Your questions answered: Power for emergency fire/life safety systems

Questions not answered during the live webcast are answered here; learn more about emergency, standby and backup power for fire and life safety systems

By Richard A. Vedvik, PE, and Rick Reyburn, PE April 29, 2020

Emergency and standby systems are used to provide backup power for building systems to provide assurance that fire/life safety systems and critical equipment can maintain their operation during a power outage. The use of these systems almost comes as second nature when designing large, complex facilities.

Questions not answered during the April 23, 2020, webcast on “power for emergency fire/life safety systems” are answered here.


  • Richard A. Vedvik, PE, Senior Electrical Engineer/Acoustics Engineer, IMEG Corp., Rock Island, Ill.
  • Rick Reyburn, PE, Executive Director of Electrical Engineering, NV5, Las Vegas. 

Question: If generator backup power is provided for the entire building, are separate transfer switches still required for essential and nonessential loads? Is separation of raceways/wiring still required for emergency and nonemergency loads?

Rick Reyburn: If the generator serves the entire building, that is considered an NFPA 70: National Electrical Code Article 702 Optional Standby System application. However, if the building requires egress lighting, exit signage, etc., then a separate dedicated wiring system must be provided and installed in compliance with NEC 700 system. This includes a separate transfer switch served from the generator, etc. If the building has NEC Article 701 Legally Required Standby System requirements, then this system requires a separate transfer switch and the wiring system can be included in the normal wiring system raceways, but must be installed in compliance with NEC Article 701 requirements.

Question: What is slot power?

Rick Reyburn: In this presentation, “slot” is referring to slot machines that are installed in casinos. It is very common for casino owners and engineers to place the slots on emergency (NEC Article 700) power instead of Optional Standby Systems power (NEC 702), which is a violation because slot machines are not life safety related.

Question: Can we put an emergency oil tank underground in flood zone area?

Rich Vedvik: Answers may vary with occupancy type. For example, International Building Code 2701.1.8 requires compliance with ASCE 24. NFPA requires protection from flood as a general statement. The Environmental Protection Agency may have an issue with this as well. Note that fuel fill locations should be coordinated with 100-year flood heights. The 2018 edition of NFPA 99: Health Care Facilities Code prohibits Level 1 or Level 2 emergency power supply system equipment to be located to minimize risk of flooding.

Question: Please discuss requirements for areas of refuge.

Rich Vedvik: Floors above the level of exit discharge create an opportunity for people unable to use the stairs to be trapped in a building. Areas of rescue assistance or areas of refuge consist of a communication system to allow people to notify the fire department of their location. IBC 1009.6 covers areas of refuge.

Question: What about dual fuel, fuel oil and natural gas as fuel source for generators?

Rich Vedvik: Some engine generator sets can run off on-site storage of propane as a backup for natural gas. I’ve seen these generators in operation and the designer should take the energy density of the backup source into consideration. Each fuel source has a specific energy density and thus the available kilowatts will vary with each fuel source.

Question: Is a ground fault sensor indication required for emergency optional loads?

Rich Vedvik: Code exempts emergency power supply systems from having ground fault trip, but ground fault sensing and alarm is listed in 2017 NEC 700.6(D).

Question: Are you seeing fewer installations requiring isolated grounds?

Rick Reyburn: Yes.

Question: When medium-voltage generators are used, how do you comply with IBC 2702.1.1 where code requires the generator to be listed in accordance with UL 2200? 

Rich Vedvik: Generator manufacturers can achieve independent IBC certification for medium-voltage generator sets when combined with shake table testing. The third edition of UL 2200 is expected to include medium voltage generator sets as well as other new technologies (based on the draft under review).

Question: When a generator backs up a NEC Article 700 load and another load and maintenance is being performed, does the temporary generator have to only be sized for the NEC Article 700 load or back feed both loads?

Rick Reyburn: Only the NEC Article 700 loads are required to be backed up per NEC 700.3(F). If the other loads being served from the generator are to be carried by the generator should the normal service fail when the temporary generator is in place, then the temporary generator would have to be sized to the loads to be served by it.

