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Topic Title: How difficult to install TT system
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Created On: 24 February 2010 07:50 PM
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 24 February 2010 07:50 PM
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antric2

Posts: 1049
Joined: 20 October 2006

Evening all,
How difficult is it to install TT system.
Would it be recommended to have a go at installing one if I have never done one before or get someone to show how to do it then attempt an install.
Never have much call for TT'ing up here.
Opinions please.
Regards
Antric
 24 February 2010 08:04 PM
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mikejumper

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Is this a new installation or a change to an existing installation?
 24 February 2010 08:10 PM
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tattyinengland

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Is this a household? Commercial? or Industrial?
 24 February 2010 08:15 PM
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antric2

Posts: 1049
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Hiya Mike,
100 year old terrace.
Ze of 190ohms on what was presumed a TNS as it was clamped on the sheath as they usually are for TNS.
Utilities came out,stating the sheath was not an effective earth and the installation needs to be put on a TT system. They then pulled fuse and left install without any power until earth sorted
I personnally feel they should get straight back and either PME it or sort out problem because a comment was made that most of the locallity had no effective earths.
Interesting that in recent years the meter has been replaced with didi meter .....what tests do utilities do when they alter there side of the system.
 24 February 2010 08:22 PM
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perspicacious

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"Ze of 190ohms on what was presumed a TNS as it was clamped on the sheath as they usually are for TNS.
Utilities came out,stating the sheath was not an effective earth and the installation needs to be put on a TT system. They then pulled fuse and left install without any power until earth sorted.
I personnally feel they should get straight back and either PME it or sort out problem"


I feel that should an incident have occurred between your measurement of 190 Ohms and the DNO making safe by removing the source of power that you would be in an uneviable position in front of the Court......

Regards

BOD
 24 February 2010 08:24 PM
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rikhill

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Relatively easy to install - buy an earth rod from your wholesaler, find something suitable to protect the end and wallop it into the ground with a sledgehammer.

Finding a good spot (Especially in a terrace) is the challenge, flowerbed is often a good start - try and work out where any drains may be by looking at manholes/inspectioin covers and keep away.

Run a 16mm g/y from it back to the board and bob's your uncle.

Many would suggest digging an inspection pit (Wholesalers sell them as well), but I am just as happy with the little black covers (Like a circular conduit end) for weather protection myself.

Testing properly involves special instruments and is a little complicated - you didn't hear it from me but power it up with all the outgoing breakers off and do a normal Ze at the board, anything under 200 Ohms and your away.
 24 February 2010 08:25 PM
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daveparry1

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Are there any rcd's in the installation.
 24 February 2010 08:26 PM
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rikhill

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Originally posted by: daveparry1

Are there any rcd's in the installation.


I'm sure there will be by the time he has finished
 24 February 2010 08:27 PM
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perspicacious

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"Run a 16mm g/y from it back to the board and bob's your uncle."rikhill

Would a close relative Aunty RCD be a necessary part of the family gathering?

Regards

BOD
 24 February 2010 08:30 PM
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mikejumper

Posts: 1701
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Originally posted by: antric2
I personnally feel they should get straight back and either PME it or sort out problem because a comment was made that most of the locallity had no effective earths.

It depends on whether PME is available in the locality.
It doesn't like it is.

Is there somewhere convenient to bash a rod in?
 24 February 2010 08:32 PM
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davyn1

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How difficult to install TT system

depends on how hard the ground is
davy

-------------------------
just because i'm paranoid doesn't mean theyre not out to get me
 24 February 2010 08:35 PM
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spinlondon

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I've seen rods placed where the tarmac pavement meets the house wall, right next to the front door before now.
 24 February 2010 08:37 PM
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MrAmps

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16mm ?

No wonder there is a shortage of copper
 24 February 2010 08:37 PM
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normcall

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And where the gas main is.
16mm to an earthing road on domestic with 30mA RCD? Slightly over the top for a 30mA current don't you think. 6mm maximum surely.

-------------------------
Norman
 24 February 2010 08:47 PM
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antric2

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The front is all paving stone slabs as is the back yard...completely covered.
Access under the house is about 4 ft so can a rod be put under the house near an accessable hatch in the floor.
Basically, this came about as the kitchen is being rewired and a new con unit is being fitted for the new wiring, so, the Ze problem came to light.

BOD, I am abit lost with what you said, about the' courts and I may be missing something,
Sorry, but I may have not fully mentioned what happened
When the high Ze was discovered the main fuse box was switched of as it is an old 3036 box with no RCD protection until utilities arrived, as usual very good service as they arrived within the hour.They pulled the fuse to make sure installation could not be re-energised.
Regards
Antric
 24 February 2010 08:52 PM
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perspicacious

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Ah Antric, you forgot to mention that you were a good electrician and made safe on finding a potentially dangerous installation

Regards

BOD
 24 February 2010 08:53 PM
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Chris123

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A protective bonding conuctor unless pme is resticted to 6mm minimum and shall not be less than half earthing conductor so 10mm is the min where protective bonding is used
 24 February 2010 08:57 PM
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alancapon

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Originally posted by: antric2
. . . . Ze of 190ohms on what was presumed a TNS as it was clamped on the sheath as they usually are for TNS. . . .

In the days before XLPE service cables were available, TT supplies were delivered on a paper/lead cable, as this is all that was available. The existance of a paper/lead cable with what may be a "diy earth clip" fitted by persons unknown does not gurantee the earthing type.

. . . . They then pulled fuse and left install without any power until earth sorted . . . .

Where we come across this scenario, we have to either install a temporary front-end 30mA RCD, or disconnect the supply of electricity before we leave.

Regards,

Alan.
 24 February 2010 09:10 PM
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mikejumper

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Originally posted by: antric2
Basically, this came about as the kitchen is being rewired and a new con unit is being fitted for the new wiring, so, the Ze problem came to light.
Antric

If your new consumer is a dual RCD unit supplying the whole installation
then all you need to do is run your main earth conductor from the rod to the consumer unit earth bar.
 25 February 2010 07:48 AM
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pjcomp

Posts: 391
Joined: 28 June 2004

Originally posted by: antric2
The front is all paving stone slabs as is the back yard...completely covered. Access under the house is about 4 ft so can a rod be put under the house near an accessable hatch in the floor.


You can always drill through the paving slabs and bash the spike down that way. Yes, putting it in udner the house is another answer, but check the spoil conditions. If it's very dry unde the hosue you won't get as good an earth as somewhere outside, where the soil can get nice and damp and conductive. Of course it's not all that damp under paving slabs either...


PJ


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