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Posted By Topic: 3.9.3 Support and Fixing 3000 2018

OctaneOutlaw
Apr 06 2019 21:33

Now I know this isn't cited yet but I'd rather ask now and understand beforehand rather than later

3.9.3.1 to me says cables shall be supported at suitable intervals and also that cables must be fixed. It also states "Exceptions:
1 Where a wiring system is resting on an immovable continuous surface,
no further support is required."

3.9.3.3 follows shortly after this with 3.9.3.3.1 listing likely disturbed locations and 3.9.3.3.2 outlining methods required to comply in these locations

Q1 - Do the requirements and Exception 1 of 3.9.3.1 still stand here and 3.9.3.3.2 add to them or are the requirements of 3.9.3.3.2 exclusive for these locations?

Q2 - Is the mechanical protection required from 3.9.3.3.2 required through out the whole location? For example 3.9.3.3.1 c "In parts of a ceiling space where access is greater than 0.6 m in
height." Is all the wiring in this location required to have the protection? Because that's the way it reads to me

Thanks for your time
   

AlecK
Apr 07 2019 11:13

Q1
Yes.
The hierarchical structure of the clause numbers means that both 3.9.3.1 and 3.9.3.3 are equally ranked under overall clause 3.9.3.
So they apply equally.

In effect we ALWAYS have to provide the support & fixing as per 3.9.3.1; those requirements apply at all times and in every situation; and the exceptions also can be applied everywhere.
If the wiring is in a location deemed likely to be disturbed as per 3.9.3.3.1; then we also have to follow 3.9.3.3.2.

However an exception to 3.9.3.1 can't 'switch off' an additional requirement of 3.9.3.3; it can only switch off the general requirement.

Q2
3.9.3.3.2 is not about mechanical protection; that's 3.9.4.1.
Like 3.9.3.1, it applies everywhere.

Theree's no direct link between support & fixing and prevention of mechanical damage.

As to where the mechanical damage protection is required; the answer is wherever the risk is.
------
So for examole, a cable running through a ceiling space.
if it's lying on the ceiling, between joists, it is sufficiently supported and Exception 1 to 3.9.3.1 days no extra support is required.

If part of the run is along an eave, with les than 0.6 m height; then it is not deemed likely to be disturbed. Or rather, not under that heading; 'cos if it passes a manhole while still under 0.6 height then the proximity to manhole heading will kick in.

So:
- under 0.6 but within 2 m of access; apply 3.9.3.3.2;
- Under 0.6 but not near manhole; no additional support or protection;
- more than 0.6 m height, apply 3.9.3.3.2.

For all thee section of this cable rune, then need to consider whether mechanical protection is required

   

OctaneOutlaw
Apr 07 2019 11:51

Awesome that clears up the first part but I think maybe I worded my second question question incorrectly but if I get the same answer that's fine

In regards to my second question I was more directly looking at 3.9.3.3.2 "(c) protected from mechanical damage as specified in Clause 3.3.2.6."

And 3.9.3.3.1 states the locations deemed likely to be disturbed

3.3.2.6 says the wire must be protected by one of either (a), (b) or (c)

So wouldn't that mean that wiring placed anywhere within those areas must be provided with a degree of mechanical protection? So anywhere where the roof space is above 0.6m or within 2m of a manhole not just the parts that pass over timber for example that people support themselves on? Or do you still read it as just the areas where there cables are in a position to be damage? What am I missing? Am I just misreading it?
   

AlecK
Apr 07 2019 17:21

Yes, and i should have covered that line of logic also.

So yes any cables in areas deemed likely to be disturbed need some basic mechanical protection. But one of the options is "location", and another is the type of wiring system (some types are robust enough);so it doesn't always have to be added protection.
For example, the cable might run beside the tie beam that links the joists; which will provide a fair bit of protection. Or run beside the joist for the other direction. But just slung across joists in an open space, need to add something. So often better to use a few more metres of cable and avoid the extra work