Section 13 electrical_installation_planning

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Section 13

Electrical installation planning

Copyright ©2011 Pearson Australia (a division of Pearson Australia Group Pty Ltd) – 9781442523258/Hampson/Electrotechnology Practice/2nd edition

Design considerations

An installation consists of the electrical wiring and connected components and fittings, including permanently wired stationary appliances, but excludes portable equipment and appliances.

The design of an electrical installation must take into account the proposed electrical load, the circuit system design, environmental aspects in which the electrical system is to be installed, client requirements, type of service to be supplied, legislation, local service rules and the AS/NZS 3000:2007 Wiring rules.


Design considerations

The electrical installation must:

safely deliver maximum demand

include correctly rated protection devices for safeguarding against over-current, fault current and earth leakage conditions

be controlled by a main switch(es)

be certified that it is electrically safe.


Supply characteristics

Frequency

Electricity supplies throughout Australia are usually an alternating-current (ac) sinusoidal waveform at a frequency of 50 Hz nominal (49.85 Hz to 50.15 Hz).

Frequency control is a function of the generation process and is generally maintained to within ± 0.2% of the nominal 50 Hz.

However, on occasions a generation event or a load event can change the frequency by a significant amount (called an ‘excursion’).



Current

While the supply to most installations in Australia is alternating current, some installations in remote areas use direct-current (dc) sources for electricity supplies. For example, energy from renewable fuel sources, particularly solar and wind, relies heavily on energy storage technologies such as lead acid batteries.



Voltage

Standard nominal voltages are: 230 V/ 400 V within a range of +10% and –6%, and 460 V, 6.6 kV, 11 kV, 22 kV, 33 kV, 44kV and 66 kV.

Standard low-voltage systems are three phase four wire 230/400 V, single phase 230 V and three wire 230/460 V.

The highest voltage allowed for a single-phase 230 V system is 253 V and the lowest voltage is 216 V.



Service mains current

To determine if an electrical installation (greater than 70 A) can be provided with the current required an electrical design consultant will need to design the installation using the electrical distributor standards and guidelines.



Possible design details required are:

Plan/layout of installation (switchboards, cable route, etc.) including a single-line diagram of the installation

Type of network connection: domestic, commercial, industrial, etc.

Total consumption and the method used to estimate load such as the AS/NZ 3000:2007 Wiring rules or VA/m2



Load patterns

Tariff details (low- or high-voltage supply)

CT metering (loads greater than 100 A)

Disturbing equipment (inverters, welders, etc.) and motor details

Transformer requirements (high voltage or low voltage)

Underground or overhead supply

Earthing details.



Prospective fault current

The prospective fault current is the maximum short-circuit current that can flow under short-circuit conditions at the point of supply within an electrical installation.

The value of the short-circuit current is reliant upon the size and impedance of the transformer and the impedance of the mains supplying the point of supply.



Protective earth

All new installations must comply with the requirements for the multiple earthed neutral (MEN) system of earthing as laid down in AS/NZS 3000:2007 Wiring rules.



Use of equipment

The equipment in an electrical installation must be arranged and operated so as to minimise or prevent adverse effects to the distribution system and other electrical installations connected to the distribution system.



Harmonics

Harmonics are generated when a load draws a non-linear current from a sinusoidal supply.

Switch-mode power supplies, used extensively in computer and IT equipment, or variable-frequency drives used to control electric motors can distort the voltage and current waveform.


Installation circuit arrangement

The creation of separate circuits in an electrical installation makes it possible to:

limit the effects of a fault to the circuit concerned

simplify fault-finding

carry out maintenance work, inspections, testing or circuit extensions without interrupting the whole electrical installation.


Installation circuit arrangementIn general the following circuit groups are used:

lighting—indoor, outdoor, communal

socket outlets—10 A, 15 A, 20 A

cooking—ranges, ovens, cooktops

fixed-space heating—air-conditioning, ventilation

water heating—instantaneous, storage, spa, swimming pool and laundry equipment

safety—emergency lighting, fire protection, security and for uninterruptible power supplies

power circuits for fixed plant—lifts, motors, kilns, welding machines, etc.

control circuits for fixed plant.



