lots of 2391 questions please help

[brucelee]

Hi to all,
i am doing a 2391 course my exam is in june
I have a few questions if someone will please help

1).state two tests for a 230v circuit with a surge protective device which cant be disconnected

2). State why regular accurraccy checks, in addition to calibration should be carried out on a inspectors test instuments

3). explain the effects on earth fault protection of a circuit if the circuit breaker is installed in the neutral conductor only

4). state the external earth return path,exteral to the installation

5). If the armouring of an swa cable not used as a cpc does it need earthing or bonding

6). whats the scale and ranges/settings for test instruments
i.e. i). Low resistance ohmeter is it low ohms 0.02 to 2ohms
ii). Insulation resistance ohmmeter Mohms 0.00 to more than 200Mohms
iii). What is it for earth fault loop impedence tester for zs is it loop impedence range ohms 0.02 to 20ohms
for external loop impedence on a TN system
external earth fault loop impedence on a TT system
earth electrode resistance test
sorry there are lots but i have been checking GN3 and other books cant find all answers any help and advice much appreciated

 

[pushrod]

3) the breaker would not operate - current would go L to CPC

4) depends on earthing system (TT, TN-S or TN-C-S) but eventually gets back to the earth of the transformer at substation through windings and then back along correct phase to original fault

5) yes even if swa armouring is not used as cpc it should be earthed at supply end

6) 6 (i) a low reading ohm meter being used to do an R1 + R2 on, say, a long lighting circuit could well be reading acceptable values of 4 or 5 ohms so i would have thought the top end of the range would be higher than 2 ohms .

no idea with 1) does it mean medical equipment ???

Hopefully will know the answers in 6 months as i'm hoping to do a 2391 in september - i'll be asking you then

 

[brucegenerator]

1.insulation resistance with live conductors connected.continuity of protective conductor.
2.wear and tear if meter is kept in a car.if meter is dropped.
6.continuity low resistance ohmeter 0-2,0-20ohm/ir 0-200mohm tn 0-20 tt 0-200-0-2000 earth electrode max=200ohms
TO BEST OF MY KNOWLEDGE

 

[Risteard]

From the most recent Chief Examiner's Report:

"There were two particular questions which caused candidates problems. There were very few candidates who understood the requirements for insulation resistance testing a circuit containing surge protection devices which cannot be removed, most linked line and neutral and tested to earth at 500 V. There were equally few who understood the requirements for testing for separation between a SELV circuit and an LV circuit within the same containment system."

 

[iceman]

to test for electrical seperation test line and neutrel of the seperated circuit together and the conductors of any adjacent circuit strapped together 250v dc 0.5megohm

 

[brucelee]

From the most recent Chief Examiner's Report:

"There were two particular questions which caused candidates problems. There were very few candidates who understood the requirements for insulation resistance testing a circuit containing surge protection devices which cannot be removed, most linked line and neutral and tested to earth at 500 V. There were equally few who understood the requirements for testing for separation between a SELV circuit and an LV circuit within the same containment system."

Hi mate
for surge protective devices is it the usual tests of between lives (L-N), then between lives and earth (L-E and N-E) at 250v d.c. min bs7671 value 1.0Mohm

For selv to lv is it
between lives of selv connected together and lives of the LV circuit connected together at 500v d.c. 1.0Mohm min

between lives of selv connected together and the protective conductor of the LV circuit and any exposed conductive parts in the same area as the selv at 500v d.c. 1.0mohm min

For selv is it between L-N of the selv at 250v d.c 0.5Mohm and
lives of selv and any exposed conductive parts at 250v 0.5 Mohm min value
cheers for help

 

[luke12345]

for surge protective devices is it the usual tests of between lives (L-N), then between lives and earth (L-E and N-E) at 250v d.c. min bs7671 value 1.0Mohm

I was under the impression if a surge protection could not be removed the live conductors are linked out and tested to earth only?
got my exam tomorrow so just trying to clear this up because ive been told different

 

[sparks_114]

"State two tests", well if these are in relation to an insulation resistance test then they are: Ling Line and Neutral conductors together and test at 500V DC or one can reduce the test voltage to 250V C I am sure it's in the GN3 but also look at page 84 OSG. Ta

 

[pushrod]

I was under the impression if a surge protection could not be removed the live conductors are linked out and tested to earth only?
got my exam tomorrow so just trying to clear this up because ive been told different

Fairly certain that brucelee is correct on this. Surge protection is to protect sensitive equipment against hi voltages, ie above 250V - the electronics then dump the extra voltage by passing a current to earth, so there is going to be no point testing at 500V between lives and earth.

 

[Liamsparks]

brought back from over a year ago, impressive!!