High Ze

[ezekiel]

If a measured Ze is higher than given maximum values from Bs7671 what would you do?

 

[Spark123]

If it is a TN then get onto the DNO
If it is a TT then it is up to you to sort the electrode.

 

[Adam_151]

Misread the OP

 

[RF Lighting]

I got one on Wednesday.

System was a TN-S, Ze 3.20Ω

I rang the DNO, and they attended within 1 1/2 hours.

New cutout and PME terminal installed following morning free of charge.

 

[sparkyspike]

If a measured Ze is higher than given maximum values from Bs7671 what would you do?

If I'm using Fluke leads, I'll retest, squeezing the earth croc clip hard!

 

[Pensdown]

System was a TN-S, Ze 3.20Ω

If I'm using Fluke leads, I'll retest, squeezing the earth croc clip hard!

Just how big is your right arm?

 

[ericmark]

1) I would report it.
But then one would have to look at the installation before working out if any further action is required. Is the Zs also too high? And can it be easy corrected either by adding RCD or reducing the MCB sizes?

Looking at previous test results will help.

My Dad's house has measured 0.38 from day TN-C-S was installed and I have no worries as it has always been little on high side.

With TN-S the limit is 0.8 and it is often hard to work out is TN-C-S or TN-S so careful how you word questions.

With TT then Ze and Nominal Voltage / PFC should be within 21 ohms of each other so you need at least 200 ohms and board can have 21 ohms to earth outside the consumers installation.

So what is the reading and what type is the supply?

You should really leave the house safe, even if that means some temporary work.

 

[sparkyspike]

System was a TN-S, Ze 3.20Ω

If I'm using Fluke leads, I'll retest, squeezing the earth croc clip hard!

Just how big is your right arm?

I was making a point about Fluke leads being c**p! Which they are.

 

[securespark]

With TT then Ze and Nominal Voltage / PFC should be within 21 ohms of each other so you need at least 200 ohms and board can have 21 ohms to earth outside the consumers installation.

Eric- not sure what you're saying here re Ze/ PFC and nominal voltage.

The recommended maximum Zs on a TT installation is 200 Ohms. If higher, then it should be investigated. The 21 ohms as you say is the maximum allowable reading on the supplier's side.

 

[ericmark]

Sorry method of testing if using an earth rod tester with two spikes then 200 ohm but if using a earth loop impedance tester then 221 ohms may be OK. And the 21 ohms on suppliers side could explain why two reading are up to 21 ohms different from each other.
On original install as no power will be on one would use a proper earth rod tester but once power is available one would tend to use the earth loop impedance tester as it is such a pain setting out spikes that's if you can even get somewhere to stick them in the ground.

Although I have had TT supplies where the tester has claimed he has reading of 1 ohm. On returning to site and disconnecting the earth rod from other earth items like water pipes, gas pipes etc. The re-test showed 40 ohm and the young lad could not explain how the earth rod had gained the 39 ohms between the two tests plus from what I could understand the last guy didn't switch the power off to test. I think to leave the house connected while the main earth to earth rod is removed is too high of a risk? I just have that feeling in back of my mind that he did not test earth rod but every earthed item in house? Had he entered a note to say unable to switch of power Ze reading taken with all bonding connected then OK but no such note. To my mind water pipes, gas pipes etc may at any time be changed to plastic and should always be disconnected before Ze reading is made.

 

[RF Lighting]

Yep, thats right. The Ze reading must be taken with no parallell paths in place.