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Posted By Topic: garden shed power point

Apr 29 2018 21:16

plan A loop off an existing point three meters away in a bedroom, put a power point in the shed, already on an RCD. customer sets up his own plug in lights
plan B submain to shed and associated wiring

whose keen for which plan and why folks?

Apr 29 2018 21:20

just do plan a and wire up some lights as well, no need for a submarine

Apr 29 2018 21:24

Opps Sub Main !!

Apr 30 2018 09:11

For a single light you could loop off the socket outlet in the garden shed(use extra switch on socket outlet for light control switch) and no need for a distribution switchboard. Loop off existing RCD protection socket outlet in house.

Read as/nzs 3000 clause (b) and figure 2.6 for details

Apr 30 2018 21:54

If the garden shed is attached to the house then option A.

If the shed isn't attached then it's an outbuilding. It requires a main switch so option B.

May 01 2018 00:11

mowgli - You're interpreting the requirement the wrong way around. I think you're referring to But this clause means that if the outbuilding has a switchboard, then it needs a main switch.

The same applies to clauses referring to a submain or methods of earthing in an outbuilding - they only apply if there is a switchboard. It's only logical - a submain runs to a switchboard. No submain, no switchboard, no main switch required.

There's nothing preventing just running any number of final subcircuits to any part of an installation, including "buildings" separated from the main building.

What Pluto described, is the simplest idea. Just one cable suitably sized and protected, connected to the power points and lights.

May 01 2018 09:26

All Pluto said was that it was okay to loop a light off a socket circuit because the fixed load was incapable of generating an overload in the smaller cable.

I accept that could be read different ways. This is my interpretation.

The clause applies to electrical installations in an outbuilding. (A) defines what must be considered a separate electrical installation. (B) requires that a main switch be installed on a switchboard in the outbuilding to control the electrical installation in the outbuilding.

"Outbuilding" and "electrical installation" are defined terms. Separate is not defined so takes it's dictionary meaning.

(A) is not exclusive. It states that certain things shall be considered separate. It doesn't say that all other things shall not be considered separate.

The definition of outbuilding 1.4.69 includes that the structure is separate from that which supply is obtained. So it easily fits the definition of separate electrical installation with POS at the main switchboard.

Regardless, (B) doesn't distinguish on "separate" only that a main switch is required on an implied switchboard in the electrical installationin an outbuilding which is already defined as separate in 1.4.69.

To me it feels right that a shed should have a small switchboard, a main switch a couple of breakers for circuit isolation. Others may do it differently and that's their call.

May 01 2018 09:33 (a) has the word "if"

May 01 2018 09:34

then also the word "and" for (i) and (ii)

May 01 2018 09:45

Correct. If (i) and (ii) then it "shall" be considered separate. It doesn't follow that all other possibilities shall not be considered separate.

May 01 2018 09:50

So how does that relate to a power point and a light in a shed connected to a power point? It's not over 100A so none of that applies.

You said "If the shed isn't attached then it's an outbuilding. It requires a main switch so option B." which is wrong.


May 01 2018 10:28

The abobve seams to be drifting away fromm the original question.

The only reason that the definition "outbuilding is provided for is to cover when as/nzs 3000 clause is being used.

This when only an active and Neutral PEN conductor (and also earth") is used to supply a standalone building adjacent to a electrical installation. A local earth electrode is required as a backup for safety reasons if an earth fault in the outbuilding occurs if the PEN conductor goes open circuit.

If the outbuilding is a garage for parking of a car, AND, a electric vehicle charger is required, the EV charger can NOT be supplied by a PEN conductor, and in this case the submain would have to be repalced with a 2 core + E submain.

May 01 2018 11:53

DougP do I understand you right?

Are you saying that if the outbuilding doesn't satisfy (A) then we don't have to consider (B)?

Is that really how it's written?

May 01 2018 11:54

I think this comes down to whether you expect the electrical needs in the shed are likely to expand in future. If not, there's no need to put in a submain and switchboard, and wiring the lights off the socket makes the job easy (although if the socket is down low the customer might want their light switch separate from the socket switches).

May 01 2018 12:24

Let's take out the formatting and other extraneous words and punctuation, and read it again..

An electrical installation in an outbuilding shall comply with the following:
An electrical installation in an outbuilding shall be treated as a separate electrical installation if the electrical installation in the outbuilding has a maximum demand of 100 A or more per phase, and is provided with a switchboard.
So everything after the "if", is conditional.

May 01 2018 13:20

DougP, yes of course A will not apply to a garden shed. But why should B be conditional on A.
An electrical installation in an outbuilding shall comply with the following:
(A) doesn't apply
(B) Main switches. General. A main or isolating switch or switches shall be installed on the switchboard in the outbuilding to control the electrical installation in the outbuilding.
The clause applies to "electrical installations in outbuildings". A directs that certain outbuildings must be considered "separate electrical installations".