External influences

The design and erection of an electrical installation must be appropriate for the external environmental influences.

This means that all parts of electrical installations must be designed to be protected against environmental influences that may cause damage.

External influences mean the surrounding environment to the extent that it has an influence on the electrical installation.



An example of where external influences affect the design of an installation is where an aerial service is used.

An aerial service must be designed and erected in such a way that its construction and location guards against dangers to persons, livestock and property.

Therefore an aerial must be routed with an adequate clearance to ground, vegetation, other types of aerials, roadways and buildings.


Protection for safety

Refer to AS/NZS 3000:2007 Wiring rules, fundamental principles.

In electrical installations two major types of risk exist:

Shock currents

Excessive temperatures likely to cause burns, fires and have other harmful effects.

In addition to the two main areas requiring protection for safety—direct and indirect contact.



There are six other fundamental principles specified in AS/NZS 3000:2007 Wiring rules where protection is needed to minimise the risk of electric shock and fire:

protection against thermal effects

protection against unwanted voltages

protection against over-current

protection against the effects of fault currents

protection against the effects of over-voltages

protection against the hazards from mechanical movement.



Fire integrity

Refer to AS/NZS 3000:2007 Wiring rules, ‘Fire integrity’.

With the introduction of the Building Code of Australia (BCA), building designers have a system for defining the ability of a wall to resist the devastating effects of fire.

Section C of the building code defines the type and class of buildings and uses three building attributes to express fire-resistance levels (FRLs) as a triple rating in terms of minutes.



Labelling and circuit schedules

Circuit reference labels of Traffolyte with black letters on a white background or other approved non-deteriorating material, fixed by means of screws, rivets or glue, must identify every relay, pushbutton, fuse, circuit breaker, switch, meter, indicator light, terminal block, motor and other apparatus including all socket outlets and light switches in commercial and industrial installations.



The circuit schedule must be installed in each switchboard in a circuit schedule holder with a clear plastic sheet.

All main switchboards in commercial and industrial installations should also have a reduced copy of an up-to-date version of a single-line circuit diagram representing the circuits controlled by the switchboard.


Seasonal and daily variations of electrical demand


Factors affecting the suitability of a wiring system

Wiring systems and accessories should be installed in locations that prevent them from being subject to mechanical damage, dampness, corrosion, chemical attack, insect attack, heat and other damaging environmental conditions.

When selecting the wiring system and cable type the systems electrician must consider these influences.



Wiring systems can consist of the following types of cables:

single-insulated cables

sheathed or armoured and sheathed cables

mineral-insulated and metal-sheathed cables

served mineral-insulated and metal-sheathed cables

fire-resistant sheathed cables



The types of wiring systems that can be used depending upon the type of cable are:

resting on a continuous surface fixed or without fixings, in free air or in thermal insulation

in a wiring enclosure such as conduit, duct, trunking or other approved enclosure

supported on a cable tray or ladder

supported by a catenary system

buried direct in the ground

buried within a wiring enclosure in the ground



Current-carrying capacity

Refer to AS/NZS 3008.1.1:1998 (Australia) or AS/NZS 3008.1.2:1998 (New Zealand) Electrical installations—Selection of cables, Section 3, ‘Current carrying capacity’.

The current-carrying capacity of a cable is dependent upon the type of conductor material, its cross-sectional area (CSA), method of installation (may require a de-rating factor) and external influences that affect the allowable operating temperature of the cable insulation.



Different methods of installation will affect the rate at which the heat generated by the current flowing in the conductor is dissipated to the surrounding environment.

A cable installed in air and clipped to a flat surface will be able to dissipate heat more easily than a similar cable which is within a wiring enclosure buried in the ground.



PVC is probably the most usual form of cable insulation, and is very susceptible to damage by temperatures above 90 °C.

Therefore the current ratings of the various CSA conductors using PVC as an insulant are designed to ensure that this will not happen.



Ambient temperature

The current-carrying capacities of cables are based on a defined ambient air and soil temperature.

AS/NZS 3008.1.1:1998 Electrical installations—Selection of cables is applicable to Australian installation conditions where the nominal ambient air and soil temperatures are 40 °C and 25 °C respectively.

