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Posted By Topic: Extending existing bare earth tps as replacing swi

Drewski
Nov 27 2018 10:00

Hi all,

As part of a job I need to replace an existing switchboard. It will be relocated about 4 metres. Am I able to extend the existing bare earth cable to reach. I don't think the client wants to rewire this area as its quite large. What are the options here?
   

DougP
Nov 27 2018 10:12

What do you mean by "bare earth cable"?

Do you mean cables that have a bare earth? -> yes.
Just sleeve the exposed parts and ensure that the circuit protective device is correct for the cable size. Some people might also say that you should mark at the switchboard that the (2.5?) cable you extend it with, is connected to a smaller cable - so people don't just assume it's larger and change the MCB later.

Or are you talking about a main earth conductor? - I would check if it is compliant first, and probably install a new earth stake and MEC. Particularly if you're getting an inspection on the work anyway.
   

pluto
Nov 27 2018 10:39

Drewski Nov 27 2018 10:00


Your comment 1

As part of a job I need to replace an existing switchboard. It will be relocated about 4 metres. Am I able to extend the existing bare earth cable to reach. I don't think the client wants to rewire this area as its quite large. What are the options here?

My comment 1
If you twin and earth TPS use a junction box at the point of extension and it is good idea that the junction box be placed somewhere acessable.

A general comment

If the wiring was done same years ago (1970s) the cable sizes will be different from todays metric cables, use the table in the appendix of 3000 to find the equal cable sizes, for example 7/029 cable is 2.9 mm2 so don't use 2.5 mm2 cable to extend this cable, use 4mm2.
   

Drewski
Nov 27 2018 11:18

Thanks for the replies.

It's the older style tps cable with the bare earth. So your suggesting it's OK to extend the cabling? There is trunking running around the switchboard room, so I can crimp/ heatshrink the join there. I thought rerouting (non compliant) cabling was considered a nono?
   

DougP
Nov 27 2018 11:26

Not sure what rule you're thinking of?

ECP51 for homeowners is the only thing that springs to mind..

There shouldn't be any problem for an electrician to move the cables.

And crimping/heatshrink would be fine. I would use heavy duty Raychem over the top, to maintain the TPS protection.
Doesn't matter if it's in a trunking or not.

   

AlecK
Nov 27 2018 11:33

I believe (strongly) that that's the case; but I am not aware of any "case law" on the matter.
basically re-routing is "installation" and not "maintenance"; and installing cable with bare earth is not permitted; though existing can remain in service.
Placing your junctions at or close to the point where re-routing is required should fall under will only need minor repositioning, which is permitted "to facilitate replacement of a fitting" under ESR 6A's definition of low risk PEW. But I wouldn't go further than the minimum necessary to make a junction.
   

DougP
Nov 27 2018 12:53

Not trying to get into an argument over the finer details and opinions...
However here's a couple of basic points..

The cable is allowed to remain in service..
"relocation" doesn't have any limit such as "minor repositioning" in ESR 6A
Yes, relocating is defined as to "install"..

So it's a judgement call as to whether you move the conductor to allow you to extend it, or cut it in a different position so you can extend it without moving it, or if you think you can't extend it, and have to replace it.

But I think that's overkill. Occasionally we extend conductors that "should" be replaced. Like some VIR at a light switch for example.
   

Satobsat
Nov 27 2018 13:33

"I don't think the client wants to rewire this area as its quite large"

I would definitely consider what cable I was using to extend the circuits with if it is a large area that the circuit is supplying otherwise you may have volt drop issues. You may also have to consider de-rating the cables for grouping if there have been circuits added and there are now more cables in the trunking than was originally there when installed.