“How does it work?” I was recently asked this question by a group of electrical engineers in conjunction with the NFPA 20 requirement for an overcurrent device protecting feeder conductors to the fire pump controller from the normal power supply source to carry a fire pump locked rotor current indefinitely. My response to these electrical consultants has indicated how the relevant Canadian Codes and Standards are responding regarding revisions to the documents that are referenced in these particular Codes and standards. So, let’s use this particular example for the benefit of the readers.
The CE Code, Part I (and other CSA Codes and standards) are continually revised based on the following criteria:
(a) a need for demonstrated improvements of electrical and fire safety,
(b) correlation of installation requirements with applicable provisions of the safety product standards.
(c) correlation with other respective Codes, where such revisions are warranted for the purpose of consistency,
(d) clarification of the language or removal of the errors in the existing codes and standards.
In fact, these criteria are transparently reflected in Annex C of Appendix C of the CE Code, so the Code users should be aware of these fundamental conditions for the amendments to the CE Code.
In respect to the NFPA 20, it should be noted that 2013 of this standard for fire pumps is referenced in the 2015 edition of the CE Code, and the leadership of Section 32 S/C of the CE Code has recognized that some changes must be initiated to Rule 32-206 of the Code, to recognize revised requirements of NFPA 20.
For the purpose of this discussion, the following NFPA 20 provisions should be noted:
- NFPA 20 mandates that the circuit breaker installed in the normal supply feeder (upstream of the fire pump controller) must carry the fire pump locked rotor current (about 600% – 700% of the FLA) indefinitely (see below)
“9.2.3.4 Where the overcurrent protection permitted by 9.2.3 is installed, the overcurrent protection device shall be rated to carry indefinitely the sum of the locked rotor current of the largest pump motor and the full-load current of all of the other pump motors and accessory equipment.”
- The circuit breaker in the fire pump controller must have the following electrical characteristics:
“10.4.3.3.1 The circuit breaker shall have the following electrical characteristics:
(1) A continuous current rating not less than 115 percent of the rated full-load current of the motor
(2) Overcurrent-sensing elements of the nonthermal type
(3) Instantaneous short-circuit overcurrent protection
(4) *An adequate interrupting rating to provide the suitability rating of the controller discussed in 10.1.2.2
(5) Capability of allowing normal and emergency starting and running of the motor without tripping (see 10.5.3.2)
(6) An instantaneous trip setting of not more than 20 times the full-load current
10.4.3.3.1.1* The circuit breaker shall not trip when starting a motor from rest in the across-the-line (direct-on-line) mode, whether or not the controller is of the reduced inrush starting type.
10.4.3.3.1.2* The circuit breaker shall not trip when power is interrupted from a running pump, or if the pump is restarted in less than 3 seconds after being shut down. If a control circuit preventing a re-start within 3 seconds is provided, this requirement shall not apply.
10.4.3.3.2* Current limiters, where integral parts of the circuit breaker, shall be permitted to be used to obtain the required interrupting rating, provided all the following requirements are met:
(1) The breaker shall accept current limiters of only one rating.
(2) The current limiters shall hold 300 percent of full-load motor current for a minimum of 30 minutes.
(3) The current limiters, where installed in the breaker, shall not open at locked rotor current.
(4) A spare set of current limiters of correct rating shall be kept readily available in a compartment or rack within the controller enclosure.
10.4.4 Locked Rotor Overcurrent Protection. The only other overcurrent protective device that shall be required and permitted between the isolating switch and the fire pump motor shall be located within the fire pump controller and shall possess the following characteristics:
(1) For a squirrel-cage or wound-rotor induction motor, the device shall be of the time-delay type having tripping times as follows:
(a) Between 8 seconds and 20 seconds at locked rotor current
(b) Three minutes at a minimum of 300 percent of motor full-load current.”
- The circuit breaker is required in the fire pump transfer switch, and this circuit breaker must have electrical characteristics similar to the circuit breaker in the fire pump controller, as shown above.
“10.8.2.1.3 Circuit Breaker. The transfer switch emergency side shall be provided with a circuit breaker complying with 10.4.3 and 10.4.4.”
These very important conditions of the NFPA 20 have been reflected in the proposal submitted to the CSA for amendment of the relevant requirements in Section 32 of the CE Code.
