CSLB General Building (B) — All Questions

What is the maximum number of service disconnecting means permitted for a single set of service-entrance conductors (each in a separate enclosure)?

• a.One
• b.Four
• c.Six✓
• d.Eight

A service is limited to a maximum of six disconnecting means. In the 2023 NEC each of the up-to-six disconnects must be in a separate enclosure or be part of listed equipment.2023 NEC 230.71

A service uses #2/0 Cu ungrounded conductors. What is the minimum copper grounding electrode conductor?

• a.#8 AWG
• b.#6 AWG
• c.#2 AWG
• d.#4 AWG✓

For service conductors over 1/0 through 3/0 Cu, the table requires a #4 Cu grounding electrode conductor.2023 NEC Table 250.66

Where the grounding electrode conductor connects only to a made ground rod, what is the largest copper conductor size ever required?

• a.#6 AWG✓
• b.#4 AWG
• c.#8 AWG
• d.#2 AWG

The portion of the GEC connecting solely to a rod, pipe, or plate electrode need not be larger than #6 Cu.2023 NEC 250.66(A)

A branch circuit is protected by a 100-A overcurrent device. What is the minimum copper equipment grounding conductor?

• a.#10 AWG
• b.#8 AWG✓
• c.#6 AWG
• d.#4 AWG

The equipment grounding conductor table requires #8 Cu for an overcurrent device rating up to 100 A.2023 NEC Table 250.122

A feeder is protected by a 400-A overcurrent device. What is the minimum copper equipment grounding conductor?

• a.#6 AWG
• b.#4 AWG
• c.#3 AWG✓
• d.#1 AWG

For a 400-A overcurrent device the table requires #3 Cu for the equipment grounding conductor.2023 NEC Table 250.122

A service has 500-kcmil Cu ungrounded conductors per phase. What is the minimum copper grounded (neutral) service conductor for bonding purposes?

• a.#4 AWG
• b.#2 AWG
• c.#1 AWG
• d.1/0 AWG✓

The grounded service conductor must be at least the size in Table 250.102(C)(1); for 500-kcmil Cu phase conductors that value is 1/0 Cu.2023 NEC Table 250.102(C)(1)

Service phase conductors total 1,500 kcmil Cu per phase (over 1,100 kcmil). Using the 12.5% rule, what is the minimum copper main bonding jumper?

• a.4/0 AWG✓
• b.3/0 AWG
• c.250 kcmil
• d.2/0 AWG

Above 1,100 kcmil, the main bonding jumper is at least 12.5% of the phase area: 0.125 x 1,500 = 187.5 kcmil, so 4/0 Cu (211.6 kcmil) is the smallest that qualifies.2023 NEC 250.28(D)

A panelboard is rated 225 A. What is the maximum rating of the overcurrent device that may protect it?

• a.200 A
• b.225 A✓
• c.250 A
• d.400 A

Each panelboard must be protected by an overcurrent device rated no more than the panelboard rating, so 225 A is the maximum.2023 NEC 408.36

Which of the following is the next standard overcurrent device rating above 95 A?

• a.90 A
• b.110 A
• c.100 A✓
• d.125 A

Standard ratings include 90, 100, 110, and 125 A. The next standard size above 95 A is 100 A.2023 NEC 240.6

Absent a specific exception, what is the maximum overcurrent protection for a #12 Cu conductor?

• a.30 A
• b.25 A
• c.15 A
• d.20 A✓

Under the small-conductor rule, #12 Cu is limited to a maximum overcurrent device of 20 A.2023 NEC 240.4(D)

Absent a specific exception, what is the maximum overcurrent protection for a #10 Cu conductor?

• a.30 A✓
• b.25 A
• c.20 A
• d.40 A

The small-conductor rule limits #10 Cu to a maximum 30-A overcurrent device.2023 NEC 240.4(D)

A conductor has an allowable ampacity of 115 A, which is not a standard rating. Under the next-standard-size rule (600 A or less), what is the largest permitted overcurrent device?

• a.110 A
• b.125 A✓
• c.150 A
• d.100 A

When ampacity does not match a standard rating and conditions are met, the next higher standard device (125 A) is permitted for 800-A or smaller circuits.2023 NEC 240.4(B)

What is the smallest conductor size generally permitted to be installed in parallel?

