System design

Health and Safety

Equipment Location

Wall-mounted enclosures shall be located to avoid injury to persons. Requirements are specified in Cabling System Installation Practice.

Telecommunications outlets shall be positioned to provide ready access without excessive bending or stretching.

The layout and location of the cabling system and pathways shall ensure that equipment, access facilities and metallic components are not be placed in a location where the earth potential rise (EPR) could exceed 430V a.c. under power system fault conditions. If a building is supplied only with 230V a.c. single phase or 400V a.c. 3 phase power, there will be no need to consider EPR unless the installation is within the hazard zone of a high voltage transformer.  Where the installation cannot be placed in an EPR hazard-free zone, the installation shall not proceed except on the basis of a design by a Chartered Professional Engineer.

Telecommunications Outlets

While telecommunications outlets (RJ45 modular sockets) pass the test probe requirements of AS/NZS 60950.1, they fail the test finger requirement which means that small children “exploring” unshuttered sockets can touch the contacts inside. Therefore, all telecommunications outlets shall be provided either with mechanical protection (e.g. a shutter or “dummy” plug) that prevents finger access to the contact springs, or be installed out of reach.

Floor-mount boxes accommodating telecommunications outlets shall not be used.

Wireless Access

To afford the best coverage and enable the output power to be set at the minimum level, telecommunications outlets for wireless access points shall be positioned high on the wall at a location central to the required coverage area in the building.

Where available, the manufacturer’s instructions for installation shall be followed.

Acoustic Noise

The location of equipment enclosures shall be selected such that noise levels in work areas arising from the enclosed equipment, when combined with other sources of work area noise, are maintained within the limits specified by AS/NZS 2107.  Recommended design sound levels are given in Table 1 of AS/NZS 2107, from which the following design details are extracted.

Seismic Bracing

Free-standing enclosures greater than 18RU in height shall be restrained to prevent toppling over during an earthquake causing injury to people and preventing access into or out of the building.

Where the coefficient of friction between the enclosure and the floor surface is quite low, such as for castor wheels on a hard floor or plastic feet on a low-pile carpet, sliding will occur before overturning. Providing the enclosure together with its contents weigh less than 40kg and the requirements laid out in Cabling System Installation Practice for excess cable length are met and the cable is free to extend from the cabinet to prevent overturning, seismic restraint may be omitted.

NZS 4104:1994 provides the basis for the design of restraints and provides sketches of many simple, practical solutions to secure computer equipment and cabinets, amongst other common items. In general, the restraint system for an item on any particular floor shall be capable of withstanding a horizontal force equal to the multiplying factor given below times the weight of the restrained item including its contents.

Equipment Rooms

Specialised computer equipment rooms are unlikely to be provided for ECE Services.  In the unlikely event that an ECE Service requires a specialised equipment room, reference shall be made to the Ministry’s Policy and Guidelines for Schools.  The latest version may be obtained from the Ministry website.

Nevertheless, equipment accommodation should be designed with due consideration of the following:

• Physical security against unauthorised entry
• Space for future expansion
• Safety – equipment layout shall not restrict escape routes
• Acoustic noise requirements identified in section 7.1.2
• Suitable access for equipment installation and to equipment for maintenance
• Provision of space for entry of public network services
• Equipment enclosures shall not be installed in positions where exposure to moisture is likely, e.g. under air-conditioning vents or in laundries
• Telecommunication service entry facilities should be planned in consultation with the service provider to minimise trenching and the length of cables, and locate the service demarcation point.
• Lighting sufficient to carry out detailed technical installation and maintenance work
• Electrical power distributed via a dedicated single phase circuit with minimum 15A rated residual current device (RCD) protection.
• The temperature and humidity in the room shall be controlled to provide an operating range between 18°C and 24°C with 30% to 55% humidity.  In most ECE Services this will be achieved with passive convection ventilation.

Equipment Enclosure

In general, a 19” rack type steel bodied, floor- or wall-mount equipment enclosure (cabinet), with either a toughened glass or steel door, should be installed. Minimum dimensions are:

• 18RU equipment space
• 600 mm deep
• 600mm wide

The enclosure should provide sufficient free space for the future installation of a small server and uninterruptible power supplies (UPS).

The minimum depth of any closet/cupboard housing the enclosure should be 900mm internal.  The minimum internal width of any closet/cupboard should be 1000mm.

Spare Capacity

Taking a reasonable approach, the cabling system at the time of installation should be dimensioned to provide spare capacity as follows:

• Enclosures should be no more than 60% occupied at installation
• Pathways should be no more than 50% occupied at installation
• Cable trays should be no more than 50% occupied at installation
• Conduits should be no more than 50% occupied at installation

Environmental Factors

Cable Equipment

The equipment comprising the cabling system shall be suitable for the environmental conditions at the particular ECE Service.

The cabling system layout, including equipment room and distributor locations, shall consider cabling and network equipment environmental performance specifications and manufacturer’s recommendations.

Lightning Protection

Special consideration should be given to earthing practices in areas prone to lighting activity.  Protection against earth potential differences shall be provided for equipment connected to outdoor copper cabling.

Transient voltage protection for cabling shall be compatible with the earthing system provided at the facility. Particular attention needs to be taken where separate building earths may not be bonded.

Salt Spray

Particular care should be taken for installations in coastal regions to minimise the exposure of equipment to salt. The equipment enclosure shall not be installed in open areas.  Equipment room vents should be fitted with filters to minimise salt spray ingress.

Chemical Corrosion

Equipment enclosures shall not be located in or near areas for storing cleaning solvents and other chemical products which may create corrosive atmospheric or environmental conditions.

Temperature Control

Equipment enclosures shall be equipped with vented panels to facilitate air flow to dissipate the heat produced by active equipment and to maintain a comfortable working temperature.

Electromagnetic Compatibility

There are presently no EMC regulations covering cabling installations and systems. However, to facilitate satisfactory EMC performance of the overall SCS, the design of cable routes and pathways shall take due consideration of the recommendation included in AS/NZS 3080 ZA.1.3.3 and AS/NZS 3080 ZA.3.2.

Security

In general, it should be necessary to pass at least two points of restriction to access equipment.  This may be achieved by using lockable doors to rooms housing lockable equipment enclosures.