Ze at origin tns

[Electricalserv]

0.01ohms? Does this comply? Tns system. Unsure because, usually given as 0.8ohms, previous test cert gives 0.08 ohms. Not sure if previous spark rang supplier or just put 0.08 anyway. Is this value ok anyhow?

 

[telectrix]

max. value is 0.8ohms. 0.01 is low. what's your measured PEFC?

 

[Sintra]

The max value for a TNS is 0.8 ohms so anything less is fine. Although at 0.01 ohms you must be on top of the supply transformer.

 

[IQ Electrical]

0.01ohms? Does this comply? Tns system. Unsure because, usually given as 0.08ohms, previous test cert gives 0.08 ohms. Not sure if previous spark rang supplier or just put 0.08 anyway. Is this value ok anyhow?

You're worrying me, is this a periodic inspection?

The agreed maximum Ze on a TN-S system is 0.8 Ohms.

0.08 Ohms could well be correct but because of your meter's inaccuracy at these values due to 'second-digit tolerances' it's difficult to measure.

0.01 is virtually impossible once transformer windings and distribution circuit impedance is considered.

 

[telectrix]

0.01 would give a PFC of 23kA, ignoring parallel paths.. that's why i asked for the measured value.

 

[SPARTYKUS]

doesn't sound right, had low readings when you can see the Sub station next door, but not that low!

 

[Electricalserv]

Sorry guys yeh value I was getting was 0.01ohms. PFC was about 23ka telectrix, dodgy instrument? Due for calb in a month all other test have been fine

 

[bugsy]

I don't think it's at all right even if he was on top the tranny ,
When was your MFT last calibrated

 

[telectrix]

well. your pfc matches your Ze. can't see the test meter being far out on both scales.

 

[SPARTYKUS]

0.01ohms? Does this comply? Tns system. Unsure because, usually given as 0.08ohms, previous test cert gives 0.08 ohms. Not sure if previous spark rang supplier or just put 0.08 anyway. Is this value ok anyhow?

Electricalserv, was the job in the sleeping quarters of a self contained unit in an electrical sub station for overnight staff

 

[IQ Electrical]

well. your pfc matches your Ze. can't see the test meter being far out on both scales.

The problem is, the meter is using the same method to determine both Ze and PFC.

The instrument has to be accurate to 0.05 Ohms (5%) when measuring impedance but at readings below about 0.5 Ohms, this accuracy pales.

This is down to second digit tolerance which can vary between 4 and up to 10.

A meter reading of 0.05 Ohms with a meter of tolerance +/- 2% (+/- 4 digits) could actually be measuring a true value of between 0.01 and 0.09 Ohms.

Do the maths as the meter does to work out a value for PFC and the discrepancy is massive.

 

[jeremy]

Ze might be within limits but wont it blow your MCBs?

 

[jeremy]

Also have you re-zeroed your test leads?

 

[Chr!s]

Its quite possible to have a pfc that high especially if the transformer is nearby.

 

[Electricalserv]

Honestly guys Ze test at origin 3 lead test meter 0.01 ohms pfc 23ka? What going on? Can't spot a sub station anywhere>>>

 

[IQ Electrical]

Its quite possible to have a pfc that high especially if the transformer is nearby.

It is theoretically possible to approach values above 16KA but in practice, it's almost unheard of.

Since becoming aware of the scenario that I described in post 11, any conventional Ze measurement that we find below 0.10 Ohms is re-measured with an adjusting impedance added to lift the meter into it's acceptable range (normally above 0.30 Ohms).

The difference always makes this a worthwhile 10 minute exercise and shows how poor our meters are at values below 0.30 Ohms.

 

[Electricalserv]

Found substation around 20m from house....why so low? Anybody?

 

[IQ Electrical]

Found substation around 20m from house....why so low? Anybody?

Lol, I've explained it twice!

 

[Chr!s]

It is theoretically possible to approach values above 16KA but in practice, it's almost unheard of.

Well if you have a 1000kva transformer, using a transformer impedance of 4.75% you would get 30.5ka at the terminals, so if your close to the transformer a high PFC is possible.

 

[IQ Electrical]

Well if you have a 1000kva transformer, using a transformer impedance of 4.75% you would get 30.5ka at the terminals, so if your close to the transformer a high PFC is possible.

Absolutely right but from my point of view as a serial measurer of Ze, I have yet to actually measure a value of Ze low enough to give a PFC higher than 16kA