Replacing consumer switchboards in existing installations
This information bulletin was developed to assist industry, Licensed Electrical Contractors and Electricians in applying the correct procedure for the replacement of switchboards in existing installations. This procedure is intended to ensure that the alterations to existing installations are efficiently and safely affected.
Issue to consider under AS/NZS 3000:2018 Wiring Rules
If I replace a switchboard in an old installation with a modern switchboard is this considered a new installation for the purpose of AS/NZS 3000:2018 Wiring Rules?
Yes it is
Refer to Clause 1.9.3 Alterations, and repairs
Every alteration of an existing electrical installation shall be deemed to be a new electrical installation, and all relevant provisions of this Standard shall apply to every such alteration.
Therefore you should consider the following in planning your job:
- Clause 2.2.2, Arrangement of Electrical Installation (Maximum Demand).
- Clause 2.5, Devices for Protection against Overcurrent.
- Clause 2.6, Protection against Earth Leakage.
- Clause 2.10, Switchboards.
- Clause 5.3, Earthing System Parts.
- Clause 5.7, Earth Fault-Loop Impedance
Appendix I provides assistance in determining the protective device ratings and metric equivalent sizes for imperial cables used in alterations additions and repairs.
Scenario to assist you in your consideration
A house built in the early 1960s has a switchboard comprising semi-rewirable fuses. The consumer’s mains comprise 7/.052 (10mm2) copper conductors, the main earth comprises a 7/.036 (4mm2) copper conductor wrapped, clamped or soldered onto the water pipe.
In quoting the job you will need to consider the following:
- Will the 10mm2 mains meet the maximum demand requirements of a modern home
- Will the 4mm2 earthing system meet the minimum requirements of AS/NZS 3000:2018
- Will the earth electrode meet the minimum requirements of AS/NZS 3000:2018
- Will the equipotential (water pipe) bond meet the minimum requirements of AS/NZS 3000:2018
- What size circuit breakers will I need to protect imperial cables
- How many RCDs will I need to install
- How will I measure and record the verification readings once I have completed and tested my work
As part of the NT WorkSafe electrical safety proactive inspection regime you may be asked to explain why you chose to upgrade the switchboard without also upgrading the earthing system, especially the earth electrode (mandatory) and the equipotential bond, and potentially the consumer mains as well, you will need to be in a position to demonstrate how you came to your decision using AS/NZS 3000:2018 and AS/NZS 3008.1.1:2009 as a guide, and the fault loop impedance measurements you made at the time you verified the installation.
Copper Water Pipe used as Earth Electrodes in old houses
Old installations in the Northern Territory utilized the underground copper water piping as an earth electrode for the earthing system, the main earth conductor was attached to the water pipe at the point it emerged from the ground, usually external to the house.
This presents risks where the old underground copper water pipe corrodes and ruptures and is replaced with PVC piping. The replacement of all or part of the water piping may leave the installation without an effective earth electrode.
It is mandatory in the Northern Territory that the earth electrode be upgraded to a vertical earth electrode when the switchboard is replaced.
Galvanized Water Pipe used as Earth Electrodes in old Houses
Old installations in the Northern Territory utilized galvanized steel water pipe as a vertical earth electrode, in many cases this has now corroded away.
It is mandatory in the Northern Territory that galvanized steel earth electrodes be replaced when the switchboard is replaced.
NT WorkSafe information bulletin
- Installation of vertical earth (stake) electrodes
- A verification check sheet is available from the NT WorkSafe email@example.com
- Speak to a NT WorkSafe Electrical Safety Inspector before undertaking the upgrade if you are in doubt.