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Posted By Topic: picking up an earth

heatshrink
Nov 11 2013 17:50

Hi all. I am wiring a house where i am adding a flouro light.I need an earth and the old lighting circuits do not have earths.It is too hard to get back to earth bar to get earth.Can i legally pick up an earth from a nearby power circuit and run it directly to earth terminal inside floro.
   

BrianW
Nov 11 2013 18:30

You can pick up an earth from anything electrically connected to the mass if earth through the earth bar, so yes is the answer you seek, but an electrician would have, or at least should have, known this already, and you say you are wiring a house????!!
   

AlecK
Nov 11 2013 18:56

5.5.2.2 says that using the PEC of one circuit to provide earthing for equipment sup[plied by another circuit is not acceptable.


   

BrianW
Nov 11 2013 19:29

Okay, I stand corrected. But one now has to ask the question. Why ???
   

heatshrink
Nov 11 2013 19:30

Thanks AlecK thats what i thought about mixing earths. And Brian W thanks for your comments.Not everybody knows everything.
   

BrianW
Nov 11 2013 19:47

Agreed Heatshrink, not everyone knows everything, but i gotta admit, i\'m scratching my head a litte on this one, especially when the note to Alek\'s quoted verse says that the use of an unenclosed common PEC for a number of different circuits is perfectly fine. Doesnt seen to be any logic whatsoever to 5.5.2.2.
   

DougP
Nov 11 2013 19:58

Not allowed

5.5.2.2 Restricted connections
5.5.2.2.1 Circuits
The protective earthing conductor for a circuit that is incorporated in the
same cable sheath or wiring enclosure as the associated live conductors for
the circuit shall only be used for the earthing of equipment supplied from
the circuit.

Exception: This does not preclude an unenclosed common protective
earthing conductor being used for a number of different circuits.
   

DougP
Nov 11 2013 20:14

You can connect an earth conductor to the main earthing conductor, if you can get to that.

You can solder the connection or use a line tap (without soldering), without cutting the main earth conductor.
   

AlecK
Nov 12 2013 08:13

Why \"without cutting the main earth conductor\"?
   

DougP
Nov 12 2013 08:36

Appears that this is another piece of misinformation I have picked up from an inspector somewhere along the way, without checking myself.

So thanks to Alec\'s question, it appears that there is no rule prohibiting joins in the main earth conductor, or requiring it to be one continuous length.
   

Andrew
Nov 12 2013 10:27

BrianW: I expect the reasoning behind 5.5.2.2 is that if the PEC is sheathed with its associated live conductors, people will assume that when they disconnect the cable at the switchboard (or other point of origin) they haven\'t affected the earthing of any other circuits. With an unenclosed earth you\'d be more likely to check what circuits it is associated with before disconnecting at the switchboard.
   

ElroyL
Nov 12 2013 14:28

Corrected:

DougP wrote:

\"
You can use a line tap, without cutting the main earth conductor.
\"

3.7.2.11 (a)
   

DougP
Nov 12 2013 18:01

I think what you are saying Elroy is that 3.7.2.11(a) says “Soldered connections Where soldering is used for the jointing or connection of earthing conductors, the earthing conductors shall be retained in position by acceptable means independently of the solder.”

However 3.7.2.7 says “Soft-soldered connections shall not be clamped under a screw or between metal surfaces.”

So I guess 3.7.2.11(a) overrides 3.7.2.7 for earthing conductors?

Or were you making a different point that I have missed?
   

ESNZ1
Nov 12 2013 21:22

3.7.2.11a When \"retained in position by acceptable means independent of the solder simply refers to using a soldered lug.
   

ElroyL
Nov 14 2013 07:16

My understanding of it is that you cannot have a soldered join, where the solder provides electrical AND mechanical integrity to the join.

Therefore we no longer solder anything because tunnel-type screw connections (or crimp) provide both of the above. There may be soldering cases I am unaware of - I am interested in where you would use these?

To me I see soldering a lug as rather pointless, as it must be crimped first to provide mechanical strength to the joint, then soldered last.
You cannot have a purely soldered lug/joint in my understanding, as if any current flowed for a sustained period, the solder would weaken/soften, increase joint resistance, more heat, more resistance, etc etc.
The clause that states you cannot screw down upon a soldered joint confirms this for me.

I guess soldering a crimped lug would add a little extra electrical integrity to a crimped lug.
Are there any other pluses for soldering crimped lugs?

Cheers
   

Sarmajor
Nov 14 2013 10:03

Elroy, you most certainly can have soldered (and not crimped) lugs. Just not for earthing conductor connections.

Note that \"3.7.2.7 says “Soft-soldered connections shall not be clamped under a screw or between metal surfaces\" is referring to the practice of soldering the end of flexible cables and then fitting them into a screwed connector.

This usually results in a connection failure over time as the soft soldered flexible cable will deform under the pressure from the screw and has no flexibilty to maintain joint integrity.

Back in the day extensive use was made of soldered lugs as not everyone had a crimp tool.

Most connections in HV terminal boxes with paper lead cables utilised soldered lugs.

It might be old school but it is not completely dead or redundant yet.

I would urge everyone to read the sections in AS/NZS3000 dealing with earthing and consider what the words actually say and the safety outcomes that are being sought. After all that is what the whole intent of the standards is.
   

ppaw1965
Nov 14 2013 12:41

The other reason for soldering a wire into a lug is to protect the connection, two places come to mind, on to lead acid and alkaline/caustic batteries and high moisture areas. I used to work in an industry where fail safe was most important and the last thing they wanted was for the battery back up to develop a high resistant joint or the cables to corrode from the inside out. I actually did a job 3 years back and they wanted all the battery lead lugs soldered for this exact reason. Spent 1/2 an hour training the other sparkies up on using soldered lugs.
   

ElroyL
Nov 17 2013 07:22

Cheers for that guys.

So the lugs used, are they specially designed for soldering, or are they just standard crimp lugs that are not crimped, just soldered?

Obviously wouldn\'t be used in a cable entry facing downwards position in terms of heating/solder loss?

Cheers.


   

ppaw1965
Nov 17 2013 18:26

Solder lugs are slightly different as there is no opening opposite the end the cable goes in to stop the solder flowing out. I have used normal crimp lugs in the past by either taping up with fiberglass tape or found cadweld putty works well. But the right lugs make a easier and nicer job
   

pluto
Nov 18 2013 09:34

Have you ever thought about when high short circuit currents flow a earthing solder lug connection, they often fail if the current duration is long enough and the solder melts and results in total disconnection or a high resistance joint.

Over my many years in the trade (+50 yrs) I have seen this about 10 times.
   

ESNZ1
Nov 19 2013 22:11

A good maintenance program would probably have removed 80 percent of those Pluto.
Unfortunately maintenance is something only done when there is a failure. check out many of the overhead lines around the country