Strange Ze

[bitty26]

I need some advice as the following has got me puzzled.

TN-S system

I measured Ze got 8.96ohms

DNO came out and measured it and they got 0.03ohms!!!

I'm using a Fluke 1652:

Switch off the main swith in the CU, Disconnected the earth, Select the EFL test, and L-PE, zero the leads, connected green to the earth (croc clip) and red/black at the supply on the main switch...

Am I doing something wrong????

 

[plugwash]

were you there when the DNO measured it? if not it is possible they didn't bother to disconnect the main bonds and therefore ended up including the affects of the main bonds in thier reading.

 

[bitty26]

I was there, even made him disconnect the main bonding to make sure that wasn't pulling the reading down. I'm thinking this Fluke is [rubbish].

 

[Jaymack]

Are your connections correct? Check with the manual - Black and Red are not usually connected together at the live.

 

[DESL]

Whenever I get a strange/high Ze reading I double check my tester on a known supply.

Could be a faulty lead which may only show up on the 20A loading used for EFLI test

 

[bitty26]

no sorry, I meant to say green to earth, red to phase, blue to neutral. Used this on other installations and it's fine..

More I think about it the more I'm kicking myself as 0.03 is no way correct, but I did see the reading on his meter... DNO Guy said that since Part P call out for high Ze have increased by 80%, wonder if there are trying to pull a fast one, surely no?

 

[Steve3948]

Bit confused here, when you say Zero the leads ???
On most machines you only zero leads for continuity.

With a reading of 0.03 Ohms I would say this is TNCS and very near to transformer sub.

 

[Spark123]

That bit confused me a bit too with zeroing the leads, as far as I was aware the leads are only zero'd for low resistance continuity readings. Blue and Red is also an odd combination. A lot of the newer testers will do a 2 wire test at 20A for efli, the Megger MFT1552 certainly does but don't know about the fluke. Things like a bad connection will increase the reading. Can you check the fluke on another known good supply? Maybe try another efli tester on the supply? Just to check, you definately had the main switch off, disconnected the Main Earthing Conductor from the MET and measured the EFLI from the main earthing conductor to the phase on the main switch? 0.03 could easily be a TN-S too

 

[securespark]

The lowest TN-S I've had is 0.1.

 

[davelx]

The lowest TN-S I've had is 0.1.

Mine's 0.09.

 

[Spark123]

Never tried it at work at source but I'd imagine it is somewhere in the region of 0.008 (PFC is somewhere in the region of 30KA) .

 

[securespark]

But not on a Dom 1P 100A supply....

 

[ricicle]

I've had a PFC of around 43kA in one of our switchrooms

 

[Jaymack]

I've had a PFC of around 43kA in one of our switchrooms

Sounds like a "Mine is Bigger than Yours" contest. This is an industrial or supplier switchroom; and probably a 1600KVA transformer source.

 

[fireman22]

can you take your meter to a friends or relatives house, if they have a tns supply you can cross check the readings. i guess the meter is being used incorrectly, or faulty, (cant be anything else if they had a low reading) why didnt you get your meter out when electricity guy was there and he could have cross checked for you?