Electrical equipment and wiring in plenums and suspended ceilings

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Electrical equipment and wiring in plenums and suspended ceilings

The approach to this subject appears to be inconsistent by many users of the Canadian Electrical Code, Part I (CE Code), including electrical designers, electrical contractors, and electrical safety regulators. The terms “suspended ceiling” and “plenum” are widely used in the CE Code, but these two terms are not identical.

In many cases, the term “suspended ceiling,” used for wiring and for recessed luminaires, does not necessarily represent a plenum. It should be noted that requirements of the National Building Code of Canada (NBC) for wiring methods and equipment in plenums are quite restrictive. It should also be noted that while a “suspended ceiling” is not defined in the CE Code or in the NBC, “plenum” is the defined term in both codes.

The NBC defines plenum as follows:

Plenum means a chamber forming part of an air duct system.

The CE Code defines plenum as follows:

Plenum—a chamber associated with air-handling apparatus for distributing the processed air from the apparatus (supply plenum) to the supply ducts or for receiving air to be processed by the apparatus (return plenum).

While these definitions in the CE Code and in the NBC are a bit different, the most important fact is that both these definitions state that a plenum is a chamber which represents a part of a duct system intended to carry environmental air. It means that where such a duct system serves more than one floor area, it may bring smoke from a contaminated floor area (i.e., an area impacted by fire or smoke) to another floor area where smoke would not exist otherwise. Therefore, the requirements for electrical equipment and wiring methods in plenums would have to ascertain that the smoke propagation from the electrical equipment and wiring in a plenum has particular limitations. It also means that if a suspended ceiling is not used as a plenum, the above stated restrictive requirements for electrical equipment and wiring methods would not apply to installations in a suspended ceiling.

Article 3.6.4.3. of the NBC mandates the following properties of materials located in a plenum:
3.6.4.3. Plenum Requirements
1) A concealed space used as a plenum within a floor assembly or within a roof assembly need not conform to Sentence 3.1.5.18.(1) and Article 3.6.5.1., provided
a) all materials within the concealed space have a flame-spread rating not more than 25 and a smoke developed classification not more than 50, except for
i) tubing for pneumatic controls,
ii) optical fibre cables and electrical wires and cables with combustible insulation, jackets or sheathes that are used for the transmission of voice, sound or data and conform to Sentences 3.1.4.3.(2) and 3.1.5.21.(2),
iii) totally enclosed non-metallic raceways with an FT6 rating, when tested in accordance with Clause 3.1.5.23.(1)(a), in buildings required to be of non-combustible construction, and
iv) totally enclosed non-metallic raceways with an FT4 rating, when tested in accordance with Clause 3.1.5.23.(1)(a), in buildings permitted to be of combustible construction, and
b) the supports for the ceiling membrane are of non-combustible material having a melting point not below 760°C.
2) If a concealed space referred to in Sentence (1) is used as a return-air plenum and incorporates a ceiling membrane that forms part of the required fire-resistance rating of the assembly, every opening through the membrane shall be protected by a fire stop flap that
a) stops the flow of air into the concealed space in the event of a fire,
b) is supported in a manner that will maintain the integrity of the ceiling membrane for the duration of time required to provide the required fire-resistance rating,
c) conforms to CAN/ULC-S112.2, “Fire Test of Ceiling Firestop Flap Assemblies,” and
d) activates at a temperature approximately 30°C above the normal maximum temperature that occurs in the return-air plenum, whether the air duct system is operating or shut down“

While FT rating of conductors in plenums will be discussed a bit later, it is interesting to note that in conjunction with the ULC standard CAN/ULC-S2577-13-AM2 Standard for Suspended Ceiling Grid Low Voltage Systems and Equipment listed in Appendix A of the CE Code, the new Subsection 12-2300 series rules (12-2300 – 12-2320) has been introduced into the 2018 edition of the CE Code, and this subsection is dedicated to Extra-low-voltage suspended ceiling power distribution systems. Rule 12-2306 outlines conditions under which such a system could be installed in a suspended ceiling, when the suspended ceiling is used as a plenum space.

