High PFC discovered prior to NIC inspection on monday!!

[EFLImpudence]

so, wander lead resistance = 0.69
Ze test with wander lead = 0.69
Ze with standard lead = 0.01

Fair enough - didn't work this time.

Buy a Fluke.

 

[westie101]

i was reading the ENA document covering advice to DNOs regarding stating PFC to electrical contractors.
It was absolutely clear that outside London the maximum possible figure was 16kA at the service joint in the highway, the length of the service cable would reduce this figure

 

[securespark]

Even with a transformer 100ft away, it can't be 0.01
If the cabing from the transformer to your property is a pair of 25mm² copper conductors, a 30m length of those is 0.04 ohms on their own.
Actual cables may well be smaller.

They could be bigger.

35mm², with the cable feeding next door, we don't know.

 

[333rocky333]

Am i missing something, even if it was 19 kva what could you do.
Domestic breakers i thought are 6kva or 10 kva, both less than 19kva

 

[ricicle]

Am i missing something, even if it was 19 kva what could you do.
Domestic breakers i thought are 6kva or 10 kva, both less than 19kva

The cut-out fuse should provide back-up protection.

If the property is sat on the Tx then the Ze measurement won't be that accurate!

 

[333rocky333]

yeah realise that, thanks
was more intriqued on what the op thought he could do, otherwise

thought id better get it sorted this afternoon!


Ive read so far that its fine to leave the 6KA breakers in because I can use the 33KA of the 1361 main fuse.

Anybody know if this is definitely NOT OK? if There is someone out there who really thinks I need to do something about it t

Thanks

 

[EFLImpudence]

Just a thought -

Martyn, I don't mean to be patronising but do you realise the meter is only acting as a calculator.

That is dividing the measured voltage by the measured impedance.

It is not actually detecting 19.9kA.





As an aside - how do Meggers deal with the lead resistance if you cannot null them when doing a loop test?

Does it remember the last nulled value on continuity or

does it automatically deduct the value for genuine Megger leads assuming you would not have the affrontery to use anything else?
If the latter, why not do the same for continuity?

 

[securespark]

I'm not sure they are clever enough to remember, though I could be wrong.

 

[Spark123]

On the HI setting the MFT drives 25A around the circuit and I think just measures the voltage difference, from this it derives the loop impedance.
To get the PFC it just uses the nominal voltage 230v/loop impedance (for a supply voltage in the range of 150v-300v), it doesn't use the measured voltage except to choose the nominal voltage.

 

[JohnW2]

On the HI setting the MFT drives 25A around the circuit and I think just measures the voltage difference, from this it derives the loop impedance. To get the PFC it just uses the nominal voltage 230v/loop impedance (for a supply voltage in the range of 150v-300v), it doesn't use the measured voltage except to choose the nominal voltage.

One can but presume that the 19.9kA PFC quoted by the OP was actually a 'maxed-out' display meaning ≥19.9kA and was obtained at a time when the meter 'thought' that the Ze was around 0.01Ω. When, as the OP initially reported, the Ze was being displayed as 0.02Ω, even in the worst case (of display rounding) of that being a rounded version of 0.015Ω (that actual figure being used for calculation), that would only correspond (at 230V) to a PFC of around 15.3 kA.

Kind Regards, John

 

[Spark123]

PFC can be either L-E or L-N, it is carried out with bonding etc connected hence can be greater than 230/Ze.

 

[EFLImpudence]

PFC can be either L-E or L-N,

That's true.

it is carried out with bonding etc connected hence can be greater than 230/Ze.

That's not quite so true.

It can be carried out at any point, except incomer, with bonding connected.

However, if it is Ze being measured (as in the OP) then it is with earthing conductor, and therefore bonding, disconnected and only between L & E which is PEFC which may not be the PFC.

 

[Martynrosscampbell]

So i'm officially compliant!

NIC representative was a very nice bloke. wasn't fussed by the readings. He even said "who cares if you've got a 0.01, you've got a great earth path don't worry about your tester!!"

You guys worry too much !!

Didn't like my voltage tester which has some tape on it where the leads have split but wasn't worried. He also spied the mark on the bus bar where my earth lead had caught after my R1 R2 tests. again wasn't worried as I knew what the problem was, why it happened and what I should've done!

Thanks for all your advice on this one though!

 

[securespark]

Excellent news! Well done!