Arc fault protection in Australian low voltage switchboards - What are the requirements?

The mandatory requirements for protection against arcing fault currents in low voltage switchboards comes out of AS/NZS 3000:2018, clause 2.5.5 and applies to switchboards, while in service or undergoing maintenance that have a rating equal to or greater than 800A.

Clause 2.5.5 calls for supply conductors up to the line side of protective devices to be provided with insulation or separation.?In addition, switchboards must comply with one of the following:

1. ?Internal separation of Form 3b, 4a or 4b including i, h and ih for insulated busbars, barriers and insulated housings (to reduce the probability of an internal arcing fault forming)
2. The use of protective devices providing automatic disconnection (to limit the effects of an internal arcing fault).
3. Both above

?

For measures that go above the mandatory requirements of AS/NZS 3000:2018, manufacturers may refer to AS/NZS 61439.1 Appendix ZC & ZD and IEC TR 61641. The application of which may further reduce an arc from forming and the risk that internal arcing faults present to operators and equipment.

?

Appendix ZC is an informative part of AS/NZS 61439. It gives guidelines to manufacturers on the design objectives which may provide increased security by prevention or control of arcing faults under normal operating conditions.?Some means to achieve this are:

1. Provision of insulating systems
2. Vented compartments designed to promote rapid extinguishing of an arc
3. Use of fault current limiting protective devices
4. Use of arc detection or similar devices

?

Appendix ZD specifies tests for the verification of any increased security provided by the design.?This section describes:

1. Standard tests, in which an arc is initiated on the load side of the protective device within a compartment.?
2. Special tests in which an arc is initiated on the line side of a protective device within a compartment.

?

The Appendix ZD tests are only valid for ?switchboards of the same design, rated voltage and current as the switchboard tested. Any significant changes to a design may lead to further testing i.e. smaller compartments, provision for venting. Tests are performed on a range of different protective devices and frame sizes from different OEM's.?The tests described are generally only applicable to outgoing units.

?

IEC TR61641 is also not mandatory but gives guidance on testing switchboards under arcing conditions in the air due to internal fault.?The report includes arcing classes for switchboards and construction requirements of arc ignition protected zones.

?

An arc ignition protected zone is part of a switchboard where measures are provided to ensure the ignition of an arc is a remote possibility.?The constructional requirements may include:

1. Insulating conductive parts such as busbars
2. Installing insulating barriers
3. Increasing phase to phase or phase to earth clearances.

?

It should be noted that the occurrence of an internal arc cannot completely be excluded but the risk may be significantly reduced.?The measures described in AS/NZS 61439 & IEC TR 61641 apply to switchboards under normal operating condition.?Maintenance is not considered a normal operating condition and an arc flash assessment may be required before performing this work.

?

Through maintenance and verified designs the aim is to prevent the occurrence of an arc fault before trying to manage the consequences.?

?

At Mayfield we are industry experts in low voltage switchboards.?We can offer a large selection of verified Appendix ZD, standard and special designs including arc ignition protected zones and remote ACB operation in our Moducell and Okken switchboards.?We pride ourselves on the ongoing development of our switchboards which supports the requirements of our clients.?

?

Talk to us about our arc fault protection features and the services that we can provide on-site through ongoing switchboard maintenance and support.