Earthing and swa cable

[Thys LOW Elektries]

Is it just me looking for a regulation out there that is not and missing it or is there such a regulation? "Earthing shall not rely on the armoring alone..."
My preference and choice of work is a bare earth conductor and a 4 core swa cable coming into the main db. I know electrical engineers uses 4core plus an earth for all the three phase installations they design. Is it an engineer spec, money making racket or is it a law?

I know tnc system is used by many counsels up to the point of control, old and cheap, the newer counsels and installations use the tns system, much safer if a neutral gets lost or loose and you have a floating earth!

I have seen people using two locknuts with an earth tag between the locknuts connected to the earth bar of the db to provide a save earth. Also people reducing the armoring so that it can fit through the inside of the gland, the drawback is the wires can snap off later or during the installation!

Am I just being over cautious or is it a case of " The earth reading was fine when I signed the form ?!"

Luckily I don't do a lot of 3 phase installations, I just had an argument with a "clever" client because the building had no incoming earth
Greetings and a festive season to you all

[GCE]

You can rely on the armouring if it passes the test and is correctly glanded with an earth tag ( 6.12.1.4 )

I do not believe it is good practice as how are you going to be sure it passes the test before installing - There is a cable called ECC that has tin copper installed in place of some of the steel armour wires and will comply with 6.12.1.1b as it has been designed to specification and takes into account 6.12.1.1d
On ECC you pull the tinned copper wires through the gland onto the earth bar.

If you use a 70sqmm ECC armour cable and the manufactures spec allow phase to carry 200Amps then the tinned copper wires installed allow for the earthing to the specification of 200Amps
I have had the argument with consultants over the tinned wires are not the same size as the phase wires - It is not a str calculation as you need to take into account the surface area which sorts out excessive temperature mentioned in 6.12.1.1d - That is why 6.12.1.1b is in the regs



6.12.1.1 An earth continuity conductor shall
a) consist of compatible conductors,
b) if it forms part of a cable other than a flexible cable, comply with the relevant
requirements of the standard for the cable,
c) if it forms part of a flexible cable, be of the same material as, and have a
nominal cross-sectional area at least equal to, that of the largest phase
conductor,
d) be able to carry the prospective fault current without excessive temperature
rise of the conductor, within the disconnecting time,
e) if it does not form part of a cable or flexible cable, have a nominal
cross-sectional area in accordance with table 6.25 and if it equals to the
phase conductor size refer to table 6.28(a), as follows: Amdt 1


6.12.1.4 An earth continuity conductor may have branch circuits provided that
the selection of the conductor size follows the requirements in table 6.28(a)
and 6.28(b) with due consideration to the maximum length from the upstream
protective device.
NOTE The information in 6.12.1.4 also applies to wire armouring if it is used as the
earth continuity path provided it meets the comparable resistance values of the
equivalent earthing continuity conductor and the armour wires are all correctly
terminated using an earthed metal captive coned gland; it may be necessary to replace
some of the steel wires with tinned copper ones or to use a supplementary earth
continuity conductor

[Isetech]

We only use ECC cables in our part of town.

When we build pump station out of town, we run a separate earth wire or use a 4 core "plain" cable for the pumps and other equip which only requires 2 phases (no neutral).

[Thys LOW Elektries]

Thanks for the information on the ECC cable. I will have a look for the cable and availability. Have to agree with using the armoring method is not foolproof and leave plenty space for future problems like rust on the db causing bad contact, loose locknuts, damage and broken wires on the armoring etc. the council not earthing the armoring at all and so the list goes on

[Isetech]

IF you can find companies which use the right gland, you know how many sites I visit and they just use a compression gland becasue it is easy to fit and much quicker than a ccg/prstely type gland

If you apply a little grease to the wires, they wont rust once secured in place.

Thanks for the information on the ECC cable. I will have a look for the cable and availability. Have to agree with using the armoring method is not foolproof and leave plenty space for future problems like rust on the db causing bad contact, loose locknuts, damage and broken wires on the armoring etc. the council not earthing the armoring at all and so the list goes on