309A Grounding and Bonding 3

Question 1

What is a concrete-encased grounding electrode (Ufer ground)?

Accepted Answer

A minimum 6 m of bare No. 4 AWG copper conductor encased in concrete foundation footing

Answer

A concrete-encased electrode (Ufer ground) consists of at least 6 m of bare No. 4 AWG copper conductor or 6 m of rebar encased in at least 50 mm of concrete in a building footing, providing excellent ground contact.

Question 2

What is the purpose of a grounding ring around a building?

Accepted Answer

To establish a continuous grounding electrode encircling the building at the foundation level

Answer

A grounding ring consists of a bare copper conductor (minimum No. 2 AWG) buried at least 750 mm deep encircling the building, providing a comprehensive grounding electrode with low resistance.

Question 3

What is the danger of a floating (ungrounded) neutral in a single-phase service?

Accepted Answer

Voltages become unbalanced, potentially causing overvoltage on lightly loaded circuits

Answer

A floating neutral causes the voltage to divide unevenly between the two legs of a 120/240 V service based on load. The lightly loaded leg receives excessive voltage that can destroy appliances and cause fires.

Question 4

According to the CEC, when must a bonding conductor be installed with non-metallic conduit?

Accepted Answer

Always — a separate bonding conductor must be pulled through the conduit

Answer

Since non-metallic conduit (PVC) cannot serve as an equipment bonding path, a separate bonding conductor must always be installed within the conduit to provide fault current return path.

Question 5

What is the purpose of exothermic welding (Cadweld) for grounding connections?

Accepted Answer

To create a permanent, molecularly bonded connection that will not loosen or corrode

Answer

Exothermic welding creates a molecular bond between conductors that is permanent, has lower resistance than the conductors themselves, and will not loosen or corrode, making it ideal for critical grounding connections.

Red Seal Electrician 309A Practice Test

Red Seal Electrician 309A Practice Test

309A Grounding and Bonding 3