A wide range of rules in the CE Code offers very specific requirements for electrical equipment and wiring in suspended ceilings and plenums, and Rules 12-010, 16-220, 54-406, 56-210, 60-314, 60-402 and Table 19 represent some of such examples.

Now is the appropriate time to discuss the CE Code requirements for FT rating of conductors located in plenums.

Rules 2-130 and 2-132 of the CE Code mandate FT marking for combustible insulations and jackets of conductors and cables and for non-metallic raceways as follows:

2-130 Flame spread requirements for electrical wiring and cables

Insulated conductors and cables installed in buildings shall meet the flame spread requirements of the National Building Code of Canada or local building legislation.

2-132 Flame spread requirements for totally enclosed non-metallic raceways
Totally enclosed non-metallic raceways installed in buildings shall meet the flame spread requirements of the National Building Code of Canada.

Appendix B Notes on these two Rules provide the following clarification of these NBC requirements for FT rating of insulated conductors and cables located in plenums without raceways and for non-metallic raceways in plenums, as follows:

Appendix B Note on Rule 2-130
The flame spread requirements for insulated conductors and cables in buildings are located in the National Building Code of Canada as follows:
a) ……………..;
b) ……………..; and
c) plenum spaces in buildings — Article 3.6.4.3.
The markings for wires and cables meeting the flame spread requirements of the National Building Code of Canada (without additional fire protection) are
a) ……………..;
b) ……………..; and
c) FT6‡ — insulated conductors and cables that are suitable for installation in
i) buildings of non-combustible and combustible construction; and
ii) spaces between a ceiling and floor, or ceiling and roof, that may be used as a plenum in buildings of combustible or non-combustible construction.
* ………………;
† ………………;
‡ Communication and optical fiber cables marked CMP, OFNP, and OFCP have been found to meet the standard criteria for FT6.
Insulated conductors and cables with combustible insulation, jackets, or sheaths that do not meet the above classifications but are located in
a) totally enclosed non-combustible raceways;
b) …………….;
c) …………….;
d) …………….;; or
e) totally enclosed non-metallic raceways conforming to Rule 2-132
may be considered to comply with the National Building Code of Canada requirements relating to flame spread.

It is the intent of this Rule to limit flame spread and smoke propagation of cables in plenum spaces to the values specified by Article 3.6.4.3 (1) (a) of the National Building Code of Canada. Authorities enforcing provisions of the National Building Code of Canada and the National Fire Code of Canada in each jurisdiction should be consulted in order to determine the acceptable volume of cables in plenums for the purpose of conformance with the National Building Code of Canada and the National Fire Code of Canada requirements.

Appendix B Note on Rule 2-132
The flame spread requirement for totally enclosed non-metallic raceways can be found in Article 3.1.5.23 of the National Building Code of Canada. The National Building Code of Canada permits the use of totally enclosed non-metallic raceways for insulated conductors and cables in buildings required to be of non-combustible construction, provided that the totally enclosed non-metallic raceways do not exceed 175 mm in outside diameter, or equivalent cross-sectional area, and conform to the vertical flame test requirement specified in Clause 6.16 of CSA C22.2 No. 211.0.

The National Building Code of Canada also permits the use of totally enclosed non-metallic raceways in plenums of buildings. Where a totally enclosed non-metallic raceway is installed in a plenum of a building permitted to be of combustible construction, such a raceway should meet, as a minimum, the requirements of an FT4 rating. Where a totally enclosed non-metallic raceway is installed in a plenum of a building required to be of non-combustible construction, such a raceway should meet the requirements of an FT6 rating.

Now is the perfect time to see where in the NBC exist the above referenced provisions for appropriate FT marking of combustible jackets of conductors and cables located in plenums of buildings permitted to be of combustible construction or installed in plenums of buildings required to be of non-combustible construction, and for appropriate FT marking of non-metallic raceways installed in plenums of buildings permitted to be of combustible construction or installed in plenums of buildings required to be of non-combustible construction.

