Electrical Panels

Should PEN be considered as live part?

A live part is a conductor or conductive part intended to be energized in normal use, including a neutral conductor but, by convention, not a PEN conductor.

What does tracking mean for isolating materials?

The progressive formation of conductive paths which are produced on the surface of a solid isolating material, due to the combined effects of electric stress and electrolyte contamination on this surface, is called tracking.

What is the recommended rated short circuit current withstand time for LV electrical panels?

AS/NZS 3439.1:2002, instructed 1 sec. rated short circuit current withstand time, unless otherwise stated by the manufacturer. If the time is shorter than 1 sec. both the rated short circuit current and the time should be stated, for example 20 kA, 0.2 sec.

What is the recommended rated frequency for LV electrical panels?

AS/NZS 3439.1:2002 – Unless otherwise stated by the manufacturer of the assembly, the limits are assume to be 98% and 102% of the rated frequency.

What degree of pollution can the normal industrial environment be categorised?

Pollution degree definitions are as below.

Pollution degree 1
No pollution or only dry, non-conductive pollution occurs.

Pollution degree 2
Normally, only non-conductive pollution occurs. Occasionally, however, a temporary conductivity caused by condensation may be expected.

Pollution degree 3
Conductive pollution occurs or dry, non-conductive pollution, occurs which becomes conductive due to condensation.

Pollution degree 4
The pollution generates persistent conductivity caused, for instance, by conductive dust or by rain or by snow.

Unless otherwise stated, assemblies for industrial applications are generally for use in a pollution degree 3 environment (AS/NZS 3439.1:2002).

What does capacitor formation serve in a FC unit?

If a FC (Frequency Convertor) unit has been non-operational for more than one year, The DC link capacitors have to be newly formed. If this is not carried out, the unit can be damaged when the line voltage is powered up.

What feeding load shall be considered to design a panel?

Definition below for load amounts is practical and could be changed based on project specifications. Loads are classified according to their nature as continuous, intermittent and standby duty. Intermittent loads are factored by a duty cycle to enable them to be summed with continuous loads into the average load.

Average load = Continuous load + Intermittent load × Intermittent factor

Maximum load = Average load + 200% of the largest standby drive on each board

Design Load = 110% of the average load + 200% of the largest standby drive on each board

The below figures also have been used in some projects.

Maximum load = Average load + the largest standby drive on each board

Design Load = 110% of the average load + the largest standby drive on each board

Is it permitted to switch the neutral or earthing conductor in the panel?

AS/NZS 3000, 2.3.2.1.1 – A switched neutral pole shall not open before and shall not close after the active poles.

AS/NZS 3000, 2.5.1 – No fuse shall be inserted in a neutral conductor.

AS/NZS 3000, 2.3.2.1.1 – Switching of earthing conductor prohibited. An earthing conductor shall NOT be isolated or switched.

Is it permitted to use semiconductor devices as isolation devices in an electrical panel?

AS/NZS 3000, 2.3.2.2.1 – A semiconductor (solid-state) device shall not be used for isolation purposes as isolation device.

What are restrictions in designing of electrical rooms’ design in which switchgears are installed?

AS/NZS 3000, section 2.9.2.2, sufficient access and exit facilities are considered to be the provision of the following:

  • Unimpeded space of at least 0.6 m around switchboards with switchgear doors in any position and large circuit-breakers racked out.
  • Adequate alternative emergency exit paths, where a switchboard
    • has a prospective short-circuit current of not less than 15 kA; or
    • is supplied by a circuit with a nominal capacity of not less than 800 A per phase; or
    • is more than three metres in length.
    • Openings or doorways that are at least 0.75 m wide by 1.98 m high to allow persons necessary access to the switchboard room or enclosure.

AS/NZS 3000, section 2.9.7.3, an opening with less than 5 mm diameter of free space is considered to be a close fit. Therefore, any opening of 5 mm diameter or greater requires sealing with a fire-retardant sealant.  Refer to wiring rules for complete requirements.

What are ARC FLASH hazard requirements in design?

There are a number of things that can be done during the design phase to reduce the arc flash risk posed by electrical installations.

Internally arc fault contained switchgear

Internal arc flash contained switchgear is designed and type tested to meet the IEC 62271.200 and TR 61641 standards for HV and LV assemblies respectfully. The design requirements for internal arc fault containment lead to reduce likelihood of initiating arcs and reduce risk f injuring people if an arc occurs. It is important to note that the internal arc flash protection afforded by switchgear is only valid when it is operated in the same way as it was type tested, that is as per the manufacturer’s instructions and with all doors and modules closed.

Arc detection system

A number of different arc flash protection devices are commercially available. These devises are designed to identify an arc fault in progress and energize elements to interrupt the fault. Protection devices shall be chosen to reduce spurious tripping and maintenance requirements, for example, devices that require both over current measurement and photo sensors to trip greatly reduce spurious tripping.

Remote switching and racking

Automation should be applied to remove operations from switchgears. The arc flash risk is removed if people are not exposed to the risk area around switchgear.

Arc flash hazard study

The study as best completed as part of power system modelling. The study will deliver as a minimum; the likelihood of initiating an arc for a list of standard activities, and consequences of an arc, in terms of arc energy.

The outcome of the study will also provide an opportunity to justify design modifications such as arc detection systems, switchgear automation and protection setting optimization in order to obtain effective health and safety outcomes.

Protection setting optimization

The nature of arc faults is high impedance across air and as such will have a lower fault current than a bolted fault. Consideration should be given to design of dual protection settings; protection settings for normal operation and separate protection setting for use during certain maintenance procedures in order to provide increased protection to personnel; this should be managed carefully under the procedure to ensure that the correct protection settings are in operation at any given time.

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