The submitted proposal has been approved by the Technical Committee for the development of the CE Code, and the following approved revisions to Section 32 will appear in the 2018 edition of the CE Code (deleted text is greyed out and newly added wording is shown in bold italics below). Renumber and revise rules as shown.
32-2300 Conductors
(see Appendices B and G)
Conductors from the emergency power source to a fire pump shall
(a) have an ampacity not less than
(i) 125% 200% of the full load current rating of the motor, where an individual motor is provided with the fire pump; and
(ii) 125% 200% of the sum of the full load currents of the fire pump, jockey pump, and the fire pump auxiliary loads, where two or more motors are provided with the fire pump; and
(b) be protected against fire exposure to provide continued operation in compliance with the National Building Code of Canada.
32-2302 Wiring method (see Appendices B and G)
32-2304 Service box for fire pumps (see Appendix G)
(1) A separate service box conforming to Rule 32-2306 shall be permitted for fire pump equipment.
32-2306 Disconnecting means and overcurrent protection (see Appendices B and G)
(1) No device capable of interrupting the fire pump circuit, other than a circuit breaker labelled in a conspicuous, legible, and permanent manner identifying it as the fire pump disconnecting means, shall be placed between the service box and a fire pump transfer switch or a fire pump controller.:
(a) the service box from the normal power supply and a fire pump controller, or
(b) the main circuit breaker of the emergency generator and a fire pump transfer switch.
(2) The circuit breaker referred to in Subrule (1) shall be lockable in the closed position.
(3) The circuit breaker referred to in Subrule (1) shall be permitted to be used in the separate service box described in Rule 32- 2 304.
(4) Where the circuit breaker conforming to this Rule is installed in an emergency supply circuit between the emergency power source and the fire pump transfer switch, the rating or setting of the circuit breaker shall comply with Rule 28-200.
(5) Where the circuit breaker conforming to this Rule is installed in a normal supply circuit upstream of the fire pump controller, the rating or setting of the circuit breaker shall be not less than the overcurrent protection that is provided integral with the fire pump controller.
(4) The overcurrent protective device of the circuit breaker referred to in Subrule (1)(a) shall be set or rated to carry indefinitely the locked rotor current of the fire pump.
(5) The overcurrent protective device of the circuit breaker referred to in Subrule (1)(b) shall be set or rated not less than the overcurrent protection provided integral with the fire pump transfer switch.
(6) Notwithstanding Subrule (1)(b), where the circuit breaker is installed in an emergency supply feeder between the emergency generator and the fire pump transfer switch, the feeder shall be permitted to bypass the generator main circuit breaker and be connected directly to the emergency generator.
Renumber and revise Appendix B Notes for Section 32 as shown:
Rule 32-2300
The intent of this Rule is to size conductors such that the conductor insulation will not be compromised during fault current conditions (see Rule 32-206 and associated Appendix B notes).
The intent of this Rule is also to protect the feeder conductors between a fire pump and an emergency power source from fire damage.
The National Building Code of Canada requires that conductors supplying life and fire safety equipment be protected against exposure to fire to ensure continued operation of this equipment for a period not less than 1 h.
NFPA 20 also mandates protection of circuits feeding fire pumps against possible damage by fire. The following examples illustrate acceptable methods for achieving this protection:
(a) using mineral-insulated cables conforming to fire rating requirements as specified in Clause 5.3 of CSA C22.2 No. 124;
(b) embedding the raceway containing fire pump feeder conductors in not less than 50 mm of concrete; or
(c) installing the raceway containing fire pump feeder conductors in a shaft enclosure or service space of at least 1 h fire resistance construction.
Specific requirements pertaining to the protection of conductors against exposure to fire fire resistance rating of a material or an assembly of materials can be found in Article 3.2.7.10. subsection 3.1.7 of the National Building Code of Canada or in the appropriate provincial/territorial legislation.
