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?

 

[StuSpiers]

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?

 

[somersetsparks]

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

 

[LukeBuckaz]

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.

 

[trev]

Mine was about a mile from the sub mate

 

[somersetsparks]

Mine was about a mile from the sub mate

Thats pretty impressive mate, you must of been to engineer54's school of earthing!

 

[SPARTYKUS]

Showing off now Trev!

 

[Richard]

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!

 

[LukeBuckaz]

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.

 

[trev]

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

 

[richy3333]

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

pmsl

 

[LukeBuckaz]

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.

 

[somersetsparks]

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.

 

[jdd]

Mate, I would definitely dissconnect the main earth and re test.

 

[trev]

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

 

[StuSpiers]

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.