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Safety and performance of Codes

Posted By Ark Tsisserev, Friday, July 01, 2011
Updated: Friday, December 21, 2012

Any electrical design and installation is based on a number of conditions. Traditionally, such conditions include reliability, performance and economics. Usually these conditions are dictated by the clients, who want such installations to function in a dependable manner and to be economically feasible.

But regardless of the client’s criteria, one condition that must be consistently met by the design and installation issafety.

This, latter condition is mandated by the appropriate codes and standards adopted for regulatory purpose in each jurisdiction where installation takes place.

Design and installation of electrical equipmentmust meet safety requirements of the Canadian Electrical Code adopted for administrative use in a province, territory or municipality.

Although the CE Code establishes minimum requirements forelectrical safetyin installations, it also covers specificfire safety provisionsfor certain equipment.

For example, Rule 2-124 of the CE Code governs criteria for fire stopping in fire separations, and it references the National Building Code of Canada (NBCC) for necessary means — to comply with these fire stopping requirements.
Rule 2-126 of the CEC mandates flame spread requirements for electrical conductors depending on a type of building construction or on location of these conductors in a building.

This rule also references fire protectionprovisionsof the NBCC for applicable FT marking of combustible insulation or jackets of electrical conductors.

Another such example could be illustratedby the requirement of Rule 32-200 for protection of conductors supplying a fire pump against exposure to fire. Appendix B Note on this rule also explains fire protection provisions of the NBCCin this regard.

Rule 32-110, for instance, regulates installation of carbon monoxide alarms and smoke alarms in the dwelling units. This rule also provides important explanatory references to the NBCC provisions for installation of these electrically connected fire safety devices

Appendix G of the CEC provides a complete cross-reference to the NBCC in respect to fire protection provisions for installation of electrical equipment, and the Appendix Gserves as a useful tool to the electrical designers, installers and regulators.
However, there are some situations where electrical designers and installers could beconfused on the extent of fire safety requirements of the NBCC.As the result, impact on the electrical design and installations might be quite drastic.

Let’s explore a few particular situations.
One of such subjects for misconception is use of locking devices on access doors to a typical commercial tenant unit. If the locking of thedoor is intended to prevent egress froma building or a tenant space, then only the use of electromagnetic locks (that do not incorporate latches, pins or similar devices that might keep the door in the closed position) is permitted by the NBCC, provided that the electromagnetic lock will release upon activation of the building fire alarm system, upon loss of power, or upon actuation of a manually operated switch accessible to authorized personnel. And such egress door must be opened from the inside with not more than one releasing operation and without requiring keys or specialized knowledge — by applying a force of not more than 90 N to the door opening hardware, so this force will initiate an irreversible process that will release the electromagnetic locking device within 15 s. And this is not the only condition that is placed by Sentence 3.4.6.15.(4) of the NBCC in conjunction with a permitted use of the electromagnetic lock.
Therefore, an electrical designer and electrical installer must take into account a need for interlocks required by the NBCC and a need for the wiring methods to be consistent with provisions of the CEC for Class 1 circuits (as this is a life safety application).

Of course, a building permit would be required to be obtained before an application for the electrical permit is submitted. Lack of understanding of the fire safety requirements of the NBCC in design and installation of an electrically connected locking device might adversely impact on a fire safety by preventing expedient exiting from a building.

If, however, a designer is incorporating a locking device only as meansof access control to a tenant unit, then the NBCC fire safety provisions do not apply for such installation, no building permit would be required in conjunction with such electrical work, and wiring of such locking devices would have to simply meet provisions of Section 16 of the CE Code for a typical Class 2 circuit (i.e., for a typical security system installation). As it could be seen from this example, a difference in design and installation could be very tangible.

Let’s review another example:
use of a UPS.

Firstof all, we’d have to clearly understand the intent of such use. If typical UPS equipment is utilized as a backup power supply source for such loads as IT equipment, kitchen preparation equipment, sump pumps, etc., then the NBCC and the CEC do not restrict such use of a UPS. It could be installed in accordance with the applicable provisions of the CE Code. If, however, a designer intends to use a UPS as arequired source of the emergency power supply, such application could be problematic (despite the fact that a typical UPS could function as a dependable source of the emergency power). The problem withsuch use is that the NBCC (Articles 3.2.7.4. and 3.2.7.9.) and the CE Code (Rule 46-202) only allow use of batteries, generators or a combination of bothas the emergency powersupply source.

