British General Distribution Board

[Theorysparky]

steps

you just don't put enuff rods in !!!!

 

[SPECIAL LOCATION]

Well if they pass you with the knowledge you have this will explain why the electrical trade is in the state it is. I am sorry but this is basic stuff surely you need to know the basics before going out into the big wide world and earning a living doing electrics.

Batty has summed up this thread very accurately in the above statement I think..

I hope not as well

I've a workshop at the bottom of the garden which is obversely on a TT system and therefore seprate to the DNO earthing.

so it looks like I'll be watering the plant next to the earth rod or praying for rain just before he comes around to try and get under the magic Ze of 21ohms.

Plus I better brush up on the earth rod impedance test.

So not only do you have a completely mixed up understanding of what and why high integrity earths area and where they are needed...

But also have an absence of understanding of TT earth arrangements..

Your "magic 21ohms"  is the usually stated max resistance of the DISTRIBUTORS EARTH ELECTRODE AT THE SUPPLY TRANSFORMER..

Not your local rod resistance..

or your local external loop impedance!

as someone has already mentioned.. bottom paragraph of page 11 OSG.

have you got copies of BS7671 & OSG ?

have you read any of it..

or just the bits the tutor highlights for the multi-choice on line exams???

 

[Theorysparky]

Specs

he is not a 5WW

which worries me more

 

[SBS Dave]

Hi Paul77,

I am the Sponsor that has been referred to by Canoeboy, but on this occasion, I am a TEF Member responding to your question.
If I recall the BG box, there is a space between the earth bar on the left and the linked neutral bar on the right, which would take an additional earth bar, with about 7 terminals. So you can insert a brass terminal strip and link it to the existing earth strip and give yourself at least 6 extra terminals.
If that is the case and that solves your problem, let me have your contact details and I will send you a terminal strip and link, which I am fairly sure will fit. There will not be a charge for this, but I am away all weekend, so unless you get back to me today, it will be Monday before I can post it to you.
My e-mail is in my signature or send me a PM or phone me on 0161 440 9042.

SBS Dave

 

[Blue Duck]

That's very kind of you Dave

try getting that at screw fix

 

[m4tty]

But will the OP come back ? Or has he been scared off lol

 

[batty]

He may be scared off its his customers I am scared for.

 

[Technician]

only at the board. sockets probably have both earths in the same terminal

Yes; I get this but are sockets not also provided with two connections

for the protective conductor(s)?

Just an observation.

 

[SLIPSHOD & SLAPDASH]

I connected my first TT  install  (builders supply) in years today.  1 rod and i got 90  hms , although i dont do much TT thats the lowest i have ever got ( even after drenching the ground)

 

[steptoe]

I connected my first TT  install  (builders supply) in years today.  1 rod and i got 90  hms , although i dont do much TT thats the lowest i have ever got ( even after drenching the ground)

thats a nice reading slips,

i'd be more than happy with that, 

 

[batty]

You need to get out into the country slip/steps around my way its usually around 30 ohms.

 

[M107]

My TT cu swap on Saturday came in at 192 ohms, joy of working at the top of a hill.

 

[steptoe]

You need to get out into the country slip/steps around my way its usually around 30 ohms.

you've never been on the Isle of Man, they dont call it the rock for nothing,

PURE slate almost everywhere,,,,,,,,,,

norn iron not much better, built on the edge of a mountain range,,,,,,,,,,,,

 

[batty]

Only time I tend to get bad ones if its on a hill made of chalk. Best ones are clay ground. 

 

[Andy™]

You need to get out into the country slip/steps around my way its usually around 30 ohms.

same up here. mostly 20-40 ohms. rarely get anything over 100

 

[bulmer]

I hope not as well

I've a workshop at the bottom of the garden which is obversely on a TT system and therefore seprate to the DNO earthing.

so it looks like I'll be watering the plant next to the earth rod or praying for rain just before he comes around to try and get under the magic Ze of 21ohms.

Plus I better brush up on the earth rod impedance test.

Where do these magical figures come from.

 

[IzzyS]

Max Ze of a TT system anything over and you need a RCD.

But as you need an RCD on a TT system anyway it is a bit irrelevant but if he wants to get picky anything over 21 and protection is down to the RCD.

Some people don't like it as protection is lost if the RCD fails.

Introduction of the onsite guide page 11

542.24

Try calculating the earth fault current if you have a 21 ohm rod, then and look up the disconnection time for a 32A type B MCB.  Will it comply?