New Zealand installation conditions are 30 °C and 15 °C respectively (AS/NZS 3008.1.2:1998).



Higher ambient temperatures prevent effective transference of heat from the cable to the surrounding environment.

Therefore cables used in ambient temperatures above the standard must have their current-carrying capacity reduced.

Operating cables at their normal current-carrying capacity and above the allowable ambient temperature will cause their electrical insulation to age at an accelerated rate.



Soil conditions

Extreme soil and environmental conditions exist where the ambient temperature exceeds 40 °C.

Hot, dry conditions in the summer create a very dry soil which produces a high thermal resistance.

Under such conditions, the environmental and soil parameters significantly influence the current-carrying capability of the cable.



Some loads connected within an installation may be cyclic in nature and a designer could upgrade the current-carrying capacity of proposed cables above those recommended in AS/NZS 3008.1.1:1998 Electrical installations—Selection of cables.

This type of variation must have documentation to support the proposed cable CSA.


Coordination between protection devices and circuit conductors

Wiring

A commonly overloaded component of an electrical system is the wiring.

The correct current-carrying capacity of a cable is a function of its insulation, temperature rating, the type of enclosure in which it is installed, number of conductors being installed in a common enclosure and whether it’s above ground or underground.



The operating characteristic of each protective device protecting a cable from overload and short circuit should satisfy the following two conditions:

The normal current or current setting (IN) of the protective device is not less than the design current (IB) of the circuit. To avoid overheating the cable insulation it is essential that the maximum sustained current (IB) carried by a cable should be less than or equal to its current carrying capacity (IZ).



The normal current or current setting (IN) of the protective device does not exceed the lowest of the current-carrying capacities (IZ) of any of the cables of the circuit. Therefore:

IB ≤ IN ≤ IZ Condition 1 (for coordination)



To ensure that the life of the cable insulation is not significantly shortened, protective devices should have an effective current tripping rating (I2) of: -

I2 ≤ 1.45 IZ Condition 2 (for overload)

The factor 1.45 is the fusing factor of the protective device.

Fusing factor = I2 / IZ


Using AS/NZS 3000:2007 for current-carrying capacity

Reference to current-carrying capacity is found in Clause 3.4.1, AS/NZS 3000:2008 which states:

Every conductor shall have a current-carrying capacity, in accordance with the AS/NZS 3008.1.1 Electrical installations—Selection of cables series, not less than the current to be carried by the conductor.

Therefore all current-carrying capacity calculations are made using AS/NZS 3008.1.1.


Using AS/NZS 3000:2007 for current-carrying capacity

Current carrying capacity of consumer's mains

Clause 1.4.33, AS/NZS 3000:2007, provides the definition for consumer’s mains while AS/NZS 3008.1.1 provides elements which are to be considered when determining the minimum size of consumer’s mains. These are:

type of conductor, type of cable

installation conditions, external influences on cables

voltage drop, short-circuit performance


Using AS/NZS 3000:2007 for current-carrying capacity In simple terms the selection of a cable involves

the selection of the correct table and then applying any necessary de-rating factors to the current-carrying capacity of the cable.


Using AS/NZS 3000:2007 for current-carrying capacity In order to understand ‘de-rating’ read Clauses 3.1

to 3.5 of AS/NZS 3008.1.1.

De-rating factors must be applied when:

cables are installed in air and the ambient temperature exceeds 40 º C (see Clause 3.4.2)

cables are grouped (see Clause 3.5.2).


Using AS/NZS 3000:2007 for current- carrying capacity

De-rating factors must be applied for underground cables if the:

ambient soil temperature exceeds 25 ºC (see Clause 3.5.3)

depth of laying exceeds 0.5 m (see Clause 3.5.4)

thermal resistivity of the soil exceeds 1.2 ºC m/w (see Clause 3.5.5)

cables are contained within wiring enclosures (see Clause 3.4.5d).



Current-carrying capacity of sub-circuits

The cable selection procedure for sub-circuits requires application of one of the following.

Using AS/NZS 3008.1.1 to determine maximum current-carrying capacity for a predetermined cable size or select a cable size to deliver a known demand current capacity



To determine the current-carrying capacity of a given cable apply the following:

Select the chosen installation method by reference to Table 2 (1 to 4), columns 3 and 5.