Question: What’s the difference between an emergency and standby generator?

Rick Reyburn: The terminology is different when used in different context. However, a generator is typically a standby generator, meaning it is not being used as the prime power for the loads it is serving, but instead is only running when it is called upon to provide power, hence standby. A standby generator can serve Emergency Loads (NEC Article 700) Legally Required Standby Loads (NEC Article 701) or Optional Standby Loads (NEC 702).

Rich Vedvik: IBC 2702.1.4 defines emergency power as load restored in 10 seconds and standby power as load restored in 60 seconds. This would correlate with NFPA 110: Standard for Emergency and Standby Power Systems Type 10 and Type 60.

Question: Does NEC Article 700 permit sprinkler coverage as an acceptable alternative to two-hour protection?

Rick Reyburn: Yes, refer to NEC 700.10(D)(2)(1) for feeder-circuit wiring and NEC 700.10(D)(3)(3) for feeder-circuit equipment.

Question: Where do you get the definition of space fully protected by an automatic fire protection system? A typical sprinklered building is considered fully protected by IBC, but wouldn’t have sprinklers above the ceiling.

Rick Reyburn: NEC 700.10(D)(2)(1) specifically states, “The cable or raceway is installed in spaces or areas that are fully protected by an approved automatic fire protection system.” The keywords here are “in spaces or areas,” which implies spaces where sprinklers do not exist are nonconforming.

Question: Per NEC 2014 Article 700.8, we have to provide surge protection devices on all emergency systems switchboards and panel boards. Do we have to provide SPD on Article 701 legally required standby systems also?

Rick Reyburn: No. It is not yet a requirement of the NEC (through 2020), however, you may install it if you want.

Question: Are there requirements on what HVAC/R equipment and systems are required to be operating for life safety requirements?

Rick Reyburn: Refer to the Informational Note in Article 700.2 Definitions of Emergency Systems in the 2020 edition of the NEC, which indicates “Emergency systems may also provide power for such functions as ventilation where essential to maintain life …” and 701.2 definition of Legally Required Standby Systems Informational Note, which states “… typically installed to serve loads, such as heating and refrigeration systems …”

Question: One thing to note regarding redundancy and having provisions for a temp genset is the designer should verify with the local authority having jurisdiction if its actually necessary to include on the project, as you can service a generator when the building is unoccupied. This provision adds additional costs to the project that may be able to be avoided.

Rick Reyburn: The writer is correct. Please refer to 2020 NEC 700.3(F) Exception, which identifies four methods of where the temporary generator is not required.

Rich Vedvik: As an engineer specializing in health care, I rarely have the luxury of an unoccupied building. Thank you for the clarification.

Question: Does the temporary generator have to cover all emergency loads or just Article 700 loads? For example, I have a generator feeding three transfer switches, a fire pump, emergency loads (Article 700) and one for legally required.

Rick Reyburn: The best solution is to size it for all three of the loads you’ve listed, however, there is no requirement to size it to serve the NEC Article 701 loads.

Question: If a generator room has two exterior walls (including the door) and two interior walls, the entire room has to be two-hour fire rated or just the two interior walls and the ceiling that separate the generator room from the rest of the building?

Rick Reyburn: This is a question for the architect who defines ratings of wall types. It is our responsibility as electrical designers to notify the architect that the room must meet the code requirements.

Rich Vedvik: Additionally, the walls should be constructed to not allow a vertical passage of fire to floors above or below, which would impact how the exterior walls are constructed.

Question: On smoke control systems: What if you use mineral insulated cable? Does it need to be in a raceway?

Rick Reyburn: MI cable is typically listed by the manufacturer with fire duration ratings and does not need to be installed in a raceway when installed per the manufacturer’s requirements.

Question: Does the required selective coordination apply to only the emergency system and the first overcurrent device after the transfer switch?

Rick Reyburn: Per the 2020 NEC 700.32 and 701.32, selective coordination must exist for all overcurrent devices in an Emergency or Legally Required Standby System. This also includes both the emergency source and the normal source to the source of supply (utility or generator).

