System capacity, fault-current rating, and load management
NEC 701.4 Legally required standby equipment must withstand available fault current, be sized per Article 220 (or an approved method) for real transient loads, and may lean on load shedding instead of raw capacity.
Q1 NEC 701.4 Code lookup
A hospital's legally required standby system feeds intensive-care lighting and equipment loads. The design engineer must confirm the system has enough capacity for these loads, sizing it per Article 220 Parts I-IV (or another approved method) and accounting for rapid load changes and transient power demands. Which section governs this capacity determination?
- A 701.4(A)
- B 701.4(B)
- C 701.4(C)
- D 701.4(D)(2)
Show answer & explanation
Correct: B — 701.4(B)
701.4(B) requires legally required standby system capacity to be calculated per Article 220 Parts I-IV or another approved method, accounting for rapid load changes and transient demands. 701.4(A) instead addresses fault-current withstand rating, not sizing for load capacity.
Commissioning, periodic testing, and maintenance records
NEC 701.3 The AHJ must witness commissioning of a legally required standby system, and the owner must keep testing it on an AHJ-approved schedule with written records.
Q2 NEC 701.3
Under Article 701, who is responsible for conducting or witnessing the commissioning of a complete legally required standby system upon installation?
- A The authority having jurisdiction
- B The equipment manufacturer's field representative
- C The installing electrical contractor
- D The building owner or their designated agent
Show answer & explanation
Correct: A — The authority having jurisdiction
701.3(A) requires the authority having jurisdiction to conduct or witness commissioning of the complete system upon installation. The contractor, manufacturer rep, and owner may all be involved in the work itself, but the code specifically assigns the commissioning witness role to the AHJ.
Generator Set Automatic Starting & Transfer
NEC 701.12(D)(1) A legally required standby generator must auto-start and auto-transfer on utility failure, with a 15-minute max retransfer delay and an independently charged starting battery.
Q3 NEC 701.12(D)(1)
A legally required standby generator's transfer switch has a time-delay feature to prevent retransfer to normal power. What is the maximum setting permitted for this delay?
- A 60 minutes
- B 15 minutes
- C 30 minutes
- D 5 minutes
Show answer & explanation
Correct: B — 15 minutes
701.12(D)(1) specifically calls for a time-delay feature permitting a 15-minute setting, to avoid retransfer if the normal source is only briefly reestablished.
Ground-fault signal requirements for high-voltage wye systems
NEC 701.6(D) Above 150V to ground with 1000A+ overcurrent devices, a legally required standby system needs a ground-fault sensor at the main disconnect, set to signal at no more than 1200A.
Q4 NEC 701.6(D)
Under 701.6(D), a legally required standby system requires ground-fault signal indication when it is a solidly grounded wye system over 150 volts to ground and the circuit-protective devices are rated at least how many amperes?
- A 1000 amperes
- B 2000 amperes
- C 800 amperes
- D 1200 amperes
Show answer & explanation
Correct: A — 1000 amperes
701.6(D) sets the threshold at circuit-protective devices rated 1000 amperes or more (on solidly grounded wye systems over 150V to ground). The 1200-ampere figure is the maximum ground-fault signal setpoint, not the device-rating threshold, and 800 and 2000 amperes don't appear in this section.
60-Second Restoration Time & Permitted Standby Source Types
NEC 701.12 Legally required standby power must be available within 60 seconds of a normal supply failure, and it can come from generators, batteries, fuel cells, or several other listed source types.
Q5 NEC 701.12
Under 701.12, what is the maximum time within which legally required standby power must be available after a failure of normal supply?
- A 60 seconds
- B There is no maximum, only an application-specific requirement
- C 3 minutes
- D 10 seconds
Show answer & explanation
Correct: A — 60 seconds
701.12 sets a hard ceiling of 60 seconds for restoration of legally required standby power, though it may need to be faster depending on the application. The 10-second figure applies to emergency systems under Article 700, not legally required standby, and there is no exception that removes the ceiling.
Battery/UPS Standby Lighting Duration
NEC 701.12(C)(4) Battery or UPS standby lighting must hold the full load for 1½ hours without dropping below 87½ percent of nominal voltage.
Q6 NEC 701.12(C)(4)
A UPS is sized to supply legally required standby illumination. Per 701.12(C)(4), for how long must it maintain the total load without the voltage falling below 87½ percent of nominal?