Refer to column 4 of Table 2 to obtain the reference table and column for the given current-carrying capacity of the cable. Note the de-rating requirements of Table 2, column 6, and the corresponding footnotes to the referenced table. After going to the referenced table record the current-carrying capacity of the known cable.

Apply any de-rating that the referenced table requires (refer to table notes).

Record the current-carrying capacity of the known cable.


Protection of cables against short-circuits


Solar radiation

Solar radiation effects must be taken into account when calculating the maximum current-carrying capacity of aerials, flexible cables and other types of cables for given environmental conditions, or when finding the time over which mitigation actions may take place.

In order to find the maximum current-carrying capacity of these cables it is necessary to consider thermal effects such as ambient temperature (°C), wind speed (m/s) and intensity of sunlight (W/m2).


Grouping of cables

Where a number of circuits are installed together, de-rating factors must apply because the cooling of the cables within the surrounding environment has been affected. All cables within the group that carry their rated current will experience an increase in temperature.

In addition to additional heating by conduction, convection and radiation from other cables, induction heating can also occur. Because of this, cables installed in groups are de-rated to determine their current-carrying capacity.


Selecting cables for consumer’s mains and sub-mains

Maximum demand of an installation

Clause 1.6.3 states that the consumer’s mains and sub-mains shall be installed to meet maximum demand.

The maximum demand of an installation is defined as the electrical loading of the installation.

This means that the conductor CSA of consumer’s mains and sub-mains must be able to carry the electrical demand.



Methods of determination of maximum demand

AS/NZS 3000:2007, Appendix C, recommends four methods for determining the maximum demand of consumer’s mains or sub-mains:

assessment

limitation

measurement

calculation



Assessment of maximum demand can be based on the duty cycle or the load characteristics of the installed equipment. For example, the maximum demand of a single-phase 3.6 kW water storage heater can be calculated by dividing the power by the nominal equipment voltage (230 V) to give a current of 15.65 A.

In the larger commercial and industrial installations where the load characteristics of the type of occupancy or the floor area and system of climate are known, the maximum demand may be assessed.



Limitation method

A fixed setting or an adjustable circuit breaker protecting all the associated final sub-circuits may be used to limit the maximum demand of consumer’s mains and sub-mains.

Alternatively, the maximum demand could be determined by the summation of the current settings of the circuit breakers protecting the final sub-circuits.



Measurement method

The maximum demand of an existing electrical installation may be measured by a maximum demand indicator (provides a guideline to the maximum current drawn) over 15 minutes or measured by the use of a data logger that measures in 15-minute intervals over a seven-day period.



The maximum demand may be calculated by following the directions in Appendix C of AS/NZS 3000:2007 for the suitable category of electrical installation. Two tables are recommended.

Note: Table 3.1 of AS 3018.1.1 is identical to the single domestic installation Table C1. Tables C1 and C2 apply the principle of diversity, which takes into account the normal operating conditions of circuits during which all equipment is not operating simultaneously at full load or for periods exceeding 15 minutes.



Diversity is applied in the calculation method on the basis that the percentage of people, lights, equipment and so on that are on (or present) simultaneously compared with the total design demand may not occur at the same time. As a consequence, the consumer’s mains or sub-mains are not required to carry the real full-load current of the installation at any one time.



The AS/NZS prescribed calculation method accounts for all items of electrical equipment connected to the main or sub-main circuits together with the appropriate diversity factors for different types of loads.

This method of assessment is generally used by installation designers for domestic installations.



In general, the maximum capacity for single-phase two-wire domestic consumer’s mains is 70 A. If the installation is larger than this either a two-phase and neutral system (70 A per phase) or a three-phase and neutral four-wire system (when demand is over 140 A) will be used. However, it is the local distribution entity in each state or territory which determines the type of supply to be used (e.g. less than 100 A uses a single-phase two-wire system; greater than 100 A uses a three-phase and neutral four-wire system).


Calculation method


Voltage drop

Voltage drop is dependent upon the impedance of the cable, the size of the circuit current and the circuit power factor.

