Earthing an Awning

[eTeam]

Hey guys,
Came across something the other day that I am not sure what the best course of action is. I went to check out a job where the customers have just had an awning installed. The builder also drilled out & ran cables for downlights & an earth cable that is connected to the frame. The house is double storey so no way to get back to MSB but there is a small section I can slide a tile & access to get down to the light switch & rondo if there is any.
Assuming I get acceptable readings would it be appropriate to connect to the lighting circuit or rondo if present?

[gregmcc]

I'm assuming you are talking about bonding the metalwork of awing? if so the minimum bonding earth is 4mm, with a maximum reading of 0.5ohm (when you test the bonding to the switchboard) Even if you were to use the earth from the light circuit (which you shouldn't) I doubt you could achieve the minimum earth resistance required.

[eTeam]

Yep, that's correct. The builders of the awning have used 4mm earth and left a few meters coming out of the end of one of the supporting beams. I can redo it if need be but the issue is that getting back to the MSB is impossible
I am going to have to go back for a better look when the weather improves but from first look & given the very limited roof access that I will have the only things I could see that are available to me are a lighting circuit & possibly rondo.
This probably seems like an amateurish question to many but my limited experiences with these types of things I have always been able to get back to the board.

[JamieP]

I'm making assumptions here but I'm thinking the awning probably needs earthing and not bonding but feel free to correct me

If this is the case you can go as small as a 2.5mm2 earth depending on size of active conductors that pose a risk

Is it the downlights in the awning that present a risk? How are they fed?

[gregmcc]

I'm making assumptions here but I'm thinking the awning probably needs earthing and not bonding but feel free to correct me

If this is the case you can go as small as a 2.5mm2 earth depending on size of active conductors that pose a risk

Is it the downlights in the awning that present a risk? How are they fed?

Structural metalwork including conductive building materials needs to be earthed, (5.4.6) there are a whole lot of details on what, when, any why.

5.4.6.3 allows you to use the PE of a circuit for earthing, but it can't exceed 0.5 ohm, this may be difficult on a lighting circuit due to the small earth wire.

[eTeam]

I'm making assumptions here but I'm thinking the awning probably needs earthing and not bonding but feel free to correct me

If this is the case you can go as small as a 2.5mm2 earth depending on size of active conductors that pose a risk

Is it the downlights in the awning that present a risk? How are they fed?

Sorry mate, I am probably not describing things as well as I could. WIll try better...
The awning is metal in construction and the builders have sold the product with lights so have cut out holes and run cable for LED downlights (fittings which they gave supplied to the customer) & a 4mm earth which they have connected to the metal frame. The cables are just coiled up where they come out of the awning so I need to get them both into the soffit & where they need to go. I could be wrong in my thinking but as there are to be downlights installed in the frame of the awning the earthing of the awning itself is essential so I want to make sure I get it right. Getting the feed for the downlights is no problem but earthing not so much.
I was always taught to get it back to the MSB (so to not exceed 0.5Ω) which I am unable to do so I am wanting to find out if there are any other ways to skin this cat. I don't know who the builders were & have just met the customers for the first time so don't want to give them the runaround as apparently other sparkies have.
Without adequate earthing am I right in assuming that without the appropriate earthing then no lights? If I run the 4mm down to the light switch or connect to rondo if there is any & get less than 0.5Ω at the MSB is this an acceptable arrangement?

[AlecK]

Yes, as per 5.4.6.1 if there is nothing electrical in the structure then earthing of framework is not required.
Unless it's domestic, when framing must be earthed regardless [5.4.6.2]

Because this is earthing, not equipotential bonding, then the min 4 mm2 for QBCs doesn't apply.
Size as per table 5.1, based on largest size of active - which will be the supply to the lights.
So just use the lighting supply cable (as gregmcc suggested).

According to "3008.1.2", Table 35; 1.0 mm2 has a resistance at 50 Hz of 23.3 ohms / km @ 45 deg C
so 2.33 ohm for 100 m
and you can go approx 20 m and still be less than 0.5 ohm.
However 0.5 ohm isn't the limit (repeat: this is earthing, not bonding),
so the max permitted resistance as as per Table 8.2, for a circuit protected by10 A c-curve we're allowed 1 ohm
- so approx 50 m with 1.0 mm2, further with 1.5 mm2.

[eTeam]

Thanks heaps guys, Appreciate all the responses