1. A master electrician is installing a new 480Y/277V, 3-phase, 4-wire service in a commercial building. The building has a structural steel frame that meets the requirements for a grounding electrode. What is the minimum length of structural steel that must be in direct contact with the earth to be considered a grounding electrode?
Grounding and Bonding
A.5 feet
B.20 feet
C.10 feet
D.30 feet
Show answerAnswer
C. 10 feet
According to NEC 250.52(A)(2), a metal underground water pipe or structural metal frame of the building that is in direct contact with the earth for 10 feet (3.0 m) or more can serve as a grounding electrode.
2. A master electrician is installing a new 200A, 120/240V, single-phase service. The grounding electrode system consists of a metal underground water pipe and a supplemental ground rod. Which of the following statements is correct regarding the connection of the grounding electrode conductor (GEC) to these electrodes?
Grounding and Bonding
A.The GEC must be connected to the ground rod first, then to the water pipe.
B.The GEC only needs to be connected to the water pipe; the ground rod is merely supplemental and does not require a GEC connection.
C.The GEC must be connected to the water pipe and then to the ground rod, or vice versa, in a continuous run or with suitable splices.
D.Separate GECs are required for each electrode, each sized independently.
Show answerAnswer
C. The GEC must be connected to the water pipe and then to the ground rod, or vice versa, in a continuous run or with suitable splices.
According to NEC 250.64(C), grounding electrode conductors that are required to be connected to more than one grounding electrode can be run to a common location and interconnected, or they can be run to one electrode and then continued to other electrodes by one or more splices or connections.
3. A master electrician is installing a new 120/240V, single-phase service for a modular home. The home is supplied by a feeder from a remote service equipment location. Which of the following statements regarding the grounding and bonding of this modular home is correct?
Grounding and Bonding
A.The main bonding jumper must be installed at the modular home's main panelboard.
B.The neutral conductor must be bonded to the modular home's metallic enclosure at the modular home's service entrance.
C.An independent grounding electrode system is not permitted at the modular home location.
D.The equipment grounding conductor must be run with the feeder conductors and terminate at the modular home's panelboard.
Show answerAnswer
D. The equipment grounding conductor must be run with the feeder conductors and terminate at the modular home's panelboard.
For a modular home supplied by a feeder from a remote service, it is considered a separately derived structure. NEC 550.33(B) and 250.32(B) require that an equipment grounding conductor be run with the feeder conductors to the modular home and be connected to the modular home's panelboard and non-current-carrying metal parts. The neutral conductor is kept isolated from ground at the modular home's panelboard.
4. A master electrician is installing a new 100A, 120/240V, single-phase service for a residential dwelling. The service entrance conductors are No. 1 AWG copper. What is the minimum size copper grounding electrode conductor required if the largest grounding electrode is a ground rod?
Grounding and Bonding
A.No. 6 AWG
B.No. 8 AWG
C.No. 4 AWG
D.No. 2 AWG
Show answerAnswer
A. No. 6 AWG
According to NEC Table 250.66, for service conductors No. 1 AWG copper, the minimum size copper grounding electrode conductor (GEC) is No. 6 AWG when connected to a ground rod, plate electrode, or concrete-encased electrode.
5. A master electrician is installing a new 480V, 3-phase, 4-wire wye service where the service entrance conductors are 500 kcmil copper. The grounding electrode conductor is connected to a concrete-encased electrode (Ufer ground). What is the minimum size copper grounding electrode conductor required for this connection, according to NEC 250.66(B)?
Grounding and Bonding
A.No. 1/0 AWG
B.No. 2 AWG
C.No. 3/0 AWG
D.No. 2/0 AWG
Show answerAnswer
D. No. 2/0 AWG
According to NEC Table 250.66, for service conductors 500 kcmil copper, the minimum size copper grounding electrode conductor (GEC) is No. 1/0 AWG when connected to a ground rod, plate electrode, or water pipe. However, per 250.66(B), if the GEC is connected to a concrete-encased electrode (Ufer), it is permitted to be reduced to No. 2 AWG copper or No. 1/0 AWG aluminum. This reduction is applied to the minimum size from the table. The table shows 1/0 AWG for 500 kcmil, so 2/0 AWG is incorrect. For a concrete-encased electrode, the GEC is not required to be larger than No. 2 AWG copper or No. 1/0 AWG aluminum. The question asks for the minimum size, which would be No. 2 AWG copper for a concrete-encased electrode.
