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LukeBuckaz

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Please be gentle...

...now I installed my first earth rod on saturday! I was expecting a really high Ze as up to 200ohms is allowed by BS7671. My Ze was 0.34. Does this seem odd to anyone that has done one/many before?
 
Firstly did you do test with bonding disconnected?

It is possible to get that, especially with the satuarated ground and all that. Out of interest, how far did you hit the rod in and what size was it 3/8" or 5/8" ?
 
It's unlikely you'll get that from one rod Luke, possible but unlikely. As the other lads have said, are you sure you were testing properly IE only using the main earth cable?
 
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SPARTYKUS

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  • #7
As alluded, I'd expect 200 - 10 Ohms, not 0.34. I would suspect there is a parallel path (Main Water Service Bond) and ....the water pipe is connected to next doors, who are TN.

?

Seen it a few times.

In fact seen an install that appears that the spark that installed it decided that it WAS a TN system (its not its TT)- No RCDs. Naughty.
 

Marvo

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.....I installed my first earth rod on saturday......My Ze was 0.34
This is the stuff dreams are made of, I can only wish one day this might happen for me :(

Anything is possible but that reading from a single rod with no parallel paths is a long shot. Are you sure about the test equipment and proceedures you used?
 
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LukeBuckaz

  • Thread Starter Thread Starter
  • #9
it was a 5/8" rod. Just one. Don't think there would have been any parallel paths as the water bond was not connected as the water pipe isn't installed yet.

The CU I installed was fed from a 3 phase fuse board at one end of some stables. A 4mm armoured cable supplied the new CU. The original 3 phase board had a Ze of 0.25 (don't know if this is relevant) The original 3 phase board is supplied in armoured cable and is earthed by the metal armouring back to the suppliers facility. I have earthed the 4mm armoured at the supply end, and used the earth rod as the earth for the new consumer unit as it will have a water supply installed.

Please, any advice will be appreciated as I am a domestic electrician and very VERY rarely deal with anything else.
 
Luke, sounds like happy days mate but if I were you I'd check it again just to make absolutely sure. Go through it step by step with GN3 in your hand just to be on the safe side.
Let us know the outcome please
 
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LukeBuckaz

  • Thread Starter Thread Starter
  • #11
I will be going back in a few weeks to start some other work so I will double check then. Would it hurt to use the armouring of the 4mm as a sort of back up earth? And again please be gentle if this is a stupid question.

Thanks for your responses!
 
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SPARTYKUS

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  • #12
....is the rod right next to fence?

Is there an enormous SUb station 1 foot the other side!!!
 
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LukeBuckaz

  • Thread Starter Thread Starter
  • #13
Haha, I'm not sure where the sub station is. The job was carried out on some farm land at the back of two old houses but a new estate has been built a couple of hundred yards away.
 
It took me 3 rods to get my record TT Ze of 0.29 Luke, sounds like you'd be kicking my butt if you sunk another one:)
 
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SPARTYKUS

  • Thread Starter Thread Starter
  • #15
Not near "Rise Park" is it? Grew up there was great in 70's. Heard its a drugs warren now
 
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StuSpiers

  • Thread Starter Thread Starter
  • #16
I have had lower than that in the past, so it is possible.

But I would say you may be getting an earth path through the armouring of your swa?

Is the earth path continuous? - Metal clad throughout?
 
It took me 3 rods to get my record TT Ze of 0.29 Luke, sounds like you'd be kicking my butt if you sunk another one:)
I have hit better then that trev, however the pole top splitphase transformer 10' away and the fact the ground was permanently soaked in sileage effluent may have helped sway it a tiny little bit!
Once all the steelwork was bonded it hit a dizzy 0.18, on just the rod, 0.20 :)
 
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LukeBuckaz

  • Thread Starter Thread Starter
  • #18
Haha, no not near Rise Park Spartykus. I do go past there nearly everyday. Rise Park its self isn't bad but nearby Top Valley is pretty rough.
 
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SPARTYKUS

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  • #21
Showing off now Trev!
 
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Richard

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  • #22
Are you sure there is definatly no contact between the suppliers earthing arrangement and where ever you tested from? Is the small DB metal clad? Did you physically d/c your earthing conductor from the earth terminal to ensure no other paths? Sorry not trying to teach you to suck eggs - just checking!
 
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LukeBuckaz

  • Thread Starter Thread Starter
  • #23
Well the armoured is glanded into a metal clad box at the 'new' end then from the metal clad box to a card meter (the stable has been converted into a dog grooming room and the owner wants the lady who is running the dog grooming to pay her own way) now the armoured is a 3core I did use one of the cores as an earth but terminated this at the metal clad box.
 
I've always put at least two rods on a TT mate as it was how I was taught but this time I'd gotten the first one in and got about 180/90 coupled another knocked that in and took 100 ohms off that then I thought oooo how low can you go so whacked the third in, read 0.29 and thought I'll stick there. Gaffer wasn't happy at first when he spotted all his shiny new rods had gone but when he saw my test sheet I had yet another convert
 
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LukeBuckaz

  • Thread Starter Thread Starter
  • #26
Now I did not disconnect the main earth when conducting the Ze (I have slapped my own wrist, and slightly embarrassed) there is only two circuits on the new DB a lighting circuit with 2 lights fitted. Both plastic light fittings fixed to wood. Also 4 double socket outlets fixed to a block built wall, so I cannot see that there are any parallel paths back to the suppliers earthing arrangement. :confused:
 
I've always put at least two rods on a TT mate as it was how I was taught but this time I'd gotten the first one in and got about 180/90 coupled another knocked that in and took 100 ohms off that then I thought oooo how low can you go so whacked the third in, read 0.29 and thought I'll stick there. Gaffer wasn't happy at first when he spotted all his shiny new rods had gone but when he saw my test sheet I had yet another convert
Just the difference between 3/8" rod and 5/8" rod is a lot though isn't it, I can't believe how many people just stick in 3/8" rod, I have only used these for temporary stakes for genny's and cabins.
 
J

jdd

  • Thread Starter Thread Starter
  • #28
Mate, I would definitely dissconnect the main earth and re test. :)
 
Is the CU metal clad and was the swa earthed to that earthing bar?
If so there's your reason for the low reading Luke.
DC the main earth when you get back to it and get a reading just off your rod then let us know:)
 
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StuSpiers

  • Thread Starter Thread Starter
  • #30
Just the difference between 3/8" rod and 5/8" rod is a lot though isn't it, I can't believe how many people just stick in 3/8" rod, I have only used these for temporary stakes for genny's and cabins.
You can't really blame people when it is standard fair at all wholesalers.

In fact most younger sparks wouldn't even be aware there is a problem with it.
 
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