[TCUG] Re: Installation Earthing
- From: "Gursharan Nijran" <Gursharan.Nijran@xxxxxxxxxxxxxxxxxxxxx>
- To: tcug@xxxxxxxxxxxxx
- Date: Thu, 26 Sep 2002 15:48:23 +0100
Please note that the Line Earth Loop Impedence is measured from the
origin of the supply. The LELI of a cable run is governed by the circuit
protection device operating in 5 seconds. The cable calculations for the
initial design of a particular cable run of the system should be based
upon the calculations for the LV cable only. From my calculations based
upon the manufacteurs Data sheet for 16 x 1.5 sq mm cable which is used by
Nottingham City Council the maximum length for a this cable is 180 mts
which requires a maximum LELI of 4.58 ohms. This is protected by the 10
amp BS 88 controller lamp switch card fuse which requires 31 amps to
disconnect the circuit witin 5 seconds.Please check with your controller
manufacteur for the rating and type of protective device which protects
your cable runs from the controller. It should be noted that many of the
cable runs have an ELV cable running along side of the LV cable thus
putting the two CPC (circuit protective conductor) i.e. steel wire
armouring, in parallel thus giving a lower LELI. The ELV cable might not
take the same route to the poles as the LV cable. Therefore care should
be taken in what is the true LELI of the cable run.
With regards to corrosion on the swa of the cable it is in the codes of
practise for the installation of cables that any outer sheathing which is
removed for gland termination should be made good with equivelent
materials to prevent corrosion.
If you are installing cable runs in excess of the 180 mts your options
might be has follows:-
1.) Increase the size of cable to suit your circuit calculations for your
cable run. i.e R1 phase conductor and R2 CPC cross sectional area (csa)
2.) Increase R2 by the means of an additional CPC run in parallel with
the LV cable CPC along its length.
The increase in the size of cable and additional R2 is determined by
circuit calculation.
Tom.Friend(at)nottinghamcity.gov.uk
-----Original Message-----
From: "Probert, Norman (Environmental Services)"
<NProbert@xxxxxxxxxxxxxxxxxxxxx>
To: tcug@xxxxxxxxxxxxx
Date: Fri, 20 Sep 2002 15:25:15 +0100
Subject: [TCUG] Installation Earthing
>
> We have been looking into providing better earth continuity at
> installations, we believe that the existing method using the armouring
> is no
> longer sufficient and can lead to high readings therefore a separate
> 10mm
> earth conductor should be used from each pole. There are two options
> either
> build this into the existing cable or install a separate armoured cable
> containing earth only. Our problem is that this is a non standard cable
> and
> would have to be purchased in significant quantities 5,000 metres at a
> go,
> we are finding it hard to convince our suppliers that they could offer
> this
> cable to others and we are also reluctant to make the purchase
> ourselves.
>
> My question is
>
> A Does anybody else agree that it is a good idea (if enough took it up
> it
> could become standard instead of special).
>
> B Does anybody currently use this type of cable already and if they
> do who
> makes it.
>
> C Has anybody got a better idea
>
>
> Norman Probert
> Senior Engineer Traffic Control Systems
>
> Tel 01905-766822
> Email nprobert@xxxxxxxxxxxxxxxxxxxxx
> <mailto:nprobert@xxxxxxxxxxxxxxxxxxxxx>
>
>
>
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