Tt board change

[m4tty]

Hi,

sorry if I'm being annoying keep posting questions re this pita board change but I'm getting somewhere now.

I understand about tns and tncs but am abit worried about tt. I haven't ever come across a tt board yet as I live in se London where mostly tncs or tns.

Do I get a split load board or hi integrity board ? And can you buy a board which is configured for tt with a 100 ma S type rcd mainswitch and the board split over 2 other 30ma rcd. Is this how to go about it? As the osg shows mainswitch and rcbos but that would work out really expensive,

What's the best way to do this?

Thanks

 

[m4tty]

Sorry forgot to add where's the best place to buy rod inspection hatch etc from and how much am I looking at roughly? Cheers

also how do you work out the size of earthing conductor and main protective bonding conductors as osg says minimum 6mm?

Thanks

also are you allowed to have a mainswitch which is non rcd and have 2 30ma rcds split load with an unprotected way?

 

[M107]

Forget about a 100mA s type, if you use a dual rcd board you'll be fine.

Earth rod enclosure

http://www.tlc-direct.co.uk/Products/MTETC.html

MEC stick with 10 or 16mm

also are you allowed to have a mainswitch which is non rcd and have 2 30ma rcds split load with an unprotected way?

Main switch before cu is ok, as for the unprotected way on a dual rcd will be what is called a high integrity board, the non rcd ways you use rcbo's as a way of complying when supply is TT.

 

[Apache]

Sorry forgot to add where's the best place to buy rod inspection hatch etc from and how much am I looking at roughly? Cheers

Do you mean what M107 has linked or one of these?

http://www.screwfix.com/prods/16092/Electrical-Supplies/Earthing/Plastic-Inspection-Earth-Pit

also how do you work out the size of earthing conductor and main protective bonding conductors as osg says minimum 6mm?

Think Batty's DNO will only connect to 16mm minimum.

 

[paul b b]

i would use 16mm anyway

board as M says, dual with 2 30ma rcd's (my house is a TT and changed board as assesment, inc new rods, i had to use 2 to get the reading down, no room for a pit but asseser was happy with covers on them, i think it was Mr M who had a nice pic of a earth rod in place recently)

 

[Apache]

i would use 16mm anywayboard as M says, dual with 2 30ma rcd's (my house is a TT and changed board as assesment, inc new rods, i had to use 2 to get the reading down, no room for a pit but asseser was happy with covers on them, i think it was Mr M who had a nice pic of a earth rod in place recently)

This one?

 

[m4tty]

Hi,

Thanks for the replies everyone...most appreciated.

So ill use 16mm from the board to the rod.

My dads mate does lightening conductors and has given me a steel rod which is about 4 foot long. This is what i used to get a reading of 29 ohms. Will this be ok to use or does it have to be copper?

Thanks

 

[m4tty]

Also would you bond the gas and water with 16mm too or would 10mm do it? thanksut the kettle on

 

[SLIPSHOD & SLAPDASH]

Not sure if the rod has to be non-ferrous, cant be arsed to look it up. You must fit an insulated consumer unit.

I have found a lot of lost earths on TNS systems in N West London, is that where you are ?

 

[m4tty]

Im in Sidcup which is South East London / Kent boarder. The BS3036 is Earthed through the old lead water pipe with a Ze of 0.19 ohms which ive got to convert to a TT (causing loads of aggro) Looped supply from next door. Suppose I better get used to dealing with all these problems lol cheers

 

[Apache]

Also would you bond the gas and water with 16mm too or would 10mm do it? thanksut the kettle on

10mm

 

[revjames]

Glad to have seen this post. I am in the South West and am changing a CU for a family member who I am staying with. He bought the Wylex box from Screwfix for

 

[sparkytim]

Test the Earth first.

You need to do a Ze just the same as on TNS, Switch off first, disconnect the incoming earth lead from the stake, making sure NO bonds are in circuit with it, then test Loop impedance between earth lead and the incoming Live terminal on your existing main switch.

This will give you the earth stake resistence and as long as its less then 200 ohms it is acceptable as a stable earth.

As you will be using 30 m A RCD to provide shock protection then the apparently HIGH Zs readings are still ok up to 1666.66 ohms!!!.

See BRB Page 50 Reg 411.5, table 41.5 + note 2

 

[paul b b]

personaly, if its not to much hassle, i would change the rod and put a nice new one on with a nice cover, i have also taken to putting the rod in the slinging the cable out of the windo to test the ze, that way if i need another rod i havent wasted time and cable (remember the cable from 1 rod to another has to be unbroken, they also have to be 1.5x the depth apart, but i put them 2x to be safe)

 

[Andy™]

(remember the cable from 1 rod to another has to be unbroken,

but it can be crimped if short

 

[revjames]

Thanks guys, will check it out in the morning.

 

[Evans Electric]

I'm doing more and more earth rods as the earthing on the distribution networks continues to break down in Birmingham and Sutton Coldfield. I would guess there are thousands of houses relying on their water pipes for an earth , working on one this week.

As I have said in a previous post, I tried to discuss it with Central Networks , who responded by writing to me to say the earthing is inadequate at ....my home address... and I should employ my own electrician to sort it out.

As it is not possible to speak to an engineer these days , I have given up . In my opinion the Scammers or the ECA should be pushing to get something done instead of pulling in the pounds with H&S exam days for ECS cards.

 

[revjames]

Just put the CU in. Tested Ze by disconnecting electrode cable and connecting from incoming feed to main switch. Got 396 ohms. Checked again after 3 hours rain - 395 ohms so looks like new earth rod and 16mm cable is in order. GHouse wiring a problem as there is a break in the ring. I suspect kitchen fitter who installed new sockets last year. Have put 2 legs on 16A MCBs for now.

 

[sparkytim]

Try another rod either 2 screwed together (Furze) to get deeper OR another Rod in Parallel, just make sure you sink it at least rod length distance away, this will often half resistence, if not then 396ohms will still comply with Regs, 200 ohm ONLY RECOMMENDATION as ideal see BRB Pg 50, 1666.66 max.

 

[dave2]

16mm g/y only required if the cable is to be burried. If earth box is above ground then use 4mm.

See page 29 OSG!