2391 practical: help..!

GT1 · Feb 11, 2009

Guys...

Having a little mental problems getting my head round the three phase part of the board.. and my practical is REAL soon..!

Im fine with the insulation testing part of it, just treat each phase separately and test between phases and neutral, phases and earth, neutral to earth.. (or a more global test with breaker closed)

From memory the board has a radial socket circuit fed from one of the phases, and a 3 phase induction motor (or similar,) on another separate circuit. Again, I think im clear about testing either side of the switch gear for the motor. However... from memory (again) the motor circuit comprises wires from all three phases, but no neutral.?. When it comes to R1+R2 for this circuit, what excactly am i doing with these 3 phase wires..? Ive a feeling i should me measuring the resistance end to end of each phase conductor and also the CPC..? I appreciate the phases should all be virtually identical, so do i just take the highest value and use that as R1..?

Also.. PFC on 3 phase board... I'm struggling in all the books I have (including the one by Chris Kitcher) to find clear instruction on how determine the figures for PFC...?

And just one more..
The secondary board (consumer unit) off the 3 phase board.. do i measure Ze at that board or use the figure off the main board..??

Im sorry if these seem simple things to ask guys, I just cant seem to find reference for them in the reading material I have. Any help would gladly accepted..
cheers

**
I think i may have answered my own question on the PFC..

double the single phase to neutral figure and use that one..!!

markspark · Feb 11, 2009

GT1 said:
Guys...

From memory the board has a radial socket circuit fed from one of the phases, and a 3 phase induction motor (or similar,) on another separate circuit. Again, I think im clear about testing either side of the switch gear for the motor. However... from memory (again) the motor circuit comprises wires from all three phases, but no neutral.?. When it comes to R1+R2 for this circuit, what excactly am i doing with these 3 phase wires..? Ive a feeling i should me measuring the resistance end to end of each phase conductor and also the CPC..? I appreciate the phases should all be virtually identical, so do i just take the highest value and use that as R1..?

Also.. PFC on 3 phase board... I'm struggling in all the books I have (including the one by Chris Kitcher) to find clear instruction on how determine the figures for PFC...?

And just one more..
The secondary board (consumer unit) off the 3 phase board.. do i measure Ze at that board or use the figure off the main board..??

I think i may have answered my own question on the PFC..

double the single phase to neutral figure and use that one..!!

hi, pfc on a 3p board is single phase pfc x2 so if its 1.5ka 1p then 3p pfc will be 3ka
the secondary board ze is classed as zdb, as you have the original ze + r1&r2 of the cable suppling the secondary db

with the motor circuit, test all the phases againt earth and record the highest , although they should all be the same.
hope this helps

GT1 · Feb 11, 2009

Mark

Thanks for that.
As it happens i just found the PFC answer in my books..

The motor circuit makes sense now, and i will disconnect the switch gear and measure upstream and downstream of it to the motor, and add the figures together.

Do I refer to the secondary board Ze as Zdb on the paperwork then I presume.. where the paperwork asks for Ze at the Nature of Supply Parameters..?

markspark · Feb 11, 2009

GT1 said:
Mark

The motor circuit makes sense now, and i will disconnect the switch gear and measure upstream and downstream of it to the motor, and add the figures together.

when testing the 3p starter circuit dont forget to watch for starter switches with electronic relays that wont make a contact with no power running through them when you do your r1&r2!!
they will be watching to make sure you notice it!!

Do I refer to the secondary board Ze as Zdb on the paperwork then I presume.. where the paperwork asks for Ze at the Nature of Supply Parameters..?

the nature of supply parameters is for boards connected directly to the suppliers cut out.
if you were doing a periodic or inspection ,you would do the seperate board on a seperate test sheet.
the first line of the schedule is for submains so fill that bit in as its classed as a sub main.
when i did the 2391 it was the 16th regs and they've changed the test sheets since then.

GT1 · Feb 11, 2009

Yep..

got all that thanks..

Ive been told by tutor to disconnect switch gear for continuity testing, and test either side of it and add figures together.. so hopefuly not falling into trap of having unexplained open circuit..!!

I suspect the forms that C&G have changed since 17th edition then, I cant seem to find reference to sub mains anywhere.. but i'll cross that bridge when i come to it and get a look at their paperwork.

Thanks for the help. I feel a little calmer now that I remember a little more of what i'm doing
Cheers