- A 2 hours
- B 1½ hours
- C 30 minutes
- D 8 hours
Show answer & explanation
Correct: B — 1½ hours
701.12(C)(4) sets the minimum at 1½ hours. Two hours and 8 hours are longer than required (and are durations associated with other emergency/standby contexts, not this rule), while 30 minutes is too short to meet the code minimum.
Fuel Supply Reliability for Standby Generators
NEC 701.12(C)(2) A legally required standby generator can't depend on a single off-site utility for fuel or cooling, and any fuel pumps or dual-fuel switching must themselves run on standby power.
Q7 NEC 701.12(C)(2) Code lookup
A hospital's legally required standby generator uses a remote day tank, and an electric-driven fuel transfer pump moves diesel from the main storage tank to the day tank. Which section requires this fuel transfer pump to be connected to the legally required standby power system?
- A 701.12(C)(4)
- B 701.12(C)(1)
- C 701.12(C)(2)
- D 701.12(D)(1)
Show answer & explanation
Correct: C — 701.12(C)(2)
701.12(C)(2) specifically requires fuel transfer pumps needed to deliver fuel to the source to be connected to the legally required standby system. 701.12(C)(1) covers on-site fuel supply quantity, not powering the transfer pump itself.
Outdoor Generator Set Disconnecting Means
NEC 701.12(D)(3) An outdoor generator's own disconnect can stand in for the building's disconnect only if it's readily accessible and within sight of the building it supplies.
Q8 NEC 701.12(D)(3)
An outdoor-housed generator set for a legally required standby system has a disconnecting means that is readily accessible per 445.18. Under 701.12(D)(3), what additional condition allows this to serve as the only disconnect, with none required at the building it supplies?
- A The generator is rated for continuous duty
- B The disconnect is located within sight of the building or structure supplied
- C The disconnect is mounted on the exterior wall of the building
- D The disconnect is rated at least 100 amperes
Show answer & explanation
Correct: B — The disconnect is located within sight of the building or structure supplied
701.12(D)(3) requires the outdoor generator's disconnect to be both readily accessible under 445.18 and within sight of the building or structure supplied before an additional disconnect can be omitted. An amperage threshold, exterior wall mounting, and continuous-duty rating are not part of this test.
Parallel operation of legally required standby sources
NEC 701.4(D) A legally required standby source can run in parallel with the normal source under Article 705, but only if full standby capacity stays available at all times.
Q9 NEC 701.4(D)
A facility runs its legally required standby generator in parallel with the normal utility source for peak load shaving. Under 701.4(D)(1), what condition must be continuously maintained?
- A A signal to the fire alarm control unit whenever paralleling begins
- B Synchronizing equipment sized only for the normal source
- C At least 50 percent of the calculated legally required standby load
- D The full source capacity required to supply the legally required standby load
Show answer & explanation
Correct: D — The full source capacity required to supply the legally required standby load
701.4(D)(1) requires the full capacity needed to supply the legally required standby load to be maintained at all times during parallel operation, not a partial percentage. There's no 50% allowance in this section, and no fire alarm signaling requirement tied to paralleling.
Required signage for standby source location and shock hazard
NEC 701.7 A sign at the service entrance must show where each legally required standby source is, and a shock-hazard warning sign must go on the normal power equipment when disconnecting its grounding path could de-ground an energized alternate source.
Q10 NEC 701.7
Under what condition does 701.7(B) require a shock-hazard warning sign at the normal power source equipment?
- A Only when the standby source is a generator larger than 100 kW
- B When removing a grounding or bonding connection there would interrupt the grounding electrode conductor connection to an energized alternate source's grounded conductor
- C Whenever a legally required standby system is installed, regardless of grounding configuration
- D Only when the alternate source is located more than 50 feet from the normal source equipment
Show answer & explanation
Correct: B — When removing a grounding or bonding connection there would interrupt the grounding electrode conductor connection to an energized alternate source's grounded conductor
701.7(B) is triggered specifically when removing a grounding or bonding connection at the normal power source equipment would interrupt the grounding electrode conductor connection to the alternate source's grounded conductor while that source is energized — not just because a standby system exists, and not based on generator size or distance, which aren't conditions in this section.
