Quick Hits

QUICK HIT 07

Underground Service Conductors

2026 NEC References: 230.30, 230.31, 230.32, 230.33

🎯 What You'll Learn

When the service goes underground, Article 230 gives you its own requirements for insulation, wiring methods, sizing, and protection.

⚡ INSULATION

Underground service conductors generally need insulation appropriate for their voltage.

Specific exceptions permit certain bare copper and aluminum/copper-clad aluminum conductors under the conditions established by the Code.

🔧 WIRING METHODS

Approved methods include specific raceways and cable types such as:

• RMC

• IMC

• PVC

• RTRC

• HDPE

• NUCC

• Type IGS

• Type USE

• Certain MV/MC/MI/TC-ER cables

The specific application and listing requirements matter.

📏 MINIMUM SIZE

General minimum:

8 AWG copper

6 AWG aluminum

Certain single limited-load branch-circuit applications allow smaller conductors under the specified conditions.

🧠 EXAM-STYLE QUESTION

What's the minimum aluminum conductor size for underground service conductors serving only a single limited-load branch circuit?

Answer: 10 AWG aluminum or copper-clad aluminum.

The corresponding copper minimum is 12 AWG copper.

📌 QUICK TAKEAWAY

Underground doesn't mean "anything rated for underground."

Wiring method + insulation + conductor size + physical protection all have to line up.

➡️ Next Quick Hit: How many sets of service-entrance conductors can you run?

← View Chapter 2 Home

← Back To Article 210 Home

← Back To Quick Hits Home