questions for electrical rules gurus

[mick 123]

Gday blokes I have a couple of questions that I have not been able to answer through AS3000.Firstly a builder I am working for has suggested that we should be earthing all new colourbond (iron) roofs. I have not heard of this before but he seems to think this is anew rule.Secondly a question regarding a domestic installation with multiple light circuits that are on different phases.Can you have different phases swithcing on the one outlet?eg A 3 gang switch with different phases going to differerent switches.Any advice or rulings on this would be really appreciated.

[applied]

For location specific answers to your questions I suggest contacting your technical regulator.
Earthing your colourbond roof probably wouldn't do much unless you had a steelframe home in whitch case the frame would already be earthed or it was galv steel and not powercoated that being said it would be dirt cheap only involving a lug and a few meters of wire.
As far as phased segregation at switch plates that's just strange there seperated, generally it's best to play ball with your builder so mabye suggest installing clipsal 90f shrouds or put all your lighting circuits on one phase, or diffrent phases just not on one plate so break the lighting up into sections seperating rooms. alternately you could do what is done in commercial buildings and label all the plates with the circuit numbers.

If all else fails break out some obsure rules on his ass like consumers mains/gas supply safety zones and the consumersmains needing mechanical protection in the wall or the concrete slab requiring earthing.

[chrisp]

Gday blokes I have a couple of questions that I have not been able to answer through AS3000.Firstly a builder I am working for has suggested that we should be earthing all new colourbond (iron) roofs. I have not heard of this before but he seems to think this is anew rule.

There is no rule about earthing the roofing material. It'd be a damn hard job to earth Colorbond roofing! Maybe he/she is confusing it with rule 5.6.2.5?
5.6.2.5 Showers and bathrooms
Any conductive reinforcing within a concrete floor or wall forming part of a shower or bathroom shall be bonded to the earthing system of the electrical installation to avoid any potential differences that may occur between conductive piping (including taps, drain, etc.) connected to, or in contact with, the electrical installation earthing system and the concrete floor or wall.

Secondly a question regarding a domestic installation with multiple light circuits that are on different phases.Can you have different phases swithcing on the one outlet?eg A 3 gang switch with different phases going to differerent switches.Any advice or rulings on this would be really appreciated.

There should be no problem with powering different banks of lights from different phases. I certainly don't see any reason that the switches can not share the same switch plate.

I would expect to see such an arrangement in commercial environments to help balance the load over the three phases.

[mick 123]

Thanks for the advice chrisp and applied.As I suspected the builder is just being a bit paranoid and over the top.Although in this game is doesnt hurt to be overcautious.:roll:

[NigeC]

I agree with Chrisp.
No need to earth roof unless on a steel frame that should be earthed anyway

No problem with have three separate phases on the one switch plate, Switchboard legend will be labelled as such.

[Frankmc]

Hi Guys

Not sure about the latest regs on having seperate circuits on the same switch plate but way back in the old S.E.C days (old yellow book) you had to shroud the mechs if on different circuits....

HTH
Frank

[elkangorito]

Hi Guys

Not sure about the latest regs on having seperate circuits on the same switch plate but way back in the old S.E.C days (old yellow book) you had to shroud the mechs if on different circuits....

HTH
Frank
This is why it is VERY important to NOT strip back too much insulation, mechanical insulation or otherwise.
If the cable is rated at 600v to 1kv, there is no problem as long as;

1] The minimum insulation has been stripped (bare wire not 'open' to another phase nearby).
2] Different phases are not applied to one (1) switch mechanism, unless the switch mech. is rated for the higher voltage.
3] Wire colours clearly indicate that different phases are in use.