Rule 32-2306
The intent of this Rule is to allow only a circuit breaker lockable in the closed position and identified as the fire pump disconnecting means to be installed upstream from the fire pump controller in a normal power supply circuit, or upstream from the fire pump transfer switch in an emergency power supply circuit. It is also intended by this Rule that this circuit breaker potentially be used in the fire pump service box described in Rule 32-2 304. When this circuit breaker is installed in the emergency power supply circuit, upstream from the fire pump transfer switch, the circuit breaker overcurrent protection provided by the requirements of Subrule (4) should be able to allow the fire pump to operate up to locked rotor current condition. This will allow an emergency generator to provide necessary power to the required fire pumps while supplying all other loads connected to the generator.
It is intended that compliance with Rule 28-200 potentially be met by selecting overcurrent protection in conformance with Table 29.
The circuit breaker installed in the normal power supply circuit, upstream from the fire pump controller, should have a rating/setting that is coordinated with the integral overcurrent protection of the fire pump controller in such a manner that the upstream overcurrent device does not disconnect the circuit prior to the operation of the fire pump controller overcurrent protection.
Appendix B
Note: Clause 10.4.3.3 of NFPA 20 requires that the controller have an instantaneous trip-setting of not more than 20 times the full load current. Clause 10.4.4 of NFPA 20 requires that a fire pump controller carry locked rotor current for a period of 8 to 20 s.
This Rule requires that an overcurrent protective device for a fire pump be set to enable uninterrupted operation under fire pump starting conditions. Such overcurrent protective devices are installed upstream from the fire pump controller or the fire pump transfer switch, and must have this capability whether they form part of the normal power supply feeder or the emergency power supply feeder.
Fire pump locked rotor currents are typically not less than 500% of the full load current, and fire pump suppliers should be consulted to determine the specific locked rotor current of a fire pump selected for a specific installation. The overcurrent device settings described in Subrule (4) should be able to carry the locked rotor current indefinitely, as required by the NFPA 20. The overcurrent device settings described in Subrule (5) should be coordinated with the integral overcurrent protection of the fire pump controller or the transfer switch in such a manner that upstream overcurrent devices do not disconnect the circuit prior to the operation of the controller/ fire pump transfer switch overcurrent protection.
The intent of Subrule (6) is to recognize that NFPA 20 allows for the generator main circuit breaker to be bypassed by a direct connection between the emergency supply feeder and the fire pump transfer switch. This permission removes the requirement for coordination between the generator main circuit breaker and the fire pump feeder circuit breaker as required by Rule 46-208(1).
It should be also noted that NFPA 20 requires that the circuit breaker in the controller or in the transfer switch must have an instantaneous trip-setting of not more than 20 times the full load current. NFPA 20 also requires that the overcurrent device in a fire pump controller or in a fire pump transfer switch must carry a minimum 300% of the fire pump full load current for a period of 8 to 20 s.”
The readers should be aware that a proposed change in newly renumbered Rule 32-300 – to upsize the fire pump feeder conductors from 125% FLA to 200% FLA may not be reflected in the 2018 edition of the CE Code, if the CSA standard C22.2 No. 263 is not revised so, as to mandate that the wiring terminals size in the standard is amended accordingly. Otherwise, the proposed change to the installation Code would create a conflict with provisions of the safety product standard.
So far, Clause 6.4 of this standard (harmonized with UL 214) states the following:
“6.4 Field wiring terminals
6.4.1 A controller shall be provided with wiring terminals for connection of conductors having an ampacity or wire size not less than the following:
- a) For power circuits, 125 percent of the full-load motor current specified in Tables 2 and 3 for the horsepower rating…”
It should be noted that Clause 6.4 of C22.2 No. 263 does not actually conflict with the newly proposed changes of the CE Code to upsize the fire pump feeder conductors from 125% FLA to 200% FLA, as it simply requires that “A controller shall be provided with wiring terminals for connection of conductors having an ampacity or wire size not less “than “125 percent of the full-load motor current.”
It should be also noted, that the Technical Committee for CSA C282 has recently formally adopted revisions proposed by the C282 Committee Task Force to the next edition of C282, and these changes will appear in the 2020 edition of C282.
“The consensus based recommendation of the task force to revise Clauses 5.1 and 8.7 of C282.
