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?

 

[Doomed]

Are you sure you have no other earth paths? Tell us more about the job.

 

[somersetsparks]

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" ?

 

[telectrix]

have you stabbed it through the neutral of the supply cable?

 

[Doomed]

have you stabbed it through the neutral of the supply cable?

You make me larf you do

 

[trev]

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?

 

[SPARTYKUS]

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]

.....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?

 

[LukeBuckaz]

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.

 

[trev]

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

 

[LukeBuckaz]

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!

 

[SPARTYKUS]

....is the rod right next to fence?

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

 

[LukeBuckaz]

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.

 

[trev]

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

 

[SPARTYKUS]

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