• a.#2 AWG
• b.#1 AWG
• c.1/0 AWG✓
• d.2/0 AWG

Conductors are generally permitted in parallel only in sizes 1/0 AWG and larger.2023 NEC 310.10(G)

Two paralleled sets of 500-kcmil Cu (75 C, 380 A each) supply one feeder. What is the combined ampacity before adjustment?

• a.500 A
• b.620 A
• c.380 A
• d.760 A✓

Paralleled conductor ampacities add: 380 A x 2 = 760 A total for the feeder.2023 NEC Table 310.16

What is the minimum service disconnecting-means rating for a one-family dwelling?

• a.100 A✓
• b.60 A
• c.125 A
• d.200 A

The service disconnecting means for a one-family dwelling must be rated at least 100 A, 3-wire.2023 NEC 230.79

What is the minimum vertical clearance of an overhead service drop (not over 300 V) above a residential driveway or sidewalk area limited to pedestrians?

• a.10 ft
• b.12 ft✓
• c.15 ft
• d.18 ft

Service-drop conductors up to 300 V to ground require 12 ft of clearance over residential property and driveways not subject to truck traffic.2023 NEC 230.24(B)

At a separately derived system such as a transformer, what conductor connects the grounded conductor to the system grounding electrode?

• a.Main bonding jumper
• b.Equipment bonding jumper
• c.System bonding jumper✓
• d.Grounding electrode conductor

The system bonding jumper connects the grounded conductor of a separately derived system to the supply-side equipment grounding/bonding at one point.2023 NEC 250.30(A)

An emergency system must be capable of supplying power to its loads within what maximum time after normal supply is lost?

• a.60 seconds
• b.30 seconds
• c.120 seconds
• d.10 seconds✓

Emergency systems must restore power to life-safety loads within 10 seconds of loss of the normal source.2023 NEC 700.12

A legally required standby system must supply its loads within what maximum time after loss of normal power?

• a.60 seconds✓
• b.10 seconds
• c.30 seconds
• d.120 seconds

Legally required standby systems must be able to supply their loads within 60 seconds of a normal-source failure.2023 NEC 701.12

Generator output conductors must have an ampacity of at least what percent of the nameplate current?

• a.100%
• b.115%✓
• c.125%
• d.110%

Generator conductors from the terminals to the first overcurrent device must be at least 115% of the nameplate current rating.2023 NEC 445.13

A feeder supplies a 60,000-VA, 208-V, three-phase load. What is the calculated feeder current?

• a.150 A
• b.200 A
• c.167 A✓
• d.144 A

Three-phase current = 60,000 / (1.732 x 208) = 166.6 A, about 167 A.

A 200-A busbar has a 200-A main breaker at one end. Using the 120% rule, what is the maximum back-fed inverter (PV) overcurrent device at the opposite end?

• a.20 A
• b.60 A
• c.30 A
• d.40 A✓

120% of the 200-A busbar = 240 A. Subtract the 200-A main: 240 - 200 = 40 A maximum for the back-fed supply breaker.2023 NEC 705.12(B)

A single made electrode (ground rod) must be supplemented unless its resistance to earth does not exceed what value?

• a.25 ohms✓
• b.5 ohms
• c.10 ohms
• d.1 ohm

A single rod, pipe, or plate electrode must be supplemented by a second electrode unless it has a resistance to earth of 25 ohms or less.2023 NEC 250.53(A)

A metal underground water pipe qualifies as a grounding electrode if it is in direct contact with earth for at least how many feet?

• a.10 ft
• b.5 ft✓
• c.3 ft
• d.1 ft

A metal underground water pipe electrode must have at least 10 ft of contact with earth (bonding connection made within 5 ft of entry).2023 NEC 250.52(A)(1)

A concrete-encased electrode (Ufer) must consist of at least how many feet of #4 or larger rebar or bare #4 Cu conductor?

• a.10 ft
• b.15 ft
• c.20 ft✓
• d.25 ft

A concrete-encased electrode requires at least 20 ft of 1/2-in (or larger) rebar or 20 ft of bare #4 Cu encased in the concrete footing/foundation.2023 NEC 250.52(A)(3)