If B is meant to follow on from A then it should reference A and use the phrase "separate electrical installation". Instead it ignores A and uses the wording from the opening "shall comply" statement "electrical installation in the outbuilding"

I don't think that either mine or DougP's interpretation is unsafe. Clearly the wording allows for (at least) two interpretations. So I'm being pedantic because these things ought to be teased out and corrected in future.

May 01 2018 13:59

I'm sorry my friend. It's an "IF" statement.

If (i) AND (ii), then (a) "shall be treated as a separate electrical installation"

There's no other interpretation.

And there's no other clauses specifying that a switchboard shall be installed in an outbuilding.

May 01 2018 14:06

But I see now what you're saying. That (b) should apply regardless.

Sure, it should apply. If there is a switchboard.

There's nowhere in the standards that say that a switchboard is required - and (b) doesn't say that it's required either.

May 01 2018 17:37

I think we're coming to a mutually confused state of agreement.

B says that there shall be a main or isolating switch. If not on a switchboard then I expect it could be a 56SW120 or similar.

I did one last week. I explained to the client that if anything bad happened electrically then he could isolate all power in the shed with one switch. The shed was being lined so it was a vynco 4way recessed DB with main switch and two MCBs. It came together well.

May 01 2018 18:43

I am going to have to go with Dougp on this one.

AS/NZS3000:2007 section give the conditions that mandate a switchboard in an outbuilding.

A simple garden shed would fail to meet the requirements of 100A and having a switchboard then there is no requirement to have a main switch.

Especially if there is no switchboard to mount it on.

Your description in your previous post quite clearly describes an installation with a switchboard and because you choose to fit a switchboard you have no choice with the main switch.because of

So a couple of circuits from the house to the outbuilding for lighting and power does not require a main switch.

May 01 2018 19:28

Curious how many ways a clause can be read. I can't find anything in that would mandate a switchboard in an outbuilding.

The clause relates to isolating switches.

May 01 2018 20:51 (a) just defines when the outbuilding is treated as a separate installation. Which can't apply for a standard domestic installation, because the maximum demand won't be over 100A. (b) states how the main switches are to be arranged for the supplies.

Neither of these clauses state that a switchboard is required. And (a) clearly states "if the electrical installation... (ii) is provided with a switchboard". So it seems clear there is no "shall" requirement.

What you really need to look at are sections 2.1 and 2.2 which clarify the functional requirements for switchgear as well as the control of all parts of the installation.

There are requirements for control and reducing the effects to other parts of the installation that might not be met by supplying the shed power and lights from "tapping off" another power point. However they may easily be met by providing a dedicated final subcircuit for the shed.

On the other hand, having a submain and switchboard creates additional requirements. Not the least of which would be discrimination between the submain overload and short circuit protection, and the final subcircuit protection on the shed switchboard.


May 02 2018 10:28

You've both missed the key point, which is that the definition of "outbuilding" includes that there is a switchboard.

A separate shed / garage may be an outbuilding for purposes of the Building Act, but unless it has a switchboard it is not an outbuilding for purposes of Wiring Rules.

The rest follows; ie
(a)(i)IF the outbuilding has 100 A then it must be treated as a separate installation.
(a)(ii) is redundant, due to effect of definition.

subclause b) has equal ranking,NOT subsidiary to (a). basically regardlerss of whether (a) applies, (b) means there has to be either a "main switch" or at least an isolating switch to control the outbuilding. (if it is treated as a separate installation, tyhen this isolator will be a "main switch" and the outbuilding switchboard will be a "main switchboard". But if it is not treated as a separate installation, then the isolator is NOT a "main switch" and the switchboard is a DB.

Little-known fact: a DB is not always required to have an isolator on the incoming submain. So the effect of (b) is to require one for any outbuilding. And of course (b)(ii) covers multiple submains, needing an isolator for each.


May 02 2018 10:52

Alec. I've said repeatedly that there is no requirement for a switchboard in an outbuilding. And I don't see anything in the definition of outbuilding, that states that to "be" an outbuilding, it must include a switchboard? Only that it is separate from "another structure containing the switchboard from which the supply is obtained". So you could say it's not an outbuilding unless it has a supply, but that seems rather pointless.

I also said that (b) would apply regardless of (a), but that first, there had to actually be a switchboard, and as there is no requirement to have a switchboard... etc.

Yes I had noticed that there is no specific requirement for a DB to have a main switch or main isolating switch - after searching all the switchboard clauses for quite some time..

May 03 2018 07:23

my bad, Doug.
It's the coming revised definition that has that bit:

1.4.88 Outbuilding—Individual
A structure containing a switchboard that is separated by an area of
land from the structure containing the switchboard that supplies it.

and of course the reason for the revision is to reduce misunderstanding

May 03 2018 08:11

Thanks for the clarification Alec.
That wording is different from the draft.
Great that small clarifications are getting addressed..

May 03 2018 08:45

DougP May 03 2018 08:11

There is an open invitation in any standard to seek correction or modification to make it clearer or easier to use for end users.

If you look in the front of any standard there is a paragraph usually called "Keeping Standards up to date" or something simular.

The paragraph explains the method of doing this.

Unfortunely, there is no equal in the Electricity (Safety) Regulations 2010.