While the impedance of circuit conductors within an installation is of a small value when carrying circuit current, a voltage drop does occur between the origin of the circuit and the load terminals.


Voltage drop


Voltage drop

Reduced voltage

Reduced voltage can cause nuisance in lighting circuits from flickering lights.

Power circuits may experience unreliable performance from electromechanical devices such as relays and contactors.

Generally speaking motor speed is a product of voltage and reduced voltage means lower speed.


Voltage drop

Voltage sags are a partial reduction in rms voltage that usually lasts from 0.5 to 30 cycles while a momentary interruption is a complete loss of ac power which can be 0.5 cycle to minutes in duration.


Voltage drop

Cable size is sometimes governed by voltage drop rather than by heating.

This occurs when the circuit route length is long and these long circuit lengths may require larger CSA conductors for a given current.

The CSA of each series-connected circuit cable should be chosen such that voltage drop from the point of supply to the load does not exceed the statutory requirement.


Voltage drop


Fault-loop impedance requirements and cable size


Tariff structures

A tariff is the agenda of an energy distributor, containing all rates and charges stated separately by type of service, the rules and regulations of the utility and any contracts that affect rates, charges, terms or conditions of service.

The kilowatt hour (kWh) is the unit in which electricity is sold to the buyer with different price tariffs for peak and off-peak usage.

The peak period is defined as 6 am to 6 pm inclusive on any day.


Tariff structures

Tariffs are charged to recover costs associated with generation and for the general provision of supply and maintenance of the network of poles, cables and electrical equipment that distribute power to consumer’s premises.


Tariff structures

Domestic light and power tariff

This is the electricity tariff for all light and power in general domestic (homes, units and flats) usage and is in the form of progressive rates. (The following rates are illustrative only.)

First: 3.2877 kWh/day @ 13.96 cents/kWh

Next: 7.6712 kWh/day @ 16.08 cents/kWh

Thereafter: 12.43 cents/kWh


Tariff structures

General supply tariff

This tariff structure is similar to that of the domestic light and power tariff due to similar load patterns.

Users of this tariff are non-domestic and include hotels, schools, shops, clubs and so on.

Specific businesses may have a high-voltage supply and their tariff pricing will vary from the general supply tariff.


Tariff structures

Off-peak or controlled load tariffs

Making the maximum use of off-peak energy supply arrangements is important in keeping energy costs down. Off-peak consumption may be as little as one-half or even one-third of the cost of the normal general supply tariff.

Operation of electrical equipment should therefore be examined to ensure off-peak supplies are used wherever possible.

The hours of energy delivery are usually controlled by a time switch or relay.


Tariff structures

Demand tariffs

Demand tariffs are generally suitable for large customers (hospitals, 24 hour supermarkets, etc.) with a minimum usage of around 160 000 kWh per year.

Usually a load test and a 12 month energy usage pattern are required to determine whether a demand tariff is suitable.

Load shifting or correcting the power factor of the electrical installation will produce real energy cost savings with demand tariffs.


Switchboards—distribution relationship


Sub-mains

A sub-main circuit can be defined as a circuit connected directly from the main low-voltage switchboard to any other sub-main distribution board.

The CSA of any sub-main cable must be able to carry the maximum demand of the portion of the installation it is supplying.

When an electrical supply is required for outbuildings such as a detached workshop, garage or garden shed, sub-mains are used to supply the power from the main switchboard.


Sub-mains

Each sub-main circuit is required to have its own protection device at the main switchboard.

In addition, each sub-main circuit may have an earthing conductor connected at the main switchboard earthing bar and taken to the earthing bar on the sub-mains distribution.

Alternatively, an MEN system may be established at the outbuilding with a separate earth stake.

RCD protection at outbuildings or on the sub-main circuit is recommended.


Final sub-circuits

The electrical distribution within an installation ends with final sub-circuits.

A final sub-circuit is that section of a wiring system that extends beyond the final circuit protection device.

Final sub-circuits can originate from either a main switchboard or a sub-main distribution board.