Question: Can be considered the main distribution frame/intermedia distribution frame rooms and the access control system of the building part of the NEC Article 701?

Rick Reyburn: Yes, in my opinion. If these rooms also serve the public safety communications systems, they may be placed on emergency power (NEC Article 700).

Question: What determines the use of IBC versus state building codes in conjunction with NFPA codes? IBC tends to have more stringent requirements.

Rick Reyburn: The strictest code having been adopted and being enforced is applicable in the jurisdiction you are designing for.

Question: Will the sprinkler activation get water into the distribution board and short out the equipment?

Rick Reyburn: Possibly, however, if the fire is within the room containing this equipment, then putting the fire out is the need, first and foremost.

Question: As for generators exhaust, do the requirements change for the exhaust fumes from the type of fuel? Example: petrol versus natural gas.

Rich Vedvik: Yes, the Environmental Protection Agency does have different rules for diesel (compression ignition) and natural gas (spark ignition) generator engines. For more information, refer to their website.

Question: Are elevators supposed to be on Article 700 or Article 701, and how is this determined?

Rick Reyburn: Depending on the use of the elevator will classify the type of power to be connected to it. Also, the jurisdictional requirements may stipulate. Refer to 202 NEC 620. Part X 620.91 Informational Note No. 2 for more information. NEC Article 700 Emergency Systems and NEC Article 701 Legally Required Standby Systems are clarified when they are to be used.

Question: Could you please explain again about generator sizing?

Rich Vedvik: The topic of generator sizing can be its own webcast and even its own class. Simply put, a generator size is not just determined by the total connected (or demand) load, but the load steps themselves. Each load steps introduces voltage dip and frequency dip as the engine struggles to react. Generators are sized to maintain specific criteria and can sometimes be increased in size well over connected load due to the need to react to large load steps. In the presentation, I mentioned that decreasing load steps or increasing the number of transfer switches, may sometimes allow for a “right sized” generator instead of a generator sized to accommodate the largest load step.

Here are some resources of on-demand webcasts:

  • How to specify backup, standby and emergency power in mission critical facilities
  • Circuit protection in electrical/power systems
  • Designing power systems for resiliency in mission critical facilities

Question: Confirm that previous NFPA 70 editions provided an exception for normal and emergency power equipment to be installed in the same space observing twice the NEC required clearances, current NFPA was done away with this exception. Correct?

Rick Reyburn: The writer may be referring to local area amendments similar to the Southern Nevada Electrical Code Amendments, which further clarified the acceptable means whereby NEC Article 700 Emergency Systems equipment and feeders were acceptable to be installed. However the NEC had no such clarification back as far as 2005.

Question: NFPA 101: Life Safety Code Section 7.2.3 (smokeproof enclosures) requires emergency power to be provided by a Type 60, Class 2, Level 2 EPSS per NFPA 110. Why is an EPSS per NFPA 111: Standard on Stored Electrical Energy Emergency and Standby Power Systems not allowed?

Rich Vedvik: I cannot speak to the logic behind the development and editing of code sections. There is no Type 60, Class 2 SEPSS listed in NFPA 111. That said, there are SEPSS that would exceed those requirements (transfer time and run duration) that an AHJ may accept as an alternative.

Question: Is a second generator required for maintenance if there are three transfer switches?

Rick Reyburn: A temporary generator connection is required if one generator is permanent and any one of the loads is designed as a NEC Article 700 Emergency System.

Question: With fire pumps and maximum number of disconnect, we are finding it difficult to comply with the NEC temporary generator connection. How have you seen this solved for electric fire pumps?

Rich Vedvik: Emergency power for a fire pump comes from the emergency side of the fire pump transfer switch, not the normal utility side that complies with NEC 230. The “six disconnect rule” applies to the transformer secondary, not a common occurrence for the EPSS distribution, but is resolved with a main overcurrent protection device. Temporary generator connections are typically applied at the paralleling gear or main generator distribution (the gear that serves the emergency side of the transfer switches). An external generator connection cabinet is typically connected to the generator/emergency distribution and is fully sized to allow for a full backup of the primary generator set. In the case of paralleling generator sets, parallel controls can be extended to the generator connection cabinet , if the owner has a contract with the generator set supplier to receive a paralleling-capable unit.

