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Posted By Topic: Main Switch Height on Tenancy Sub-board

Chrusty
Jan 07 2019 15:51

I have got into a debate with an engineer regarding the maximum height of the "Main Switch" on a tenant distribution board in a hotel / commercial multistory building.
Their interpretation of a "Main Switch" is that it only applies to the Main Switch on the Main Switchboard. The tenancy board is a sub-board and has a main isolator but it is not deemed to be a "Main Switch" when requirement for 2m height restriction as per AS/NZS3000:2007 2.3.3.3(a) is concerned.
From their response to my query...
"the sub board (DB) is part of the single MEN installation and is within the same building. It is certainly an isolator for that part of the installation, however is not deemed a main switch."

Is this a correct interpretation?
It seems to go against the whole point of having an easily accessible means of isolation for the installation.

I referenced Figure 5.1 (MEN General Arrangement) which calls the Main Switch on the DB a Main Switch but to no effect...

Should we proceed with installing the DB at 2.2m from the floor as specified?
   

DougP
Jan 07 2019 17:44

As it's a tenancy as part of one non-domestic installation, they are correct. It isn't a "main switch" - As per 2.3.3.3(b). One installation, multiple occupiers, it's an isolating switch.
   

Chrusty
Jan 08 2019 07:36

Thanks for the prompt reply Doug. I'll start warming the humble pie now...
   

AlecK
Jan 08 2019 09:37

Just to clarify:

Fig 5.1 shows two DBs, but only the one labelled as being "separate MEN installation in an outbuilding" has a "main switch" - which is i.a.w. 5.5.3.1(b).
The other DB doesn't have an isolating switch on the incoming submain at all.
Both are i.a.w 2.3 'control of an installation' ; provided the unswitched DB is not a "separate domestic installation forming part of a multiple installation" [2.3.3.2].

The point of Figs 5.1 & 5.2 is to illustrate the various earthing configurations that are acceptable as "MEN" under clause 5.1.3; so should really only be used in that context. Figs do not always show elements that are not directly relevant to their intent. Showing everything that should, let alone could, be there would simply add visual clutter; making the Fig less good at conveying its primary message. However where any other aspects are included, they will be not inconsistent with the rules that govern them.

Back to switchboard height.
These DBs may not have "main switches"; depending on whether the tenancies are "domestic", and on whether each tenancy is set up as a separate "installation" or as just part of a larger "installation". That doesn't relate in any way to whether or not it's separately metered; nor to whether there are different network ICPs for them. Being in a single building is also not relevant; one installation can spread across multiple buildings, or several installations can exist within one building. Clearly the engineers believe there is one large installation; and they may well be right.

But all switchboards must comply with 2.9, including location & accessibility [2.9.2].
So while the absolute limit for main switch height may not be strictly enforceable; the specified 2.2 m is in my view not consistent with 2.9.2.1(c)'s requirement for ease of operation & servicing. Although within definition of "arm's reach"; that's for avoidance of being able to touch things at all. A person of average height can't operate, let alone work on, switches etc at 2.2 m without a ladder.