6. A master electrician is inspecting a previously installed grounding electrode system for a dwelling. The system includes a metal underground water pipe electrode and a supplemental electrode. The water pipe has 10 feet of contact with the earth. What is the minimum length of the supplemental electrode required if it is a ground rod, according to NEC 250.53(A)(2)?
Grounding and Bonding
A.8 feet
B.10 feet
C.6 feet
D.4 feet
Show answerAnswer
A. 8 feet
NEC 250.53(A)(2) states that if a metal underground water pipe electrode is used, it must be supplemented by an additional electrode, and the supplemental electrode must comply with 250.52(A)(2) through (A)(8). For a ground rod [250.52(A)(5)], the minimum length driven into the earth is 8 feet.
7. A master electrician is installing a new service for a commercial building. The service consists of a 480Y/277V, 3-phase, 4-wire system. Which of the following is the primary purpose of the main bonding jumper?
Grounding and Bonding
A.To provide a low-impedance path for fault currents to the earth.
B.To connect the neutral conductor to the equipment grounding conductor and the service enclosure.
C.To connect the equipment grounding conductor to the grounding electrode conductor.
D.To bond all non-current-carrying metal parts of the electrical system together.
Show answerAnswer
B. To connect the neutral conductor to the equipment grounding conductor and the service enclosure.
The main bonding jumper's primary role is to connect the neutral conductor (which is grounded at the service) to the equipment grounding conductors and the service enclosure, ensuring a low-impedance path for ground-fault current to return to the source.
8. A master electrician is installing a new 480V, 3-phase, 3-wire delta service for an industrial facility. The service will be supplied by a transformer bank. Which of the following statements regarding the grounding of this service is true?
Grounding and Bonding
A.One of the phase conductors must be intentionally grounded.
B.A corner-grounded delta system is not permitted for services.
C.The system must be grounded, but the grounding electrode conductor is sized differently.
D.The system must be ungrounded, with ground-fault detection equipment.
Show answerAnswer
A. One of the phase conductors must be intentionally grounded.
For a 3-phase, 3-wire delta system, NEC 250.26(3) requires that if a system is grounded, one phase conductor must be intentionally grounded (a corner-grounded delta). Alternatively, the system can be ungrounded, requiring ground-fault detection equipment per 250.21(B). Option A describes a permitted grounded configuration.
9. A master electrician is installing a new 100A, 240V, single-phase motor in an industrial facility. The motor is supplied by a 1-inch rigid nonmetallic conduit (RNC) containing 3 AWG copper ungrounded conductors. What is the minimum size copper equipment grounding conductor (EGC) required for this motor circuit?
Grounding and Bonding
A.No. 4 AWG
B.No. 8 AWG
C.No. 6 AWG
D.No. 10 AWG
Show answerAnswer
B. No. 8 AWG
According to NEC 250.122(B) and Table 250.122, the minimum size EGC is based on the rating of the overcurrent protective device. For a 100A circuit, the minimum size copper EGC is No. 8 AWG.
10. A master electrician is installing a new 200A, 120/240V, single-phase service for a dwelling. The service entrance conductors are 3/0 AWG copper. What is the minimum size copper grounding electrode conductor required if the largest grounding electrode is a metal underground water pipe?
Grounding and Bonding
A.No. 1/0 AWG
B.No. 6 AWG
C.No. 4 AWG
D.No. 2 AWG
Show answerAnswer
C. No. 4 AWG
According to NEC Table 250.66, for service conductors 3/0 AWG copper, the minimum size copper grounding electrode conductor (GEC) to a concrete-encased electrode, ground rod, or plate electrode is No. 4 AWG. Since a metal underground water pipe is listed as an electrode, the same sizing applies. (Note: For services larger than 1100 kcmil copper or 1750 kcmil aluminum, 250.66(A) and (B) might apply, but for typical residential services, Table 250.66 is used.)
11. A master electrician is installing a new subpanel in a detached garage, fed from the main service panel of a dwelling. The subpanel is supplied by a 240V, 3-wire feeder. According to the NEC, how must the neutral conductor be handled at the detached garage subpanel?
Grounding and Bonding
A.The neutral conductor must be bonded to the subpanel enclosure and isolated from the equipment grounding conductor.
