Really low Ze from earth rod!

[LukeBuckaz]

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?

 

[trev]

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.

Hell yeah mate I won't use those little bloody twigs, I've seen them used a million times and then heard"Oh that'll be fine".
Not in my book

 

[LukeBuckaz]

the CU is metal clad but the earth from the armouring or that 3rd core was not connected. I will go back, disconnect the earth rod conductor from the earth bar and re-test. Would it hurt to connect that 3rd core of the armoured into the earth bar?

 

[trev]

Is the armouring earthed?

 

[jdd]

You need to disconnect all parallel paths dude, the only way to effectively do that is to disconnect from MET and test to that only, I think you may have been reading through the SWA.

Did you get my personal message?

 

[LukeBuckaz]

yes the armouring is earthed but it is glanded to a seperate metal clad box, not the metal clad fuse board. Sorry I didnt make this clear.

 

[LukeBuckaz]

When I go back I shall definitely disconnect from the earth bar and retest. If the reading was through a parallel path, and the reading through JUST the earthrod was unacceptable, I shall obviously install more earth rods until an acceptable reading is obtained!

 

[Richard]

yes the armouring is earthed but it is glanded to a seperate metal clad box, not the metal clad fuse board. Sorry I didnt make this clear.

Is there any chance that you've screwed these metal enclosers through plasterboard (or what ever) and into cellotex or other foil insulation which could give you a path between the two?

 

[LukeBuckaz]

No mate everything fixed directly to a block wall using brown plugs and 1 1/2" x 10 screws

 

[SPARTYKUS]

Luke it would be really interesting to know the result.

 

[soulman]

I very much doubt there are no parallel paths. But i am taking on board trev's & others post's as i usually use the twigs, I will start using the 5/8 and try and get a couple in. I hate putting rods in just in case you hit any service pipes.

Cheers

 

[Engineer54]

I personally can't see how a single 1m rod of any size can give a value that low... To measure your Ra value, the rods earthing conductor is tested in isolation to any other earthing conductors, bonding conductors or CPC's...

Maybe a rod driven into ground that's been soaked with effluent for many years (such as on a farm) may give a lower value, but then the electrode isn't going to last too long at all, unless it's made of a high grade Stainless Steel... lol!!

I wonder how many electricians just lately have been thinking that they've done well with values they have obtained, mainly due to driving a rod into water sodden soil?? Perhaps they all ought to go back and check again after a dry period!! The truth is, if they have only driven in a single rod, the chances are that the TT system they were so proud of, has risen in value by many ten's of Ohms and in all probably is'nt even stable....

 

[SPARTYKUS]

We'll find out soon when Luke reports back!

 

[MKS]

Rise Park, Top Valley, Bulwell Hall, Bulwell, quality!!!

 

[SPARTYKUS]

Victoria centre. Big fair (goose fair). Hyson green, beeston

 

[MKS]

Vic will look special once the upgrade is complete!!! Westfield, the owners, usually do a quality job! Some of their big centres in Oz are quality and they did a sterling job of the old Eagle centre in Derby! Broadmarsh needs rebuilding! Currently in Lace Market which I don't mind, but right next to some god awful flats filled with all sorts!!!