TNCS High ZE at origin

[AdamGiguere]

Hi there

Testing at origin of a domestic property, I have found:

L-N: 0.44 Ohms
L-E: 9.89 Ohms

I had the DNO attend clients address, there response was that it was quite high and confirmed readings of 0.44 for ZE. (Pleasee attached document with their response)

My concern is they don't seem to have checked the reading between L-E......

Anyone know what could be the cause of this? MET connections are tight and in good condition....

Many thanks in advance.

Adam

 

[westward10]

I am a bit confused have they now made it TN-C-S with a Ze of 0.44.

 

[AdamGiguere]

Hi Westward10

No they have not done anything...

L-N still reads 0.44 (but as all circuits are protected by rcd's isn't so bad)

But L-E is far too high.....

 

[westward10]

If L/N measures 0.44 so should L/E on a PME system. Why does their letter indicate an earth reading of 0.44, is this were you are deeming as being high.

 

[Ian1981]

The email says an earth reading 0.44 ohms no?

 

[AdamGiguere]

They haven't mentioned about the L-E reading which is why I'm a little concerned as I'm aware the highest should be recorded....

But in any case the L-N and L-E readings should be more or less the same for TNCS...

I'm just wondering what could be the cause of the high ZE on L-N...

The only thing I can think of is the earthing connection could be damaged somewhere.

Perhaps an earth rod would fix.

 

[AdamGiguere]

They have mentioned this yes, however any board I test L-E at I get Ze of about 9 ohms, the same as when I test Ze at end of circuits I get 9 ohms.

I will call them tomorrow but I'm sure they'd have checked both L-N & L-E surely.

If so why am I getting 9 ohms...baffling me...

 

[Ian1981]

They have mentioned this yes, however any board I test L-E at I get Ze of about 9 ohms, the same as when I test Ze at end of circuits I get 9 ohms.

I will call them tomorrow but I'm sure they'd have checked both L-N & L-E surely.

If so why am I getting 9 ohms...baffling me...

well it's the pen conductor getting tested so if your testing at the consumer unit L-E it would be the same result more or less as testing L-N unless the earth connection going into the cut out needs attention giving you a high impedance

 

[westward10]

I have had this on PME where there is no connection to the supply neutral. So to clarify you have 0.44 L/N and 9.00 P/E?

 

[Wilko]

Reading the OP note from DNO, they have provided PME at 0.44 Ohms. They expect the Electrician to connect to the new PME tail and confirm you now have Ze of 0.44 and that it is sufficient to meet ADS in the installation.
Have you done that?

 

[AdamGiguere]

I have had this on PME where there is no connection to the supply neutral. So to clarify you have 0.44 L/N and 9.00 P/E?

Correct....

 

[AdamGiguere]

Reading the OP note from DNO, they have provided PME at 0.44 Ohms. They expect the Electrician to connect to the new PME tail and confirm you now have Ze of 0.44 and that it is sufficient to meet ADS in the installation.
Have you done that?

Stuggling with their wording and action to be taken. When they say

When they say provide new PME tails what do they mean exactly...?

 

[ImpededLoop]

You'd be best to go back to site and have a look. If you're unsure, take a few pictures and post them on here.

Let us know the outcome either way.

 

[AdamGiguere]

well it's the pen conductor getting tested so if your testing at the consumer unit L-E it would be the same result more or less as testing L-N unless the earth connection going into the cut out needs attention giving you a high impedance

When you say the "cut out" what do you mean?

Understand the N and E are one in the same more or less but need to sign off the work but at each point measuring Ze (L&E) it's far to high -

 

[Ian1981]

When you say the "cut out" what do you mean?

Understand the N and E are one in the same more or less but need to sign off the work but at each point measuring Ze (L&E) it's far to high -

 

[Ian1981]

 

[AdamGiguere]

The cut out does not come with the earth brass bar as shown above the 25mm earth comes from elsewhere - I'll have to investigate further.

As there must be a problem with the earthing connection?

Just baffling as to why the DNO have not picked this up, would they have just done the test between L-N?

Surely not?

 

[AdamGiguere]

The MET is just screwed on next to the cutout

 

[Ian1981]

Any pics?

 

[AdamGiguere]

Not of the origin - I should have. Apologies...

I'll question the DNO tomorrow when I call.

I'll have to return to the site. There must as you mentioned be something wrong with the earth connection but I couldn't for the life of me see anything wrong earlier when I was looking....