high pfc reading

[SimpleSimon]

Is that the one that states when a BS 1361 type II (33Ka) is the fuse cutout. All MCBs protected by this can be taken as rated as 16Ka?

 

[IQ Electrical]

Is that the one that states when a BS 1361 type II (33Ka) is the fuse cutout. All MCBs protected by this can be taken as rated as 16Ka?

That's the one

 

[Ladders]

Hi. I know this an old post but have just come across the same problem and the highest reading is 19.9kV. So to comply the breakers MUST be higher than the potential fault current otherwise the breakers will be damaged if they disconnect because of this. Or so I think! Anyone know where the regs say different please? e.g. having read the above posts 434.5.1, is that saying the BS1361 Type II fuse on the supply side (in my case) is sufficiently rated at 33kA that the MCB/RCBOs in the board can be 6kA? Follow?! Help! lol

 

[IQ Electrical]

What type of installation is this?

ie. domestic, commercial?

 

[Ladders]

Apologies, domestic.

 

[gamblor6]

536. 1 is the boy for you i think ladders

 

[gamblor6]

imo 434.5.1is saying that as long as there is discrimination between the fuses

 

[IQ Electrical]

imo 434.5.1is saying that as long as there is discrimination between the fuses

Inverse discrimination really, the upstream device is required to open before the time frame for damage to occur to the mcb (in this case).

The fact that the mcb is actually mechanical means that the simple fuse (on higher fault currents) will operate faster.

 

[Ladders]

Thanks for the pointers.
Now the problem is a real mistery...I thought the L port was faulty and this was the reason for the high PFC readings. I thought this as when I used the plug in L probe tester, instead of standard L lead, the PFC were within limts, well under 6kA (using Megger 1552).
Now I have been sent a loan unit because of this problem but when I repeat the test it is exactly the same?!
So using the standard L and E leads the PFC are well outside of limts but when I use the L plug in probe and E standard lead the results are fine?!
Any ideas why this is please? Thanks.

 

[IQ Electrical]

I don't know about the differences but I know that at values of less than around 0.5 Ohms, the meters that we generally use are innacurate.

Add this to the difference 0.02/3 of an Ohm can make to PFC and you see where the problems are magnified.

I'll type out my method of measuring Zs close to the supply transformer, it helps to lift the meter into it's accurate 'sweet spot'.

 

[malcolmsanford]

Thanks for the pointers.
Now the problem is a real mistery...I thought the L port was faulty and this was the reason for the high PFC readings. I thought this as when I used the plug in L probe tester, instead of standard L lead, the PFC were within limts, well under 6kA (using Megger 1552).
Now I have been sent a loan unit because of this problem but when I repeat the test it is exactly the same?!
So using the standard L and E leads the PFC are well outside of limts but when I use the L plug in probe and E standard lead the results are fine?!
Any ideas why this is please? Thanks.

If you have a 3 probe meter are you using all 3 probes?

 

[Ladders]

Hi. The PFC with a megger 1552 is 2 leads only Red (L) and Green (E). So L lead to incoming live and E lead to the earth bar, then the other test is L lead to incoming live and E lead to incoming neutral.