items in the 2026 edition, per second revision 8333 in the code-making panel 5 second draft. source
• NEC 250.64 Grounding electrode conductor installation, including the two 18 inch rules.
• NEC 250.66 Sizing, and the three ceilings that cap the table.
• NEC 250.97 Bonding for circuits over 250 volts to ground, and its exception.
• NEC 250.100 Bonding in hazardous classified locations, regardless of voltage.
• NEC 270.30 Grounding separately derived ac systems over 1000 volts, the twin of 250.30 in the article that took the over-1000-volt rules out of 250. source