TT or TNC-s

flyer · Jan 15, 2012

Hi, Just doing some work in the garage for sign off, the garage is fed TNC-S from the house, with the addition of an earth to an adjacent spike, as in TT. There are no extaneous conductive parts in garage. trying to finish the paperwork on this and how to describe the arrangement.

Comments welcome

Flyer

Deleted member 26818 · Jan 20, 2012

There are two options, either remove the earth rod, or as you say, run a 10mm² earthing/bonding conductor from the house.
To my mind the best answer is to remove the rod.

flyer · Jan 20, 2012

Thanks Spinlondon, The present earth is only a 1.5mm back to the cu in the house, so i think i shall install a 10mm earth back to the , i could leave the earth spike though. Does that make sense?

Cheers

Flyer

Deleted member 26818 · Jan 20, 2012

I don't know if it makes sense?
What's the difference in cost for installing the 10mm² as oposed to disconnecting the rod?

SPARTYKUS · Jan 20, 2012

What is the run back to the CU in the house like? Can you protect (in fact do you need to) the 10mm2 cable. How far is it.

flyer · Jan 20, 2012

hi Spartykus

The total run is about 18metres from CU to Cu. Trying to run it so it is hidden as mush as possible, don't believe it wil need extra protection. Will need however to drill through external wall as close to the CU as possible.

Flyer

SPARTYKUS · Jan 20, 2012

Spin how did you do a proper "squared" symbol...?

MarkieSparkie · Jan 20, 2012

SPARTYKUS said:
Spin how did you do a proper "squared" symbol...?

At the bottom of the text box is tab "Go Advanced" click that and then toggle "x[SUP]2[/SUP]" from the right of bottom row tool bar.

CrazyScozzese · Jan 20, 2012

SO, why not just lose the 1.5 and keep the rod? If the rod is good, if the Ze is good...

Garage is a TT. Save 10mm back to the MET. £40.

Shoulda made good the armour, armour is your friend.

SimpleSimon · Jan 21, 2012

Keep the rod and do away with the 1.5. Disconnect the armour at the garage end so your not exporting the TNCS.
PS. Can anyone enlighten me why 10mm is the minimum?
I thought was 4mm? Or is that if its mechanically protected and against corrosion?

Sent from my GT-I9100 using Tapatalk

Deleted member 26818 · Jan 21, 2012

10mm² is the minimum CSA for both main earthing and bonding conductors, where PME conditions apply.

SimpleSimon · Jan 21, 2012

spinlondon said:
10mm² is the minimum CSA for both main earthing and bonding conductors, where PME conditions apply.

How right you are. I overlooked it was a PME system. Duh!!!!

Sent from my GT-I9100 using Tapatalk

Guitarist · Feb 17, 2012

Reading a publication from the IEE a few years ago (wriiten by John Ware), it states that you only need to supply a 10mm to an outbuilding if there are extraneous-conductive-parts entering said outbuilding. Therefore, if there is no water pipe etc. entering the garage you wouldn't need a stake or a 10mm earth back to the CU, merely the cpc of the supply cable and an RCD in the circuit.
Please throw some regs at me if this is no longer the case.

Engineer54 · Feb 17, 2012

Guitarist said:
Reading a publication from the IEE a few years ago (wriiten by John Ware), it states that you only need to supply a 10mm to an outbuilding if there are extraneous-conductive-parts entering said outbuilding. Therefore, if there is no water pipe etc. entering the garage you wouldn't need a stake or a 10mm earth back to the CU, merely the cpc of the supply cable and an RCD in the circuit.
Please throw some regs at me if this is no longer the case.

That's correct, ....no extraneous-conductive-parts, then no need to bond anything, and no need for a bonding conductor!!!