These requirements are as follows:
1. For combustible jackets of conductors and cables installed in plenums of buildings permitted to be of combustible construction:
3.1.4.3.(2) Except as permitted in Sentences (3) and (4), optical fibre cables and electrical wires and cables with combustible insulation, jackets or sheathes that are used for the transmission of voice, sound or data and are installed in a plenum in a building permitted to be of combustible construction shall exhibit the following characteristics when tested in conformance with CAN/ULC-S102.4, “Test for Fire and Smoke Characteristics of Electrical Wiring, Cables and Non-Metallic Raceways,” (FT6 rating).

2. For combustible jackets of conductors and cables installed in plenums of buildings required to be of non-combustible construction:
3.1.5.21.( 2) Except as permitted in Sentences (3) and (4), optical fibre cables and electrical wires and cables with combustible insulation, jackets or sheathes that are used for the transmission of voice, sound or data and are not located in totally enclosed non-combustible raceways are permitted to be installed in a plenum in a building required to be of non-combustible construction, provided the wires and cables exhibit a horizontal flame distance of not more than 1.5 m, an average optical smoke density of not more than 0.15, and a peak optical smoke density of not more than 0.5 when tested in conformance with CAN/ULC-S102.4, “Test for Fire and Smoke Characteristics of Electrical Wiring, Cables and Non-Metallic Raceways,” (FT6 rating).

3. For non-metallic raceways installed in plenums of buildings permitted to be of combustible construction:
3.1.4.4. Non-metallic Raceways
1) Totally enclosed non-metallic raceways used in a plenum in a building permitted to be of combustible construction shall meet the requirements of Clause 3.1.5.23.(1)(a).
“3.1.5.23.(1)(a) where the wires and cables in the raceways meet or exceed the requirements of Clause 3.1.5.21.(1)(a), the non-metallic raceways meet the requirements for at least an FT4 rating.

4. For non-metallic raceways installed in plenums of buildings required to be of non-combustible construction:
3.1.5.23.( 2) Totally enclosed non-metallic raceways used in a plenum in a building required to be of non-combustible construction shall exhibit a horizontal flame distance of not more than 1.5 m, an average optical smoke density of not more than 0.15, and a peak optical smoke density of not more than 0.5 when tested in conformance with CAN/ULC-S102.4, “Test for Fire and Smoke Characteristics of Electrical Wiring, Cables and Non-Metallic Raceways,” (FT6 rating).

Hopefully, the above presented brief tour through the relevant provisions of the CE Code and NBC helps to clarify the subject of this article.

It should be noted that Appendix G of the CE Code provides cross-reference between relevant provisions of the CE Code and the NBC. Introduction to Appendix G and application of Appendix G provides the following information to the CE Code users:

Appendix G — Electrical installations of fire protection systems
Note: This Appendix is an informative (non-mandatory) part of this Standard.
G1 Introduction
G1.1
This Appendix lists requirements related to electrical installations that are not governed by Rules of the Canadian Electrical Code, Part I but are required by the National Building Code of Canada.

G1.2
References listed in this Appendix are associated with electrical installations that are a part of the fire protection requirements contained in the National Building Code of Canada.
G2 Application
G2.1
The intent of this Appendix is to advise Canadian Electrical Code, Part I users of performance requirements for electrically connected fire-protective equipment required by the National Building Code of Canada.
G2.2
Special fire protection requirements, such as use of thermal insulation, fire spread, flame spread requirements for electrical wiring and cables, flame-spread requirements for combustible raceways, and construction of electrical equipment vaults are covered by this Code (e.g., Rules 2-126, 2-128, 2-130, 2-132, 26-354, etc.).

G2.3
Provincial and municipal building codes may deviate from the National Building Code of Canada, and users of this list should also check those codes.

And as usual, local Authorities Having Jurisdiction, who are responsible for the administration of the legally adopted CE Code, should always be consulted regarding specific issues related to this subject.

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