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Posted By Topic: Seperate Netural

Mr101
Sep 28 2017 13:03

I have an installation where there is a 3 core Alu SWA cable and some bright spark has used the SWA ( not neutral screen) to give a neutral for 230v. It is to a separate building so has its own driven earth. Can I just run a neutral in a trench near/next to the existing cable or is it a new cable to get the required Neutral?
   

pluto
Sep 28 2017 13:15

the use of a single core TPS cable for the neutral conductor is OK but needs to be same conductivity as an active core of the SWA cable.

When the neutral conductor is provided and connected, remove the MEN link in the remote switchboard as the mains switchboard while provide the sole MEN link for the electrical installation.
   

Andrew
Sep 28 2017 14:00

Given there's no mention of a PEC from the supplying switchboard, how do you justify removing the MEN link?
   

pluto
Sep 28 2017 14:33


I would have it would have been un-necessay to point out that the SWA of the mutli-core cable reverts back to being PEC and the new additional single TPS cable is the new neutral conductor.

We after-all require a valid licence to do electrical work!
   

DougP
Sep 28 2017 16:14

Sorry Pluto, your posts aren't really providing enough information.

Using the SWA as the PEC, fine, but they will also need to disconnect the driven earth and MEC at that switchboard.

You're usually much more pedantic... ;)
   

AlecK
Sep 28 2017 16:45

I suspect he meant for the SWA to be re-purposed as a PEC.
My question is about "needs to be same conductivity"/.
Certainly a neutral needs to have a CCC suitable for the load to be carried [3.4.1]; and generally not less than the associated active, but can always be greater (and in some cases less) [3.5.2]. However "same conductivity" will only be achieved with same size and material, and I don't know of any such rule for neutrals.

There is one along those lines for conductors in parallel.
   

pluto
Sep 28 2017 17:28

With the widespread use of AL cables and cables together one has to be careful that we are talking about the same carrying ability.

In approx terms you need approx 1/3 more crossesctional area for AL for the same condutivity of a Cu cable.
   

pluto
Sep 28 2017 17:31

type in first line it should read

With the widespread use of AL cables and CU cables together one has to be careful that we are talking about the same current carrying ability.

   

Mr101
Oct 03 2017 09:24

Hadn't thought about the earthing arrangements. It's prone to lightening damage so was going to stick with driven earth rods to cope with that rather risk feeding back into the main board. Drive motor is bolted to the drive tower which has seperate earthing rods. It's a ski lift for anyone guessing.