Repair guidance information for flood affected switchboards

Flood water due to its many contaminates will pose a serious ongoing risk to all affected switchboards.

Where switchboards have been partially or fully exposed to flood water, all components are at risk of further ongoing corrosion and galvanic effects causing high resistance in active and neutral conductive paths within the switchboard.

Bus bar assemblies, the metal fixings holding insulating mounting supports and mounting panels used to fix isolation/protection switchgear will be exposed to ongoing corrosion.

Corrosion will also affect the metal structure of the switchboard which relies on all segments of a switchboard enclosure for a continuous low resistance earth path as a protective electrical barrier.

All protective switchgear will be considered unrepairable and will need replacement.

This also includes any control equipment, SPD’s, Power factor correction, CT’s, metering and any electronic devices.

The only exception will be where the original equipment manufacturer can provide an inhouse repair and subsequent test certificate to confirm the device is operational to the original manufactured specification.

Switchboard Assessment

32-250A Main-Distribution boards (approximate current ratings)

Small scale distribution boards may have been manufactured from single components (protective switchgear, small bus systems, neutral-earth bars, and an enclosure) or supplied as a complete assembled product.

Replacement of the protective switchgear, extensive cleaning of contaminants from the enclosure and the re-termination of all conductors will need to be considered unless complete replacement is a viable option. Depending on the degree contamination including condensation and the length of time before maintenance is performed, rust prevention should also be considered on steel components.

250- 650A Main-Distribution switchboards (approximate current ratings)

This type of switchboard is predominately manufactured to AS/NZS 3439 or 61439 by a switchboard manufacturer.

The same maintenance requirements will apply as described for small scale switchboards. It is advised to contact the manufacturer for advice on specific risks to the equipment and if possible, provide the manufacturer with photos of the complete switchboard or preferably in conjunction with a site visit to assess the required repair actions.

800A and above Main switchboards

High current switchboards of this rating will require assistance from the manufacturer. The correct replacement of functional units where the original specified switchgear is no longer available will require a documented engineered solution. A discrimination study may need to be engineered to ensure protective devices meet the reliability of only the specific fault is disconnected and the kA rating is in excess of the available prospective fault current. Thermal heat rise is also to be considered using the original type tested assembly results.

Consultation with Industry Specialists

It is essential that when any repairs are considered, the manufacturer if still available be consulted. Where this is not possible, engage the services of a manufacturer of the same level of expertise to advise on functional unit substitution and parts/fixings specifications.

Consultation with the Owner

The urgency to re-establish supply to the installation is of paramount importance to the owner but not at the cost of the ongoing reliability and safety of the installation.

Critical replacement of electrical equipment can be the first priority with the acknowledgement from the owner that important subsequent repairs are to be done on the switchboard parts that may not be immediately impaired but over time will fail.

Document as soon as possible a repair timetable identifying each part of the process from procurement to installation and then timely additional procurement and installation of lessor priority repairs but essential to the ongoing reliability and safety of the design.

This will assist insurance claims for all costs required to bring the switchboard back to a compliant status.

Pre-repair considerations

It is necessary to consult with the owner of the installation to assess the risk of future flood conditions.

Where the site and environment cannot be flood mitigated by other means, the re-location of the switchboard to a higher position within the building should be a serious consideration of the owner.

Local council flood assessment or by hydraulic engineering assessment may assist in the decision of relocation in conjunction with the insurer’s involvement.

Parts Replacement

Where the original specified parts can be sourced, the dis-assembly-reassembly process is straight forward.

High current terminations of switchgear/fusing and conductors/buss bars will require fixings to be correctly tensioned using a torque wrench to the products termination specifications.

Fixings (washers, nuts, and bolts) will need to meet the tensile strength specified by the manufacturer and be corrosion rated for the applications environment.

Assembly/Buss insulation and their insulated supports will need to be insulation resistance tested at specified voltage levels to ensure effective insulation.

Supply and outgoing conductors

All supply conductors (PEN), the MEN link and main earth termination need to be disconnected and inspected for any corrosion or damage and re-terminated.

Note: the main earth connection to the building earth electrode/conductive terminal should also be disconnected and re‑terminated to ensure the installation has a low resistance connection to the general mass of earth.

Subcircuits and final subcircuits terminations may need to be re-terminated as exposed portions of the conductor may have suffered oxidation.

Enclosure assessment

Where the protection devices, switchgear and neutral-earth fault loop paths have been confirmed by low resistance tests, consideration shall be extended to the metal enclosure and internal form factor barriers assessed for corrosion and oxidisation.

It is essential that the customer understands ongoing maintenance and replacement of the enclosure fixings and earthing washers will need to be performed in an organised shutdown. This will also identify to an insurer that the complete costs of rectification may not be initially confirmed and an allowance for additional costs will be needed.