B.The neutral conductor must be isolated from the subpanel enclosure and connected to its own grounding electrode.
C.The neutral conductor must be bonded to the subpanel enclosure and a grounding electrode.
D.The neutral conductor must be isolated from the subpanel enclosure and connected to the equipment grounding conductor.
Show answerAnswer
D. The neutral conductor must be isolated from the subpanel enclosure and connected to the equipment grounding conductor.
For a separately derived system or a feeder to a separate building, the neutral must be isolated from the panel enclosure and connected only to the equipment grounding conductor, which is then connected to the grounding electrode system at the detached structure. This prevents objectionable current on the grounding path.
12. A master electrician is installing a new 200A, 120/240V, single-phase service for a residential dwelling. The service entrance conduit is 2-inch rigid metal conduit (RMC) and the service conductors are 3/0 AWG copper. What is the minimum size copper bonding jumper required to bond the service raceway to the service enclosure?
Grounding and Bonding
A.No. 8 AWG
B.No. 2 AWG
C.No. 4 AWG
D.No. 6 AWG
Show answerAnswer
D. No. 6 AWG
According to NEC 250.102(C)(1) and Table 250.102(C)(1), the bonding jumper for a service raceway is sized based on the size of the ungrounded service-entrance conductors. For 3/0 AWG copper service conductors, the minimum size copper bonding jumper required is No. 6 AWG.
13. A master electrician is installing a new 480V, 3-phase, 3-wire delta service for an industrial facility. The service entrance conductors are 300 kcmil copper. What is the minimum size copper grounding electrode conductor (GEC) required for this service?
Grounding and Bonding
A.No. 2/0 AWG
B.No. 2 AWG
C.No. 4 AWG
D.No. 1/0 AWG
Show answerAnswer
B. No. 2 AWG
According to NEC 250.66 and Table 250.66, the GEC is sized based on the largest ungrounded service-entrance conductor. For 300 kcmil copper service conductors, the minimum size copper GEC required is No. 2 AWG.
14. A master electrician is installing a lightning protection system on a commercial building. According to NEC 250.60, what is the requirement for bonding the lightning protection system to the building's electrical grounding system?
Grounding and Bonding
A.They must be kept entirely separate to prevent lightning energy from entering the electrical system.
B.They must be bonded together at multiple points to maximize lightning current dissipation.
C.They must be bonded together at a single point to equalize potential.
D.Bonding is only required if the building contains sensitive electronic equipment.
Show answerAnswer
C. They must be bonded together at a single point to equalize potential.
NEC 250.60 requires that the lightning protection system grounding electrode system be bonded to the building's electrical grounding electrode system. This bonding provides a common reference point and helps to equalize potential between the two systems, preventing dangerous voltage differences during a lightning strike.
15. A master electrician is installing a new panelboard in an existing commercial building. The panelboard is fed by a feeder from the main service panel. The raceway consists of EMT. Which of the following statements is true regarding the use of the EMT as an equipment grounding conductor (EGC) for this feeder circuit?
Grounding and Bonding
A.EMT is permitted as an EGC only for circuits operating at 120V or less.
B.EMT is permitted as an EGC if the fittings are listed for grounding and installed correctly.
C.EMT is never permitted to be used as an EGC.
D.EMT is permitted as an EGC only if it is liquidtight flexible metal conduit.
Show answerAnswer
B. EMT is permitted as an EGC if the fittings are listed for grounding and installed correctly.
NEC 250.118 lists acceptable types of equipment grounding conductors. EMT is specifically listed in 250.118(4) as an acceptable EGC when installed in accordance with Chapter 3, and all fittings and connections are made up tight. This means the fittings must be listed for grounding and properly installed to ensure electrical continuity.
16. A master electrician is installing a new 480V, 3-phase, 4-wire wye system for a commercial kitchen. The main service will be located in a dedicated electrical room. What is the minimum size copper main bonding jumper required if the ungrounded service-entrance conductors are 700 kcmil copper?
Grounding and Bonding
A.No. 2/0 AWG
B.No. 1/0 AWG
C.No. 3/0 AWG
D.No. 4/0 AWG
Show answerAnswer
A. No. 2/0 AWG
According to NEC 250.28(D)(1) and Table 250.102(C)(1), the main bonding jumper shall not be smaller than the sizes shown in Table 250.102(C)(1). For ungrounded service-entrance conductors of 700 kcmil copper, the minimum size copper main bonding jumper required is No. 2/0 AWG.
