PFC on 3 phase with a megger 1552

[pushrod]

I know that often people will just test PSCC as that should be higher than PEFC so test between L1 - N, L2 - N and L3 - N then take largest value double it and record that value. However was looking through the user guide for the 1552 and noticed that you can test phase-phase pfc. Does this mean that you would just test L1-L2, L2-L3, and L1-L3 and just record the highest value ie not double it.
If correct would you be allowed to do this in a 2391 exam (it would be more accurate?) or do they prefer the L-N and rule of thumb double method.
cheers

 

[malcolmsanford]

The biggest fault current you will get on a 3 phase circuit is phase to phase. Yes test phase to phase even on your 2391-10

 

[IQ Electrical]

The biggest fault current you will get on a 3 phase circuit is phase to phase. Yes test phase to phase even on your 2391-10

I don't know if it's a centre specific rule but the 2 centres that I do 2391 pre-exam refreshers for strictly forbid line-line PFC measurement on the practical, even though the instruments are capable.

 

[malcolmsanford]

I don't know if it's a centre specific rule but the 2 centres that I do 2391 pre-exam refreshers for strictly forbid line-line PFC measurement on the practical, even though the instruments are capable.

You maybe right now IQ I did my 2391 a fair few years ago, and then we took it phase to phase, it may have changed since. If that's the case then appologies pushrod for giving false information.

Saying that though in real life I would take phase to phase on a PSCC test as that is liable to give you your biggest fault current.

 

[IQ Electrical]

Also, if a Zs can't be measured with the BS 1363 lead, it must be calculated-it's all becoming rather pathetic!

 

[malcolmsanford]

Also, if a Zs can't be measured with the BS 1363 lead, it must be calculated-it's all becoming rather pathetic!

That's our friends from the NICEIC doing, all the statutory documents recognise that at certain times live working is unavoidable and sometimes neccessary, just ask the DNO guys about live working. Live testing is a recognised discipline. I want to take my Zs live with all those parallel paths, as that will be the condition of the installation when a fault occurs, not on a piece of paper.

 

[pushrod]

Thanks guys for the info - suppose i'll just have to ask what they want - i have a feeling that the only live testing being done is Ze, PFC and i think an rcbo via a plug lead - (not even certain about that) just a few nerves before the test.

 

[bugsy]

NIC-EIC guide states that Unless the test instrument is designed to operate at 400v then the pfc is to be calculated chapter 7 or 8 Inspection testing and certification

 

[nick611]

i would take just one phase test then times by 1.8.all line supply,s would have same resistance or should do.and i agree live testing is a must and also helps with polarity test.it say,s measured zs not calculated

 

[IQ Electrical]

i would take just one phase test then times by 1.8.all line supply,s would have same resistance or should do.and i agree live testing is a must and also helps with polarity test.it say,s measured zs not calculated

Guidance Note 3 says to multiply by 2 as we're not to be trusted with 1.732!
Where fo you get 1.8 from?

 

[brucelee]

hi when i did 2391 in june was just told to measure between lines and neutrals and multiply the highest by 2 as they dont like you measuring between the lines even though the megger says you can and calculate all Zs except for sockets
the Ze or Zdb at the single phase is also the Zs for the circuit supplying the single phase from the three phase if that makes any sense lol

 

[IQ Electrical]

hi when i did 2391 in june was just told to measure between lines and neutrals and multiply the highest by 2 as they dont like you measuring between the lines even though the megger says you can and calculate all Zs except for sockets
the Ze or Zdb at the single phase is also the Zs for the circuit supplying the single phase from the three phase if that makes any sense lol

That's exactly the same as we teach it, namby pamby calc's!