Required audible/visual signal types for standby systems
NEC 701.6 Legally required standby systems need signals for three conditions: source malfunction, source carrying load, and battery charging malfunction.
Q11 NEC 701.6
Which of the following is one of the signal conditions explicitly required by 701.6(A) through (C) for legally required standby systems?
- A That the standby source is carrying the load
- B Low fuel level in the generator's day tank
- C Improper phase rotation at the transfer switch
- D Loss of availability of the normal power source
Show answer & explanation
Correct: A — That the standby source is carrying the load
701.6(B) requires a signal indicating the standby source is carrying load, alongside malfunction (A) and battery charging malfunction (C) signals. Normal-source loss, transfer switch phase rotation, and day-tank fuel level are not among the three signal purposes listed in 701.6.
Selective coordination of legally required standby OCPDs
NEC 701.32 Legally required standby OCPDs must be selectively coordinated with every supply-side and load-side OCPD, and that coordination gets re-checked whenever a device is replaced or the system is modified.
Q12 NEC 701.32
A legally required standby system has two OCPDs in series, with no loads connected in parallel to the downstream device. Per 701.32, what is required?
- A Selective coordination is required because all legally required standby OCPDs must coordinate with every device
- B Selective coordination is required only during the initial installation, not afterward
- C Selective coordination is required only if a PE approves an exception
- D Selective coordination is not required between these two devices
Show answer & explanation
Correct: D — Selective coordination is not required between these two devices
701.32 states selective coordination is not required between two OCPDs in series if no loads are connected in parallel with the downstream device. This is a specific, narrow exception — it doesn't require PE sign-off, and it isn't a blanket 'coordinate with everything' rule since this configuration is explicitly excluded.
Field marking transfer equipment short-circuit rating
NEC 701.5(D) Transfer equipment for legally required standby systems must be field marked with a short-circuit current rating tied to the exact overcurrent protective device type and settings protecting it.
Q13 NEC 701.5(D) Code lookup
A hospital's automatic transfer switch for its legally required standby system has just been installed and connected to its overcurrent protective device. Per the NEC, which section requires that the transfer equipment's short-circuit current rating be field marked on its exterior?
- A 701.4(A)
- B 701.5(D)
- C 701.3(D)
- D 701.5(A)
Show answer & explanation
Correct: B — 701.5(D)
701.5(D) specifically requires field marking the transfer equipment's short-circuit current rating, tied to the actual OCPD type and settings protecting it. 701.5(A) covers general transfer equipment requirements, 701.4(A) covers capacity/rating of the standby source itself, and 701.3(D) covers written maintenance records, none of which address the exterior marking requirement.
Transfer equipment requirements and automatic transfer switches
NEC 701.5 Legally required standby transfer equipment must be automatic, listed for the use, and built so normal and alternate sources can never connect at the same time.
Q14 NEC 701.5
A contractor proposes using a meter-mounted transfer switch for a legally required standby system. Per 701.5(A), is this permitted?
- A No, because it would require parallel operation approval under Article 705
- B Yes, as long as the switch is automatic and listed
- C Yes, if it is mechanically held in both positions
- D No, meter-mounted transfer switches are not permitted for legally required system use
Show answer & explanation
Correct: D — No, meter-mounted transfer switches are not permitted for legally required system use
701.5(A) specifically prohibits meter-mounted transfer switches for legally required standby system use, regardless of whether the switch is otherwise automatic, listed, and mechanically held. The Article 705 reference in 701.5(A) applies only to equipment intended to parallel with the normal source, not to this prohibition.
Scope of legally required standby systems
NEC 701.1 Article 701 covers permanently installed standby systems that a government agency requires to kick in when normal power fails — not systems that just protect life safety egress.
Q15 NEC 701.1
According to 701.1, what type of installation does Article 701 apply to?
- A Portable generators brought on-site temporarily during outages
- B Only the transfer switch and distribution equipment, with the generator covered elsewhere
- C Any backup system regardless of installation method, as long as it restores power within 10 seconds
- D Systems permanently installed in their entirety, including the power source
Show answer & explanation
Correct: D — Systems permanently installed in their entirety, including the power source
701.1 states the article covers only systems permanently installed in their entirety, including the power source. A portable generator or a system where the power source itself isn't permanently installed falls outside this scope.