TT earthing on a rewire

[J.C.E]

Evening men!

Looked at a upcoming rewire
it is for a mid terrace old house.

A single phase comes into the house next door- one 60a head in next doors house >>meter>>cu
Then a 2nd feed goes into the house I am planning to rewire into a 60a head>>meter>>cu

I have seen this before- but what concerns me is the earthing
it is just a bonding clamp around the incoming servive- then into a met in each house
so a TNS

however upton getting a quick ze reading it was 4.3ohms- likely to be loose clamp

The builder got UKPN out and they said this to him:

"Single supply to no17 with a link to no 15 through the wall as we knew.

When Installed by London Electricity Board 50 or so years ago no earth was provided. UKPN having adopted the network will not and do not provide an earth where it is not present such as on a TT supply like this one.

The earth next door is not fitted or owned by UKPN (nor is the link between 15 and 17 oddly but they do own the head in 15...) If the steel pipe that covers the lead insulation of the supply underneath is in good contact and the pipe is very clean of rust under the earth bonding it could be a good earth. If its not it wont be.

2 options.

1- New Supply - PME.

2 - Earth Spike"

the client can not afford a new PME supply

If I go down the route of install a rod and making it a 'offical' TT system do I need a upfront RCD

they want the c/u remote from the meter so it will go meter >> sw isolator>> cu via 3c SWA
the consumer unit will be dual 30ma rcd

do I need a upfront 100ma rcd to cover the SWA sub main or am I over thinking again!

 

[Wilko]

Hi JCE - I would put 100mA S RCD isolator and fuse after meter, then swa to new board.

 

[J.C.E]

Hi JCE - I would put 100mA S RCD isolator and fuse after meter, then swa to new board.

can you get this in a combined rather than a 100ma rcd and seperate isolator

 

[Wilko]

Yes - I use this Wylex one :
100 Amp 100mA Time Delayed RCD 2 Pole - Wylex - https://www.tlc-direct.co.uk/Products/WYWRMT100slash2.html

 

[Leesparkykent]

Buy a Lewden switch fuse and change the main switch for an 100mA time delayed RCD.

 

[kingeri]

Think he meant fuse/RCD combo.

Edit: not meant for you Leesparkykent!

 

[kingeri]

Buy a Lewden switch fuse and change the main switch for an 100mA time delayed RCD.

View attachment 38646

View attachment 38647

Bloody neat solution!

 

[J.C.E]

Buy a Lewden switch fuse and change the main switch for an 100mA time delayed RCD.

View attachment 38646

View attachment 38647

cant find it online though!!

 

[Dave OCD]

I've used Lee's solution a few times, even the same manufacturer. Great minds and all that eh....

 

[Leesparkykent]

Lewden 100A DP Fused Switch - Lewden from Discount Electrical Wholesaler UK - http://www.discount-electrical.com/circuit-protection-c26/consumer-units-accs-c63/lewden-100a-dp-fused-switch-p5403/s6248?utm_source=google&utm_medium=cpc&utm_term=lewden-100a-dp-fused-switch-fs6380100&utm_campaign=product%2Blisting%2Bads&gclid=EAIaIQobChMI7_Dp0ZLV1gIVRbvtCh013wPnEAQYBSABEgL9W_D_BwE

Lewden 80 AMP 100MA 2 POLE TIME DELAY RCCB / RCD - https://www.superlecdirect.com/p-801002s-lewden-80-amp-100ma-2-pole-time-delay-rccb-rcd?gclid=EAIaIQobChMI1oKM6pLV1gIV5rftCh28-gMjEAQYASABEgJfofD_BwE

 

[Deleted member 9648]

Don't forget you'll need to take precautions bringing tails into that enclosure with a likely high Ra. Unless of course you are a certain engineer who used to be on here who always got sub 1 ohm Ra's

 

[Leesparkykent]

Or......

https://www.electricalcounter.co.uk...+Metal+Clad+Fused+Switch+IP54+100A/4027090827

Europa RCD Time Delay 80A 100mA - http://www.hlilleyelectricalandplumbing.co.uk/europa-rcd-time-delay-80a-100ma.html

 

[Leesparkykent]

Just use a tail gland and make sure the tails are adequately supported.

 

[J.C.E]

would you guys feel inclined to leave the 16mm connected to the clamp around the incoming next door- as this is giving me 4.3ohms as well as the rods

would struggle to get that with a few rods??

 

[Leesparkykent]

The pipe will be extraneous and need bonding...the main earthing conductor will be the one from the electrode....consequently bonding the the pipe will drag your EFLI values down.

 

[bigspark17]

How expensive would a pme supply be? Have you asked if it is available? Yes you will need the s type rcd upfront to cover the swa.

 

[Leesparkykent]

Cheers lads for the advice, ideas, links etc...it's much appreciated

 

[J.C.E]

what he said ^^^^

cheers guys- mainly Lee

 

[J.C.E]

So put a temp board in for this job this morning.
2meter of rod into ground with 16mm earth into MET
100ma time delaying RCD+ fuse carried combo (used PROTEK as wholesaler stocked it)

into a temp board

I got a live Ze reading (test meth 2) as I do not have a electrode tester

The reading was supprising 3.05ohms (I was expecting alot higher for 2m rod!?)

but it did go down pretty easy so guessing the ground was nice and soft

1)on my easycert form what is the 'resistance to earth' reading?
2) what is the 'rated time delay in ms' value- doesnt say on the protek rcd which is model 'T80-100-2TD'

 

[Wilko]

Hi - that is very good and that's your number.
For rated time delay - it depends on which standard the RCD was made to. If you've got your OSG the info is in chapter 11, p112.

 

[J.C.E]

Hi - that is very good and that's your number.
For rated time delay - it depends on which standard the RCD was made to. If you've got your OSG the info is in chapter 11, p112.

That reading obviously goes into 'measured Ze value' but does it to go in 'resistance to earth' box too?