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Location of Electrical Distribution Equipment in a Building — Are we consistent on this subject?

Posted By Ark Tsisserev, Tuesday, May 01, 2012
Updated: Friday, September 07, 2012

The subject of the required location for such electrical equipment as switchgear, panelboards, MCCs, switches, circuit breakers, capacitorsand transformers and of the required clearances (working space) about these types of equipment is not new.

Electrical designers, installers and inspectors encounter this subject on a daily basis. And yet, consistency in dealing with this issue is far from being perfect.

Let’s try the following mini-quiz(half of dozen questions only):

1. All electrical equipment such as switchgear, panelboards, MCCs, switches, circuit breakers, capacitors and transformers, etc., must be located in an electrical equipment vault:true_____false_____

2. All electrical equipment listed above must be located in an electrical equipment room:true_____ false_____

3. All electrical equipment listed above is permitted to be located in any floor area, provided that the floor area is sprinklered: true_____ false_____

4. If the electrical equipment listed aboveis located in an electrical equipment room, such electrical equipment room must be separated from the remainder of the building by a fire separationwith a fire resistance rating not less than 1 hour: true_____ false_____

5. All electrical equipment installed in a service room must be located in a dedicated room only (where other service equipment is not permitted to be installed): true_____ false_____

6. Clearance (working space) about all electrical equipment listed abovemust be not less than 1.5 m: true_____ false_____

If the mini quiz is already completed, I’d like to share with you myanswers to the above posted questions. I hope that there is no surprise that my answer to all of them is: false!

Let me elaborate starting with the first question.

Sentence 3.6.2.7.(1) of the National Building Code of Canada (NBCC) states: "(1) An electrical equipment vault shall conform to Sentences (2) to (8) if it is required by (a) provincial or territorial regulations or municipal bylaws, or (b) CSA C22.1 "Canadian Electrical Code, Part I,” in the absence of the regulations or bylaws referred to in Clause (a).”

This is a very interesting statement. While sentences (2) to (8) of this NBCC article mandate construction requirements for an electrical equipment vault, the actual need for a vault (to contain electrical equipment) is actually spelled out by the provisions of the Canadian Electrical Code (or by provincial/territorial regulations).

While, this discussion will not touch on the regulatory requirements on this subject, it is very timely for us to check out the relevant requirements of the CEC on this subject.
The answer could be found in Subrule 26-012(1) which states:

1) Dielectric liquid-filled electrical equipment containing more than 23 L of liquid in one tank, or more than 69 L in a group of tanks, shall be located in an electrical equipment vault.

Now it is abundantly clear that only equipment that contains dielectric liquid withspecific quantities is actually required to be installed in the electrical equipment vault. And when the vault is, in fact, necessary in accordance with the CE Code, in addition to the NBCC construction requirements (as described in Article 3.6.2.7.), the CEC also offers a number of specific conditions for a vault in Rules 26-350 – 26-356.

Electrical equipment vaults
26-350 General
(1) For the purposes of Rules pertaining to the construction of electrical equipment vaults, the single word "vault(s)” shall be understood to have the same meaning as "electrical equipment vault(s).”
(2) Vaults shall not be used for storage purposes.

26-352 Vault size
Vaults shall be of such dimensions as to accommodate the installed equipment with at least the minimum clearances specified in the pertinent Sections of this Code.

26-354 Electrical equipment vault construction (see Appendices B and G)
Every electrical equipment vault, including the doors, ventilation, and drainage, shall be constructed in accordance with the applicable requirements of the National Building Code of Canada.

26-356 Illumination
(1) Each vault shall be provided with adequate lighting, controlled by one or more switches located near the entrance.
(2) Luminaires shall be located so that they may be relamped without danger to personnel.
(3) Each vault shall have a grounding-type receptacle installed in accordance with Rule 26-700 and located in a convenient location inside the vault and near the entrance.

So, it looks like the answer to question1 of the mini-quiz is sufficiently substantiated.

But what about electrical equipment rooms?

Aren’t they automatically mandated for all types of the distribution equipment mentioned earlier?
Let’sreview Subrule 26-012(2) of the CEC. This subrule describes the cases where an electrical equipment room is a must.

(2) Except as permitted in Subrule (4), dielectric liquid-filled electrical equipment containing 23 L of liquid or less in one tank, or 69 L or less in a group of tanks, shall be
(a) installed in a service room conforming to the requirements of the National Building Code of Canada;
(b) provided with a metal pan or concrete curbing capable of collecting and retaining all the liquid of the tank or tanks;
(c) isolated from other apparatus by fire-resisting barriers, with metal-enclosed equipment considered as providing segregation and isolation; and
(d) separated from other dielectric liquid-filled electrical equipment by such a distance that, if the liquid in such equipment were spread at a density of 12 L/m2, the areas so covered would not overlap; these areas being deemed to be circular if the tank (or group of tanks) is in an open area, semi-circular if the tank is against a wall, and quarter-sector if the tank is in a corner.

In fact, the CE Code makes an exception for capacitors that are filledwith flammable liquids of 14 L or less in each tank — by not mandating their location in the electrical equipment rooms as follows:

(4) Notwithstanding Subrule (2), capacitors filled with flammable liquids of 14 L or less in each tank shall not be required to be installed in an electrical equipment vault nor in a service room, provided that
(a) a metal pan or concrete curbing that is capable of collecting and retaining all the liquid of the tank or tanks is installed;
(b) no other dielectric liquid-filled electrical equipment nor any combustible surface or material is within 4.5 m unless segregated by fire-resisting barriers, with metal-enclosed equipment considered as providing segregation; and
(c) each capacitor tank is provided with overcurrent protection to minimize rupture of the case.

