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Posted By Topic: Responsibilities

Dec 02 2019 14:54

Hey guys

Just something I’ve been thinking about. What are your responsibilities to making sure a house dosent draw more and trips a main switch, was thinking when adding a aircon unit into a exisiting 1980s house, we don’t calculate Andy thing we just add it on. What are our responsibilities to ensure it isn’t overloaded and what can we do make sure what we’re adding isn’t going to overload it?


Dec 02 2019 15:41

Read AS/NZS 3000:2007 clause 1.9.3 for what should be happening for each extension.

Dec 02 2019 16:05


Alterations or additions to an existing electrical installation shall not cause any portion of the original electrical installation, or electrical equipment connected thereto, to—
(a) carry currents or sustain voltages in excess of those permitted by this standard

How would we ensure the circuit we add on to isn’t going to be overloaded? Say with adding aircon to a exisiting power circuit?

Dec 02 2019 16:45

Also ESR 13 (1)(b).

When adding any load, need to ensure the extra doesn't cause existing conductors to become overloaded. and the the volt drop limits will not be exceeded - not just for the circuit added, but also the effects of that load on all the other circuits due to eg increased VD in mains.

The get-out-of jail card for mains is the fact that while networks don't have to provide overload protection for mains, most of them do; and that generally allows us to apply "maximum demand by limitation".

For adding to an existing circuit, the only way to be sure is to work out what the current loading (max demand) is, and then see whether it can handle the additional load being proposed. Easy enough; just count up what's connected to that circuit, estimate circuit route length, and apply App C. Same again for the rest of the house and the size & route length of mains (using MD = supply fuse rating); and do a quick calc. No brain power needed, the volt drop tables are easy to find and your phone includes a calculator.

Failing to check is a gamble that will often be OK, but sometimes not. Basically it's relying on the person who originally installed it having left some "headroom", and whatever additions there have been over the years since not having used it all up. That sort of gamble is unprofessional.