Licensed Electrical Contractor Licensed Electrical Contractor Grounding and Bonding Questions and Answers 2

Question 1

What is the minimum size copper grounding electrode conductor required for a 400-amp service per NEC Article 250?

Accepted Answer

1/0 AWG

Answer

NEC Table 250.66 requires a minimum 1/0 AWG copper grounding electrode conductor for services up to 500 kcmil.

Question 2

When using a concrete-encased electrode (Ufer ground), what is the minimum length of bare copper conductor that must be encased in the concrete?

Accepted Answer

20 feet

Answer

NEC 250.52(A)(3) requires at least 20 feet of bare copper conductor encased in concrete for a Ufer ground.

Question 3

What is the primary purpose of equipment bonding jumpers in an electrical system?

Accepted Answer

To ensure electrical continuity and conductivity between metal parts

Answer

Equipment bonding jumpers ensure electrical continuity between metal parts so fault current can flow and protective devices can operate.

Question 4

Per NEC 250.104, what metal piping system within a building must be bonded to the electrical service grounding system?

Accepted Answer

Interior metal water piping

Answer

NEC 250.104(A) requires interior metal water piping to be bonded to the service equipment enclosure or grounding electrode conductor.

Question 5

What is the maximum resistance to ground allowed for a single rod, pipe, or plate grounding electrode before a supplemental electrode is required?

Accepted Answer

25 ohms

Answer

NEC 250.53(A)(2) requires a supplemental electrode if a single rod, pipe, or plate electrode exceeds 25 ohms resistance to ground.

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