Final sub-circuits

Final sub-circuits make up the greatest wiring part of an electrical installation and are divided into four general groups:

Lighting circuits

Socket outlet circuits

Fixed-wiring circuits (appliances)

Fixed-wiring circuits (range, ovens, cooktops,

water heater)


Switchboard design and arrangement of equipment

Switchboard design and arrangement of equipment on the panel board depends on several factors:

the load demand of the installation and the number and type of circuits required

the prospective fault current

fault current rating of the switchboard (residential switchboards should have a minimum fault rating of 6 kA)

accessibility, location and environmental conditions


Switchboard design and arrangement of equipment


Mounting of equipment

The mounting of equipment within a switchboard shall comply with AS/NZS 3000:2007 Wiring rules and local energy distributor requirements where applicable.

Equipment to be fixed on the mounting chassis plate should be achieved by means of bolts, washers and nuts or by bolts screwed into tapped holes in the chassis plate. In the latter case the minimum thickness of the chassis plate should not be less than 2.5 mm. Self-tapping screws are not an acceptable method as the screws may penetrate cables.


Busbars

Busbars are constructed in the form of straps which are first cut to length and can be provided with sets of punched holes through which bolts are received for mounting the busbars on suitable supports within a switchboard, for connecting them to each other and for mounting electrical cable connectors thereon.

All busbars should be of solid drawn, high-conductivity copper. However, other types of material such as aluminium, brass and copper-clad aluminium are also used.


Busbars

Busbars if joined together should overlap for a distance equal to twice the width of the bar to prevent localised heating.

Copper and brass contact surfaces should be tinned (acid-base flux may not be used) or silver-plated and bolted together with cadmium-plated bolts and nuts.


Busbars


Busbars

Busbars are usually provided for the following applications:

distribution of supply voltage (phase or active busbars)

connection of equipment with ratings exceeding the current rating of 70 mm2 conductors

connection of outgoing circuits with current ratings in excess of that allowed for 70 mm2 conductors

collector bars for parallel cables


Busbars

connection bars for neutral conductors (brass busbars)

connection bars for earth conductors (brass busbars)

busbar connections to miniature circuit breakers in domestic switchboards (comb-type copper busbar).


Equipment for damp situations

A damp situation is a location of high risk in which moisture is either permanently present or occasionally present to such a degree as would be likely to weaken the effectiveness of cable insulation or endanger persons and equipment.

Precautions to be taken are therefore thorough. Electrical installations containing damp situations must comply with Section 6, AS/NZS 3000:2007 Wiring rules, ‘Damp situations’.



A damp situation includes the following:

locations containing baths, showers or other fixed water containers (sinks, laundry tubs)

swimming pools, paddling pools and spa pools or tubs, fountains and water features

locations containing sauna heaters

refrigeration rooms—cold rooms, freezer rooms and locations where general hosing down operations are carried out

no switchboard is allowed in any damp situation.



Protective measures against electric shock

AS/NZS 3000:2007 Wiring rules does not allow the following direct contact protective measures against electric shock in baths, showers and other fixed water containers:

protection by obstacles

protection by placing out of reach.



The protective measures, separated extra-low voltage and protected extra-low voltage may be used in a location containing a bath or shower, subject to the following requirements.

The only protective measures against electric shock permitted in zone 0 is SELV or PELV at a nominal voltage not exceeding 12 V ac rms or 30 V ripple-free dc with the safety source being located outside of zones 0, 1 and 2.

The only electrical equipment allowed in zone 0 is an IPX7-rated luminaire or one designed for damp situations and supplied by an SELV or PELV voltage.



Degree of protection

Every item of electrical equipment to be used in damp situations must be selected and installed so as to be suitable for the environmental influences likely to occur at the point of installation.

Environmental influences are likely to include falling drops of water, sprays/jets of water from shower heads or vegetable sprays and steam.



Socket outlets

Shaver supply units complying with AS/NZS 3194:1993 and socket outlets supplied by SELV or PELV circuits are permitted in bath, shower, laundry or other similar locations but must be installed outside of zones 0 and 1.

Socket outlets can be installed in zone 2 provided they are protected by a 30 mA RCD and installed in a cupboard or are of the automatic switching type or a shaver supply unit complying with AS/NZS 3194:1993.