17. A maintenance technician is replacing a fuse in a motor circuit. The motor nameplate indicates a service factor (SF) of 1.15. If the continuous full-load current (FLA) of the motor is 40 amperes, what is the maximum continuous current that the motor can safely draw without tripping its separate overload protection device, assuming the overload device is sized per NEC 430.32(A)(1)?
Overcurrent Protection
A.46 amperes
B.40 amperes
C.57.5 amperes
D.50 amperes
Show answerAnswer
A. 46 amperes
According to NEC 430.32(A)(1), for motors with a service factor of 1.15 or greater, the separate overload device shall be selected to trip at no more than 125% of the motor's nameplate full-load current. Therefore, 40 A * 1.15 (service factor) = 46 A. Then, the overload protection is sized based on the FLA, not the service factor adjusted FLA, but the service factor dictates the percentage multiplier for the overload device. So, 40 A * 1.25 (for SF 1.15+) = 50 A. However, the question asks for the maximum continuous current the motor can safely draw, not the overload trip setting. The maximum continuous current is determined by FLA * SF = 40A * 1.15 = 46A. The overload device would trip at 50A, protecting it up to 46A.
18. An electrician is installing a new 15-ampere branch circuit for general-purpose receptacles in a dwelling unit. Which of the following conductor types, if protected by a 15-ampere overcurrent device, would comply with NEC requirements for conductor protection without requiring adjustment factors?
Overcurrent Protection
A.16 AWG copper, Type UF
B.14 AWG copper, Type THHN
C.12 AWG copper, Type THWN-2
D.10 AWG aluminum, Type XHHW-2
Show answerAnswer
B. 14 AWG copper, Type THHN
According to NEC Table 310.16, 14 AWG copper conductors are rated for 15 amperes at 75°C (THHN's 90°C rating can be used for ampacity calculations, but the overcurrent protection is limited to 15A per 240.4(D)). This matches the 15-ampere overcurrent device. 12 AWG copper is rated for 20A, 10 AWG aluminum for 25A, and 16 AWG copper is generally not permitted for 15A branch circuits in dwelling units unless part of a listed assembly (e.g., flexible cord, fixture wire) and not a general-purpose branch circuit conductor.
19. A commercial office space is being renovated, and new 120V, 20-ampere general-purpose receptacle branch circuits are being installed. The circuits will supply computer workstations and lighting. Which of the following conditions mandates the use of an Arc-Fault Circuit Interrupter (AFCI) for these circuits?
Overcurrent Protection
A.The area is designated as an office space in a commercial occupancy.
B.The circuits are supplied by a 480Y/277V panelboard.
C.The circuits are located in a dwelling unit's sleeping area.
D.The circuits are installed in a metal raceway system.
Show answerAnswer
C. The circuits are located in a dwelling unit's sleeping area.
AFCI protection is primarily mandated by NEC 210.12 for dwelling units in specific locations, including sleeping areas. Commercial office spaces generally do not require AFCI protection unless specified by local codes or specific circumstances, which are not mentioned here.
20. A newly installed industrial motor has a full-load current (FLA) of 60 amperes. Per NEC, what is the maximum rating for the inverse time circuit breaker used for short-circuit and ground-fault protection if the motor is not a special type and is started across the line?
Overcurrent Protection
A.150 amperes
B.200 amperes
C.75 amperes
D.175 amperes
Show answerAnswer
D. 175 amperes
NEC Table 430.52 allows an inverse time circuit breaker to be sized up to 250% of the motor's full-load current for short-circuit and ground-fault protection. Therefore, 60 A * 2.50 = 150 A. However, if 150 A is not a standard size, the next higher standard size is permitted if it does not exceed 400% of FLA.
21. A new commercial refrigeration unit with a total connected load of 45 amperes (continuous) is being installed. The circuit conductors are rated for 75°C. What is the minimum continuous current rating required for the overcurrent protective device (OCPD), considering NEC 210.20(A) for continuous loads?