- To revise Clause 5.1 by adding new paragraph (b), by renumbering current paragraphs (b) to (f) as paragraphs (c) to (g) and by revising newly re-numbered paragraph (f) as shown below:
“5.1 The emergency electrical power supply system shall consist of all of the equipment and systems necessary to supply reliable electrical power, including the following:
a) the engine generator set, which can include an auxiliary supply tank;
b) lockable disconnecting means and overcurrent devices described in Clause 8.7.1;
c) the fuel supply system, including tanks and piping as described in Clause 7.3;
d) automatic transfer switches and all associated wiring;
e) the emergency generator ventilation and cooling system;
- f) wiring and all electrical components between an emergency generator and the emergency supply terminals of transfer switches specified in Clause 9, including wiring and overcurrent protective devices;
- g) overcurrent protective devices installed in the feeders supplying permanent or temporary load banks; and
- h) the exhaust silencer and piping to outdoors.”
- To delete existing Clause 8.7.1 and to replace it with the new Clause 8.7.1):
Each emergency generator shall be provided with a single lockable overcurrent device to connect it to the remainder of the emergency electrical power supply system. This device shall be monitored with a local alarm indication and a remote alarm annunciation in accordance with Table 1. Notwithstanding this requirement, any components of the emergency electrical supply system required to ensure operation or allow testing of the emergency generator set may be connected upstream of the single lockable overcurrent device.
Note: The single lockable overcurrent device may be provided as part of the emergency generator set or may be provided in a separate enclosure remote to the generator set depending on the site- specific design and installation requirements.
8.7.1.1.1 Each emergency generator shall be provided with a single overcurrent device and disconnecting means, to connect the generator to the remainder of the emergency electrical power supply system.
- To delete existing Clause 8.7.2 and to replace it with the new Clause 8.7.2):
8.7.2
The overcurrent devices in the emergency distribution system shall be coordinated with the overcurrent device described in Clause 8.7.1 to maximize the selective tripping of the overcurrent devices described in Rule 46-208 of the Canadian Electrical Code, Part I when a short-circuit occurs. At a minimum, sufficient selective tripping shall be provided to ensure that a fault in any circuit directly downstream of an automatic transfer switch operates its respective overcurrent device while power is maintained to the other emergency circuits. Short-circuit currents of sufficient magnitude shall be made available from the generator to satisfy this coordination requirement.
Note: See Clause B.18 for commentary on this Clause.
8.7.2 Any following components of the emergency electrical supply system required to ensure operation or allow testing of the emergency generator set, shall be permitted to be connected upstream of the main disconnecting means and overcurrent device connecting the generator to the remainder of the emergency electrical power system:
(a) the disconnecting means and overcurrent device(s) protecting fire pump feeder(s) supplied by the emergency generator;
(b) the disconnecting means and overcurrent devices protecting feeders to components of the cooling and ventilation systems required for the operation of the emergency generator:
(c) the disconnecting means and overcurrent devices protecting feeders to components of the fuel supply system required for the operation of the emergency generator;
(d) the disconnection means and overcurrent device protecting a feeder that supplies a permanent or temporary load bank utilized to test the emergency generator.
Note: See Clause B.18 for commentary on this Clause
- To add Clauses 8.7.3 – 8.7.6 to read as follows:
8.7.3 The emergency generator main overcurrent protection device shall be coordinated with the overcurrent devices of feeders and branch circuits supplying life safety systems and other electrical equipment connected to the emergency generator, as described in Clause 5.1(f).
8.7.4 At a minimum, sufficient selective tripping shall be provided to ensure that a fault in any circuit directly downstream of an automatic transfer switch operates its respective overcurrent device while power is maintained to the other emergency circuits. Short-circuit currents of sufficient magnitude shall be made available from the generator to satisfy this coordination requirement.
8.7.5 Notwithstanding Clause 8.7.3, where the overcurrent protective devices are permitted to be installed in accordance with Clause 8.7.2, selective coordination between overcurrent protective devices shall not be required.
8.7.6 The overcurrent device described in Clause 8.7.1 shall be monitored with a local alarm indication and a remote alarm annunciation in accordance with Table 1.
