PFC measurement?

[Colin33]

Hi all, have read various threads on this forum regarding PFC measurement but still need a little advice please. Does anyone have a definitive calculation for PFC in ac single phase supplies?
I have just measured PFC in a particular SP domestic installation and I get a reading of 549 amps. Should I not be getting a reading of several thousand amps?? The ZE is 0.37 on this TNCS supply.

 

[chiplard]

Its ohms law mate

I = V/R

230/0.37 = 621A

The reason you have 549 is that your supply voltage will be not be exactly 230.

 

[Colin33]

Its ohms law mate

I = V/R

230/0.37 = 621A

The reason you have 549 is that your supply voltage will be not be exactly 230.

Thanks, but why then does the certificate ask for a reading in KA?
And why, when asking the supply company, do they say it's 'about 6KA' ?

 

[JUD]

Thanks, but why then does the certificate ask for a reading in KA?
And why, when asking the supply company, do they say it's 'about 6KA' ?

549A = 0.549kA. The DNO will probably give you 16kA as the PFC.

The ZE is 0.37 on this TNCS supply.

0.37Ω is too high for TN-C-S. It should be 0.35Ω maximum. You may want to report this to the DNO.

 

[c.boy]

Hi all, have read various threads on this forum regarding PFC measurement but still need a little advice please. Does anyone have a definitive calculation for PFC in ac single phase supplies?
I have just measured PFC in a particular SP domestic installation and I get a reading of 549 amps. Should I not be getting a reading of several thousand amps?? The ZE is 0.37 on this TNCS supply.

Are you defo sure it is TNCS and not TNS is the earth coming of the armour??? TNS max is .8 and as said TNCS is .35

 

[sparkylad]

Colin the DNO olways give you the worse case scenario value , in practice its always lower .

When you do the Calculation it is never exactly the same as the Meter reading.

When you say PFC is that PSSC or PEFC .. what are the two values- this will give guidance on TNCS or TNS.

 

[Colin33]

It's TNCS...the earth connected at the suppliers cutout. I shall check again tomorrow, maybe my tester is at fault but was calibrated not long ago...

If it is still 0.37, should I contact DNO?

The reading I got was 549A PSSC and 740A PEFC

I shall give my tester a 'gentle tap' and see what happens

 

[JUD]

It's TNCS...the earth connected at the suppliers cutout. I shall check again tomorrow, maybe my tester is at fault but was calibrated not long ago...

If it is still 0.37, should I contact DNO?

The reading I got was 549A PSSC and 740A PEFC

I shall give my tester a 'gentle tap' and see what happens

In that case your PFC is 740A and the different readings would suggest it is TN-S.

 

[SirKit Breaker]

It's TNCS...the earth connected at the suppliers cutout. I shall check again tomorrow, maybe my tester is at fault but was calibrated not long ago...

If it is still 0.37, should I contact DNO?

The reading I got was 549A PSSC and 740A PEFC

I shall give my tester a 'gentle tap' and see what happens

Make sure you have a good clean connection with your clips or probes.

 

[xraytek]

I have just measured PFC in a particular SP domestic installation and I get a reading of 549 amps. Should I not be getting a reading of several thousand amps?? The ZE is 0.37 on this TNCS supply.

I thought that PFC was measured with main bonds connected.

 

[JUD]

I thought that PFC was measured with main bonds connected.

It is.

 

[sparkylad]

It's TNCS...the earth connected at the suppliers cutout. I shall check again tomorrow, maybe my tester is at fault but was calibrated not long ago...

If it is still 0.37, should I contact DNO?

The reading I got was 549A PSSC and 740A PEFC

I shall give my tester a 'gentle tap' and see what happens

Colin. if its TNCS then both the PSSC and the PEFC should be the same shouldnt they as they are Combined at the cut out . how are you measuring it ,is it a 2 lead or 3 lead tester and what configuration of the leads are you using for each of the tests ?

 

[Colin33]

Hi all, thanks for your comments/suggestions...

Having had a fresh look at this today, I can confirm that it is indeed a TNS supply and not TNCS.
This explains my readings!
I haven't come across many of these and it's a while since I did any testing and I failed to spot the difference

Cheers all for your help