Question: Fire alarm systems need to be on emergency or legally required?

Rick Reyburn: Fire alarm systems are NEC Article 700 Emergency System loads.

Question: Is not emergency power legally required?

Rick Reyburn: This is a play on words. Emergency Power Systems shall not be misconstrued as Legally Required Standby Systems. Refer to NEC Articles 700 and 701 definitions as to what types of loads are acceptable under each and the rest of the requirements of each system.

Question: What usually differentiates emergency and legally required?

Rick Reyburn: Emergency is for the life and safety of persons to evacuate the facility while Legally Required Systems are for the firefighters use in clean-up operations.

Question: Can using a central lighting inverter be used as a redundancy source for an emergency generator?

Rick Reyburn: Yes, the Inverter will be required to comply with NEC 700.12 (B) & (C).

Question: Can industrial uninterruptible power supplies act as emergency power?

Rich Vedvik: Industrial is a relative term, but any emergency power source would need to comply with NFPA for runtime based on the class required by other codes. Additionally, a risk assessment may be required to determine what risks exist if the UPS fails due to an issue with the normal utility source. Typically, an EPSS is not connected to the normal source except at the transfer switch. A UPS is always connected the normal source and would replace not only a generator, but also a transfer switch. As a result, the list of the UPS would be called into question as would the reliability and risk associated with that system.

We commonly use batteries for emergency lighting inverters and that process has decades of applications. These systems are easier to size because the load is fairly static. Sizing batteries for dynamic emergency systems may require the designer to assume continuous duty for typically dynamic loads.

Question: What system should the mass notification system be on?

Rich Vedvik: A mass notification system is an emergency communication system and would be on the Emergency or Life Safety branch.

Question: Can you connect optional loads to a level 1 emergency generator?

Rich Vedvik: Yes, through an optional standby or separate equipment branch transfer switch. As noted in 2017 NEC 517.31.1, any optional loads would have load shed controls to prevent overloading the generators.

Question: Two-hour fire rating for riser in a shaft is mandatory in high-rise? If we have two separate risers, one redundant, then we can leave this requirement of two hours?

Rich Vedvik: NFPA 70 Article 700.10(D)(2) does not provide an exemption due to routing. There are four options listed in this section for compliance.

Question: Are flywheels a type of EPS?

Rich Vedvik: Flywheels are a type of energy conversion equipment and are listed under NFPA 111 as an SEPSS, or Stored-Energy Emergency Supply System. Applicability depends on the type and class that the flywheel can satisfy.

Question: Is the emergency transfer switch permitted to be in the same room as the normal power service equipment or normal power panels?

Rick Reyburn: Yes, as long as the room containing the transfer switch is rated in conformance with the NEC 700.10 requirements.

Question: Please explain the differences between the NEC Article 517 and Article 700 ratings?

Rick Reyburn: NEC Article 517 and NEC Article 700 are in agreement with each other. In the past codes, there was a difference in the understanding by some code officials but in recent code cycles the differences have been cleared up and now the articles are in sync with each other.

Question: What is the major application of standby genset in the cannabis industry?

Rich Vedvik: A grow facility will still have emergency needs, which may be limited to egress lighting and components, but may extend to purge systems for extraction facilities working with heat or flames for oil extraction. A standby application would be lights and irrigation.

Question: Do you need a shunt trip tied to the emergency systems for all elevators?

Rick Reyburn: No, not all elevators require a shunt trip signal to be provided.

Question: Are flywheels still considered emergency units in the U.S.?

Rich Vedvik: Because a flywheel has a very limited timeframe of operation at load, the typical answer is no. An emergency power source is required to operate for at least two hours per IBC 2702.1.5. Most flywheel systems are limited to Class 0.25 or lower per NFPA 111.

Question: For NEC Articles 700 and 701, we need to meet coordination study from both normal and generator power sources upstream of automatic transfer switches all the way down to branch circuit breakers, is it correct?

Rick Reyburn: Yes. Refer to NEC Articles 700.32 and 701.32.