- To delete existing Clause B.18 and to replace it with the new Clause B.18 (as shown below in the italics):
B.18 (Clause 8.7.2)
Most systems use moulded-case circuit breakers for protection; unfortunately, the ability to achieve selective tripping under short-circuit conditions is extremely limited. At a minimum, it is considered reasonable to allow a loss of selective tripping with the breaker that feeds the normal input of the automatic transfer switch so long as the transfer switch can transfer to emergency power and restore power to all other loads. This prohibits the use of a main circuit breaker with an instantaneous trip (e.g., a moulded-case breaker) in the main emergency panel or switchboard and necessitates that, if the generator breaker or any generator feeder breakers have instantaneous trips (e.g., moulded-case breakers), the trips need be set higher than the available fault current from the generator.
It should be noted that moulded-case breakers with electronic trips with short time delays still have instantaneous trips (instantaneous override trips), which operate at a relatively low value and are not necessarily adjustable.
The use of air circuit breakers or power circuit breakers with a true short time rating and no instantaneous trips allows a much greater level of coordination to be achieved when compared with the use of moulded-case breakers.
It is generally not possible to ensure selective tripping under short-circuit conditions between downstream panel breakers and the breakers that feed the panels because moulded-case breakers are typically used. Selective tripping is achieved only when the magnitude of the fault current in the branch circuit is so low that it does not release the instantaneous trip of the breaker that feeds the panel. The cost of air circuit breakers in these applications is prohibitive.
B.18 (Clause 8.7.2)
Most systems use moulded-case circuit breakers for protection; unfortunately, the ability to achieve selective tripping under short-circuit conditions is extremely limited.
It is generally not practicable to ensure selective tripping under short-circuit conditions between the generator main overcurrent device and overcurrent devices that protect downstream feeders. For example, NFPA 20 recognizes this fact and allows connection of a fire pump feeder ahead of the generator main O/C device.
It is not intended to provide selective coordination between the generator main overcurrent protective device and downstream feeder or branch circuit overcurrent devices, where overcurrent devices protecting feeders or branch circuits supplied by the emergency generator, are permitted to be connected upstream of the generator main overcurrent protective device by Clause 8.7.2.
- To submit request for amendment to Rule 46-208 of the CE Code (to be submitted to Section 46 S/C of the CE Code as part of this proposal)
To amend Rule 46-208 as follows (proposed changes are shown in bold italics)
“46-208 Overcurrent protection (See Appendix B)
(1) The overcurrent device for an emergency power supply shall be coordinated with the overcurrent devices of feeders and branch circuits supplying life safety systems and other electrical equipment connected to the emergency power supply in order to provide selective operation of the branch circuit overcurrent device when a fault occurs in that branch circuit.
(2) The branch circuit overcurrent devices shall be accessible only to authorized persons.
(3) Notwithstanding Subrule (1), where the overcurrent protective devices are permitted to be installed in accordance with Clause 8.7.2 of the CSA standard C282, selective coordination between overcurrent protective devices shall not be required.”
To add Appendix B Note on Rule 46-208 as follows:
Appendix B Note on Rule 46-208(1) “(1) The Code users should be aware that the feeder or branch circuit overcurrent devices described by this Subrule may be also provided as part of the emergency generator supply, in accordance with Clauses 5.1(f) of C282. The generator suppliers and electrical designers should coordinate all aspects of installation of these overcurrent protective devices.”
Appendix B Note on Rule 46-208(3) “(3) It is not intended to provide selective coordination between the generator main overcurrent protective device and downstream feeder or branch circuit overcurrent devices (see Figure 8) when the feeder or branch circuit overcurrent protective devices are permitted to be connected upstream of the generator main overcurrent protective device in accordance with Clause 8.7.2 of C282”
- To add annunciation to Table 1 of any circuits connected upstream of the generator main disconnecting device.
Table 1
Any disconnecting device in the open position, connected upstream of the generator main protective device, for items listed in 8.7.2 a), b), or c)
Any disconnecting device in the closed position, connected upstream of the generator main protective device, for 8.7.2 d).”
It should be also noted that recommendation six of C282 Task Force, shown above, has been submitted to the Section 46 S/C for the CE Code, Part I to revise Rule 46-208 accordingly, and this revision will most likely show up in 2021 edition of the CE Code.
So, the above shown example of necessary correlation between applicable codes and standards clearly demonstrates that such coordination and correlation activity works.
This example also underlines a need for each stakeholder of electrical safety to timely raise any issues, when certain provisions of applicable codes and standards are out of sync.
Meanwhile, as usual, the local AHJ should be consulted accordingly.
