Some building developers and owners like to consider the buildingIT infrastructure, building heating and air-conditioning systems, elevators, sump pumps andwater treatment equipmentas the "essential electrical system.” As such, these developers might demand from electrical designers additional provisions for reliability in performance of the loads comprising these "essential electrical systems.” There is no problemfor designers and installers in this regard, as a redundancy could be easily provided in the design and installation of the electrical infrastructure.
But who is to say what constitutes an "essential electrical system”?
And if it is, in fact, such a system, what power supply arrangementsmust be provided for the loads of this "essential” system?
There are some folks who might eventreat their fridge or TV set as an "essential electrical system,” as they might need to ensure that their beer is always cold and the TV could always be turned on for their favourite show.
So, what is this mysterious "system”? Is it defined anywhere? Does any code or standard explain what it comprises of and how to arrange the power supply to the loads of this system?
The answer could be found in two CSA documents:
- CSA standard Z32-09 "Electrical safety and essential electrical systems in health care facilities”; and
- Section 24 of the CE Code, Part I.
Let’s take a look at provisions of these two documents.
Scope of Z32 states the following:
This Standard deals with the following subjects:
(a) electrical safety associated with health care provision; and
(b) essential electrical systems for health care facilities.
This standard defines essential electrical systemas an "electrical system that has the capability of restoring and sustaining a supply of electrical energy to specified loads if the normal supply of energy is lost.”
It is also stated in the scope of this standard that it applies to
It is important to note the statement in Z32 that its "provisions are supplementary to the installation requirements specified in Sections 24of the Canadian Electrical Code, Part I.”
This becomes quite interesting. Now we know that an essential electrical system is only covered by the scope of Z32 for health care facilities and by Section 24 of the CE Code.
(a) patient care areas of Class A, Class B, and Class C health care facilities; and
(b) areas outside health care facilities that are intended for patient diagnosis, treatment, or care involving intentional electrical contact of any kind between patients and medical electrical equipment.
Let’s check out the CE Code.
Scope of Section 24 of the Code indicates in part that this section applies to the portions of the electrical systems of health care facilitiesdesignated as "essential electrical systems.”
This is a very significant revelation.
It indicates that only certain circuits and loads of a health care facility could be designated as being part of an "essential electrical system.”
This means that developers of a typical two story commercial building ora six story office building might misuse this defined terminology when they consider their loads in such buildings as being an essential electrical system, unless certain areas of these buildings are defined as patient care areas of health care facilities. It should be noted that such definitions are provided in the CSA standard Z32 and in Section 24 of the CE Code.
Section 24 of the CEC also dedicates the entire set or Rules (24-302 – 24-306)to the requirements for circuits and emergency power supply to the essential electrical system.
Rule 24-300 of the CEC clearly articulates that the above mentioned rules
apply to those portions of a health care facility electrical system in which the interruption of a normal supply of power would jeopardize the effective and safe care of patients, with the object of reducing hazards that might arise from such an interruption.
Rule 24-302 of the CE Code explains that an essential electrical system must comprise only circuits that supply loads designated by the health care facility administration as being essential for the life, safety, and care of the patient and forthe effective operation of health care facility. This rule also guides the designers and installers to the fact that an essential electrical system must comprise at the minimum a vital branch, but it as well may include a delayed vital branch and a conditional branch, or both of these branches.
This clarification of the Code is important to the electrical designers, as it allows the use of a single transfer switch for all the loads (vital, delayed vital and conditional) for connecting the essential electrical system to an emergency power supply source.
So, how does a designer or an installer know which loads are deemed as being essential "for the life, safety, and care of the patient and forthe effective operation of health care facility”?
The answer could be found in the CSA standard Z32-09.
Table 7 of this standard not only lists and classifiessuch loads, but it assigns the status to the essential systembranches designating them as vital, delayed vital or conditional.
It is interesting to note that the life safety systems defined in Section 46 of the CEC become part of the essential electrical system when these "life safety systems” are utilized in a health care facility.
Rule 24-302(1) of the CE Code and Table 7 of Z32 clearly reflect this fact. This means that a separate dedicated transfer switch mandated for the loads of a life safety system by Section 46 is not required, if these loads comprise a part of the essential electrical systems of a health care facility.
In this lattercase, a dedicated transfer switch would be sufficient to connect all loads of the essential electrical system (including the loads of a life safety system described in Section 46) to the required emergency power supply, as long as the following provisions of Z32 are met:
6.2.1 Vital and delayed vital branches
The vital and delayed vital branches shall be connected to the emergency power supply by one or more transfer switches that are arranged to allow the vital and delayed vital branch loads to be transferred within 10 s and 2 min, respectively, and retransferred automatically.
The conditional branch shall be manually or automatically connected to the emergency power supply.
And what type of an emergency power supply is required for an essential electrical system?
The answer could be also found in the CEC and Z32. Rule 24-306 of the Code clearly states that nothing else, but "one or more generator sets” must be used to provide the emergency power supply to the loads comprising an essential electrical system.
Clause 6.7.2 of Z32 explains the required quantity and arrangement of the emergency generatorsas follows:
6.7.2 Generator set redundancy
The following requirements shall apply to generator set redundancy:
(a) An emergency power supply shall be provided by not less than two generator sets conforming to CSA C282 and arranged in such a manner that upon failure of one of the generators, the second generator will automatically provide power supply to the loads described in Clause 6.3within 10 s of unsatisfactory condition in the service in use.
(b) Notwithstanding Item (a), where it is acceptable to the administrator of a HCF, a single generator set may be used.
Similarly, Z32 sets out the criteria for the arrangement of the normal power supply sources as follows:
18.104.22.168 Supply or consumer’s services
The following requirements shall apply to supply or consumer’s services:
(a) Normal power supply shall be provided by not less than two separate supply or consumer’s services arranged in such a manner that upon failure of one of the services, the second service will automatically provide power supply to the loads described in Clause 6.2.1 within 10 s of unsatisfactory condition in the service in use.
(b) Notwithstanding Item (a), where it is acceptable to the administrator of a HCF, a single supply or consumer’s service may be used.
Note: Definitions of "supply service” and "consumer’s service” are provided in the Canadian Electrical Code, Part I.
So, it is up the administrator of a health care facility to advise the designers on how many normal power supply services and emergency generators are deemed to be necessary for the specific type of the HCF.
It appears that a mystery of the "essential electrical system” has been now resolved.
However, as usual, in order to prevent any surprises when a design ofsuch essential electrical systems is undertaken, relevant authorities with the jurisdiction power must be consulted.
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