  
2. Technical CornerTechnical corner has been jointly produced by the Board, Energy Safety Service and Standards NZ Q Can an RCD be used as a main switch? A Yes, but please remember the following: - First, the RCD must be capable of handling the duties of being an isolator. This means that the RCD has to have an adequate "gap" when open to provide a safe isolation rather than just a switching operation.
- The RCD supplier should be able to advise whether the RCD is "isolation" rated.
- Second, unless the RCD is an RCBO type (which also acts as a circuit breaker), it should be remembered that the RCD will not provide overcurrent protection.
- Third, as the RCD will also be protecting the stove, water heater and any other permanently connected units, tripping can occur. This is because of the sum of the leakage currents involved. In addition, tripping can occur if there is a pilot wire for the water heater.
- Fourth, care must be taken that the MEN system is retained. That is a link between the supply neutral and the earth electrode is present.
- The neutral/earth link has to be established before the RCD (otherwise the RCD will trip). This may require two segments of neutral bar to be installed.
- Fifth, you need to consider whether using an RCD as a main switch is in the best interests of your client. Any fault that causes the RCD to trip will disconnect the entire installation (including all the lights) rather than just one or two circuits. Splitting the installation over at least two RCDs may well be a better solution.
- Finally, remember that it is permissible to have more than one main switch in an installation provided appropriate labelling is used. One or both of the main switches can also be a circuit breaker.
Q Is retrospective installation of RCDs required in domestic installations? A No. - The Electricity Regulations 1997 do not require retrospective installation of RCDs. However it must be remembered that when there is a change in use of an area (e.g., a change to a damp area) or a new final sub-circuit is being installed an RCD is required to be fitted.
- The RCD may be installed either on the switchboard or on the first socket outlet. (See Amendment A to AS/NZS 3000).
Q Why is the sleeving of green wire restricted? A The restriction in AS/NZS 3000:2000 is because of a number of electrical accidents that occurred in Australia when a cable run was broken in mid-span and re-terminated. The main safety outcome of this provision is to ensure that green coloured conductors of fixed wiring are always earth conductors. Q What are the requirements for new distribution switchboard neutral to earth linking? A From January 2003 where AS/NZS 3000:2000 is used as a means of compliance on an installation, distribution switchboard neutral to earth linking is not permitted. Note that the main (MEN) switchboard MUST have a link.
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