TT-no earth rod

[Dean Williams]

hi
just been to a house in Rhyl. the occupants were getting shocks from the sink.
Its TT and i found out it had just been rewired.
there was no connection to earth, no rod and no equipotential bonding!!!

We fitted a rod and bonded everything. i got a Ze of 25.1 ohms after we did the work.
im going back tomorrow to do a EICR.

Are 100ma RCds still required? they have got a 16th ed split load board. half circuits on 30ma rcd, other half just MCBs.

also, for TT is the max Ze 200 ohms.

any help and guidance would be helpful...in 8 years of testing its my first TT!!!

 

[Engineer54]

How can the installation be a TT system if there is no earth electrode/rod(s) installed?? lol!!!

 

[keniff]

How can the installation be a TT system if there is no earth electrode/rod(s) installed?? lol!!!

Lol that made me laugh

 

[Engineer54]

So if this is your first time for installing/creating a TT system, how did you install, what size, and how deep did you drive the rod(s)?? Did you provide a flush to ground earth pit/chamber to protect the rod/conductor connection??

 

[Dean Williams]

my boss was there too. he installed it. we put a pit and a rod in. we used 16mm earth.

 

[A&S Electrical]

every circuit within a TT system should be RCD protected i personally doing a job on a TT system today would use a current 17th edition split rcd consumer unit. A reading of 25ohms in for an earth rod in these dry conditions is good and i would expect it to be lower in wetter weather. 100ma rcd protection on lighting circuits although not to 17th edition (asumming cable buried) would be advisory to change to 30ma. TT systems are easier to understand and work with, than people think. When you dont encounter them and come across one the immediate fear kicks in but if you step back use you knowledge follow the regs/OSG they are straight foward although the zs/ze results can be different on any given day!!!

 

[Engineer54]

So you installed a single 1m rod?? ...Do you and your boss think that the single rod is going to be a stable earth electrode?? Stability comes with depth, and i would always advise you couple a minimum of 2 X 5/8'' (16mm) extendable rods on any domestic TT installation.

Good to know a flush earth pit was included in this install though!!

 

[richy3333]

Why is there a 16th Ed board on a rewire?
No earthing?
Sounds like the customer got stiffed by the sparky? Are they Welsh and was the Spark English

 

[Dean Williams]

customer is welsh....and the spark is only known by the name 'scouse john'. hmmmmmmm

 

[richy3333]

LOL, but I do know a Scouse John (angry little chap)

 

[Edward Amsden]

Loads of tt's round me. all in the regs... Not many earth pits.. not entirely essential.. Into most ground 1 mtr rod is fine (depending on install...) I got a rod stuck 200mm in one day. Thought I would test it.. Same reading as the 1 mtr rod i put in next to it...

Cant believe the no earth install.. And in this sort of case agree with the Electrical Trainee generation.. :smilewinkgrin:

 

[Richard Burns]

That house had not been rewired it had been made deadly!

If you have a 16th edition board then the half without 30mA RCD protection does not meet the TT requirements for all circuits to have RCD protection so you would need an upfront 100mA RCD or the like. A nicer solution would be to replace the single RCD board with at least a dual RCD board or fit RCBOs; so long as the supply circuit does not need RCD protection.

The regulations state that a Ra value above 200 ohms may not be stable , though as you have heard from E54 this is potentially a misleading statement.
a stable reading is key and if you believe that will be obtained from your current rod installation then this is OK. I would say 25.1 ohms is fine for a Ze reading for a TT, but you would need the RCD protection to get the disconnection times for earth faults.

 

[richy3333]

Cant believe the no earth install.. And in this sort of case agree with the Electrical Trainee generation.. :smilewinkgrin:

Bit of a sweeping statement isn't it without the facts? May as well blame women or hamsters? Could have been an old die-hard sparky, past his prime that won't update, else could have been a plumber 'pretending' to be a sparky?

 

[Des 56]

Bit of a sweeping statement isn't it without the facts? May as well blame women or hamsters? Could have been an old die-hard sparky, past his prime that won't update, else could have been a plumber 'pretending' to be a sparky?

I can assure you,I had nothing to do with the job
:smilewinkgrin:

 

[Dean Williams]

Thanks for your help folks. as i've never come across a TT since i started my apprenticeship in 2000, i wasn't too familiar with its requirements.

 

[Engineer54]

Loads of tt's round me. all in the regs... Not many earth pits.. not entirely essential.. Into most ground 1 mtr rod is fine (depending on install...) I got a rod stuck 200mm in one day. Thought I would test it.. Same reading as the 1 mtr rod i put in next to it...

Cant believe the no earth install.. And in this sort of case agree with the Electrical Trainee generation.. :smilewinkgrin:

This post just shows that you know absolutely Nothing about installing a TT earthing system!!!

 

[snoopydo]

what is the proceedure when coming across dangerous installs like this? would you riddor it like a gas installation?

 

[Steve Richards]

Should also remember not to install a rod within rod x 2 length of other extraneous parts buried in the ground e.g metallic water or gas mains.

 

[Engineer54]

Should also remember not to install a rod within rod x 2 length of other extraneous parts buried in the ground e.g metallic water or gas mains.

Fine if you have a service layout drawing to hand!! Neigh on impossible to confirm one way or the other in normal circumstances though!!

The best way is as Marvo employs, dig a square hole to around a metre deep, then drive your rod(s) in the ground. Then you can be relatively sure, that at least your not going to hit a service pipe... lol!!!

 

[rich.250]

25 ohms is a good enough Ra although i would still supply a 100mA rcd upfront (type s) and then follow the need for 30mA for additional protection where required.