Socket outlets

Socket outlets can be installed in zone 3 provided they are protected by a 30 mA RCD or supplied individually as a separate circuit (washing machine, clothes dryer, ironing station circuit) or supplied as an SELV or PELV system.


Swimming pools, paddling pools and spa pools or tubs

A location containing a swimming pool, paddling pool, spa pool or tub is considered to be a location where there is an increased risk of electric shock due to:

a reduction in body resistance caused either by complete wetness or by moist skin

likely contact between significant areas of the body and earth potential.

The requirements for the safety of people and equipment in these locations are based on the application of a zonal model.



Equipotential bonding

Where any electrical equipment in a classified zone is required to be earthed then all extraneous conductive parts in the other zones require supplementary equipotential bonding if they are within arm’s reach of the pool’s edge.

This is to prevent the occurrence of voltages between any such extraneous conductive parts of such magnitude as could cause danger of electric shock.



Examples of parts that may be found in a swimming pool, paddling pool and spa pool or tub situation that may meet the definition of an extraneous conductive part if they are within arm’s reach of the pool’s edge include: Metallic fences and gates, metallic heating pipes and metallic light poles and columns

Accessible metallic structural parts of the building (metallic door architraves, window frames and similar parts are not considered to be extraneous conductive parts unless they are connected to metallic structural parts of the building).




Every item of electrical equipment to be used in swimming pool, paddling pool, spa pool or tub classified zones must be selected and installed so as to be suitable for the environmental influences likely to occur at the point of installation.



Socket outlets

Socket outlets for pool equipment only supplied by separate circuits or protected by a 30 mA RCD or SELV or PELV circuits are permitted in swimming pool, paddling pool, spa pool or tub locations but they must be installed outside of zone 0.



Fountains and water features

A location containing a fountain and/or water feature is considered to be a location where there is an increased risk of electric shock due to:

a reduction in body resistance caused either by complete wetness, partial wetness or by moist skin





Every item of electrical equipment to be used in fountain and water feature classified zones must be selected and installed so as to be suitable for the environmental influences likely to occur at the point of installation.


Saunas

A location containing a sauna heater is considered to be a location where there is an increased risk of electric shock due to:




Saunas


Refrigeration rooms—cold rooms, freezer rooms

A location containing a refrigeration room is considered to be a location where there is an increased risk of electric shock due to:




Locations where general hosing down operations are carried out

A location where general hosing down operations is considered to be a location where there is an increased risk of electric shock due to:

a reduction in body resistance caused either by complete wetness or by moist skin.



Voltage definitions

Extra-low voltage

Refer to AS/NZS 3000:2007 Wiring rules, ‘Extra-low voltage electrical installations’.

Extra-low voltage as defined in AS/NZS 3000:2007 Wiring rules is a voltage not exceeding 50 V ac or 120 V ripple-free dc.

Extra-low voltage is a measure designed to protect people and livestock from direct and indirect contact with live parts without automatic disconnection of the supply.


Voltage definitions

Separated extra-low voltage (SELV)

Protection by SELV is used in high-risk situations where the operation of electrical equipment presents a serious hazard, for example swimming pools.

This method of protection requires supplying power from a safety isolating transformer (uses double or reinforced insulation).

For zone 0 containing water containers the nominal voltage must not exceed 12 V ac or 30 V ripple-free dc.


Voltage definitions

These conditions of use must be applied when using SELV to provide protection against indirect contact:

No live conductor at SELV potential must be connected to the earth.

Exposed conductive parts of SELV circuits or equipment must not be connected to the earth, other circuits and their exposed conductive parts or extraneous conductive parts.


Voltage definitions

In SELV systems where the voltage does not exceed 25 V a.c. or 60 V ripple-free d.c. there is no need to provide protection against direct contact hazards.

Each SELV circuit must be segregated from all other wiring systems including other SELV systems. Segregation may not be required in some situations. Socket outlets and plugs for a SELV wiring system must not have an earth-pin contact and must be of a design that prevents connection to a different voltage level.


Voltage definitions

Direct and indirect protection of a SELV wiring system is provided by:

the extra-low voltage

the low risk of accidental contact with a higher voltage

no return path through a protective earth that a current could take in case of contact.