In fact, Article 700, Emergency Systems, and Article 701, Legally Required Standby Systems, of the NEC also permit use of batteries or generators as the source of the emergency power supply. No UPS is specifically recognized by each of the referenced codes for such purpose.Thus, if a designer utilizes a UPS unit as the emergency power supply source for life safety systems defined in Rule 46-002or for essential electrical systems described in Rule 24-302 of the CEC, and such use of a UPS is undertakeninstead of the required batteries or a generator, then this approach is a definite recipe for trouble, as this approach is inconsistent with the NBCC and the CEC, and the regulators would not accept it.

If, however, a UPS unit is used as a convenient means for a secondary backup to a battery or a generator, this approach does not conflict with the life and fire safety provisions of the NBCC and the CEC.

One more example related to the fire safety could be also appropriate in this discussion. If a designerdecides to use a generator as a backup power source forthe IT loads, and such generator is not required by the NBCC to be used as the emergency power source for life safety systems, then all loads connected to this generator could be supplied via a single transfer switch. If, however, the generator is used as the emergency power supply source for any component of life safety system defined in Rule 46-002 of the CE Code, then all life safety system loads must be supplied from the generator via a dedicated transfer switch [see Rule 46-108(5) and Figure 8 of the CEC].

Let’s switch gears, and review performance aspectsof a typical electrical system in respect to a selective coordination of the overcurrent devices installed in the system.

Does the CE Code mandate coordination of the overcurrent devices in an electrical system, and does such coordination represent a
safety issue from the Code perspective?

In general (except for a few specific instances shown below) the CE Code does not mandate selective coordination of the overcurrent devices, as such coordination deals with a performance of the system components but not with the safety of the system. Therefore, in order to ascertain the acceptable performance of an electrical system, the designers must take into the account a good engineering practice in providing a selective coordination of the overcurrent devices installed in various parts of the system. Otherwise, a single fault in a branch circuit might disconnect the entire system if the overcurrent devices in branch circuits are not coordinated with the overcurrent devices installed in distribution feeders or in the building service. If not sure how to resolve selective coordination issues, the designers should communicate these issues with the experts representing manufacturers of the overcurrent devices.

However, there are several places in the CE Code, where selectivecoordinationis specifically mandated by the Code requirements.

Rule 14-102(8), for example, permits use of upstream protective device settings to exceed the values mandated by Subrule (2) in ground fault schemes where it is necessary to obtain desired coordination between the overcurrent devices.

Appendix B Note on Rule 32-206 (which explains provisions for overcurrent protection in a fire pump circuit) clarifies that the overcurrent protection selected in the circuit breaker installed upstream of a fire pump controller should be coordinated with the overcurrent device inside the fire pump controller "in a such a manner that the upstream overcurrent device does not disconnect the circuit prior to the operation of the fire pump controller overcurrent device.” The reason for such reference in the Code is quite obvious — fire safety.

A similar fire safety provisionis the basis for coordination requirement of Rule 46-206(1) of the CEC— between the generator overcurrent protection device and overcurrent devices installed in feeders and branch circuits that supply life safety systems and other electrical equipment connected to the load side of the emergency generator.This rule mandates selective operation of the branch-circuit overcurrent devicewhen a fault occurs in that branch circuit. The designers should be aware that in a distribution arrangement where the main overcurrent device is rated, let’s say, at 1600 A and downstream overcurrent devices are rated at 400 A or 200 A, compliance with this coordination criteria would not create a problem. But if the main overcurrent device is set, let’s say at 400 A, and downstream feeder overcurrent devices are rated at 200 A or 100 A, then it would be quite difficult to accomplish the desired coordination, and the manufacturing experts should be consulted on the best approach in solving this issue.

And as usual, designers and installers should discuss all questionable aspects of relevant codes and standards with the applicable AHJs, so there are no unpleasant surprises when design or installation is completed, and the regulators are asked to accept this design or installation.


Read more by Ark Tsisserev

Tags:  Canadian Perspective  July-August 2011 

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