It appears that by now, no additional discussions are necessary regarding the questions 2 and 3 of the mini-quiz.

Although some dry type transformers, panelboards, etc., may be installed in a floor area without being specifically placed in electrical equipment rooms, in realitybuilding owners prefer to have the electrical distribution equipment being located in service rooms accessible to the authorized personnel, and the electrical designers and installers diligently execute such wishes in their design and installations.

Perhaps, it is timely now to reviewthe question 4 above.

How does an electrical designer, contractor and inspector know whether the room containing an electrical equipment must be fire rated, and if the fire resistance rating is required, what type of rating of the fire separation between this service room and the remainder of the building is necessary?

The answer could be found in Article 3.6.2.1. of the NBCC. This particular article of the Building Code describes under what conditions a service room containing electrical equipment mustbe fire rated, and what fire resistance rating is deemed to be applicable in each specific case.

Electrical designers, installers and inspectors are encouraged to communicate on this subject with the building code experts in order to assure that the fire safety of the design and installation is not compromised.

It should be noted that the NBCC does not mandate fire separation requirements for some electrical rooms under specific conditions of their use (i.e., when a building is sprinklered, and the quantity of service equipment is limited, and the service equipment does not constitute a fire hazard, and the equipment is not essential to the operation of fire safety systems in the building, etc.).

For example, Article 3.6.2.3. of the NBCC permits installation of a certain electrical service equipment in the same service room that contains space heating, space cooling and service water heating appliances.

On contrary, Article 3.6.2.8. of the NBCCrequires that the emergency generator that provides the alternate source of power to the life safety systems described in Section 46 of the CE Code or to the essential electrical systems referred to in Section 24 of the CEC, must be located in a dedicated service room that contains only equipment related to the emergency power supply system, and that such a generator room must be separated from the remainder of the building by a fire separation with fire-resistance rating not less than 2 h.

It should be noted that Rule 36-004 of the CE Code mandates that the live parts of the high voltage electrical equipment must be accessible only to authorized personnel. Many electrical safety regulators interpret this requirement of the CE Code so, as to allow access to the HV electrical service rooms only to the persons who are authorized to operate such energized equipment. Many jurisdictions do not permit the installation of fire alarm and communication equipment in such high voltage electrical service rooms, and local electrical inspections authorities should be always consulted before planning to install communication and similar equipment in such HV electrical rooms.

Let’s discuss the last question of the mini-quiz.

The CE Code recognizes that maintenance of the specific electrical equipment is required. Such electrical apparatus as fuses, circuit breakers, control and metering devices installed in switchgear, panelboards, motor control centers and in similar piecesof electrical equipment that may need adjustment, replacement, calibration, etc.

Rule 2-308 of the CEC mandates a minimum working space of 1 m at such equipment — in order to safely perform the required maintenance procedure. This Rule also sets out minimum clearances around the equipment with exposed live parts, and such clearance requirements are prescribed in Table 56 based on the nominal voltage to ground.
Provisions of Rule 2-308 are shown below:

2-308 Working space around electrical equipment
(1) A minimum working space of 1 m with secure footing shall be provided and maintained about electrical equipment such as switchboards, panelboards, control panels, and motor control centres that are enclosed in metal, except that working space is not required behind such equipment where there are no renewable parts such as fuses or switches on the back and where all connections are accessible from locations other than the back.
(2) The space referred to in Subrule (1) shall be in addition to the space required for the operation of drawout-type equipment in either the connected, test, or fully disconnected position and shall be sufficient for the opening of enclosure doors and hinged panels to at least 90°.
(3) Working space with secure footing not less than that specified in Table 56 shall be provided and maintained around electrical equipment such as switchboards, control panels, and motor control centres having exposed live parts.
(4) The minimum headroom of working spaces around switchboards or motor control centres where bare live parts are exposed at any time shall be 2.2 m.

If the room contains an electrical equipment with the nameplate rating of 1200 A or more, or the equipment that is rated at more than 750V, and such equipment consists of transformers, disconnecting means, overcurrent devices, MCCs and similar apparatus, thenthe minimum clearance of 1 mrequired by Rule 2-308 must be increased to 1.5 m, if it is not possible to leave the electrical equipment room without passing the failure point (i.e., if the room does not have two egress doors that would allow the maintenance personnel to exit the room without passing by the referenced energized electrical apparatus).

These particular requirements of the CE Code are described by Rule 2-310 as follows:

2-310 Entrance to, and exit from, working space (see Appendices B, G, and I)
(1) Each room containing electrical equipment and each working space around equipment shall have unobstructed means of egress in compliance with the National Building Code of Canada.
(2) Where a room or space referred to in Subrule (1) contains equipment that has a rating on the equipment nameplate of 1200 A or more, or is rated over 750 V, and consists of transformers, overcurrent devices, switchgear, or disconnecting means, such equipment shall be arranged so that, in the event of a failure in the equipment, it shall be possible to leave the room or space referred to in Subrule (1) without passing the failure point, except that where this cannot be done, the working space requirement of Rule 2-308(1) and (2) shall be not less than 1.5 m.
(3) For the purposes of Subrule (2), the potential failure point is any point within or on the equipment.
(4) Doors or gates shall be capable of being readily opened from the equipment side without the use of a key or tool.

So, the substantiation to the answer "false” has been adequately provided to eachquestionof the mini-quiz.

However, it should be noted that during the design of the electrical installation that involves the selection of the most appropriate location for electricalequipment, all applicable experts (including the AHJ) should be consulted, in order to avoid costly changes at the construction stage and potential shock and fire safety hazards during the operation of the electrical equipment.


Read more by Ark Tsisserev

Tags:  Canadian Perspective  May-June 2012 

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