Voltage definitions

Protected extra-low voltage (PELV)

This type of wiring system is used where low voltage is required but the situation is not as high risk as with SELV wiring situations. A PELV power supply includes two protective measures (double insulation) against direct and indirect contact with exposed conductive parts by means of a safe separation of the primary and secondary transformer windings (e.g. IP2X or an insulation rating of 500 V ac for one minute). For this reason no separate protective earth conductor is required in a PELV system.


Hazardous areas

There are particular environments where special competencies concerning knowledge and skill need to be exercised so that electrical equipment does not provide the energy and temperature to act as an ignition source.

A system for categorising these particular environments with potentially explosive atmospheres has been developed. These particular environments are called hazardous areas.


Hazardous areas

Fire and explosion

A fire or explosion can occur when a flammable gas, vapour or mist, dust or powder is mixed with oxygen in the air in suitable proportions to create a hazardous zone.

The extent of a hazardous zone is in all directions from the point of release to where the ratio of fuel to air results in no risk.


Hazardous areas

For a fire or explosion to occur three conditions must be present:

There must be a fuel.

There must be sufficient oxygen.

There must be a source of ignition.


Hazardous areas

Zones

Hazardous areas are classified into zones based upon the frequency of the hazardous occurrence from the point of release, the duration of the explosive fuel mixture and the quality of ventilation.

Hazardous zoning makes possible the proper selection and installation of electrical equipment that can be used with safety in those zones.


Hazardous areas

Gas zones

For gas hazardous areas each gas zone is defined by the proportions, amount and volume of the hazardous gas that can be expected.

Dust zones

There are three hazardous areas for dusts


Hazardous areas

Ex certification

In Australia, design standards such as AS 2381.7:1989 Electrical equipment for explosive atmospheres specifies the design, manufacturing and testing measures to which electrical equipment intended for use in a hazardous area should be produced.

Electrical equipment conforming to Australian standards will have a Certificate of Conformity and the electrical equipment is then classed as ‘Certified Equipment’.


Hazardous areas

Standards

Table 13.11 refers to some of the Australian standards that govern the certification and installation of electrical equipment in hazardous areas. Additional Ex related standards are:

AS/NZS 60079.10:2004 Electrical apparatus for explosive gas atmospheres—Part 1

AS/NZS 61241.14:2005 Electrical apparatus for use in the presence of combustible dust—Selection and installation


Hazardous areas

Standards

AS 60529:2004 Degrees of protection provided by enclosures (IP Code)

AS/NZS 1768:2007 Lightning protection

AS/NZS 4761:2003 series Competencies for working with electrical equipment for hazardous areas.

All persons who are directly involved with hazardous areas must be trained to recognise the Ex hazard classifications.


High voltage

The term ‘high voltage’ applies to electrical equipment that operates at more than 1000 V ac rms or 1500 V dc.

The government Electrical Safety Act, regulations, AS/NZS 3000:2007 Wiring rules and codes of practice and High Voltage Isolation and Access Procedures Manuals must always be consulted when any high-voltage work is to be undertaken.


High-voltage procedures

Work on, near or associated with high-voltage production and consumption devices and service lines should only be carried out on the authority of certified access permits and switching schedule sheets.

Written lockout, isolation and switching events are an essential part of high-voltage procedures before any work is planned on de-energised production and consumption devices and service lines.



A switching schedule sheet defines the sequence of each individual operation for the isolation, testing and earthing of the production and consumption devices and service lines to be worked on.



In addition, a list of personnel who will work in the high-voltage location needs to be established. This enables the person in control to restrict their tasks within the bounds of their experience,

responsibilities and authorisation.



All persons required to enter the work area should sign the Permit-To-Work access.

At the completion of work, all signatories must be informed before any temporary cables (earths) providing protection to the workers are removed and the reverse switching sequence engaged.


Safety clearances and high voltages

Details of clearances (exclusion zones) for untrained, instructed, authorised persons and for safety observers are detailed within codes of practice for electrical work and the electrical safety regulations.


END

Section 13 electrical_installation_planning

Business

Transcript of Section 13 electrical_installation_planning