Question: Should all loads on the generator should be connected to an ATS for step loading? There should never be any loads connected directly to a breaker on the generator. Also, only the life safety branch is required to have a separate vertical section in the switchboard. Can you confirm?

Rick Reyburn: The writer is correct.

Question: Does shore power for temporary generators have to be from life safety circuit when doing maintenance of main generators?

Rich Vedvik: When temporary generators are being used as the primary source for emergency, legally required, life safety or critical branches then yes, I believe the requirements of those associated sections would apply to the temporary generator as well.

Question: Does life safety branch in an NEC Article 517 facility need to meet selectivity requirements of Article 700?

Rick Reyburn: Yes.

Question: Normally who is in charge or risk assessment? Is the electrical engineer?

Rich Vedvik: NFPA 99 specifically requires the health care facility’s governing body under NFPA 99 Simply put, that is the person legally responsible for the facility; at no point does NFPA assign that role to a consultant. For more information, refer to this article on the topic of NFPA 99.

Question: Are there other resources that might help determine if a particular system is emergency, legally required or optional?

Rich Vedvik: The best resource is the informational notes in the NEC under Articles 700, 701 and 702. The second resource would be a risk assessment to determine the severity of risk to occupants if the system is not on emergency power.

Question: Can you elaborate on selective coordination requirements for emergency? How far upstream are you required to coordinate overcurrent protective devices? Obviously, the more devices, the harder the coordination becomes.

Rick Reyburn: Please refer to 2020 NEC Articles 700.32 and 701.32, which require full selective coordination from the branch circuit to the sources of power generator (or equivalent) and utility. In some cases there are numerous upstream normal overcurrent protection devices requiring selective coordination, including medium-voltage.

Question: Is labeling Emergency Systems conduits and J-boxes driven by code?

Rick Reyburn: Yes. Refer to 2020 NEC 700.10(A) Wiring, Emergency Systems Identification.

Question: Are two transfer switches required for applications where the entire building is on generator power when the power fails?

Rick Reyburn: If the facility requires compliance with NEC Article 700 Emergency Systems (i.e., as defined by the IBC or local ordinances).

Question: Have you had any experience with temporary emergency tent facility for COVID-19 patients on breathing apparatus where strict adherence to codes is difficult?

Rich Vedvik: We can expect future versions of code to cover tent hospitals and other temporary facilities. “Difficult” is a relative term that could imply expensive, inconvenient, untimely, etc. For example, access to the critical branch may be difficult because it is a long distance from the tent facility or the existing system is already at maximum capacity or the components needed have a lead time exceeds the need for the facility. We have been assisting clients and dealing with all of those issues. My rules are that the temporary solution should not endanger lives by using undersized wire or overloading existing systems and the classification of the patient’s acuity should drive the decision of how reliable the power should be.

Question: If you have two elevators, can you have them both on an emergency legally required panel?

Rick Reyburn: Yes.

Question: Is there a specified minimum generator runtime for health care systems in the standards or are these legally required to be unlimited runtime?

Rich Vedvik: Yes! There is a specified runtime and it relates to the class in NFPA 110. Most health care facilities are Class 48 or Class X (meaning 96 hours). 2018 NFPA 99 requires a Type 10, Class X, Level 1 EPS as defined in NFPA 110. IBC 2702.1.5 requires a minimum of two hours of run time. Each municipality, location and occupancy will have different runtime requirements. Unlimited runtime is not feasible with on-site storage; however, health care occupancies should have emergency power systems capable of running as long as the outage persists.

Question: Can automatic transfer switches be replaced by a Kirk Key interlock arrangement?

Rich Vedvik: No. By definition, a Kirk Key is not an automatic system and cannot respond in the specified amount of time (10 seconds or 60 seconds). A Kirk Key system can be used for manual transfers, but not automatic transfers.

Author Bio: Richard A. Vedvik, PE, Senior Electrical Engineer/Acoustics Engineer, IMEG Corp., Rock Island, Ill.; Rick Reyburn, PE, Executive Director of Electrical Engineering, NV5, Las Vegas