2391 exam

[citybluesmith]

i am currently studying for my 2391 exam.i am testing friends and families houses which they love when i tell them there is something wrong.could you please help.
when you test for continuity what readings should i be getting ? i get around 0.80 for sockets 1.70 lights etc ( give and take ) is there a max reading ?
when testing cont on sockets and i test a spur do i use this reading as my r1 r2 ?
when testing rcd what readings should i be looking for ? i know its your highest from your x5 but is there a wrong reading ? or is it that is does not trip ?
zs diconnection times ? i have looked at them in the 17th regs and compered them to mine.do my zs readings need to be under what the regs say for each breaker in the table ? if they are nt what next ?
same with the pfc ?any wrong readings ?
hope all the above makes sense.sorry if i am making this a bit hard than what it is,but it am bit worried on the readings part and checking that reading results are safe.
thanks for any help.cheers

 

[telectrix]

first, understand the diffewrence between R1 and r1, R2 and r2, Rn and rn. the lower case letters denote end/end of a ring final. the upper case letters denote the resistance on the circuit from supply to end of circuit. so in a ring final, r1=2R1. etc.

R1+R2 is the measurement from which you calculate your Zs as in Zs=Ze+(R1+R2).

Youe Zs readings must be below the max. figure given in 7671, and ideally below the corrected figure in the OSG.( if not there are ways to reduce it. e.g. increase the cable size or decrease the breaker rating). ( except on a TT system, RCD protection on all circuits) where the max. value is 1667ohms. this is due to the higher value of Ze.

Rcdtests involve 6 tests. 1/2x rated , 1 x, and 5x. both at 0 and 180. the highest of the x1 and x5 are recorded. trip times should not exceed 300mS @ x1, 40mS @ x5.

Your measured pefc should be compared to the value obtaind when dividing 230/Zs ( ohms law).

 

[gpz900jim]

re continuity, , the reading will very with the length of the circuit to to get a continuity reading, test between the 2 wires you have on your cu (ring main)
On a ring main, to get your r1 and r2, you must cross connect at the cu, then take readings at all sockets, your highest reading (will be from spur) will be your r1/r2
on testing rcd, your times 1 reading should be less than 200 ms and your 5 times reading should be less than 40 ms
pfc /psc take the highest reading, that should be lower than the rating on your protetective device, usually 6ka for breakers

I was thinking if doing my 2391, how far into it are you? are you finding it very difficult?

 

[john25]

re continuity, , the reading will very with the length of the circuit to to get a continuity reading, test between the 2 wires you have on your cu (ring main)
On a ring main, to get your r1 and r2, you must cross connect at the cu, then take readings at all sockets, your highest reading (will be from spur) will be your r1/r2
on testing rcd, your times 1 reading should be less than 200 ms and your 5 times reading should be less than 40 ms
pfc /psc take the highest reading, that should be lower than the rating on your protetective device, usually 6ka for breakers

I was thinking if doing my 2391, how far into it are you? are you finding it very difficult?

If the RCD is from a BS number its 200ms or 300ms from a BS EN numbered RCD

Im starting this Course next Wednesday can't wait.

 

[gpz900jim]

yes youre right. Ive bought one of those pirate copies of the 2391 course for a fiver off ebay, im going to see how I do with that before I try. The reason being that there seems to be a very high failure rate on the exam. looking at the chief examiners report, i think that they are very particular on how questions are answered and you have to be very precise in what you say.

 

[citybluesmith]

cheers mate.the bit i am finding difficult is not watching anyone test.i am reading the books every min i get.thanks to everyone helping me on the forum.