Overcurrent Protection
A.60 amperes
B.45 amperes
C.50 amperes
D.56.25 amperes
Show answerAnswer
A. 60 amperes
According to NEC 210.20(A), the overcurrent device for continuous loads must be sized at 125% of the continuous load. For a 45-ampere continuous load, 45 A * 1.25 = 56.25 A. Since 56.25 A is not a standard overcurrent device size (NEC 240.6), the next higher standard size is permitted, which is 60 amperes.
22. A master electrician is inspecting a new residential service installation. The main service disconnect consists of a circuit breaker. What is the minimum interrupting rating required for this circuit breaker if the available short-circuit current at the service entrance is calculated to be 15,000 amperes?
Overcurrent Protection
A.15,000 amperes
B.5,000 amperes
C.10,000 amperes
D.22,000 amperes
Show answerAnswer
C. 10,000 amperes
For residential and light commercial services with an available fault current of 10,000 A or less, a standard 10,000 A interrupting rating (AIC) breaker is generally acceptable by NEC 240.86(A) and 230.65. If the available short-circuit current is 15,000 A, the breaker must at least meet that, but 10,000 A is the minimum readily available for residential.
23. A residential garage circuit requires AFCI protection. Which of the following conditions is specifically addressed and protected against by an Arc-Fault Circuit Interrupter (AFCI) that a standard circuit breaker would not typically detect?
Overcurrent Protection
A.A sustained overload exceeding the circuit breaker's rating.
B.A bolted short-circuit between line and neutral conductors.
C.A low-level series or parallel arc fault caused by damaged insulation.
D.A ground fault current of 5 milliamperes to a human body.
Show answerAnswer
C. A low-level series or parallel arc fault caused by damaged insulation.
AFCIs are specifically designed to detect and interrupt hazardous arc faults (both series and parallel) that are not typically detected by standard overcurrent protective devices (which respond to overcurrents and short circuits) or GFCIs (which respond to ground faults). These arc faults can occur due to damaged insulation, loose connections, or frayed wires.
24. An industrial facility is being designed with a 480V, 3-phase electrical system. To comply with NEC 240.21(B)(2), what is the maximum length of a tap conductor that is protected by an overcurrent device rated at 300% of the tap conductor's ampacity, and terminates in a single circuit breaker or set of fuses?
Overcurrent Protection
A.25 feet
B.100 feet
C.10 feet
D.50 feet
Show answerAnswer
A. 25 feet
NEC 240.21(B)(2) permits tap conductors up to 25 feet long under specific conditions. These conditions include the tap conductor having an ampacity not less than one-third the rating of the overcurrent device protecting the feeder, terminating in a single OCPD that limits the load current to the tap conductor's ampacity, and being protected from physical damage.
25. A residential dwelling unit has a 200-ampere service. A new electric range with a nameplate rating of 12 kW (120/240V) is being installed. The branch circuit conductors for the range are 6 AWG copper with THHN insulation. What is the minimum size overcurrent protective device required for the branch circuit supplying this range?
Overcurrent Protection
A.30 amperes
B.40 amperes
C.60 amperes
D.50 amperes
Show answerAnswer
D. 50 amperes
First, calculate the current: I = P/E = 12,000 W / 240 V = 50 A. According to NEC 210.19(A)(3) and 210.20(A), for household cooking appliances, the branch circuit OCPD must be sized at 100% of the calculated load. Thus, a 50 A OCPD is required. For 6 AWG THHN copper, its ampacity at 90°C is 75 A, which is sufficient. The 60°C column ampacity for 6 AWG is 55 A, also sufficient.
When multiple grounding electrodes are used, the GEC can be connected to them in a continuous run or with suitable splices, ensuring all electrodes are effectively bonded.
When a modular home is supplied by a feeder from remote service equipment, an equipment grounding conductor must be run with the feeder, and the neutral isolated at the modular home's panelboard.
When a grounding electrode conductor is connected to a concrete-encased electrode, it is not required to be larger than No. 2 AWG copper or No. 1/0 AWG aluminum, even if Table 250.66 would indicate a larger size.
Found in NEC 250.66(B).
Applies specifically to concrete-encased electrodes (Ufer grounds).
Provides a maximum size, often resulting in a smaller GEC than otherwise calculated.
The size of the grounding electrode conductor is determined by the size of the largest ungrounded service-entrance conductor or equivalent area for parallel conductors, referenced in NEC Table 250.66.
Based on the largest ungrounded service conductor size.
Different rules for connection to specific electrode types apply (e.g., ground rods vs. concrete-encased).
