2391 sum practical help

[simpson93]

Oh I see....so the general consensus is that is that it's someone elses install and your testing it? So you should test as such?

yeh well the 2391 exam is so that you can test your and also others work compared to a 2392 testing ur own only

 

[Phil]

yeh well the 2391 exam is so that you can test your and also others work compared to a 2392 testing ur own only

the 2392 is more for initial verification and the 2391 is applicable to periodic testing and more commercial/ industrial 3 phase systems where as the 92 is aimed at level2 for say domestic installations

 

[daveyzadams]

Any body help here just been going through the practical test rig and the tests involved with my lecturer and i cant seem to get my head round Zdb,can any one help am I right in thinking you can obtain the zs of a particular circut by adding Zdb to the (R1 plus R2)and this is why you dont have to carry out a loop impedance test on the sub mains lighting circuits (on the test rig)

 

[brucelee]

Hi mate your Zdb is at the sub board which is a single phase ccu supplied from your three phase db

So if you test R1+R2 for the circuit that is supplying your single phase ccu from the three phase DB then this with your ZE at origin ie supply is your Zdb(Ze) for that board and also the Zs for that circuit
Zs = Ze + R1 +R2

then if you add this to the R1 +R2 for your single phase circuit for the lighting you get the Zs for that circuit
ie
Zs = Ze + (R1+R2) distribution circuit + (R1+R2) final circuit of single phase ccu

hope that makes sense lol

 

[daveyzadams]

Sorry mate in the formula Zs + Ze (R1+ R2) +(R1+R2) where is the Zs taken from
did I send you those copies of the June and Feb past papers and do you have any other recent papers I think I may have just scraped throughbut was taken by surprise at a few questions that had not popped up on past papers,would you mind if I fired a few more questions at you mate

 

[daveyzadams]

Is the Ze in the formula at the origin or is it the Zdb

 

[brucelee]

Hi mate
the Ze is at the origin of the three phase and is the highest of the three lines to earth eg say for tns
L1- E = 0.3
L2- E= 0.32 record this as its the highest so this is Ze
L3- E = 0.3

then do R1 + R2 for all circuits in the three phase Db
recording highest

when you add Ze 0.32 to the R1+R2 this is the Zs calculated for the three phase board
the circuit that is running from the 3 phase board to supply the single phase is also the Ze(zdb) for that board as well as the Zs for that circuit

then when you have done all your R1+R2 for the single phase ccu add these values to above to give you the Zs calculated for these circuits so
Ze from origin plus R1+R2 for the distribution circuit to the single phase board gives you the ZS and Zdb which is the Ze for this board and recorded on the second schedule of test results eg 2 boards 2 schedules of test results

the only circuits that you have to actually measure the Zs on is for socket outlets using the adaptable plug in lead that comes with the tester

the Ze is always at the origin the supply main switch eg at the main isolator switch off the three phase DB
the Zdb is for the sub board but this is still ze but for this board and also the Zs for the circuit supplying the board

oh and no mate you didnt send the copies of the papers you have
cheers mate hope this helps

 

[daveyzadams]

Hi Brucelee do you want the copies in case any body ask you for them

 

[daveyzadams]

So the lighting circuit (R1+R2) + the feeder circuit (R1 +R2) +Ze at origin 0.32 will give you the lighting circuit Zs is that right please tell me it is

 

[brucelee]

yes mate thats it it will give you the calculated Zs of the complete earth fault loop path from the last light on the circuit all way back to the star point of the transformer and back down the line conductors to the point where measured at the time of test

and this is recorded as the Zs for the lighting circuit also because you calculated write Zs Calc in the remarks box at the side of the relevent circuit for all calculated circuits

 

[brucelee]

Hi Brucelee do you want the copies in case any body ask you for them

No mate i want the copies of the certs as a revision help to keep things fresh in my mind cheers mate

 

[daveyzadams]

If you send your e mail adress I've got about 20 past papers and test sequences plus them two recent ones from june and feb which are a bit diferent to all the others [email protected] any body else need them save paying them sharks on e bay that should be passing them on for free

 

[brucelee]

cheers mate i have the feb and the june but the rest wold be appreciated i will pm you my email addy

 

[jackos]

Hi can you help im starting to study for 2391 before i enroll could you tell me what books i need. I have the 17th edition & would appreciate any tips to make sense out of this all thanks.

 

[SirKit Breaker]

Hi can you help im starting to study for 2391 before i enroll could you tell me what books i need. I have the 17th edition & would appreciate any tips to make sense out of this all thanks.

The IET guidance note 3 has everything you need to know for the 2391 it is the bible for this course. Buy it, read it and read it again until you can recite it in your sleep. Get all the correct terminology into your mind. Also 2391 exam success book will tell you how to construct your answers, how to interpret what they are asking and the best way to answer it.

Cheers...........Howard