A wiring system whose power is derived from a source other than a service, having no direct connection to the service conductors except through the earth, and whose neutral is grounded at the source of the separately derived system.
Neutral must be bonded to ground at the source of the separately derived system.
Neutral must be isolated from equipment grounding conductors downstream.
Often applies to transformers, generators, or feeders to separate buildings.
The bonding jumper for a service raceway must be sized according to NEC Table 250.102(C)(1) based on the size of the ungrounded service-entrance conductors.
Sized per Table 250.102(C)(1).
Based on ungrounded service-entrance conductor size.
The grounding electrode conductor (GEC) for a service is sized based on the largest ungrounded service-entrance conductor, referencing NEC Table 250.66.
The grounding electrode system of a lightning protection system must be bonded to the building's electrical grounding electrode system to ensure equipotential and prevent dangerous potential differences.
Electrical Metallic Tubing (EMT) is recognized by the NEC as an acceptable equipment grounding conductor when properly installed with listed fittings that ensure electrical continuity.
The main bonding jumper size is determined by the size of the largest ungrounded service-entrance conductor or equivalent area for parallel conductors, referenced in NEC Table 250.102(C)(1).
Sized based on the largest ungrounded service conductor.
Found in NEC 250.28(D) and Table 250.102(C)(1).
Ensures a low-impedance path for fault current at the service.
A motor's service factor (SF) indicates how much overload it can safely tolerate above its nameplate full-load current (FLA) for short periods without damage. An SF of 1.15 means it can run at 115% of FLA.
SF of 1.15 or greater allows overload device sizing at 125% of FLA.
SF less than 1.15 (or not marked) requires overload device sizing at 115% of FLA.
The motor can continuously draw FLA x SF without overheating.
Conductor ampacity is the maximum current a conductor can carry continuously without exceeding its temperature rating. Overcurrent protection must be sized to protect the conductor's ampacity, often with specific limitations for smaller conductors.
NEC Table 310.16 provides ampacities based on insulation type and temperature rating.
NEC 240.4(D) limits overcurrent protection for small conductors (e.g., 14 AWG to 15A, 12 AWG to 20A).
The OCPD must protect the conductor at its lowest temperature rating or the terminal rating.
Arc-Fault Circuit Interrupters (AFCIs) are primarily required by NEC 210.12 for 120-volt, single-phase, 15- and 20-ampere branch circuits supplying outlets or devices in specific dwelling unit locations.
NEC 210.12 governs AFCI.
Applies to 15A and 20A, 120V circuits.
Required in dwelling unit bedrooms, family rooms, etc.
The maximum rating of a motor's short-circuit and ground-fault protective device is determined by the motor's full-load current (FLA) and the type of protective device, as specified in NEC Table 430.52.
Inverse time breakers are generally allowed up to 250% of FLA.
If the calculated value isn't a standard size, the next higher standard size is permitted.
The maximum for inverse time breakers, even with the next size rule, is 400% of FLA.
For continuous loads (expected to operate for 3 hours or more), the overcurrent protective device (OCPD) must have a rating not less than 125% of the continuous load current.
Continuous load is 3 hours or more (NEC 100).
OCPD must be sized at 125% of the continuous load (NEC 210.20(A)).
Next higher standard OCPD size is permitted if 125% value is not standard.
The minimum interrupting rating for a circuit breaker in a residential service is typically 10,000 amperes (10 kAIC) unless the available fault current is calculated to be higher and explicitly requires a greater rating.
Required to safely interrupt short-circuit currents.
Residential standard is 10,000 AIC.
Must be equal to or greater than the available short-circuit current.
An Arc-Fault Circuit Interrupter (AFCI) is a circuit breaker designed to detect and trip on potentially dangerous electrical arcs, thereby reducing the risk of electrical fires.
Detects both series and parallel arc faults.
Protects against fire hazards from damaged wiring.
Required in specific dwelling unit locations by NEC 210.12.
The NEC 240.21(B)(2) 25-foot tap rule permits tap conductors up to 25 feet long, provided their ampacity is at least one-third of the feeder OCPD rating, they terminate in an OCPD, and are protected from physical damage.
Tap conductor length limited to 25 feet.
Tap conductor ampacity must be at least 1/3 of the feeder OCPD.
Tap conductors must terminate in an OCPD sized for the tap's ampacity.
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